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CEN/TC 250/SC 7 N 1330

CEN/TC 250/SC 7Eurocode 7 - Geotechnical design

Email of secretary: [email protected] Secretariat: NEN (Netherlands)

prEN 1997-1 Geotechnical design - General rules (PT6 draft 2019-10)

Document type: Other draft

Date of document: 2019-11-04

Expected action: COMM

Action due date: 2020-01-31

Background:

Committee URL: https://cen.iso.org/livelink/livelink/open/centc250sc7

mailto:[email protected]

https://cen.iso.org/livelink/livelink/open/centc250sc7

Document type: European Standard Document subtype: Working Document Document stage: v4 31/10/2019 Document language: E

CEN/TC 250 Date: 2018-04

prEN EN 1997-1:2018

CEN/TC 250

Secretariat: NEN

Eurocode 7: Geotechnical design — Part 1: General rules

Eurocode 7: Entwurf, Berechnung und Bemessung in der Geotechnik — — Teil 1: Allgemeine Regeln

Eurocode 7: Calcul géotechnique — — Partie 1 : Règles générales

ICS:

M515.SC7.T6 prEN 1997-1:20xx (E) Draft October 2019

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Contents

Page

Drafting foreword by PT6........................................................................................................................................... 7

European foreword ....................................................................................................................................................... 8

Introduction to EN 1997-1 ......................................................................................................................................... 9

1 Scope ................................................................................................................................................................. 11 1.1 Scope of EN 1997 .......................................................................................................................................... 11 1.2 Scope of EN 1997-1 ...................................................................................................................................... 11 1.3 Assumptions ................................................................................................................................................... 11

2 Normative references ................................................................................................................................. 12

3 Terms, definitions and symbols .............................................................................................................. 13 3.1 Terms and definitions ................................................................................................................................ 13

Ground terms used in EN 1997 ............................................................................................................... 13 Reliability terms used in EN 1997 .......................................................................................................... 15 Values properties terms used in EN 1997 ........................................................................................... 15 Terms relating to actions and resistance ............................................................................................ 16 Terms relating to verification methods ............................................................................................... 16 Terms relating to analysis and models ................................................................................................ 17 Terms relating to groundwater .............................................................................................................. 17 Terms relating to execution ..................................................................................................................... 18

3.2 Symbols and abbreviations ...................................................................................................................... 18 Latin upper-case letters ............................................................................................................................. 18 Latin lower-case letters ............................................................................................................................. 19 Greek upper-case letters ........................................................................................................................... 20 Greek lower-case letters ............................................................................................................................ 21 Abbreviations ................................................................................................................................................ 22

4 Basis of design ............................................................................................................................................... 23 4.1 General rules .................................................................................................................................................. 23

Basic requirements ..................................................................................................................................... 23 Geotechnical reliability .............................................................................................................................. 23 Consequence of failure ............................................................................................................................... 24 Robustness...................................................................................................................................................... 25 Design service life ........................................................................................................................................ 26 Durability ........................................................................................................................................................ 26 Sustainability ................................................................................................................................................. 26 Quality management ................................................................................................................................... 26 Geotechnical Category ................................................................................................................................ 27

4.2 Principles of limit state design ................................................................................................................ 28 General ............................................................................................................................................................. 28 Design situations .......................................................................................................................................... 29

4.3 Basic variables .............................................................................................................................................. 29 Actions and environmental influences ................................................................................................. 29 Material and product properties ............................................................................................................ 31 Geometrical data .......................................................................................................................................... 32

4.4 Verification by the partial factor method ............................................................................................ 33


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General ............................................................................................................................................................. 33 Design values of actions and effects-of-actions ................................................................................. 34 Design values of material properties and resistance ...................................................................... 35 Design values of geometrical data .......................................................................................................... 36 Combination of actions ............................................................................................................................... 36

4.5 Verification by prescriptive measures .................................................................................................. 36 4.6 Verification by testing ................................................................................................................................. 36 4.7 Verification by the Observational Method .......................................................................................... 37 4.8 Design assisted by testing .......................................................................................................................... 37

5 Materials .......................................................................................................................................................... 38 5.1 General ............................................................................................................................................................. 38 5.2 Soils .................................................................................................................................................................... 39

Weight density ............................................................................................................................................... 39 Shear strength ................................................................................................................................................ 39 Stiffness, compressibility and swelling ................................................................................................. 39 Creep ................................................................................................................................................................. 40 Consolidation ................................................................................................................................................. 40 Hydraulic conductivity ............................................................................................................................... 40

5.3 Rock and rock masses ................................................................................................................................. 41 Weight density ............................................................................................................................................... 41 Intact Rock ...................................................................................................................................................... 41 Discontinuities in rock mass .................................................................................................................... 41 Strength and stiffness of rock mass ....................................................................................................... 42 Time dependent properties of rock mass ............................................................................................ 43 Hydraulic conductivity of rock mass ..................................................................................................... 44

5.4 Fill ....................................................................................................................................................................... 44 5.5 Other materials ............................................................................................................................................. 45

Geotextiles and geosynthetics .................................................................................................................. 45 Concrete ........................................................................................................................................................... 45 Ground treatment, incl. grout and vertical drainage ....................................................................... 45 Steel ................................................................................................................................................................... 45 Timber .............................................................................................................................................................. 46 Masonry ............................................................................................................................................................ 46

6 Groundwater .................................................................................................................................................. 47 6.1 General ............................................................................................................................................................. 47

Design considerations ................................................................................................................................. 47 Properties of groundwater ........................................................................................................................ 47

6.2 Surface water, groundwater, and piezometric levels ...................................................................... 48 6.3 Groundwater pressures ............................................................................................................................. 48

General ............................................................................................................................................................. 48 Representative values of groundwater pressures ............................................................................ 48 Design values of groundwater pressures for ultimate limit state design ................................ 50 Design values of groundwater pressures for serviceability limit state design ...................... 50

6.4 Groundwater in freezing conditions ...................................................................................................... 50

7 Geotechnical analysis .................................................................................................................................. 52 7.1 Calculation models ....................................................................................................................................... 52

General ............................................................................................................................................................. 52 Empirical models .......................................................................................................................................... 53 Analytical models ......................................................................................................................................... 53 Numerical models ......................................................................................................................................... 53 Calculation models for cyclic and dynamic actions .......................................................................... 54

7.2 Model factors .................................................................................................................................................. 54


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8 Ultimate limit states .................................................................................................................................... 55 8.1 General ............................................................................................................................................................. 55 8.2 Types of ultimate limit states .................................................................................................................. 55

Failure by rupture ........................................................................................................................................ 55 Failure of the ground due to excessive deformation ....................................................................... 55 Failure by loss of static equilibrium of the structure or ground ................................................. 56 Hydraulic failure caused by seepage ..................................................................................................... 57 Failure caused by time-dependent effects .......................................................................................... 59 Failure caused by cyclic effects ............................................................................................................... 60

8.3 Procedure for numerical models............................................................................................................ 60

9 Serviceability limit states .......................................................................................................................... 63 9.1 General ............................................................................................................................................................. 63 9.2 Overall ground movements ...................................................................................................................... 63 9.3 Structural serviceability limit states ..................................................................................................... 64

10 Execution ......................................................................................................................................................... 65 10.1 General ............................................................................................................................................................. 65 10.2 Supervision ..................................................................................................................................................... 66 10.3 Inspection ....................................................................................................................................................... 66 10.4 Monitoring ...................................................................................................................................................... 66 10.5 Maintenance ................................................................................................................................................... 67 10.6 Observational Method ................................................................................................................................ 67

11 Testing .............................................................................................................................................................. 68 11.1 General ............................................................................................................................................................. 68 11.2 Planning of tests ........................................................................................................................................... 68 11.3 Test evaluation .............................................................................................................................................. 69

12 Reporting ........................................................................................................................................................ 70 12.1 General ............................................................................................................................................................. 70 12.2 Ground Investigation Report ................................................................................................................... 70 12.3 Geotechnical Design Report ..................................................................................................................... 71

General ............................................................................................................................................................. 71 Ground properties and Geotechnical Design Model ........................................................................ 71 Basic parameters .......................................................................................................................................... 71 Verification of limit states ......................................................................................................................... 71 Plan of supervision, inspection, monitoring, and maintenance .................................................. 71

12.4 Geotechnical Construction Record ........................................................................................................ 72 12.5 Geotechnical test report ............................................................................................................................ 72

(Normative) Partial factors for ground properties .................................................................... 73 A.1 Use of this Normative Annex .................................................................................................................... 73 A.2 Scope and field of application .................................................................................................................. 73 A.3 Partial factors in ULS for ground properties ...................................................................................... 73 A.3.1 General ............................................................................................................................................................. 73 A.3.2 Fundamental (persistent and transient) design situations .......................................................... 73 A.3.3 Accidental design situations .................................................................................................................... 74 A.3.4 Consequence factors for material properties in geotechnical structures ............................... 75 A.3.5 Reduction factor for transient design situations .............................................................................. 75

(informative) Characteristic value determination procedure ................................................ 77 B.1 Scope and field of application .................................................................................................................. 77 B.2 Background .................................................................................................................................................... 77 B.3 Characteristic value determination procedure ................................................................................ 78

(informative) Limiting values of structural deformation and ground movement ........... 83


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C.1 Use of this Informative Annex .................................................................................................................. 83 C.2 Scope and field of application .................................................................................................................. 83 C.3 General ............................................................................................................................................................. 83

(Informative) Implementation of design during execution ..................................................... 87 D.1 Use of this Informative Annex .................................................................................................................. 87 D.2 Scope and field of application .................................................................................................................. 87 D.3 Supervision ..................................................................................................................................................... 87 D.3.1 General ............................................................................................................................................................. 87 D.3.2 Control of ground and fil ............................................................................................................................ 88 D.3.3 Control of water flow and groundwater pressures .......................................................................... 88 D.4 Inspection ........................................................................................................................................................ 89 D.5 Monitoring ....................................................................................................................................................... 90 D.6 Execution using Observational Method ................................................................................................ 91

(normative) Additional requirements and recommendations for reporting ..................... 93 E.1 Use of this Normative Annex ..................................................................................................................... 93 E.2 Scope and field of application .................................................................................................................. 93 E.3 Minimum content of reports ..................................................................................................................... 94 E.4 Ground Investigation Report .................................................................................................................... 94 E.5 Geotechnical Design Report ...................................................................................................................... 95 E.5.1 General content ............................................................................................................................................. 95 E.5.2 Specification of the Geotechnical Design Model ................................................................................ 96 E.5.3 Verification of limit states ......................................................................................................................... 97 E.5.4 Minimum content of supervision, inspection, monitoring, and maintenance plans ............ 98 E.5.5 Simplification for Geotechnical Category 1 ......................................................................................... 98 E.6 Geotechnical Construction Record ......................................................................................................... 98 E.6.1 General content ............................................................................................................................................. 98 E.6.2 Record of construction ............................................................................................................................... 99 E.6.3 Record of supervision, monitoring and inspection .......................................................................... 99 E.7 Geotechnical test report .......................................................................................................................... 100

(Informative) Ground properties..................................................................................................... 101 F.1 Use of this Informative Annex ............................................................................................................... 101 F.2 Scope and field of application ............................................................................................................... 101 F.3 General .......................................................................................................................................................... 101

(Informative) Qualification and professional experience ..................................................... 103 G.1 Use of this Informative Annex ............................................................................................................... 103 G.2 Scope and field of application ............................................................................................................... 103 G.3 Guideline ....................................................................................................................................................... 103

(Informative) Observational method ............................................................................................ 107 H.1 Use of this Informative Annex ............................................................................................................... 107 H.2 Scope and field of application ............................................................................................................... 107 H.3 General .......................................................................................................................................................... 107 H.4 Analytical approach .................................................................................................................................. 108 H.5 Framework ................................................................................................................................................... 108 H.6 Application of the ab initio approaches (A and B) ......................................................................... 109 H.6.1 Parameter selection .................................................................................................................................. 109 H.6.2 Calculation.................................................................................................................................................... 109 H.6.3 Alarm values and contingency measures.......................................................................................... 110 H.6.4 Construction phase ................................................................................................................................... 110 H.7 Application of the ipso tempore approaches (C and D) ................................................................ 110 H.7.1 Evaluation of the structure’s performance and calibration of parameters.......................... 110 H.7.2 Calculation.................................................................................................................................................... 110


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H.7.3 Alarm values and contingency measures .......................................................................................... 110 H.7.4 Monitoring system ..................................................................................................................................... 110 H.7.5 Remaining construction stages ............................................................................................................. 110

(Informative) Bibliography ................................................................................................................ 111


7

Drafting foreword by PT6

This document (prEN 1997-1:20xx) has been prepared by project team M515.SC7.T6.

This document is a working document, which was delivered to NEN on 2018-10-31.

Motive/references for the alterations of the text have been submitted in a separate document, dated 2018-04-30. Title: M515.SC7.T2 prEN1997-1:200xx (E) Draft 2018-April Reference.

This separate reference document has the following content:

- Major alterations of the text since the October-2018 draft based on received comments.

- Motive/reference for the alteration of the text

- List of deleted clauses from previous version of EN 1997-1

- List of National choices

- List of references to EN 1997-3 and EN 1997-2

<Drafting note: This Drafting foreword will be deleted during the enquiry stage.>


8

European foreword

[DRAFTING NOTE: this version of the foreword is relevant to EN Eurocode Parts for enquiry stage]

This document (EN 1997-1) has been prepared by Technical Committee CEN/TC 250 “Structural Eurocodes”, the secretariat of which is held by BSI. CEN/TC 250 is responsible for all Structural Eurocodes and has been assigned responsibility for structural and geotechnical design matters by CEN.

This document will partially supersede EN 1997-1:2004.

The first generation of EN Eurocodes was published between 2002 and 2007. This document forms part of the second generation of the Eurocodes, which have been prepared under Mandate M/515 issued to CEN by the European Commission and the European Free Trade Association.

The Eurocodes have been drafted to be used in conjunction with relevant execution, material, product and test standards, and to identify requirements for execution, materials, products and testing that are relied upon by the Eurocodes.

The Eurocodes recognise the responsibility of each Member State and have safeguarded their right to determine values related to regulatory safety matters at national level through the use of National Annexes.


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Introduction to EN 1997-1

Introduction to the Eurocodes

The Structural Eurocodes comprise the following standards generally consisting of a number of Parts:

• EN 1990 Eurocode: Basis of structural and geotechnical design • EN 1991 Eurocode 1: Actions on structures • EN 1992 Eurocode 2: Design of concrete structures • EN 1993 Eurocode 3: Design of steel structures • EN 1994 Eurocode 4: Design of composite steel and concrete structures • EN 1995 Eurocode 5: Design of timber structures • EN 1996 Eurocode 6: Design of masonry structures • EN 1997 Eurocode 7: Geotechnical design • EN 1998 Eurocode 8: Design of structures for earthquake resistance • EN 1999 Eurocode 9: Design of aluminium structures • <New parts>

Introduction to EN 1997

[Drafting note: This contains information formerly included in “Scope of EN 1997”]

EN 1997 is intended to be used in conjunction with EN 1990, which establishes principles and requirements for the safety, serviceability, robustness, and durability of structures, including geotechnical structures, and other construction works.

EN 1997 establishes additional principles and requirements for the safety, serviceability, robustness, and durability of geotechnical structures.

EN 1997 is intended to be used in conjunction with the other Eurocodes for the design of geotechnical structures, including temporary geotechnical structures.

EN 1997 establishes rules for the calculation of geotechnical actions.

Design and verification in EN 1997 are based on the partial factor method, prescriptive measures, testing, or the observational method.

Verbal forms used in the Eurocodes

The verb “shall" expresses a requirement strictly to be followed and from which no deviation is permitted in order to comply with the Eurocodes.

The verb “should” expresses a highly recommended choice or course of action. Subject to national regulation and/or any relevant contractual provisions, alternative approaches could be used/adopted where technically justified.

The verb “may" expresses a course of action permissible within the limits of the Eurocodes.

The verb “can" expresses possibility and capability; it is used for statements of fact and clarification of concepts.

—


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National annex for EN 1997-1 (to be completed)

This standard gives values within notes indicating where national choices can be made. Therefore, the national standard implementing EN 1997-1 can have a National Annex containing all Nationally Determined Parameters to be used for the design of buildings and civil engineering works to be constructed in the relevant country.

National choice is allowed in EN 1997-1 through the following clauses:

4.1.2.3 (3), 4.1.3 (1), 4.1.9.1 (2), 4.4.3 (4)

6.3.2 (2), 6.3.3 (2), 6.3.3 (12)

7.1.1 (9), 7.2 (1)

8.2.4.2 (4)

9.1 (2)

10.3 (5)

A.3.1.2, A.3.1.3, A.3.1.5, A.3.1.6

National choice is allowed in EN 1997-1 on the use of informative annexes.

Annex B Characteristic value assessment procedures

Annex C Limiting values of structural deformation and ground movement

Annex D Checklist for construction supervision and performance monitoring

Annex F Ground properties

Annex G Qualification and professional experience

Annex H Observational method

Annex I Bibliography


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1 Scope

1.1 Scope of EN 1997

EN 1997 is intended to be used in conjunction with EN 1990, which establishes principles and requirements for the safety, serviceability, robustness, and durability of structures, including geotechnical structures, and other construction works.

EN 1997 establishes additional principles and requirements for the safety, serviceability, robustness, and durability of geotechnical structures.

EN 1997 is intended to be used in conjunction with the other Eurocodes for the design of geotechnical structures, including temporary geotechnical structures.

EN 1997 establishes rules for the calculation of geotechnical actions.

Design and verification in EN 1997 are based on calculations using partial factor method or other reliability-based methods, the partial factor method, prescriptive measures, testing, or the Observational Method.

1.2 Scope of EN 1997-1

EN 1997-1 provides the general rules to be applied for design and verification of geotechnical structures.

EN 1997-1 is intended to be used in conjunction with EN 1997-2, which provides requirements for assessment of ground properties from ground investigation.

EN 1997-1 is intended to be used in conjunction with EN 1997-3, which provides requirements for the design of specific geotechnical structures.

Additional requirements can be necessary for geotechnical structures outside the scope of EN 1997-3.

1.3 Assumptions

In addition to the assumptions given in EN 1990, the rules in EN 1997 assume that:

data required for design are collected, recorded, and interpreted by appropriately qualified and experienced personnel;

geotechnical structures are designed by personnel with appropriate qualifications and experience in geotechnical design;

adequate continuity and communication exist between the personnel involved in data-collection, design, and execution.


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2 Normative references

<Drafting note: This list of normative references has been updated. According to N1250 and IR3 only references that are cited normatively in the text shall be listed in the normative references. According to IR3 8.6.1 References to non-normative documents should be avoided.

A few non-normative references have been included in the bibliography in Annex I.

The list of normative references will be cross-checked by PT6 and adjusted to correspond to part 2 and 3.>

The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this European standard. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

EN 1990, Eurocode: Basis of structural and geotechnical design

EN 1991, Eurocode: Actions on structures

EN 1992, Eurocode 2: Design of concrete structures

EN 1993, Eurocode 3: Design of steel structures

EN 1995, Eurocode 5: Design of timber structures

EN 1996, Eurocode 6: Design of masonry structures

EN 1997-2, Eurocode 7: Geotechnical design – Part 2: Ground properties

EN 1997-3, Eurocode 7: Geotechnical design – Part 3: Design of geotechnical structures

EN 1998, Eurocode 8: Design of structures for earthquake resistance

EN 1999, Eurocode 9: Design of aluminium structures

ISO 6707-1, Buildings and civil engineering works. Vocabulary. General terms


13

3 Terms, definitions and symbols

<Drafting note: this section is under development until October 2020>

3.1 Terms and definitions

For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

− IEC Electropedia: available at www.electropedia.org − ISO Online browsing platform: available at www.iso.org/obp

NOTE Table 3.1 lists the terms defined hereafter in alphabetical order with reference to the number hereafter where they are defined (different table for each language).

Table 3.1 (NDP) Terms in alphabetical order with reference to reference numbers for definition

Term Reference

To be completed at the end To be completed at the end

Drafting note: this table is similar to the table presented in EN 1990.

Ground terms used in EN 1997

3.1.1.1 ground soil, rock, and fill existing in place prior to execution of the construction works

[SOURCE: EN 1990]

3.1.1.2 soil aggregate of minerals and/or organic materials which can be disaggregated by hand in water

[SOURCE: EN ISO 14688]

3.1.1.3 rock naturally occurring assemblage or aggregate of mineral grains, crystals or mineral based particles compacted, cemented, or otherwise bound together and which cannot be disaggregated by hand in water


http://www.iso.org/obp


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3.1.1.4 rock mass rock comprising the intact material together with the discontinuities and weathering zones

NOTE 1. [SOURCE: EN ISO 14689]

3.1.1.5 rock material (intact rock) intact rock between the discontinuities


3.1.1.6 weathering zone distinctive layer of weathered ground material, differing physically, chemically, and/or mineralogically from the layers above and/or below

3.1.1.7 discontinuities bedding planes, joints, fissures, faults and shear planes


3.1.1.8 foliation planar arrangements of constituents such as crystals in any type of rock (3.5), especially the parallel structure that results from flattening, segregation and other processes undergone by the grains in a metamorphic rock in geology refers to repetitive layering in metamorphic rocks


3.1.1.9 interface surface where two systems of ground interact

3.1.1.10 infill material that fills or is used to fill a space, hole or discontinuity

3.1.1.11 fill material used for raising the level of the ground [SOURCE: EN ISO 14689]

3.1.1.12 made ground (fill, US) ground that has been formed by using material to fill in a depression or to raise the level of a site


3.1.1.12 engineered fill material placed in a controlled manner to ensure that its geotechnical properties conform to a predetermined specification


15

3.1.1.13 non-engineered fill material placed with no compaction control and likely to have heterogeneous and anisotropic geotechnical properties within its mass.

Reliability terms used in EN 1997

3.1.2.1 desk study (see also EN1997-2-see annex B of EN 1997-2) analysis of information about the construction site from existing documentation

NOTE 2. NOTE to entry A desk study includes, for example, the history of the site, observations of neighbouring structures, previous construction activities, information from aerial photographs, satellite observations, local experience in the area, and seismicity

3.1.2.2 Geotechnical Complexity Class classification of a geotechnical structure on the basis of the complexity of the ground and ground-structure interaction, taking account of prior knowledge

3.1.2.3 comparable experience documented previous information about ground and structural behaviour that is considered relevant for design, as established by geological, geotechnical and structural similitude with the design situation

Values properties terms used in EN 1997

[SOURCE: EN 1990, 3.1.4.1]

3.1.3.1 derived value of a ground property (to be modified according to EN1997-2) value of a ground property obtained by theory, correlation or empiricism from test results or field measurements

3.1.3.2 nominal value of a ground property cautious estimate of the value of a ground property that affects the occurrence of a limit state

NOTE to entry: further explanation of ‘cautious estimate’ is given in 4.3.2.

3.1.3.3 characteristic value of a ground property statistical determination of the value of a ground property that affects the occurrence of a limit state having a prescribed probability of not being attained. This value corresponds to a specified fractile (mean, superior or inferior) of the assumed statistical distribution of the particular property of the ground.

3.1.3.4 representative value of a ground property Nominal or representative value taking into account the conversion factor

NOTE to entry: further explanation is given in 4.3.2.

3.1.3.5 best estimate value of a ground property estimate of the most probable value of a ground property


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Terms relating to actions and resistance

3.1.4.1 ground resistance capacity of the ground, or part of it, to withstand actions without failure

3.1.4.2 ground strength mechanical property of the ground indicating its ability to resist actions

3.1.4.3 overall stability resistance to failure of the ground that encompasses the entire geotechnical structure

3.1.4.4 local stability resistance to failure that encompasses only a certain part of the entire geotechnical structure without failure of the entire geotechnical structure.

Drafting note: check how the term is used in EN1997-1 and EN1997-3.

3.1.4.5 cyclic actions variable load that can induce significant stiffness and strength degradation, generation of excess pore pressure, liquefaction or permanent settlements

Terms relating to verification methods

3.1.5.1 Observational Method (to check) limit state verification method that comprises a continuous, managed, integrated process of design; construction control, monitoring and review that enables previously defined modifications to be incorporated during or after construction as appropriate.

NOTE to entry: Definition based on CIRIA Report 185, 1999, slightly adapted

3.1.5.2 prescriptive measures pre-determined, experienced-based, and suitably conservative rules for design

3.1.5.3 verification assisted by testing testing of a structural element to verify design ground properties or resistance

NOTE to entry: Verification assisted by testing includes, for example, the determination of skin friction and end bearing of piles; the pull-out strength of anchors; and the shear strength of lime-cement columns

3.1.5.4 verification by testing testing performed to verify that the performance of the geotechnical structure (or part of the structure) is within the acceptable limits

NOTE to entry: Verification by testing includes full-scale test or reduced scale tests


17

Terms relating to analysis and models

3.1.6.1 zone of influence volume of ground that is affected by the construction works and that, conversely, affects the behaviour of the structure itself

3.1.6.2 geotechnical analysis procedure or algorithm for determining effects-of-actions in and resistance of the ground

3.1.6.3 Geotechnical Design Model physical, mathematical, or numerical representation of the geotechnical system used for the purposes of analysis, design, and verification containing ground information for engineering design purposes developed for a particular design situation and limit state

NOTE 1 to entry: Guidelines on the contents of a Geotechnical Design Model are given in Clause 12 and Annex E

3.1.6.4 geotechnical unit volume of ground or ground layer that is defined as a single material in a Geotechnical Design Model

3.1.6.5 Ground Model Site specific outline of the disposition and character of the ground and groundwater based on results from ground investigations and other available data

3.1.6.6 numerical models calculation models involving numerical approximation to obtain solutions

NOTE to entry: Numerical methods include, but are not limited to finite-element, finite-difference, boundary-element, and discrete-element analysis methods; and limit-analysis, beam-spring approaches, and discontinuity layout optimization.

3.1.6.7 validation process of determining the degree to which a calculation model and its input parameters represent a real design situation

Terms relating to groundwater

3.1.7.1 groundwater level level of the water surface in the ground

3.1.7.2 piezometric level level to which water would rise in a standpipe designed to detect the pressure of water at a point beneath the ground surface

3.1.7.3 surface water level


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level of water above the ground surface

Terms relating to execution

3.1.8.1 limit value value of material property, deformation, or stress that defines the attainment of the limit state

3.1.8.2 alarm value value of material property, deformation, or stress that, with an appropriate safety margin, defines the point at which corrective action should be taken to avoid exceeding the limit state

3.2 Symbols and abbreviations

For the purposes of this document, the following symbols apply.

NOTE 3. NOTE 1 The symbols commonly used in all Eurocodes are defined in EN 1990

NOTE 4. NOTE 2 The notation of the symbols used is based on ISO 3898:1997

Latin upper-case letters

Cd,ULS design value of the excessive deformation that is considered to cause an ultimate limit state;

E modulus of deformability / Young’s Modulus, that measures the stiffness of the ground material;

Ed design value of the effect of actions;

Gd,dst design value of any permanent destabilising force not caused by groundwater;

Gd,stb design value of the stabilising (downward) forces;

Gw permanent component of groundwater pressure

Gwk characteristic value of Gw;

Gwk;inf inferior (lower) characteristic value of Gw;

Gwk,mean mean charactesristic value of Gw;

Gwk;sup superiror (upper) characteristic upper value of Gw;

Gw,rep representative value of Gw;

H hydraulic head;

Ja joint alteration number of a discontinuity

Jn joint set number of discontinuities in the rock mass

Jr joint roughness number of a discontinuity

Jw joint water reduction factor of water inside a discontinuity

K0 at-rest “in situ” earth pressure coefficient;


19

KF consequence factor applied to actions;

KM consequence factor applied to material properties;

KR consequence factor applied to resistance;

Ktr reduction factor for a transient design situation;

L0 reference length;

Lv vertical dimension of the zone of influence for the limit state under consideration;

NSPT blow count measured in standard penetration test;

Pe probability of exceedance;

Qd,dst design value of any variable destabilising force not caused by groundwater;

Qw variable component of the groundwater pressure;

Qw,comb combination value of Qw

Qw,freq frequent value of Qw;

Qw,k characteristic value of Qw;

Qw,qper quasi-permanent value of Qw;

Qw,rep representative value of Qw;

Rd design value of resistance;

Ranchor value of anchor resistance force;

Rfriction value of friction resistance;

Tref design situation period;

Ud,dst design value of destabilising (uplift) force due to groundwater pressures;

VX coefficient of variation of the ground material property X;

X ground material property;

Xav estimate of the average value of X;

Xav,data average value of independent site-specific data of X;

Xav,pre pre-assessed average value of X;

Xbest best estimate value of X;

Xd design value of X;

Xk characteristic value of X;

Xmean mean value of X from test results;

Xnom nominal value of X;

Xrep representative value of X;

Latin lower-case letters

c′ effective cohesion;

cu undrained shear strength of soil;

cv vertical consolidation coefficient;


20

fs sleeve friction in a CPT;

hw vertical distance from the surface-water level to the ground surface;

id design value of the hydraulic gradient;

ic;d design value of critical hydraulic gradient (when soil particles begin to move);

k hydraulic conductivity;

kn coefficient that depends on n used to estimate Xk;

n number of sample test results or of site-specific data; and

degrees of freedom for the Student law;

qu unconfined compressive strength;

pl pressure meter limit pressure;

p′v effective vertical overburden or surcharge pressure at the ground surface;

p′vk characteristic value of any effective vertical overburden or surcharge pressure at the ground surface;

qc cone resistance in a CPT;

qu unconfined compressive strength of soil;

s settlement;

t95 represents student’s t-factor, evaluated for a 95% confidence level and (n – 1) degrees of freedom;

u groundwater pressure at a point in the ground;

ud design groundwater pressure at a point in the ground;

udst destabilising (uplift) groundwater pressures;

udst;d design value of destabilising (uplift) groundwater pressures;

z vertical distance or depth of the point in the ground below the ground surface (not including any overlying fill).

Greek upper-case letters

∆ relative deflection;

∆/L deflection ratio;

∆a deviation related to geometrical data;

∆inhs coefficient of variation of the property due to inherent ground variability;

∆obs coefficient of variation of the observed property values;

∆quality coefficient of variation of the measurement error;

∆trans coefficient of variation of the transformation error;

∆X estimate of uncertainty affecting the ground property;

ΔX,data coefficient of variation of the of independent site-specific data property values;

ΔX,def indicative value of parameter uncertainty;


21

Greek lower-case letters

α angular strain;

β angular distortion;

γ partial factor (safety or serviceability)

weight density of the ground;

γ’ effective value of the weight density, buoyant weight density of the ground;

γc material factor applied to cohesion;

γcu material factor applied to undrained shear strength of soil;

γE partial factor on effect-of-actions;

γF partial factor on actions;

γHYD partial factor for hydraulic heave;

γrep representative value of the weight density of the ground

γM partial material factor;

γpv,stb partial factor for effective vertical overburden pressure;

γqu material factor applied to unconfined compressive strength of soil;

γtanδ material factor applied to coefficient of ground/structure interface friction;

γtanϕ partial material factor applied to the coefficient of internal friction of the ground;

γw,rep representative weight density of groundwater;

γσc partial factor on uniaxial compressive strength of rock mass;

γτs is the partial factor on effective shear strength of soil;

δ ground/structure interface angle of friction;

δs differential settlement;

δX vertical scale of fluctuation of the property;

η conversion factor.

θ rotation angle;

σc uniaxial compressive strength of rock mass;

σv vertical total stress in the ground;

σv;d design value of the vertical total stress in the ground;

τs effective shear strength of soil

ϕ angle of internal friction of the ground;

ϕ′ effective value of the angle of internal friction of the ground;

ϕd design value of the angle of internal friction of the ground;

ϕrep representative value of the angle of internal friction of the ground;


22

tan δ coefficient of the ground/structure interface angle of friction;

tan ϕ′ coefficient of effective angle of internal friction;

ω tilt.

Abbreviations

CC Consequence Class

DC Design Case

DCL Design Check Levels

DQL Design Qualification Level and experience

EFA Effects Factoring Approach

GC Geotechnical Category

GCC Geotechnical Complexity Class

GCR Geotechnical Construction Record

GDM Geotechnical Design Model

GDR Geotechnical Design Report

GIR Ground Investigation Report

GM Ground Model

IL Inspection Level

MFA Material Factor Approach

OCR Over-consolidation Ratio

OM Observational Method

RFA Resistance Factor Approach


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4 Basis of design

4.1 General rules

Basic requirements

<REQ> The assumptions given in EN 1997-1, 1.3 shall be verified.

NOTE Other basic requirements are given in EN 1990, 4.1.

Geotechnical reliability

4.1.2.1 Ground Model

<REQ> Processed results from ground investigation and other available data shall be collected together in a Ground Model.

4.1.2.2 Geotechnical Design Model

<REQ> A Geotechnical Design Model shall be developed for each geotechnical design situation and associated limit states.

NOTE 5. NOTE Different Geotechnical Design Models can be developed as subsets of a more comprehensive Geotechnical Design Model.

4.1.2.3 Geotechnical Complexity Class

<REQ> The geotechnical structure shall be classified into one of three Geotechnical Complexity Classes (GCC) – Lower, Normal, or Higher – depending on the complexity of its most critical design situation.

NOTE 6. NOTE 1 Different parts of a structure can be classified in different Geotechnical Complexity Classes.

NOTE 7. NOTE 2 It is not necessary to treat the whole structure according to the highest Geotechnical Complexity Class that is selected.

<RCM> A preliminary GCC should be established as part of the desk study.

<RCM> The GCC should be selected taking into account uncertainty in the ground conditions.

NOTE 1 Features causing uncertainty that are considered when selecting the GCC are given in Table 4.1 (NDP) unless the National Annex gives different features.

NOTE 2 Additional features to be considered for specific geotechnical structures are given in EN 1997-3.


24

Table 4.1 (NDP) Selection of Geotechnical Complexity Class

Geotechnical Complexity

Class

Complexity

General features causing uncertainty

GCC 3 Higher Any of the following apply: • considerable uncertainty regarding ground conditions, • highly variable or difficult ground conditions, • significant sensitivity to groundwater conditions • significant complexity of the ground-structure interaction

GCC 2 Normal It covers everything not contained in the features of GCC 1 and GCC3 GCC 1 Lower All the following conditions apply:

• negligible uncertainty regarding the ground conditions • uniform ground conditions • low sensitivity to groundwater conditions, • low complexity of the ground-structure-interaction

NOTE 8. a The terms ‘considerable’, ‘significant’, ‘highly’ etc. are relative to any comparable experience that exists for the particular geotechnical structure and design situation

NOTE 9.

<REQ> The GCC shall be reviewed and, if appropriate, changed at each stage of the design and construction process.

Consequence of failure

<REQ> The consequences of failure of a geotechnical structure shall be classified according to EN 1990, 4.3

NOTE 10. NOTE Table 4.2 (NDP) gives examples of geotechnical structures in Consequence Classes CC0 to CC4 unless the National Annex gives other examples.


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Table 4.2 (NDP) Examples of geotechnical structures in different Consequence Classes

Consequence class Description of

consequence Examples

CC4 Highest Geotechnical constructions whose integrity is of vital importance for civil protection, e.g. underground power plants, road/railway embankments with fundamental role in the event of natural disasters, earth dams connected to aqueducts and energy plants, levees, tailing dams and earth dams with extreme consequences upon failure (very high risk-exposure), etc. In cases with significative landslide hazards

CC3 Higher Retaining walls and foundations supporting public buildings, with high exposure. Man-made slopes and cuts, retaining structures with high exposure. Major road/railway embankments, bridge foundations that can cause interruption of service in emergency situations. Underground constructions with large occupancy (e.g. underground parking).

CC2 Normal All geotechnical structures not classified as CC1 or CC3 or CC4

CC1 Lower Retaining walls and foundations supporting buildings with low occupancy. Man-made slopes and cuts, in areas where a failure will have low impact on the society. Minor road embankments not vital for the society. Underground constructions with occasional occupancy.

CC0 Lowest Not applicable for geotechnical structures

Robustness

<REQ> Geotechnical structures shall be designed to have the level of robustness specified in EN 1990, 4.4.

NOTE 1 The aim of designing for robustness is either to prevent disproportionate consequences as a result of an adverse or unforeseen event or to provide some additional resistance to reduce the likelihood and extent of such an event.

NOTE 2 There is a distinction between design for identified accidental actions and design for robustness. Design for accidental actions, a target level of reliability is expected to be achieved while design for robustness are measures to increase margin without aiming for a specified target reliability.

<RCM> To ensure robustness of a geotechnical structure, particular attention should be paid to: - interaction between failures of different design elements; - interaction between different limit states; - communication of geotechnical information between different parties involved in the design.

<PER> Strategies for designing geotechnical structures for robustness may include: - providing enough ductility and deformation capacity - increased bearing capacity of identified critical elements within the geotechnical structure.

<PER> The design methods for design for robustness may be linked to the Geotechnical Category.


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Design service life

<REQ> The design service life of a geotechnical structure shall be specified according to EN 1990, 4.5.

Durability

<REQ> The durability of a geotechnical structure shall conform to EN 1990, 4.6.

<REQ> Environmental influences shall be considered when assessing the durability of any material incorporated into the geotechnical structure.

<REQ> Reference shall be made to provisions for protection against erosion caused by surface water or groundwater (see Clause 6), where appropriate.

<REQ> The durability of structural materials in contact with the ground shall be assessed.

<RCM> Durability provisions for structural materials in contact with the ground should be taken from relevant material and execution standards.

Sustainability

<REQ> Geotechnical structures shall be designed for sustainability according to EN 1990, 4.7.

Quality management

<REQ> The quality management measures specified in EN 1990, 4.8, shall be implemented for geotechnical structures.

<PER> Controls at the stages of design, detailing, execution, use, and maintenance may be implemented using the design check levels (DCLs) and design qualification and experience levels (DQLs) specified in EN 1990, Annex B. <New B9

<PER> Design Check Levels (DCLs), Design Qualification and Experience Levels (DQLs) and Inspection Levels (IL) may be related to Geotechnical Categories (GC).

NOTE 1 Inspection Levels, Design Check Levels and Design Qualification and Experience Levels are defined in EN 1990, Annex B.

NOTE 2 The relationship between Geotechnical Category (GC) and Inspection Level (IL), Design Check Levels (DCL), Design Qualification and Experience Levels (DQL) is given in Table 4.3 (NDP) unless the National Annex gives a different relationship.

Table 4.3 (NDP) Minimum management measures for different Geotechnical Categories

Geotechnical Category

(GC)

Minimum Design Check Level

(DCL)

Minimum Design Qualification Level and Experience Level(DQL)

Minimum Inspection Level

(IL)

GC3 DCL3 DQL3 IL3

GC2 DCL2 DQL2 IL2

GC1 DCL1 DQL1 IL1


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4.1.9.1 General

<REQ> Geotechnical structures shall be classified into a Geotechnical Category that combines the consequence of failure of the structure and the geotechnical complexity of the ground and ground-structure interaction.

<RCM> The Geotechnical Category should be determined from a combination of the Consequence Class of the structure and Geotechnical Complexity Class.

NOTE 11. NOTE The relationship between Geotechnical Category, Consequences Class, and Geotechnical Complexity Class is given in Table 4.4 (NDP) unless the National Annex gives a different relationship or specifies a direct determination of the Geotechnical Category.

NOTE 12. NOTE For Geotechnical structures in Consequence Class 4 additional provisions to those of Geotechnical Category 3 can be necessary.

Table 4.4 (NDP) Relationships between Geotechnical Categories, Consequences Classes, and Geotechnical Complexity Classes

Consequence Class (CC)

Geotechnical Complexity Class (GCC) Lower (GCC1)

Normal (GCC2)

Higher (GCC3)

Highest (CC4) GC3 GC3 GC3 Higher (CC3) GC2 GC3 GC3 Normal (CC2) GC2 GC2 GC3 Lower (CC1) GC1 GC2 GC2

<REQ> The Geotechnical Categories shall be used to specify the: − minimum amount of ground investigation (see 4.1.9.2); − minimum validation of calculation models (see7.1.1); − minimum supervision (see 10.2); − minimum inspection (see 10.3); − minimum monitoring (see 10.4); − minimum designer qualifications and experience (see Clause 10 and Annex G); − minimum amount of reporting (see 12).

4.1.9.2 Minimum amount of ground investigation

<RCM> The minimum amount of ground investigation should be specified according to Table 4.4.

NOTE 13. NOTE 1 Ground investigation methods include desk studies, site inspections, laboratory tests, field tests, and monitoring as described by EN 1997-2.

NOTE 14. NOTE 2 The minimum amount of ground investigation for specific geotechnical structures is given in EN 1997-3.

<PER> In case the minimum amount of ground investigation of Table 4.4 is not satisfied, additional measures should be taken into account.


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NOTE 15. NOTE 2 Observational Method or design assisted by testing are examples of these additional measures.

<PER> Ground investigations for GC3 may also include more advanced laboratory or in situ tests than are specified in EN 1997-2, using methods adapted to the local conditions. <New B5>

<PER> In certain situations, sufficiently reliable ground properties for GC1 may be determined based on a desk study and site inspection, without performing additional ground investigation. <New B5>

Table 4.5 Minimum amount of ground investigation for different Geotechnical Categories


Minimum amount of ground investigation

GC3 All items given below for GC2 and, in addition: − sufficient investigations to evaluate the variability of critical ground

parameters for all critical geotechnical units at all locations; − measures to ensure high quality sampling and testing procedures.

GC2 All items given below for GC1 and, in addition: − additional investigations of ground conditions by methods described in

EN 1997-2; − sufficient investigation points so that all critical geotechnical units that

need to be described in the Geotechnical Design Model are recognized at various locations;

− determination of relevant ground parameters using more than one ground investigation method.

GC1 All items given below: − desk study of the site, review of comparable experience; − site inspection.

4.2 Principles of limit state design

General

<REQ> Geotechnical structures shall be designed according to the principles of limit state design given in EN 1990, Clause 5.

<REQ> Exceedance of limit states for geotechnical structures shall be verified by one or more of the following:

− calculations using partial factor method (4.4) or other reliability-based methods; − prescriptive measures (4.5); − testing (4.6); − the Observational Method (4.7).

<REQ> Verification of limit states by any of the methods given in (2) shall consider the possibility of: - failure in the ground; or - failure of structural elements in contact with the ground; or - combined failure of the ground and structural elements.


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NOTE Details of limit states for specific geotechnical structures are given in EN 1997-3.

<REQ> For all design situations verification of limit states by any of the methods given in (2) shall provide a level of reliability no less than that required by EN1990.

Design situations

<REQ> Design situations shall take into account the effect of the new structure on existing structures, services, and the local environment.

NOTE Design situations are classified in EN 1990, 5.2.

<REQ> The zone of influence of the structure shall be taken into account in the definition of design situations.

NOTE Guidance on selection of the zone of influence for different geotechnical structures is given in EN 1997-3.

<REQ> Environmental influences on actions and resistances shall be taken into account when selecting design situations.

<REQ> Design situations shall take into account the effects of dynamic or cyclic actions.

4.3 Basic variables

Actions and environmental influences

4.3.1.1 Classification and representative values of actions

<REQ> Actions shall be classified according to EN 1990, 6.1.1.

<REQ> Representative values of actions shall be derived according to EN 1990, 6.1.2.

4.3.1.2 Permanent and variable actions

<REQ> In addition to the actions coming from the supported structure, the following actions shall be included in relevant design situations for geotechnical structures:

- the weight of the ground and groundwater; - in situ ground stress and pressure conditions, both vertically as horizontally; - groundwater pressures and seepage forces; - ground movements and pressures arising from loads imposed on the ground directly or through

other structural elements; - ground movements and pressures caused by pre-existing stresses in the ground or changes

thereof; - ground movements and pressures caused by environmental influences.

<RCM> Actions other than those given in (1) should be included in relevant design situations as necessary.

<REQ> The design of geotechnical structures shall consider the effects of interaction between the structure and the ground.

<REQ> When evaluating groundwater actions, the criteria given in Clause 6 shall be followed.


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4.3.1.3 Cyclic and dynamic actions

<RCM> Variable actions should be considered as:

- cyclic actions, when they induce significant strength and stiffness degradation of the ground parameters, generation of excess pore pressures, permanent settlements, vibration in the surrounding;

- dynamic actions, when they induce inertial effects on the geotechnical structures; or - cyclic and dynamic actions when the two previous conditions both hold.

NOTE 1: Examples of cyclic or dynamic actions include wind, waves, eccentricities of rotating masses, and regular operation of machineries and wind turbines.

NOTE 2: Dynamic actions are defined in EN 1990.

<REQ> The potential effects of the following actions on the geotechnical structure shall be considered:

- cyclic actions caused by eccentricities of rotating masses; - cyclic actions transmitted by regular operation of machineries, wind turbines, chimneys; - traffic loads

NOTE Potential effects of cyclic actions are ground strength degradation, stiffness degradation, densification, generation of excess pore pressures, permanent settlements, vibrations in the surrounding ground.

<RCM> Actions other than those given in (1) should be verified as necessary.

4.3.1.4 Environmental influences

<REQ> Environmental influences shall be considered in the assessment of: − design situations; − geometrical data; − actions; − material properties.

<REQ> The adverse effects on the geotechnical structure of the following environmental influences shall be considered:

− existing climate conditions; − atmospheric interactions leading to changes in ground water content; − biological activity, including swelling and shrinkage caused by vegetation; − freezing and/or thawing of groundwater; − scour; − chemical composition of neighbouring ground and groundwater; − ground degradation, weathering: change of physical, chemical and/or mineralogical composition; − natural and man-made cavities and underground spaces; − pre-existing activities at regional scale (dewatering, oil or gas extraction, mining).

<Drafting note: Drafting EN 1997-3 it should be considered that, if environmental influences justify it, prescriptive measures may be used in geotechnical design.>

<RCM> The adverse effects on the geotechnical structure of environmental influences other than those given in (2) should be verified as necessary.


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<RCM> The following effects on the environment caused by the geotechnical structure should be considered:

− groundwater changes in the ground; − surface water changes above the ground; − temperature changes in the ground.

Material and product properties

<REQ> The determination of representative values of ground properties to be used in ULS and SLS verifications shall be based on the derived values determined in the ground investigation.

NOTE 16. NOTE 1 The representative value refers to a particular ground property of a single geotechnical unit.

NOTE 17. NOTE 2 Guidance on the selection of structural material properties is given in the other Eurocodes.

<REQ> The determination of representative values of ground properties shall take into account: - pre-existing knowledge including geological information and data from previous projects; - uncertainty due to the quantity and quality of site-specific data; - uncertainty due to the spatial variability of the measured property; and - the zone of influence of the structure at the limit state being considered.

<REQ> The representative value of a ground property shall be the value affecting the occurrence of the limit state, corresponding to:

- a mean value of the ground property, when the verification of the limit state in study is insensitive to the spatial variability of the ground property in the volume of the ground involved in the limit state; or

- an inferior or superior value of the ground property, when the verification of the limit state in study is sensitive to the spatial variability of the ground property in the volume of the ground involved in the limit state.

<REQ> The representative value of a ground material property Xrep shall be determined from either Formula (4.1a) or Formula (4.1b) :

𝑋𝑋rep = 𝜂𝜂 𝑋𝑋nom (4.1.a)

𝑋𝑋rep = 𝜂𝜂 𝑋𝑋k (4.1.b)

where:

η is a conversion factor accounting for effects of scale, moisture, temperature, ageing of materials, anisotropy, stress path or strain level;

Xnom is the nominal value of the ground property;

Xk is the characteristic value of the ground property.

<REQ> The nominal value of a ground property Xnom shall be selected as a cautious estimate of the value affecting the occurrence of the limit state (mean or extreme value based on the knowledge of the construction site and experience in comparable cases.

NOTE 18. The nominal value can be a mean, inferiror, or superior value as defined in (3).


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<REQ> The characteristic value of a ground property Xk shall be determined by statistical methods with a confidence level of 95%, as follows:

- when a mean value is to be used: an estimate of the 50% fractile of the ground property; - when an inferior value is to be used: an estimate of the 5% fractile of the distribution of the ground

property; or - when a superior value is to be used: an estimate of the 95% fractile of the distribution of the

ground property.

<RCM> The characteristic value of a ground property (Xk) should be determined using Formula (4.2):

𝑋𝑋k = 𝑋𝑋mean[1∓ 𝑘𝑘n𝑉𝑉x] = 𝑋𝑋mean[1∓𝑘𝑘n𝜎𝜎x𝑋𝑋mean

] (4.2)

where: Xmean is the mean of the ground property X from a number (n) of sample derived values; VX is the coefficient of variation of the ground material property X; kn is a coefficient that depends on the number of values (n) used to estimate Xmean; ∓ denotes that knVX should be subtracted when a lower value of Xk is critical and added when an

upper value is critica;. σx is the standard deviation of X.

NOTE 1 Formula 4.2 assumes that the values X follow a normal distribution. Other expressions are used for other statistical distributions.

NOTE 2 Annex B gives a procedure to evaluate the different terms in Formula (4.2) and provides indicative values of VX for common ground and test parameters .

NOTE 3 The characteristic value assessed by Formula (4.2) and Annex B is such that the calculated probability of a worse value governing the occurrence of the limit state under consideration is not greater than 5%.

<PER> Geometrical and mechanical properties of geotechnical units may be described in probabilistic terms.

<REQ> Any assumed spatial trend in ground properties shall be identified in the Geotechnical Design Model.

<RCM> Best-estimate values should be obtained as: − the mean or the median of a sample of derived values, whichever it is considered more

appropriate; − the values used in back-analysis to reproduce the performance of a geotechnical structure known

by monitoring.

NOTE Best-estimate values are used for prognosis in contrast to the representative values that are used for SLS verification.

Geometrical data

<REQ> The ground surface, surface water and groundwater levels, boundaries between geotechnical units, and the dimensions of the geotechnical structure shall be treated as geometrical data.

<RCM> Representative values of ground level and dimensions of geotechnical structures or elements should normally be nominal values.


33

NOTE 19. Representative values of groundwater and surface water levels are defined in Clause 6.

<RCM> Representative values of boundaries between geotechnical units should be cautious estimates of the values affecting the occurrence of the limit state.

<PER> The geometrical properties of discontinuities within a geotechnical unit may be either: − accounted for as properties of discretely defined discontinuities within the unit; or − taken into account when defining equivalent ground properties for the unit.

4.4 Verification by the partial factor method

General

<REQ> When checking ultimate limit states of a geotechnical structure (or part of it), the inequality given by Formula (4.3) shall be verified:

𝐸𝐸𝑑𝑑 ≤ 𝑅𝑅𝑑𝑑 (4.3)

where:

Ed is the design value of the effect of actions;

Rd is the design value of the corresponding resistance. NOTE 20. This is a more specific version of EN 1990, 8.3.1(1).

<RCM> When checking ultimate limit states caused by excessive deformation of the ground, the inequality given by Formula (4.4) should be verified:

𝐸𝐸𝑑𝑑 ≤ 𝐶𝐶𝑑𝑑,𝑈𝑈𝑈𝑈𝑈𝑈 (4.4)

where, in addition to the symbols defined for Formula (4.2):

Cd,ULS is the design value of the excessive deformation that is considered to cause an ultimate limit state.

NOTE 21. This is a more specific version of EN 1990, 8.3.1(2).

NOTE 22. In Formula (4.3), Ed is a displacement or strain, rather than a force or stress.

NOTE 23. NOTE 3 In ductile materials, in particular, an ultimate limit state of excessive deformation can occur before rupture of the material.

NOTE 24. Guidance on the selection of Cd,ULS is given in EN 1997-3.

<RCM> When checking serviceability limit states, the inequality given by Formula (4.5) should be verified:

𝐸𝐸𝑑𝑑 ≤ 𝐶𝐶𝑑𝑑,𝑈𝑈𝑈𝑈𝑈𝑈 (4.5)

where: Ed is the design value of the effects of actions specified in the serviceability criterion, determined

on the basis of the relevant combination; Cd,SLS is the limiting design value of the relevant serviceability criterion. NOTE 25.


34

Design values of actions and effects-of-actions

<RCM> Ultimate limit states involving failure of the ground should be verified using partial factors for actions and effects-of-actions from Design Cases 1-4, as specified in EN 1997-3.

NOTE 1 Design Cases 1-4 are defined in EN 1990, Annex A.

NOTE 26. In Design Case 1, partial factors > 1.0 are applied to unfavourable actions. Design Case 1 can be used with the Resistance Factor Approach, RFA (with partial factors on action) or with the Material Factor Approach (MFA).

NOTE 27. In Design Case 2, which is a combined verification of strength and static equilibrium, partial factors are applied to actions in two different combinations. Design Case 2 is static equilibrium with partial factors applied on actions.

NOTE 28. In Design Case 3, partial factors = 1.0 are applied to most actions (except to variable actions). Design Case 3 is used primarily with the Material Factor Approach (MFA).

NOTE 29. In Design Case 4, partial factors are applied to effects of actions (and not to actions). Design Case 4 can be used with the Resistance Factor Approach (RFA) or the Material Factor Approach (MFA).

NOTE 30. Table 4.6 summarizes the general applicability of Design Cases 1-4 in geotechnical design. Rules for the geotechnical structures covered by EN 1997-3.

Table 4.6 General applicability of Design Cases 1-4 in geotechnical design Ultimate limit

state Design Case (and indicative values of partial factors)

DC1 DC2 DC3 DC4

DC2a DC2b

Structural resistance

Static equilibrium and uplift Geotechnical design

γQ > γG > 1.0 γQ > γG > 1.0 γG = 1.0 γQ > 1.0

γG = 1.0 γQ > 1.0

γE > 1.0 γQ > 1.0

Failure by rupture Failure due to

excessive deformation

Loss of rotational equilibrium

Loss of vertical equilibrium due to

uplift forces

Time-dependent effects

<RCM> When design values of the effects of actions are calculated using Formula (8.4) of EN 1990, partial factors γF should be applied to actions.

NOTE 31. Values of the partial factor γF for ultimate limit states are given in Annex A of EN 1990.


35

<RCM> When design values of the effects of actions are calculated using Formula (8.5) of EN 1990, partial factors γE should be applied directly to the effects-of-actions.

NOTE 32. Values of the partial factor γE for ultimate limit states are given in Annex A of EN 1990.

Design values of material properties and resistance

<RCM> Ultimate limit states involving failure of the ground should be verified using partial factors for material properties or resistance, as specified in EN 1997-3.

<RCM> When design values of geotechnical resistance are calculated using Formula (8.20) of EN 1990, partial factors γM should be applied to material properties.

NOTE 33. Values of the partial factor γM are given in Annex A of this standard.

NOTE 34. This is commonly known as the “material factor approach” (MFA).

<RCM> When design values of geotechnical resistance are calculated using Formula (8.21) of EN 1990, partial factors γR should be applied directly to the resistance.

NOTE 35. Values of the partial factor γR are given in EN 1997-3 for specific geotechnical structures.

NOTE 36. This is commonly known as the “resistance factor approach” (RFA).

<RCM> Except as given in (5) below, the design value of a ground property Xd should be calculated from Formula (4.6):

𝑋𝑋d = 𝑋𝑋rep𝛾𝛾M

(4.6)

where:

Xrep is the representative value of the geotechnical material property;

γM is a partial material factor;

NOTE 37. The weight density of the ground is not usually factored although actions arising from weight density can be factored.

<RCM> The design value of the angle of internal friction of the ground ϕd should be calculated from Formula (4.7):

tan𝜑𝜑d = �tan𝜑𝜑rep𝛾𝛾tanφ

� (4.7)

where, further to the symbols already defined for Formula (4.6):

ϕrep is the representative value of the angle of internal friction of the ground;

γtanϕ is a partial material factor applied to the angle of internal friction of the ground.

NOTE 38. The symbol γϕ was used previously (in EN 1997-1:2004) for γ tanϕ.

NOTE 39. Values of the partial factor γ tanϕ for different design situations are given in Annex A.

<PER> Design values of geotechnical material properties may be assessed directly.


36

<REQ> Only one of the consequence factors KR, KM and KF shall be applied at the time.

<PER> Provided that the resulting partial factor is not less than 1,0, the value of γM may be adjusted according to the consequences of failure, using the consequence factor KM .

NOTE 40. Values of KM for different classes of consequences are given in Annex A.

<PER> Provided the conditions specified in (10) below are satisfied, the value of γM for transient design situations may be multiplied by a factor Ktr ≤ 1,0 provided that the product KtrγM is not itself less than 1,0.

NOTE 41. Values of Ktr are given in Annex A.

<RCM> The reduction factor Ktr should only be applied if: − the ground responds in a ductile manner; − contingencies are available to deal with any arising problems that would affect the safety of the

works; − the consequences of failure for adjacent structures or for the general public are limited.

Design values of geometrical data

<REQ> Design values of geometrical data shall be determined according to EN 1990, 8.3.6.

NOTE 42. NOTE: Values of ∆a to be entered into Formula (8.17) of EN 1990 are given in EN 1997-3 for specific geotechnical structures.

Combination of actions

<REQ> Combinations of actions for ultimate limit states shall be determined according to EN 1990, 8.3.7.

<REQ> Combinations of actions for serviceability limit states shall be determined according to EN 1990, 8.4.5.

4.5 Verification by prescriptive measures

<PER> Limit states involving geotechnical structures may be verified using the prescriptive measures specified in EN 1997-3.

NOTE 43. Limitations and application of prescriptive measures are given in EN 1997-3.

4.6 Verification by testing

<PER> Limit states involving geotechnical structures may be verified directly by testing.

NOTE 44. Testing limit state directly is known as “verification by testing”.

NOTE 45. Methods of testing to verify limit states directly are given in EN 1997-3 for specific geotechnical structures.

< REQ> The following shall be considered when using verification by testing: − differences in the ground conditions between the test and the actual construction; − time effects; − scale effects; − effects of stress levels;


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− effects of particle size.

<PER> Testing may also be used to determine the performance of the geotechnical structure (or part of it).

4.7 Verification by the Observational Method

<PER> Limit states involving geotechnical structures may be verified by using the Observational Method.

<REQ> Different sets of assumed behaviour of the geotechnical structure shall be established, covering all foreseeable ground responses and ground-structure interactions.

<PER> Empirical and prescriptive methods may be used, nevertheless including a Contingency Plan with its different design variants.

<REQ> For each set of behaviour, the design including a contingency plan with design variants shall be established and verified.

<REQ> For each Contingency Plan and its design variants, alarm values shall be specified.

<REQ> The design variants shall be sufficiently similar to each other to allow rapid replacement of a design variant by one matching the observed behaviour.

<REQ> A plan of monitoring, observation, and testing shall be devised that enables the assumptions for each design variant to be verified or rejected based on the specified alarm values.

<REQ> The monitoring, observation, and testing programme shall be planned so that the frequency of measurements, observations, and tests – as well as the procedures for reading and analysing the results – allow for rapid detection of and reaction to changes from the assumed behaviour of the current design variant.

<REQ> The results of monitoring, observation, and testing shall be assessed at regular intervals and the design shall be adapted to it by using the Contingency Plan.

<REQ> The design variants matching the actual geotechnical behaviour shall be put into operation immediately if the alarm values for the current design variant are exceeded.

4.8 Design assisted by testing

<PER> Testing may be used to determine ground and structural parameters for design.

NOTE 46. Testing to determine parameters is known as "design assisted by testing".

<PER> Representative values of ground resistance may be determined from the results of ground investigation, field testing of the ground-structure interface, or a combination of these.

NOTE 47. NOTE Guidance on the selection of representative resistance from field testing of the ground-structure interface is given in EN 1997-3.


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5 Materials

Drafting Note: Clause 5 structure on ground, soil and rock will be accordingly addressed by PT6, when part 1 and 2 are further drafted by PT6 to avoid doubling for soil and rock separately and to avoid doubling or contradictions between part 1 and 2. In this draft soil and rock are still kept separate in order to develop the clause for both materials equally.

5.1 General

<REQ> Values of ground properties shall be obtained from test results – either directly or through correlation, theory, or empiricism – and from other relevant information.

NOTE 48. Fill and manufactured materials (such as geosynthetics, concrete, steel, timber, and masonry) are often incorporated into geotechnical structures. These materials can be designed and specified according to the other Eurocodes and European Standards. See 5.4 and 5.5.

NOTE 49. Indicative values of ground properties are given in Annex F.

NOTE 50. Indicative values of ground properties are given in Annex F. For derivation of property values from laboratory and field tests, see EN 1997-2.

<REQ> Values of ground properties shall be interpreted appropriately for the limit state considered.

<RCM> Consideration should be given to possible differences between the behaviour of the ground in the test and in the real design situation owing to, and not limited to:

− quality of samples and test procedures and interpretation of results; − applicability of the test type for the particular ground conditions; − stress history of the ground − stress level and mode of deformation; − soil and rock structure; − time effects; − deterioration of the ground during the lifetime of the structure. − scale effects; − fluctuations in temperature; − effect of moisture content changes; − salinity of porewater; − effect of static, cyclic and dynamic actions, including load changes; − brittleness or ductility of the ground; − influence of workmanship on placement of fill; − effect of construction activities on ground properties.

<RCM> When determining values of ground properties, the following should be considered, as appropriate:

− the value of each ground property compared with relevant published data and local and general experience;

− results of any large-scale field trials and measurements from neighbouring constructions; − correlations between the results from more than one type of test.


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5.2 Soils

Weight density

<RCM> The weight density of fine soil should be determined from specimens taken from undisturbed samples.

<PER> The weight density of coarse soil may be derived from well-established or documented correlations.

<PER> The weight density may be determined from well-established or documented correlations, if no or not enough samples can be obtained.

Shear strength

<RCM>When determining the shear strength of soil, the influence of the following should be considered, as appropriate:

− initial stress, over-consolidation ratio, imposed stress level, stress path; − anisotropy of strength, especially in layered soils with e.g. sedimentary variability; − fissures; − strain rate effects; − imposed strain levels in the zone of influence; − pre-existing slip surfaces where progressive failure may have occurred; − time effects; − effects of temperature variations; − sensitivity of cohesive soil; − degree of saturation.

<RCM> The time period for which a soil is considered undrained should be based on its hydraulic conductivity, its stiffness, its degree of saturation,, and the proximity of drainage boundaries.

<RCM> The values of soil strength parameters should be applied only within the stress-range over which they are evaluated.

<RCM> Shear strength properties at the interface between two soil layers should be considered.

<REQ> The greater variance of effective cohesion (c′) compared to coefficient of internal friction (tan ϕ′) shall be considered when determining their characteristic values for use in the Mohr-Coulomb failure criterion.

NOTE 51. The Mohr-Coulomb failure criterion assumes a linear relationship between shear strength and normal stress, characterized by two parameters: effective cohesion c′ and the effective angle of internal friction ϕ′.

Stiffness, compressibility and swelling

<RCM> When determining soil stiffness, compressibility, and swelling behaviour the influence of the following should be considered, as appropriate:

− drainage conditions; − degree of saturation − temperature − level of mean effective stress; − over-consolidation; − stress path and stress changes;


40

− dilation; − level of imposed volumetric and shear strains <New :8> − stress or strain rate; − anisotropy.

<RCM> Recorded behaviour of previous similar constructions in comparable soil conditions should be taken into account when determining stiffness parameters.

<RCM> Linear stiffness parameters adopted in design should be appropriate for the strain level occurring in the soil.

<PER> Non-linear stiffness material models may be used to take account of the variation of soil stiffness with strain.

NOTE 52. Soil stiffness depends on the level of strain applied to the soil and varies significantly over the typical strain ranges for common geotechnical structures.

Creep

<RCM>When determining creep rate parameters, the influence of the following should be considered, as appropriate:

− in situ stress level; − final stress after loading; − pre-consolidation pressure and over-consolidation ratio; − stress or strain rate.

<PER> Materials likely to undergo significant creep strain or stress relaxation may be modelled explicitly in a non-linear form or in a linear form, provided that stiffness values take account of expected strain levels during the design service life of the structure.

Consolidation

<RCM> When determining consolidation parameters, the influence of the following should be considered, as appropriate:

− heterogeneity of the soil; − anisotropy (difference in horizontal and vertical consolidation characteristics); − stress level.

Hydraulic conductivity

<RCM> When determining hydraulic conductivity parameters, the influence of the following should be considered, as appropriate:

− soil heterogeneity; − soil anisotropy; − soil saturation − hydraulic gradient; − stress changes.

<RCM> Hydraulic conductivity parameters should be based on in situ tests which measure average properties within the zone of influence of the test.

NOTE 53. The accuracy of the hydraulic conductivity parameter value is highly dependent on the type of test as well of the homogeneity and isotropy of the sample and its representativeness for the relevant geotechnical unit; its inaccuracy is often normally greater than one order of magnitude.


41

NOTE 54. Presence of coarse soils within a fine soil layer can influence the permeability significantly.

<RCM> Consideration should be given to possible changes in hydraulic conductivity with increased effective stress above the in situ value.

<PER> In case of homogeneous and isotropic soils, the hydraulic conductivity may be estimated from knowledge of the soil’s grain size distribution.

5.3 Rock and rock masses

Weight density

<RCM> The weight density of rock should be determined from specimens taken where possible from intact rock samples.

<PER> The weight density may be determined from well-established or documented correlations, if no or not enough samples can be obtained

Intact Rock

5.3.2.1 Strength of intact rock

<RCM> When determining the strength of intact rock, the influence of the following should be considered, as appropriate:

− orientation of the axis of loading with respect to specimen anisotropy, bedding planes, and foliation;

− anisotropy of strength, especially in relation to its foliation; − rock strength degradation (softening); − method of sampling, storage history, and environment; − effects of drilling, cutting or blasting; − geometry of the tested specimens; − water content and degree of saturation at time of test; − test duration and loading rate.

5.3.2.2 Stiffness of intact rock

<RCM> When determining stiffness of intact rock, the influence of the following should be considered, as appropriate:

− method of determining the Young's modulus and the stress levels at which it is determined; − strain level; − orientation of the axis of loading with respect to specimen anisotropy, bedding planes, and

foliation; − rock stiffness degradation (softening); − geometry of the tested specimens; − effects of drilling, cutting or blasting; − loading rate.

Discontinuities in rock mass

5.3.3.1 Geometrical data of discontinuities

<REQ> When determining geometrical data of the location of discontinuities, the influence of the following shall be considered:

− amount / number of orientation groups and main discontinuity orientations;


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− orientation, strike and dip, of the discontinuities / discontinuity groups; − length / radius of the discontinuities − persistence; − spacing or frequency of the discontinuities; undulation.

5.3.3.2 Geotechnical data of discontinuities

<REQ> When determining geotechnical data of the location of discontinuities, the influence of the following shall be considered:

− aperture and its characterisation of the discontinuities; − roughness / smoothness of the discontinuities; − weathering and alteration of the discontinuities; − cohesion and friction of the discontinuities; − presence of infill inside the discontinuity and/or non-rock material within the discontinuity; − presence of water inside the discontinuity; − temperature and temperature range of the water, if present, inside the discontinuity.

5.3.3.3 Shear strength of and stiffness along discontinuities

<REQ> When determining the shear strength of and stiffness along discontinuities in the rock mass, the influence of the following should be considered in conjunction with the geometrical and geotechnical data described, as appropriate:

− testing conditions; − orientation of the joint in the rock test in relation to the assumed direction of stresses; − orientation of the shear test; − volume of the specimens tested; − loading rate; − dimensions of the sheared area; − pore-water pressure conditions; − possibility of progressive failure governing the behaviour of the rock in the ground.

<REQ> When addressing failure planes, the geometrical and geotechnical data of discontinuities shall be incorporated in shear strength analysis.

Strength and stiffness of rock mass

<REQ>When determining the properties of the rock mass, the influence of the following shall be considered:

− type of rock; − strength of intact rock and rock mass; − geometry and qualification of discontinuities; − anisotropy of the rock mass; − in situ stress levels in the rock; − quality of rock mass; − weathering and alteration of discontinuities; − groundwater condition.

<PER>Rock mass classification methods may be used for determination of rock mass shear strength and stiffness, if no other determination methods possible or available.

<RCM> Properties of rock mass should be determined based on well-established experience complemented by testing.


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Time dependent properties of rock mass

<REQ> The occurrence possibility and possible types of time dependent behaviour of rock mass shall be addressed.

<REQ> When determining any time dependent properties of rock mass, the influence of all the following shall be considered:

− in situ stress levels in all main stress directions; − groundwater conditions; − natural water content; − water pressure conditions; − sensitivity to changes in moisture or water content; − temperature and temperature fluctuations; − effect of temperature and climate; − effect of sampling and transportation of samples; − environmental conditions for the transient and persistent design situations.

<REQ> When determining any time dependent properties of rock mass, its relation with and effect as a function of the design service life shall be considered:

5.3.5.1 Swelling

<REQ> When determining swelling of rock mass, the influence of the following shall be considered:

− content of possible swelling material components in the rock; − the swelling capacity of the material components in the rock.

5.3.5.2 Dissolution

<REQ> When determining dissolution properties of rock mass, the influence of the following shall be considered:

− material or content of possible material components in the rock susceptible to dissolution; − sensitivity of dissolution.

5.3.5.3 Disintegration

<REQ> When determining disintegration properties of rock mass, the influence of the following shall be considered:

− material or content of possible material components in the rock susceptible to disintegration; − disintegration (ravelling) resistance of rock.

5.3.5.4 Squeezing and creep

<RCM>When determining squeezing and creep rate parameters, the influence of the following should be considered, as appropriate:

− creep and squeezing potential of the rock mass or materials in the rock; − ductility; − final stress after loading or unloading; − stress or strain rate.

<PER> Materials likely to undergo significant creep strain may be modelled explicitly in a non-linear form, provided that stiffness values take account of expected strain levels during the design service life of the structure.


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5.3.5.5 Spalling, crushing and rock burst

<RCM>When determining spalling, crushing and rock burst, the influence of the following should be considered, as appropriate:

− spalling and rock burst potential of the rock mass or materials in the rock; − brittleness; − final stress after loading or unloading; − stress or strain rate.

Hydraulic conductivity of rock mass

<REQ> The hydraulic conductivity of a rock mass shall be measured by in situ tests or determined from local experience.

<PER> The hydraulic conductivity of rock may be measured for other media.

<RCM> When determining hydraulic conductivity parameters, the influence of the following should be considered, as appropriate:

− degree of jointing and anisotropy; − existence of other discontinuities such as weathering zones, fractures and fissures; − discontinuity apertures; − discontinuity infill; − hydraulic gradient.

NOTE 55. The inaccuracy of the hydraulic conductivity parameter value is normally greater than one order of magnitude.

<RCM> In situ hydraulic conductivity should be determined by a system of pumping tests combined with flow logging, with due consideration of the spatial, hydrogeological flow conditions around the structure and the mapping of the patterns of joints and other discontinuities.

<PER> If hydraulic conductivity parameters. cannot be reasonably obtained from in situ tests or in situ tests cannot be conducted, parameter values may be derived from well-established or documented correlations.

<RCM> When determining the hydraulic conductivity of the rock mass, the scale effect should be considered, which describes the difference between the tested volume and the volume affected by the groundwater flow in the geotechnical unit.

5.4 Fill

<REQ> The criteria for specifying material as suitable for use as engineered fill shall be based on achieving the required strength, stiffness, durability and permeability, including classification and index properties, after placing.

<REQ> The criteria shall take account of the purpose of the engineered fill and the requirements of any structure that is placed on it.

<REQ> EN 16907 shall be used for specification of engineered fill for earthworks.

<REQ> The design shall include adequate measures to ensure material placed as fill within the construction works does not cause contamination of the environment, ground, or groundwater.


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5.5 Other materials

Geotextiles and geosynthetics

<REQ> Geosynthetics and geotextile-related products incorporated into geotechnical structures shall conform to ENs 13249 to 13257 and 13265.

<REQ> Geosynthetic reinforcement shall conform to the requirements of EN 14475.

Concrete

<REQ> Concrete incorporated into geotechnical structures shall conform, also regarding durability, to EN 1992 and EN 206, except where specified otherwise in EN 1997.

<REQ> Sprayed concrete incorporated into geotechnical structures shall conform to EN 14487.

<REQ> Steel reinforcement for concrete foundations shall conform to EN 10080.

Ground treatment, incl. grout and vertical drainage

<REQ> Grouting in ground shall conform to EN 12715.

<REQ> Jet-grouting in ground shall conform to EN 12716.

NOTE 56. Guideline on requirements on grout for a specific geotechnical structure is given in EN 1997-3.

<REQ> Deep mixing in ground shall conform to EN 14679.

<REQ> Ground treatment by deep vibration in ground shall conform to EN 14731.

<REQ> Vertical drainage in ground shall conform to EN 15237.

Steel

<REQ> Steel incorporated into geotechnical structures shall conform, also regarding its durability, to EN 1993, except where specified otherwise in EN 1997.

NOTE 57. Steel properties for rock bolts are specified in EN 1993 and EN 1997.

NOTE 58. Durability aspects of steel reinforcement for use in reinforced soil structures are specified in EN 1997-3.

<REQ> Steel piling shall conform to EN 1993-5.

<REQ> Hot rolled steel products incorporated into geotechnical structures shall conform to EN 10025. Otherwise, it shall be demonstrated by additional testing that the products meet the requirements of EN 10025 relevant for the geotechnical design.

<REQ> Cold formed steel products incorporated into geotechnical structures shall conform to EN 10219. Otherwise, it shall be demonstrated by additional testing that the products meet the requirements of EN 10219 relevant for the geotechnical design.


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Timber

<REQ> Timber incorporated into geotechnical structures should conform to EN 1995, EN 335, and EN 350.

<Drafting note: SC5 is developing a standard for wooden piles – this clause will be updated when this is avaliable>

Masonry

<REQ> Masonry incorporated into geotechnical structures shall conform to EN 1996.

<RCM> Masonry units should conform to the relevant part of EN 771.


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6 Groundwater

6.1 General

Design considerations

<REQ> The spatial and temporal variation of surface water, groundwater and piezometric levels and the resulting distribution of groundwater pressures, hydraulic gradients, and seepage forces shall be determined for the design of geotechnical structures.

<RCM> The determination of groundwater pressures, hydraulic gradients, and seepage forces should consider:

- surface water level of and its possible variation over time; - groundwater level and its possible variation over time; - possible variations in groundwater pressure and ground permeability over time; - artesian groundwater pressure; - possible changes of groundwater pressures due to the growth or removal of vegetation; - sensitivity of each limit state to variations in groundwater pressures and levels; - heterogeneity and anisotropy of the ground permeability, including the effects of layering or

fissuring; - supply of water by rain, flood, burst water mains or other means; - any geometrical features (e.g. corners of excavations or narrow excavations below groundwater

level) that could cause flow to concentrate; - construction activities including their effects on drainage; - effects of drainage accounting for future maintenance and possible malfunction; - influence of the completed structure on the groundwater regime; - climate change.

<RCM> Groundwater pressures arising from a common source of groundwater or surface water should be considered as a single action.

NOTE 59. This rule is commonly known as the ‘single-source principle’ (see EN 1990 x.xx).

<REQ> When a single-source of groundwater action produces both favourable and unfavourable effects, the critical load cases involving upper and lower groundwater pressures shall be identified and verified.

<REQ> Soil suction based on unsaturated soil conditions shall only be included in the design when the assumed degree of saturation can be maintained throughout the design situation.

NOTE 60. Conservative design normally assumes zero groundwater pressure above the piezometric level.

<REQ> When unsaturated soil conditions are assumed, representative values of soil properties shall be selected corresponding to the assumed soil degree of saturation.

<RCM> When surface water has a significant flow, water hydrodynamic actions should be considered.

Properties of groundwater

<REQ> The effects of groundwater chemistry on the ground and on construction materials in contact with the ground shall be considered.


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<PER> In the absence of significant quantities of solutes in groundwater, the representative value of weight density of groundwater may be approximated to 10 kN/m3.

6.2 Surface water, groundwater, and piezometric levels

<REQ> Surface water, groundwater, and piezometric levels shall be determined to give the most critical design situation.

<RCM> Surface water, groundwater, and piezometric levels should be determined by direct measurements, taking into account the historical data available.

<PER> When direct measurements are not reliable enough for the design service life of the structure, surface water, groundwater, and piezometric levels may be determined only from historical data.

<RCM> Representative values of piezometric levels should correspond to the annual probability of exceedance of the groundwater pressures that arise from them.

NOTE 61. The annual probability of exceedance of the representative values of the groundwater pressures is given in 6.3.2.

6.3 Groundwater pressures

General

<RCM> Groundwater pressures should be determined from direct measurements in accordance with EN 1997-2, taking into account the historical data available.

<PER> In the absence of direct measurements, groundwater pressures may be determined from historical data available.

<RCM> Where groundwater and surface water are connected to each other, the resulting groundwater pressures should be applied in the design as a physically consistent load system.

<REQ> The calculation of groundwater pressures shall take into account possible non-hydrostatic conditions.

<REQ> If the groundwater pressure is not hydrostatic, the variation of groundwater pressures with depth shall be determined in all geotechnical units identified in the Ground Model.

<PER> Groundwater pressures may be classified as accidental actions when: - the annual probability of exceedance is less than that specified in EN 1990, 6.1.4.2; - they are caused by extreme events with a probability of exceedance less than specified in 6.3.3(2); - engineered systems fail owing to deficiency in sealing or barrage; - drainage system fails.

Representative values of groundwater pressures

<RCM> The representative value of groundwater pressure Gw,rep should be selected as either: - a single permanent value, equal to the characteristic upper Gwk;sup or lower Gwk;inf value of

groundwater pressure (whichever is more adverse); - the combination of:

o a permanent value Gwk, equal to the mean value of groundwater pressure, and


49

o a variable value, equal to the representative value Qw,rep of the variation in groundwater pressure.

NOTE 62. The values of Gwk,sup and Gwk,;inf are based on an annual probability of exceedance of 2 % (which

corresponds to a return period of 50 years), unless the National Annex gives a different value.

NOTE 63. Figure 6.1 illustrates the different terms used to denote representative values of groundwater pressure, as defined in EN 1990, 3.1.3.17.

Figure 6.1 Representative values of groundwater pressures – illustration of characteristic, combination, frequent, and quasi-permanent values

<RCM> If there is insufficient data to derive their values on the basis of the annual probability of

exceedance, Gwk,sup and Gwk,inf should be selected as cautious estimates of the most adverse values likely to occur during the design situation.

The representative value Qw,rep of the amplitude of the variation in groundwater pressure shall be selected as one of the following, depending on the design situation:

- the characteristic value Qwk; or - the combination value Qw,comb; or - the frequent value Qw,freq; or - the quasi-permanent value Qw,qper.

NOTE 64. The values of Qwk, Qw;comb, Qw;freq, and Qw;qper are based on the probabilities of exceedance specified in EN 1990, 6.1.4.2.

<REQ> In persistent and transient design situations, Qw,rep shall be selected as:

- the characteristic value (Qwk), when groundwater pressure is the leading variable action; or - the combination value (Qw,comb), when groundwater pressure is an accompanying variable action.

Tref = design situation period

Characteristic Value - lower

Frequent Value - lower

Quasi-permanent value (mean)

Once in Tref

Combination Value - lower

Once in Tref

Frequent: 1 % of Tref

Frequent Value - higher

Characteristic Value - higher Combination value - higher

Groundwater pressure

Time


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<PER> For simplicity, the combination value (Qw,comb) may be replaced by the (more adverse) characteristic value (Qwk ≥ Qw,comb).

<RCM> If there is insufficient data to determine their values on the basis of annual probability of exceedance, the characteristic value Qwk and the combination value Qw,comb should be selected as a cautious estimate of the most adverse value likely to occur during the design situation.

<REQ> In accidental design situations, Qw,rep shall be selected as: - the accidental value (Aw,d) where groundwater pressure is the leading variable action; or - the frequent value (Qw,freq) where groundwater pressure is an accompanying variable action.

NOTE 65. The value of Awd is based on the annual probability of exceedance specified in EN 1990, 6.1.4.2.

<PER> The quasi-permanent combination of actions including groundwater pressures as defined in EN 1990 may be used for analyses of long term loading effects, including long term settlements.

Design values of groundwater pressures for ultimate limit state design

<REQ> Design values of groundwater pressures in ultimate limit states shall be determined by one of the following methods:

− direct assessment; or − applying a deviation to the representative piezometric level or to the representative groundwater

pressure; or − applying a partial factor to the representative groundwater pressures or to their action effects.

NOTE 66. Methods that involve direct assessment or application of a deviation are usually suitable in cases where groundwater pressures are used to calculate shear strength from effective stresses (e.g. overall stability analyses or retaining wall design). Application of a partial factor is usually suitable in cases where groundwater pressures are used to calculate forces and bending moments on structural elements.

NOTE 67. The value of the partial factor is specified in EN 1990.

<REQ> When assessing design groundwater pressures directly or by applying a deviation to the representative piezometric level or groundwater pressure, design values of groundwater pressures for ultimate limit states shall have a probability of exceedance as specified in EN1990.

<PER> For accidental design situations, where the groundwater pressures are not the accidental action, design groundwater pressures may be taken equal to a combination of the representative permanent value Gwk and the frequent variable value Qw;freq.

NOTE 68. For accidental design situations, the design value of the leading action is selected directly. The accompanying design actions are set equal to frequent values.

Design values of groundwater pressures for serviceability limit state design

<REQ> Design values of groundwater pressures in serviceability limit states shall be equal to the representative values defined in 6.3.2.

6.4 Groundwater in freezing conditions

<REQ> The design shall consider the effect of groundwater in freezing conditions, if all of the following apply:

— there is groundwater or sufficient moisture available; — the geotechnical structure is in an area with temperatures below zero;


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— the ground is frost-susceptible.

NOTE 69. Guidance on the determination of ground frost-susceptibility is given in EN 1997-2.

<REQ> If freezing of groundwater is possible during the design service life, the following shall be

considered, as appropriate: — frost heave; — thaw weakening; — deformations and ultimate limit state due to frost and subsequent thaw; — change of material properties due to frost and its effect on frost heave; — change of material properties due to thaw and its effect on thaw weakening; — change of material properties with temperature in general;<New B3> — iteration effects of freeze thaw occurrences.


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7 Geotechnical analysis

7.1 Calculation models

General

<REQ> Calculation models shall be appropriate for the limit state under consideration.

NOTE 70. Calculation models for specific geotechnical structures are given in EN 1997-3.

NOTE 71. Knowledge of the ground and workmanship control are usually more significant in fulfilling the fundamental requirements than is precision in the calculation models.

<REQ> Calculation models shall account for the geometry and governing geotechnical behaviour at the relevant limit state and be consistent with the design assumptions.

<RCM> The assumptions, including idealisations and limitations, of geotechnical calculation models should be stated in the Geotechnical Design Report.

<RCM> Model input parameters with large effects on the model results should be clearly identified and reported.

<PER> Parametric analyses may be used to help in the selection of input parameters.

<REQ> Limit state verifications by calculation models shall consider the following, as appropriate: − discretization of geometry, including discontinuities; − initial stress states; − preceding construction stages; − boundary conditions; − drainage conditions (including permeability) and rates of loading; − the constitutive model; − strength and stiffness of structural elements; − actions and material parameters; − effects of cyclic and dynamic actions.

<REQ> Calculation models that are used for geotechnical design shall provide a level of reliability no less than that required by this standard.

<REQ> Calculation models used for geotechnical design shall be validated.

NOTE 72. NOTE Validation ensures that the calculation models used are appropriate for the specific design situation and are applied within their limitations.

<REQ>The minimum validation of calculation models used in geotechnical design shall be chosen according to the Geotechnical Category.

NOTE 73. The minimum validation of calculation models used in geotechnical design is given in Table 7.1 (NDP) unless the National Annex gives different minima.

NOTE 74. The minimum validation of calculation models for specific geotechnical structures is given in EN 1997-3.


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Table 7.1 (NDP) — Minimum validation of calculation models used in geotechnical design

Geotechnical Category Minimum validation of geotechnical calculation models

GC3 All the measures given below for GC2 and, in addition: • Calibration of the calculation model for the specific

site against another suitable calculation model or site observations.

GC2 All the measures given below for GC1 and, in addition: • Documentation showing that the assumptions for

the calculation model used are relevant for the specific site and structure

GC1 All the measures given below: • Literature reference that the calculation model has

been used for similar conditions • Local experience shows that the calculation model is

suitable for the local conditions • When using calculation models contained in EN

1997-3, confirmation that the design falls within the limits of application stated in EN 1997-3.

Empirical models

<PER> Empirical models may be used for the verification of limit states.

NOTE 75. Empirical models are often intended for certain ground and site conditions. Therefore, they often have a narrow range of such conditions for which they are suitable or conservative.

Analytical models

<PER> Analytical models may be used for the verification of limit states.

<RCM> For the verification of serviceability limit states, limit equilibrium and limit analysis models should only be used in accordance with 9.1(5).

<Drafting note: sub-clause to be modified>

<RCM> Limit equilibrium analysis of rock masses should be based on shear strength along discontinuities in the rock mass that control the limit state in accordance with 9.1(5).

<Drafting note: sub-clause to be modified>

Numerical models

<PER> Numerical models and advanced constitutive models may be used for the verification of limit states.

<PER> Numerical models including advanced constitutive models may be used to obtain predictions of ground movements.


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NOTE 76. Advanced constitutive models include e.g. non-linear stress- and strain-dependent stiffness, dilatancy effects or creep behaviour.

<RCM> The validation according to Table 7.1 should be consistent with the complexity of the numerical model.

Calculation models for cyclic and dynamic actions

<RCM> Appropriate calculation models should be selected to assess the effects of cyclic actions.

NOTE 77. Calculation models to assess cyclic effects are provided in EN 1997-3.

<RCM> The characteristic combination of SLS should be used to assess the significance of cyclic effects listed in 4.3.1.4(1).

<REQ> When the expected effects of dynamic actions are significant a full dynamic interaction analysis with modelling of the vibration system and the dynamic action shall be performed.

NOTE 78. For machine foundations design analyses aim at predicting their response to ensure that both ULS and any SLS are verified. SLS are typically specified in terms of peak velocity or displacement or of acceleration amplitudes during normal operation of the machinery.

<RCM> When dynamic actions are represented by quasi-static actions, ground parameters should take into account the effects of the frequency and the amplitude of the dynamic actions.

NOTE 79. Quasi-static actions are defined in EN 1990.

NOTE 80. Clause 10 of EN 1997-2 provides the ground parameters to use in ULS and SLS verifications when cyclic and dynamic actions are involved.

7.2 Model factors

<RCM> Model factors should be used to adjust any significant bias and additional uncertainty in a calculation model compared with the reference model, to ensure that they are sufficiently accurate for their intended purpose or provide a level of reliability no less than that required by EN1990.

NOTE 81. Reference models (to be defined) are given in EN 1997-3.

NOTE 82. Partial factors for the reference model already include allowance for some bias and uncertainty.

NOTE 83. The value of the model factor is 1.0 unless the National Annex gives a different value for a specific calculation model.


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8 Ultimate limit states

8.1 General

<REQ> Verification of ultimate limit states involving geotechnical structures shall be performed according to EN 1990, 5.3 and 8.3.

NOTE 84. Guidance on the applicability of EN 1998-5 for verification of geotechnical structures within seismic areas is given in EN 1997-3.

8.2 Types of ultimate limit states

<REQ> All the relevant limit states and the associated failure modes shall be verified for the design of geotechnical structures.

Failure by rupture

<REQ> This sub-clause 8.2.1 shall apply to all limit states where failure in the ground or structural element occurs because the ultimate strength of the material is reached.

<REQ> The following (non-exclusive list of) types of ground rupture shall be considered, as appropriate:

− loss of overall stability; − translational and rotational failure of soil or rock blocks or mass; − rock falls; − flexural toppling; − sliding.

NOTE 85. Further guidance on overall stability is given in Clause 4 of EN 1997-3.

NOTE 86. Guidance on specific forms of rupture to consider for different geotechnical structures is given in EN 1997-3.

<REQ> Rupture of structural elements shall be avoided by verification of ultimate limit states according to the appropriate structural Eurocode.

<REQ> Specific requirements related to the type of geotechnical structure according to EN 1997-3 shall be met.

NOTE 87. Rupture of a structural element does not necessarily imply failure of the whole geotechnical structure.

Failure of the ground due to excessive deformation

<REQ> The sub-clause 8.2.2 shall apply when failure occurs in a ductile manner (without rupture) and the limit state is caused due to excessive deformation of the ground.

NOTE 88. The failure includes excessive deformation prior to collapse, reducing the possibility to use, with retained safety, the geotechnical structure for the intended application.

Failure of the ground by excessive deformation includes, but is not limited to, the following mechanisms: creep and squeezing; swelling; shrinkage; consolidation settlement; accumulation of permanent strains under cyclic actions.


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<RCM> Account should be taken of comparable experience when assessing the deformation that is considered excessive.

Failure by loss of static equilibrium of the structure or ground

8.2.3.1 Loss of rotational equilibrium

<REQ> Loss of static equilibrium due to overturning of the structure shall be prevented sing Design Case 2 by verifying that any destabilizing design moments are less than or equal to the stabilizing design moment about the assumed point of rotation.

8.2.3.2 Loss of vertical equilibrium due to uplift forces

<REQ> Loss of static equilibrium due to uplift of an impermeable structure or a ground layer of low permeability shall be prevented by verifying that any destabilizing design vertical forces are less than or equal to the stabilizing design vertical forces (including any design resistance to uplift).

NOTE 89. The effects of all actions are compared with the resistances. Therefore, the actions consist of destabilising (permanent and variable) actions of groundwater pressures and other forces and the stabilising actions due to the weight of the structure. Resistance can be provided by anchors or piles or friction along the sides of the structure.

NOTE 90. This verification can also be applied for other fluids than water.

<REQ> When checking ultimate limit states of uplift, if the structure or ground layer acts as a rigid body, then the inequality given by Formula (8.1) shall be verified (see Figure 8.1a):

𝑈𝑈𝑑𝑑𝑑𝑑𝑑𝑑;𝑑𝑑 + 𝐺𝐺𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑;𝑑𝑑 + 𝑄𝑄𝑑𝑑𝑑𝑑𝑑𝑑;𝑑𝑑 − 𝐺𝐺𝑑𝑑𝑑𝑑𝑑𝑑;𝑑𝑑 ≤ 𝑅𝑅𝑑𝑑 (8.1)

where:

Udst;d is the design value of destabilising (uplift) force due to groundwater pressures;

Gdstb;d is the design value of any permanent destabilising force not caused by groundwater;

Qdst,d is the design value of any variable destabilising force not caused by groundwater;

Gstb;d is the design value of the stabilising (downward) forces;

Rd is design value of any resistance to uplift.

NOTE 91. Partial factors for actions are given in EN 1990; for ground properties in Annex A; and for resistances in EN 1997-3.

NOTE 92. When piles, anchors, etc. contribute to the resistance to uplift Rd, their design is covered by EN 1997-3.

<REQ> When checking ultimate limit states of uplift, if the structure or ground layer does not act as a rigid body, then the inequality given by Formula (8.2) shall be verified (see Figure 8.1b):

𝑢𝑢𝑑𝑑𝑑𝑑𝑑𝑑;𝑑𝑑 − 𝜎𝜎𝑣𝑣;𝑑𝑑 ≤ 0 (8.2)

where:

udst;d is the design value of destabilising (uplift) groundwater pressures;


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σv;d is the design value of the (stabilising) vertical total stress at the base of the layer that is subject to uplift.

NOTE 93. NOTE Design values of groundwater pressures are determined according to 6.3.3.

Figure 8.1 — Examples of design situations where uplift might be critical

<RCM>When additional structural verifications are necessary, they should be carried out according to 8.2.1 and 8.2.2.

Hydraulic failure caused by seepage

8.2.4.1 General

<REQ> In the presence of groundwater flow, the following limit states shall be verified for all ground conditions:

− hydraulic heave; − internal erosion and piping.

<RCM> The anisotropy of permeability of ground layers and of the ground stratigraphy should be considered in the assessment of groundwater seepage and groundwater pressures, together with the possible occurrence of confined aquifers.

8.2.4.2 Hydraulic heave

<REQ> In order to prevent a limit state of failure by hydraulic heave, vertical equilibrium shall be maintained in the ground by the combination of design values of the self-weight of the ground, groundwater pressures, and shear resistance in the ground.

<RCM> Components of shear resistance that are affected by groundwater pressure should be treated with special caution.


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<REQ> In cases of upward-flowing groundwater, it shall be verified that sufficient effective stress exists in the ground to support the self-weight of the ground and any supported structures, vehicles, and personnel.

<REQ> When checking an ultimate limit state of hydraulic heave, the inequality given in Formula (8.3) shall be verified for all points in the ground (see Figure 8.2):

𝑢𝑢d ≤ 𝛾𝛾w,k(𝑧𝑧 + ℎw) + 𝛾𝛾HYD �𝛾𝛾rep − 𝛾𝛾w,rep�𝑧𝑧 (8.3)

where:

ud is the design groundwater pressure at a point in the ground; γw,rep is the representative weight density of groundwater; z is the vertical distance of the point in the ground below the ground surface (not including any

overlying fill); hw is the vertical distance from the surface water level to the ground surface; γHYD is a partial factor for hydraulic heave; γrep is the representative value of the weight density of the ground.

NOTE 94. The purpose of the factor γHYD is to ensure that the effective stress in the ground remains positive

and also to allow for local variations of stresses at a granular scale, relevant to hydraulic failures.

NOTE 95. The values of γHYD is 0.67 unless the National Annex gives different values.

NOTE 96. In some cases, friction can be incorporated as per 8.2.4.2 (1).

NOTE 97. For an analysis method for retaining structures in steady state seepage using the equilibrium of a single soil column, see EN 1997-3.

Figure 8.2 One dimensional upward flow of water

8.2.4.3 Internal erosion and piping

<REQ> Where seepage of groundwater occurs through coarse soil, as defined in EN ISO 14688, it shall be verified that an ultimate limit state due to internal erosion or piping is not exceeded.


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<REQ> The design values of hydraulic gradients and seepage velocities shall be calculated on the basis of the design groundwater pressures specified in 6.3.3.

<REQ> When checking an ultimate limit state of internal erosion or piping, the inequality given in Formula (8.4) shall be verified:

𝑖𝑖𝑑𝑑 ≤ 𝑖𝑖𝑐𝑐𝑑𝑑 (8.4)

where:

id is the design value of the hydraulic gradient;

icd is the design value of critical hydraulic gradient (when soil particles begin to move).

<REQ> The critical hydraulic gradient for internal erosion and piping shall be determined taking into consideration, as appropriate:

− the direction of flow; − the grain size distribution and shape of grains; − layering of the ground.

NOTE 98. Values of ic;d greatly depend on particle size and grading of the soil. Typical values are between 0.3 and 0.9.

NOTE 99. Methods of assessing critical hydraulic gradients are given in The International Levee Handbook, CIRIA Report C731 (2013).

<RCM> Exceedance of an ultimate limit state due to internal erosion and piping should be prevented by measures including:

− filter protection at the free surface of the ground or at the end of any potential seepage path; − increase of the length of the seepage path; − reducing the hydraulic gradient; − sufficient safety against failure by heave in case of a horizontal ground surface; − sufficient stability of the surface layers in sloping ground (local slope stability).

<RCM> Filter protection should be provided by use of soil that fulfils adequate design criteria for filter materials or by the use of geosynthetic filters that prevent transport of fines without clogging.

<RCM> When determining the outflow hydraulic conditions for the verification of failure by piping, account should be taken of joints and interfaces between the structure and the ground which can become preferred seepage paths.

<RCM> Where prevailing hydraulic and soil conditions can lead to the occurrence of piping and where piping endangers the stability or serviceability of the hydraulic structure, prescriptive measures should be taken to prevent the onset of the piping process, either by the application of filters or by taking measures to control or to block the groundwater flow.

Failure caused by time-dependent effects

NOTE 100. Degradation, weathering, and change of chemical composition are not treated as separate limit states, but as environmental actions.

<Drafting note: this heading is kept as a place holder, to be consistent with the limit states mentioned in EN 1990. The heading might be needed for specific structures in EN 1997-3>


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Failure caused by cyclic effects

<REQ> Degradation of the ground resistance due to cyclic effects shall be considered.

<REQ> Liquefaction and generation of excess pore pressure should be considered for geotechnical structures located on saturated soils subjected to cyclic actions.

NOTE 101. Guidance to include cyclic effects for verifications of specific geotechnical structures is given in EN 1997-3.

<RCM> The ULS verifications should be carried out by using the persistent combination of the actions taking into account cyclic effects.

8.3 Procedure for numerical models

<RCM> For geotechnical structures, verification of ultimate limit states by numerical models should be based when relevant on the less favourable outcomes given by the:

− Material Factor Approach (MFA), using: — factors on actions γF from Design Case 3 and; — factors on material properties γM from Set M3;

− Effect Factor Approach (EFA), using: — factors on effects-of-actions γE from Design Case 4 and; — factors on material properties γM from Set M1.

NOTE 102. Values of γF and γE are given in EN 1990, Annex A.

NOTE 103. Values of γM are given in Annex A of this standard.

NOTE 104. The Material Factoring Approach (MFA) often determines the limiting ground resistance, whereas the Effects Factoring Approach (EFA) often determines the limiting structural resistance.

NOTE 105. In MFA, all possible geotechnical ultimate limit states are verified by demonstrating that equilibrium can still be obtained with design values of input parameters, without excessive deformation or a failure mechanism being activated.

<RCM> The ground strength mobilized in numerical models should not exceed the design value.

NOTE 106. The mobilized ground strength calculated by numerical models is influenced by the failure criterion as well as other input parameters, such as dilatancy and excess pore pressure. When using effective stress analysis to predict undrained or partially drained ground strength, for example, it is possible for the mobilized ground strength to exceed its design value.

<RCM> Strength reduction (as shown in Figure 7.1) should be used to reach design values of ground strength parameters.

NOTE 107. Different procedures are available to account for stress and strain changes caused by strength reduction and it is important that a suitable procedure is adopted in order to predict the most critical failure mechanisms accurately. Standard strength reduction procedures may not be applicable to advanced constitutive models.

<PER> Alternatively, design values of ground strength may be used as input at the start of a numerical model calculation (Figure 8.3), provided that consideration is given to the effect of using design values throughout the calculation on the accuracy of simulations.


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NOTE 108. The use of design values from the start of a numerical model calculation can be detrimental to the intended degree of conservatism. The effect can be conservative or non-conservative and can increase with successive stages of the analysis.

<PER> Ground strength reduction may be combined with structural strength or resistance reduction to help identify potentially critical collapse mechanisms of combined ground and structure failures.

NOTE 109. Reducing structural material strength or resistance reduces the effective stiffness of structures. Therefore, structural forces can be underestimated.

<RCM>Design values of axial force output in axially-loaded, slender structures obtained by EFA should be used to verify adequate resistance in addition to the MFA verification of ground failure.

NOTE 110. The axial resistance of slender structures such as piles, ground anchors and soil nails are highly dependent on the properties of the interface and disturbed ground immediately around such structures. Consequently, factoring the undisturbed ground strength alone cannot provide a sufficiently reliable means of verifying the ultimate limit state of such structures under axial loads.

NOTE 111. An additional check is necessary by comparing the governing values of design axial force obtained from the material and action effect factoring approaches with the corresponding resistance.

Figure 8.3 Procedures for ULS analyses with numerical methods

Initial stage

MFA (alternative) Material factoring approach with design values of ground strength parameters from the start. γF from Design Case 3, γG from Set M1.

Representative ground strength, actions and water levels

Design ground strength and actions, representative. water levels.

Design ground strength, actions and water levels

Representative ground strength, Characteristic actions and water levels

Apply γE to effects-of-actions to obtain design values of structural forces Ed.

Design ground strength, actions and water levels. Obtain design values of effects-of-actions Ed

Design water levels, apply γF and reduce ground strength to design values. Check output for any geotechnical failure, obtain design values of effects-of-actions Ed

Construction stage 1 if ULS clearly non-critical, no ULS stage necessary

Continues through any subsequent stages in the same way.

MFA (recommended) MFA with strength reduction, starting with representative values of ground strength. γF from Design Case 3, γG from Set M1.

EFA: γF and γE from Design Case 4, γM from Set M1

Construction stage


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<PER> Design values of outputs from geotechnical structure types other than those referred to in (6) above may also be compared with geotechnical resistances to assess the reliability against particular failure mechanisms occurring.

NOTE 112. MFA allows the most critical geotechnical ultimate limit state to be verified but does not necessarily provide the degree of safety against particular failure mechanisms occurring. If this is required, it can sometimes be obtained in this way (e.g. comparing the design value of spread foundation lateral load with its corresponding value of sliding resistance). The resistance value can be obtained from a separate calculation or by numerical models in accordance with (8) below.

<PER> Geotechnical resistances may be calculated by numerical models by forcing geotechnical structures to fail by particular mechanisms.

NOTE 113. Geotechnical resistances can be obtained by numerical models by simulating particular failure forms, usually separately from the simulation of the construction and normal use of geotechnical structures. For example, the vertical displacement of a rigid spread foundation can be increased until failure in order to obtain the bearing resistance from the output of force at failure.


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9 Serviceability limit states

9.1 General

<REQ> Serviceability limits states involving geotechnical structures shall be verified in accordance with EN 1990, 5.4 and 8.4, and this Clause 9.

<RCM> Design values of ground properties for serviceability limit states should be obtained by applying partial factors γM to representative values.

NOTE 114. The value of γM for SLS verifications is 1.0 unless the National Annex gives a different value.

<RCM> Representative values of ground properties should be used for the verification of SLS.

<RCM> Best-estimate predictions of performance should use best-estimate values of material properties and actions.

NOTE 115. Best-estimate prediction of performance is used for comparison with site observations.

<PER> A check on strength mobilisation may substitute for a direct verification of a serviceability limit only if:

− a sufficiently low fraction of the ground strength is used as mobilisation limit − established comparable experience exists with similar ground, structures and application

method.

NOTE 116. Guidance on application of this clause is given in EN 1997-3.

NOTE 117. Where relevant non-linear stress-strain behaviour has been obtained, the fraction of ground strength mobilised at serviceability limit state can be determined more accurately.

9.2 Overall ground movements

<RCM> Ground movement due to the following causes should be considered: − change in groundwater conditions and corresponding groundwater pressures; − vibrations induced by dynamic actions; − nearby excavations, quarrying, tunnelling and backfilling; − consolidation and creep; − volume loss of deep soluble strata or due to oxidation of organic content; − mining (active or historical) or similar works such as gas extraction; − effects of cyclic actions.

<RCM> When calculation models used to provide predictions of ground movement are unreliable, exceedance of serviceability limit states should be avoided by one of the following:

− limiting the mobilised shear strength to values specified in the design; − observing the movements and specifying actions to reduce or stop them, if necessary, as described

in 4.7.

<RCM> Calculations of ground movement should take account of: − expected rate of ground movements; − the loading distribution; − the construction method (including the sequence of loading); − the stiffness of the structure during and after construction; − the degradation of the stiffness and the accumulation of permanent strains due to cyclic effects.


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<PER> Improved predictions of ground movement and corresponding movements of geotechnical structures may be obtained by ground-structure interaction analysis to take account of structure stiffness and a structure’s ability to redistribute loads to the ground.

<RCM> When cyclic effects are significant, as assessed in 7.2 (2), cyclic effects should be taken into account in the verification of the three SLS combinations: quasi-permanent, frequent and characteristic.

9.3 Structural serviceability limit states

<Drafting note: This section is subject to change depending on new draft of EN1990.>

<REQ>Limiting values shall be established for ground movement and corresponding movement (including differential) of foundations, retaining walls, and other geotechnical structures at which a serviceability limit state is deemed to occur in the supported structure and other structures within its zone of influence.

<REQ> The selection of limiting ground movement criteria shall take account of the following, where relevant:

− the confidence with which the acceptable value of the movement can be specified; − the occurrence (or recurrence) and rate of ground movements; − the effect of horizontal as well as vertical ground movements; − the type and age of structure; − the requirements of any plant or machinery (during both construction and the service life of the

structure) and the proposed use of the structure; − the changing state of the structure during construction; − the mode of deformation; − relative movement between buildings or parts of buildings of different characteristics; − allowable movements of services entering the structure.

<PER> In the absence of specified limiting values of structural deformations of the supported structure, the values of structural deformation given in Annex C may be used.


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10 Execution

<Drafting note: This clause has been revised in an attempt to take into account the discussions on the need of a clause related to Execution in a design code. The aim is to make it clear why it is needed. Some part of the clause including some of the tables has been moved to Annex D. Comments on this proposal is appreciated.

The drafting guidelines restrict the possibility to change the title of this clause. But a question will be raised to TC 250 for the permission to change the title to Implementation of design during execution.>

10.1 General

<REQ> The design of a geotechnical structure shall include specification of supervision, inspection, monitoring and maintenance to verify the design during execution.

NOTE This Clause covers planning of measures needed for verification of the design during execution to ensure that design requirements are satisfied for the ground conditions encountered at the site. The measures aim is also to ensure limited environmental impact, appropriate safe working environment and quality of the geotechnical structure.

<RCM> It should be verified that the execution of geotechnical structures provides a level of reliability no less than that required by EN1990.

<RCM> The type, level and amount of supervision, inspection, monitoring, and maintenance shall be related to the Geotechnical Category of the geotechnical structure, or the relevant part of it.

<REQ> The type, level and amount of supervision, inspection, monitoring and maintenance shall correspond to the specific requirements of the design.

<REQ> The objectives, type, extent, and level of supervision, inspection, monitoring and maintenance shall comply with the specific requirements of EN 1997-3 and relevant execution standards.

<REQ> The plans for supervision and inspection shall specify the objectives, type, quality, and frequency of supervision of construction.

<REQ> The plans for supervision and inspection shall specify acceptance criteria for any visual or other observation and/or measurement taken during execution.

<REQ> The plans for monitoring shall specify trigger values, alarm values and limit values for each critical monitored object.

<RCM> The plans for supervision, inspection and monitoring should include contingency action required for safety if the acceptance criteria are not met.

<REQ> Prior to and during construction, design assumptions shall be verified on the basis of the results of monitoring, supervision and inspection.

<RCM> Verification should include a careful review of the most unfavourable conditions that occur during construction, with respect to:

− ground conditions; − groundwater conditions; − actions on the structure;


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− environmental impacts and changes including landslides and rockfalls.

<REQ> The results of the verification shall be checked for compatibility with any other design assumptions, before any design revisions are decided.

NOTE Annex D gives additional recommendation for supervision, monitoring, inspection and maintenance.

10.2 Supervision

<REQ> Supervision of the implementation of the design during construction shall include, but not limited to:

− assessment of the design, by checking the validity of design assumptions in relation to the encountered in-situ conditions;

− assessment of ground and groundwater conditions, by identifying differences between actual conditions and those assumed in the design;

− assessment of the suitability of the execution procedures and sequence of operations adopted in the design, in the light of the encountered ground conditions;

− comparison of the behaviour of the structure as predicted in the design, with its observed performance.

NOTE The aim of supervision is to ensure that design requirements are satisfied for the ground conditions encountered at the site.

<RCM> Other measures than those given in (1) should be included as necessary.

<REQ> The Supervision Plan shall specify the objectives, type, quality, and frequency of supervision of construction.

<REQ> The Supervision Plan shall address foreseeable ground responses and ground-structure interaction.

10.3 Inspection

<REQ> The execution shall be inspected according to the Inspection Plan, by checking that execution is carried out in according to the design and that all design revisions are adopted.

NOTE The aim of inspection is to ensure safe working environment, limited environmental impact and quality of the geotechnical structure

<REQ> The Inspection Plan shall specify the objectives, type, methods, quality, and frequency of inspection of the works.

10.4 Monitoring

<REQ> Monitoring shall include visual and other observations and/or measurements of the behaviour of the structure and its surroundings in order to:

− check the validity of the Geotechnical Design Model and other design assumptions; − check the validity of predictions of performance made during the design; − ensure that the structure will continue to perform as required after completion.


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NOTE The aim of monitoring is to ensure compliance with the requirements in the design and to ensure safe working environment, limited environmental impact and quality of the geotechnical structure

<REQ> The monitoring system shall either be replaced or extended if it fails to supply reliable data of appropriate type or in sufficient quantity.

<REQ> In the case of unexpected events, the methods, extent, and frequency of monitoring shall be reviewed.

10.5 Maintenance

<REQ> The specification of maintenance shall describe any maintenance measures that is required to ensure the safety and serviceability of the structure after construction.

<RCM> The Maintenance Plan should provide information on:

− critical parts of the structure which require regular post-construction inspection − the frequency of post-construction inspection.

10.6 Observational Method

<Drafting note: This sub-clause we be reviewed again based on the content of both part 1 and part 3 in next step. This to ensure that they are coherent. >

<REQ> If design by Observational Method is applied, the Supervision Plan shall be compatible with the required monitoring, corresponding control tolerances and required contingency actions for all design variants.


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11 Testing

11.1 General

<PER> Testing may be used for verification that the geotechnical structure or part of it fulfils the specified design requirements in order to check the limit states.

<PER> Testing may be used to determine values of the ground or structural parameters for design.

<RCM> The types, numbers, and other testing requirements of a structural element should be consistent with the Geotechnical Category.

<RCM> For geotechnical structures a distinction should be made between the following types of tests:

a) Tests to obtain specific material properties using specified testing procedures such as ground investigation.

b) Control tests to check the identity or quality of delivered products or the consistency of production characteristic; for example, lime-cement columns and geosynthetics.

c) Tests carried out during execution in order to obtain information needed for part of the execution; for instance, testing of pile resistance, anchor capacity.

d) Investigation tests on structural elements not to be incorporated in the works, to verify the ultimate resistance of the elements at the ground/structure interface and to determine their characteristics in the working load range. Applicable for structural elements such as piles, anchors and soil nails.

e) Suitability Tests, to confirm that a particular design and construction methodology is suitable for the present ground conditions.

f) Acceptance tests, to confirm that the specified acceptance criteria are fulfilled. Can be performed either as a Test carried out during the execution (c) or as a Control test (b).

NOTE The Geotechnical Design Model is established according to 4.1.2.2 and guideline for relevant ground investigations for different ground properties are given in EN 1997-2.

<PER> Tests may be carried out on a sample of the actual geotechnical structure or structural element or on full scale or reduced scale models.

<RCM> If the design parameters from tests are established directly, the more adverse of the upper and lower design values should be used in the verification of the limit state.

<RCM> If test results are not available at the time of design, representative or design values should be conservative estimates that are confirmed through acceptance tests during execution.

<PER> During and after execution, testing of structural elements or complete geotechnical structures may be used with any of the following:

− the Observational Method; − verification by calculation; − geotechnical monitoring, to verify, supplement or correct design assumptions; − monitoring of existing structures to assist in obtaining ground parameters for back-analyses (e.g.

unstable slopes) or in assessing on-going deformations or incipient failure.

11.2 Planning of tests

<RCM> Prior to carrying out tests, a test plan should be compiled including, but not limited to:


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− test objectives and scope; − specifications of sample preparation, as required; − loading specifications; − testing arrangement; − period of time from execution to test, where relevant; − equipment (characteristics, maintenance and calibration requirements); − measurement plan and frequency; − prediction of test results; − method for test evaluation and reporting; − acceptance criteria; − requirements from comparable experience, if any.

NOTE 118. Guidance on the content of the test plan for different geotechnical structures is given in EN 1997-3.

11.3 Test evaluation

<RCM> Test evaluation should include comparison of the test results with corresponding predictions.

<RCM> When significant deviations from predicted behaviour occur, the reasons should be established.

<RCM> In case of unexpected deviations, the test should be repeated, or different tests should be performed.


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12 Reporting

12.1 General

<REQ> The geotechnical aspects of the design of geotechnical structures and other works shall be reported.

<REQ> The extent and details of the reporting shall be adequate for a technical independent review.

<RCM> The reporting should include documentation of ground investigations, the ground model, the basis of design, design results, deviations from design during execution, supervision, inspection, and the results of monitoring.

<REQ> Reporting shall include information specified for the Ground Investigation Report (GIR), Geotechnical Design Report (GDR), Geotechnical Construction Record (GCR), and any geotechnical test reports.

NOTE 119. The format of the reports is not specified in this standard. The reports can e.g. be single volume, multivolume, digital, paper copy, partly consist of drawings, or a Building Information Model (BIM).

<REQ> The content of the reporting shall include documentation as specified in Annex E.

<RCM> The extent and details of the reporting should be appropriate for the type of geotechnical structure and the Geotechnical Category.

NOTE 120. Guidance on specific reporting for different geotechnical structures is given in EN 1997-3.

<REQ> To prevent uncertainty, compliance with the assumptions given in 1.3 should be documented in the Geotechnical Design Report.

<REQ> The responsibility for reporting and keeping the records shall agree by the relevant authority or, for a specific project, by the relevant parties.

12.2 Ground Investigation Report

<REQ> The results of ground investigation shall be compiled in a Ground Investigation Report (GIR).

NOTE 121. Additional requirements for the Ground Investigation Report are given in Annex E.4.

NOTE 122. The Ground Model is the output of the Ground Investigation Report as described above.

<REQ> The Ground Investigation Report shall, for each stage of the ground investigation, consist of a factual account of site information and all results from the ground investigation.

<REQ> The Ground Investigation Report shall state limitations of the results.

<REQ> The Ground Investigation Report shall report the environmental conditions encountered during the ground investigation.

NOTE 123. The environmental conditions can include temperature, time between sampling and testing in lab, conditions during transportation of ground samples from site to lab, weather conditions.


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NOTE 124. Guidance on which environmental conditions to record for different soils, parameters, tests can be found in EN 1997-2.

<REQ> The results from ground investigations shall be presented and reported according to EN 1997-2.

12.3 Geotechnical Design Report

General

<REQ> Documentation of the verification and design process of all construction phases and the final design shall be compiled in a Geotechnical Design Report (GDR).

NOTE 125. Additional requirements for the Geotechnical Design Report are given in Annex E.5.

<REQ> The Geotechnical Design Report shall give a description of the site and the planned geotechnical structure.

<REQ> For each design situation, the Geotechnical Design Report shall record the Consequence Class, the Geotechnical Complexity Class, and the Geotechnical Category.

<PER> The extent and details of the reporting for design situations and design assumptions which do not govern the design may be reduced.

Ground properties and Geotechnical Design Model

<RCM>Selected ground properties of the geotechnical units, geometric specification, and groundwater conditions should always be reported when describing any Geotechnical Design Model.

<REQ> It shall be documented that subdivision into geotechnical units assumed from desk studies and site inspections were reconsidered in light of the results obtained.

<REQ> The data sources used to determine the representative value of a ground property shall be stated in the Geotechnical Design Model.

Basic parameters

<REQ> The Geotechnical Design Report shall include documentation of the evaluation of the nominal value of geometrical data.

<REQ> The Geotechnical Design Report shall include documentation of the evaluation of the representative values of actions and resistances, if used.

<REQ> The Geotechnical Design Report shall include documentation of the evaluation of the representative value of material properties.

Verification of limit states

<REQ> The design situations considered in the design shall be described.

<REQ> The verification of the limit states shall be documented.

Plan of supervision, inspection, monitoring, and maintenance


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<REQ> The Geotechnical Design Report shall include a plan of supervision, inspection, monitoring, and maintenance.

NOTE 126. Minimum contents of the Plan of Supervision, Plan of Inspection, Plan of Monitoring, and Plan of Maintenance are given Annex E.

<RCM> The Supervision, Inspection, Monitoring, and Maintenance Plans should be related to the Geotechnical Category of the geotechnical structure, or the relevant part of the Geotechnical Structure.

<REQ> The Geotechnical Design Report shall clearly identify any important design modifications, contingency plans, and corresponding control criteria and tolerances that are influenced by the results of supervision, inspection, monitoring, or maintenance.

<REQ> If the Observational Method is applied, a separate contingency plan shall address foreseeable ground responses and ground-structure interactions and give required contingency actions for all design variants.

12.4 Geotechnical Construction Record

<REQ> Documentation of construction, supervision, monitoring, inspection of each execution phases and the final structure shall be compiled in a Geotechnical Construction Record (GCR).

NOTE 127. Additional requirement for the Geotechnical Construction Record are given in Annex E.6.

NOTE 128. The aim of the GCR is to assist with future maintenance, design of additional works and decommissioning of the works.

<REQ> For design by the Observational Method, the Geotechnical Construction record shall, in addition, include a record of encountered scenarios at site and the measures implemented, with justification of deviation from the planed actions.

12.5 Geotechnical test report

<REQ> The results of testing, in full-scale or reduced scale, of the performance of a geotechnical structure or the ground, or part thereof, for design, supervision, inspection or monitoring shall be compiled in a geotechnical test report.

<REQ> If standardised test methods are used, the documentation shall be presented and reported according to the requirements defined in applicable test standards.

NOTE 129. Guideline on applicable test standards for specific geotechnical structures is given in EN 1997-3.

NOTE 130. Guideline on applicable test standards for ground investigation is given in EN 1997-2.

NOTE 131. Complementary guidelines on documentation of pumping test, geophysical testing, thermal testing, characterisation of ground and other non-standardised ground investigation methods is given in EN 1997-2.

<REQ> The geotechnical test report shall state limitations of the results.

NOTE 132. Geotechnical test report is a part of the GIR, GDR, or GCR.


73

(Normative)

Partial factors for ground properties

<Drafting note: In line with the new instructions from N1250 on content of clause 4, verification with partial factor approach has been added to clause 4 (not clause 8 ULS). However, to ensure that the values of the partial factors are strictly separated between ULS and SLS, they were moved to Annex A for this draft. Ease-of-use perspective and avoid mixture of values for ULS and SLS. >

A.1 Use of this Normative Annex

This Normative Annex provides additional requirements and recommendations to those given in Clause 4, regarding verification of limit states for geotechnical structures using the partial factor method.

A.2 Scope and field of application

This Normative Annex provides values of the partial factors on material properties for verification of ultimate and serviceability limit states.

This Normative Annex is intended to be used in conjunction with EN 1990 Annex A, which provides values of partial factors on actions and action-effects, and with EN 1997-3, which provides values of partial factors on ground resistance.

A.3 Partial factors in ULS for ground properties

A.3.1 General

<RCM> When design values of geotechnical resistance are calculated using Formula (8.12) of EN 1990, partial factors γM should be applied to material properties.

A.3.2 Fundamental (persistent and transient) design situations

NOTE 133. Values of the partial factor γM for persistent and transient design situations are given in Table A.1 (NDP) unless the National Annex gives different values.

M515.SC7.T2 prEN 1997-1:20xx (E) Draft April 2018

74

Table A.1 (NDP) — Partial factors on ground properties for fundamental (persistent and transient) design situations

Ground parameter Symbol Set1

M1 M2 M32

Effective shear strength of soil (τs) γτs 1,0 1,25 1,25 KM

Effective cohesion (c´) γc 1,0 1,25 1,25 KM

Coefficient of internal friction3 (tan ϕ) γtanϕ 1,0 1,25 1,25 KM

Coefficient of ground/structure interface friction2 (tan δ)

γtanδ 1,0 1,0 1,0 KM

Undrained shear strength (cu) γcu 1,0 1,4 1,4 KM

Unconfined compressive strength of soil (qu) γqu 1,0 1,4 1,4 KM

Uniaxial compressive strength of rock mass (σc)

γσc 1,0 1,4 1,4 KM

1 M1, M2, M3 are three independent sets of material factors. EN 1997-3 specifies which one to use for specific geotechnical structures 2Values of KM are given in Table A.3 (NDP). 3 See Formula 4.5.

A.3.3 Accidental design situations

NOTE 134. Values of the partial factor γM for accidental design situations are given in Table A.2 (NDP) unless the National Annex gives different values.

Table A.2 (NDP) — Partial factors on ground properties for accidental design situations Ground parameter Symbol Set1

M1 M2 M32

Effective shear strength of soil (τs) γτs 1,0 1,1 1,1 KM

Effective cohesion (c´) γc 1,0 1,1 1,1 KM

Coefficient of internal friction3 (tan ϕ) γtanϕ 1,0 1,1 1,1 KM

Coefficient of ground/structure interface friction2 (tan δ)

γtanδ 1,0 1,0 1,0 KM

Undrained shear strength of soil (cu) γcu 1,0 1,2 1,2 KM

Unconfined compressive strength of soil (qu) γqu 1,0 1,2 1,2 KM

Uniaxial compressive strength of rock mass (σc)

γσc 1,0 1,2 1,2 KM

1 M1, M2, M3 are three independent sets of material factors. EN 1997-3 specified which one to use for specific geotechnical structures 2Values of KM are given in Table A.3 (NDP). 3 See Formula 4.5.


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A.3.4 Consequence factors for material properties in geotechnical structures

NOTE 135. Values of KM for different consequence classes are given in Table A.3 (NDP), unless the National Annex gives different values.

Table A.3 (NDP) — Consequence factors KM for materials in geotechnical structures Consequence class (CC) Description of consequences Consequence factor KM

CC3 Higher 1,1

CC2 Normal 1,0

CC1 Lower 0,9

A.3.5 Reduction factor for transient design situations

NOTE 136. NOTE The value of the reduction factor Ktr is 1.0 unless the National Annex gives a different value.


77

(informative)

Characteristic value determination procedure

B.1 Scope and field of application

<RCM> This Informative Annex should be used to determine the characteristic values of ground properties.

NOTE The way in which this Informative Annex can be used in a Country is given in the National Annex. If the National Annex is silent on the use of this informative annex, it can be used.

B.2 Background

(1) There are several sources of uncertainty that affect the evaluation of ground properties.

(2) These sources include inherent variability, measurement error, statistical uncertainty and transformation uncertainty.

NOTE 137. Statistical uncertainty describes the errors associated with estimating parameters (e.g. mean) of a population based on a limited number of samples

(3) Transformation uncertainty is only relevant if the property is not measured directly but inferred from a separate measurement (e.g. undrained strength from Standard Penetration Test blow count).

(4) Only inherent variability is a site property, the rest are design-dependent.

(5) For the purposes of this Annex, it is assumed that the different sources of uncertainty are related to the observed variability value through Formula (B.1):

Δ𝑜𝑜𝑑𝑑𝑑𝑑 = �Δ𝑖𝑖𝑖𝑖ℎ2 + Δ𝑞𝑞𝑞𝑞𝑞𝑞𝑞𝑞𝑖𝑖𝑑𝑑𝑞𝑞2 + Δ𝑑𝑑𝑡𝑡𝑞𝑞𝑖𝑖𝑑𝑑2 (B.1)

Where: Δ𝑜𝑜𝑑𝑑𝑑𝑑 is the coefficient of variation of the observed property value;


78

Δ𝑖𝑖𝑖𝑖ℎ is the coefficient of variation of the property due to inherent ground variability; Δ𝑞𝑞𝑞𝑞𝑞𝑞𝑞𝑞𝑖𝑖𝑑𝑑𝑞𝑞 is the coefficient of variation of the measurement error; Δ𝑑𝑑𝑡𝑡𝑞𝑞𝑖𝑖𝑑𝑑 is the coefficient of variation of the transformation error.

B.3 Characteristic value determination procedure

<RCM> The determination procedure’ described should be used to determine the characteristic value of a ground property by statistical methods.

<RCM> The derived values of the ground property being determined, explicitly indicated in the Ground Investigation Report, should be used in the determination of the characteristic value of the ground property.

<PER> The procedure described in this Annex may be applicable for the determination of the characteristic value of a ground property, considered as an estimate of either:

− the mean value [Case A]; or − the inferior (5% fractile) or superior (95% fractile) value [Case B].

NOTE Alternative assessment procedures can be given in the National Annex.

The procedure in this Annex shall be used to evaluate the different terms in Formula (B.2) [repeated from Formula 4.2]:

𝑋𝑋𝑘𝑘 = 𝑋𝑋𝑚𝑚𝑚𝑚𝑞𝑞𝑖𝑖[1∓ 𝑘𝑘𝑖𝑖𝑉𝑉𝑥𝑥] (B.2)

where:

Xk is the characteristic value of the ground property X;

Xmean is the mean of the ground property X from a number (n) of sample derived values; kn is a coefficient that depends on the number of sample derived values (n) used to calculate Xmean ;

VX is the coefficient of variation of the ground property X [VX = (standard deviation)/(mean value)]; ∓ denotes that knVX should be subtracted when a lower value of Xk is critical and added when an upper value is critical.

NOTE 138. Formula in B.2 is based on the following assumptions: the ground property values follow either a Normal or a Log-Normal distribution; there is no prior knowledge about the mean value.

<PER> The determination procedure may be applied for three different cases: Case 1 “VX known”, Case 2 “VX assumed” and Case 3 “VX unknown.

<RCM> Case 1 “VX known” should be used when the coefficient of variation of the ground property being determined is known from prior knowledge.

<RCM> Case 2 “VX assumed” should be used when the designer decides to use the indicative values in Table B.2, for ground parameters, or Table B.3, for test parameters.

<RCM> Case 3 “VX unknown” should be used when the coefficient of variation of the ground property being determined is unknown ab initio.

NOTE 139. Prior knowledge might come from the evaluation of previous tests in comparable situations. Engineering judgement may be used to determine what can be considered as “comparable”.


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NOTE 140. In practice, it is often preferable to use Case 2 "VX assumed" together with a conservative upper estimate of VX, rather than to apply the rules given for Case 3 "VX unknown".

<RCM> The value of Xmean should be calculated by Formula (B.3).

𝑋𝑋𝑚𝑚𝑚𝑚𝑞𝑞𝑖𝑖 = ∑ 𝑋𝑋𝑖𝑖𝑛𝑛𝑖𝑖=1𝑖𝑖

(B.3)

where xi is the value of the i-sample derived value. n is the number of sample derived values used for the evaluation of Xmean.

<RCM> The value of kn should be obtained from Table B.1 which collates Formulas (B.4) to (B.7) for the Cases defined above.

Table B.1 —Values of kn for different cases and type of estimations CASES Case 1: “VX known &

Case 2: “VX assumed” Case 3

“VX unknown”

Case A: Estimate of the mean value 𝑘𝑘𝑖𝑖 = 𝑁𝑁95 �

1𝑛𝑛

(B.4) 𝑘𝑘𝑖𝑖 = 𝑡𝑡95,𝑖𝑖−1 �1𝑛𝑛

(B.5)

Case B: Estimate of the inferior or superior value

(5 or 95 % fractile) 𝑘𝑘𝑖𝑖 = 𝑁𝑁95 �1 +

1𝑛𝑛

(B.6) 𝑘𝑘𝑖𝑖 = 𝑡𝑡95,𝑖𝑖−1 �1 +1𝑛𝑛

(B.7)

where: N95 represents the Normal distribution, evaluated for a 95% confidence level and infinite degrees of freedom. t95,n-1 represents the Student’s t distribution, evaluated for a 95% confidence level and n–1 degrees of freedom, being n as defined above.

<PER> For Case 2 “Vx assumed”, indicative values of Vx may be taken from Table B.2, for ground parameters, or Table B.3, for test parameters, unless the National Annex gives different values.

Table B.2 (NDP) — Indicative values of coefficient of variation for different ground parameters

Soil / Rock Type Ground parameter Symbol Coefficient of variation

Vx (%)

All soils and rocks Weight density ρ 0-10

Fine-grained soils Undrained shear strength cu 30-50

All soils and rocks Cohesion c 30-50

All soils and rocks Angle of internal friction ϕ 5-15

All soils and rocks Non –linear shear strength τ 15-25

All soils and rocks Unconfined compressive strength

qu 20-80

All soils Modulus of deformability(1) E or G 20-70


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Soil / Rock Type Ground parameter Symbol Coefficient of variation

Vx (%)

Fine-grained soils Vertical or horizontal consolidation coefficient

cv or ch 30-70

All soils At-rest “in-situ” coefficient K0 20-100

All soils Hydraulic conductivity(2) k 70-250

Note (1): It refers to the different modulus of deformation whose symbols appear in 3.2.1. & 3.2.7/EN 1997-2.

Note (2): Given the high value of the coefficient of variation for the hydraulic conductivity, this procedure should not be used.

Table B.3 (NDP) — Indicative values of coefficient of variation for different test parameters

Soil / Rock Type Test parameter Symbol Coefficient of variation

Vx (%)

Coarse soils SPT NSPT 15-45

All soils Pressuremeter limit pressure pl 5-15

All soils Cone resistance qc 5-15

All soils Sleeve friction fs 5-15

<RCM> For Case 3 “Vx unknown”, the value of VX should be calculated by Formula (B.8):

𝑉𝑉𝑋𝑋 = 𝑑𝑑𝑥𝑥𝑋𝑋𝑚𝑚𝑚𝑚𝑚𝑚𝑛𝑛

; 𝑠𝑠𝑥𝑥 = �∑ (𝑋𝑋𝑖𝑖−𝑋𝑋𝑚𝑚𝑚𝑚𝑚𝑚𝑛𝑛)2𝑛𝑛𝑖𝑖=1

𝑖𝑖−1 (B.8)

where sx is the standard deviation of the sample derived values.

NOTE 141. Tables B.4 to B.7 collates the values of Normal and Student’s t factor (N95 or t95,n-1) and resulting kn for the different Cases and type of estimation, according to Formulas (B.4) to (B.7)

Table B.4 — Selected values of N95, t95,n-1 and kn to estimate the characteristic value as the mean value [Case A1 & A2], according to Formula (B.4)

N 2 3 4 5 6 7 8 9 10 12

N95 1.64 1.64 1.64 1.64 1.64 1.64 1.64 1.64 1.64 1.64 kn 1.16 0.95 0.82 0.74 0.67 0.62 0.58 0.55 0.52 0.47

N 14 16 18 20 25 30 35 40 50 100

N95 1.64 1.64 1.64 1.64 1.64 1.64 1.64 1.64 1.64 1.64 kn 0.44 0.41 0.39 0.37 0.33 0.30 0.28 0.26 0.23 0.16

Table B.5 — Selected values of N95, t95,n-1 and kn to estimate the characteristic value as the mean value [Case A3], according to Formula (B.5)

N 2 3 4 5 6 7 8 9 10 12


81

t95,n-1 6.31 2.92 2.35 2.13 2.02 1.94 1.89 1.86 1.83 1.80 kn 4.46 1.69 1.18 0.95 0.82 0.73 0.67 0.62 0.58 0.52

n 14 16 18 20 25 30 35 40 50 100

t95,n-1 1.77 1.75 1.74 1.73 1.71 1.70 1.69 1.68 1.68 1.66 kn 0.47 0.44 0.41 0.39 0.34 0.31 0.29 0.27 0.24 0.17

Table B.6 — Selected values of N95, t95,n-1 and kn to estimate the characteristic value as the inferior or superior value (5 or 95% fractile) [Case B1 & B2], according to Formula (B.6)

n 2 3 4 5 6 7 8 9 10 12 N95 1.64 1.64 1.64 1.64 1.64 1.64 1.64 1.64 1.64 1.64 kn 2.01 1.90 1.84 1.80 1.78 1.76 1.74 1.73 1.73 1.71

n 14 16 18 20 25 30 35 40 50 100

N95 1.64 1.64 1.64 1.64 1.64 1.64 1.64 1.64 1.64 1.64 kn 1.70 1.70 1.69 1.69 1.68 1.67 1.67 1.67 1.66 1.65

Table B.7 — Selected values of N95, t95,n-1 and kn to estimate the characteristic value as the inferior or superior value (5 or 95% fractile) [Case B3], according to Formula (B.7)

n 2 3 4 5 6 7 8 9 10 12 t95,n-1 6.31 2.92 2.35 2.13 2.02 1.94 1.89 1.86 1.83 1.80

kn 7.73 3.37 2.63 2.34 2.18 2.08 2.01 1.96 1.92 1.87

n 14 16 18 20 25 30 35 40 50 100 t95,n-1 1.77 1.75 1.74 1.73 1.71 1.70 1.69 1.68 1.68 1.68

kn 1.83 1.81 1.79 1.77 1.74 1.73 1.71 1.71 1.69 1.67

NOTE 142. When the ground property is considered to follow a log-normal distribution, Formulas (B2), (B3) and (B8) becomes:

Xk = exp[Ymean (1 ∓ kn VY)] (B.2-log)

where: Xk is the characteristic value of the ground property X; Ymean is the mean from a number (n) of sample derived log values; (Formula B.3-log); 𝑌𝑌𝑚𝑚𝑚𝑚𝑞𝑞𝑖𝑖 = ∑ 𝑞𝑞𝑖𝑖𝑋𝑋𝑖𝑖

𝑛𝑛𝑖𝑖=1𝑖𝑖

(B.3-log) where xi is the value of the i-sample derived value. n is the number of sample derived values used for the evaluation of Ymean.

kn is a coefficient that depends on the number of sample derived values (n) used to calculate Ymean; (Table B.1); VY is the coefficient of variation of the log values of the ground property X [VY = sY / Ymean], being sx the standard

deviation of the sample derived log values (Formula B.8-log)

𝑠𝑠𝑌𝑌 = �∑ (𝑞𝑞𝑖𝑖𝑋𝑋𝑖𝑖−𝑌𝑌𝑚𝑚𝑚𝑚𝑚𝑚𝑛𝑛)2𝑛𝑛𝑖𝑖=1

𝑖𝑖−1 (B.8-log)

∓ denotes that kn VY should be subtracted when a lower value of Xk is critical and added when an upper value is critical.

Adopting a log-normal distribution has the advantage that no negative values can occur as, for example, for geometrical and resistance variables.


82

NOTE 143. There are determination procedures, different from the one described in this Annex, to determine the characteristic relation (line) of the values of a ground property with depth (z) or the characteristic values of dependent parameters (e.g cohesion and friction angle).


83

(informative)

Limiting values of structural deformation and ground movement

C.1 Use of this Informative Annex

This Informative Annex provides additional guidance to that given in clause 9 regarding limiting values of structural deformation and ground movement.

NOTE 144. The way in which this Informative Annex can be used in a Country is given in the National Annex. If the National Annex is silent on the use of this informative annex, it can be used.

C.2 Scope and field of application

This Informative Annex provides guidelines on limiting values of structural deformation and ground movement.

The limiting deformations in this Annex do not apply to buildings or structures which are out of the ordinary or for which the loading intensity is markedly non-uniform.

C.3 General

The components of geotechnical structure movement to consider include settlement, relative (or differential) settlement, rotation, tilt, relative deflection, angular distortion, deflection ratio, horizontal displacement and vibration amplitude.

NOTE Definitions of some terms for foundation movement and deformation are given in Figure C.1.

Burland & Wroth’s (1975) terms for describing foundation movement:

settlement, s differential settlement, δs rotation, θ angular strain, α relative deflection, ∆ deflection ratio, ∆ /L tilt, ω

angular distortion, β

Figure C.1— Definitions of foundation movement

The damage criteria shown in Table C.1 is a guide to setting serviceability limit state damage criteria to walls based on ease of repair.


84

NOTE 145. The boundary between Damage Classes 2 and 3 typically forms a serviceability limit state while Damage Class 5 is typically considered an ultimate limit state.

Based on the damage criteria in Table C.1, Figures C.2 to C.5 provide an example of the derivation of allowable deflection ratio for visual damage to walls in bending with different levels of horizontal strain.

NOTE 146. The derivation of the values in Table C-1, Figure C-2 to C-4 is described in Burland (1997) and Burland et al (1977).

Figure C.2 — Example determination of deflection ratio limits for walls in bending (zero horizontal strain)

Figure C.3 — Example determination of deflection ratio limits for walls in bending (0.05% horizontal strain)


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Figure C.4 — Example determination of deflection ratio limits for walls in bending (0.1% horizontal strain)

In the absence of specified limiting values of structural deformations of the supported structure, the values of structural deformation given below is a guide.

Suggested limit on tilt of tall structures (height H) for visual appearance:

ω=1/250 (H<24m)

ω=1/330 (24m<H<60m)

ω=1/500 (60m<H<100m)

ω=1/1000 (H>100m)

Other suggested serviceability limits:

Leakage of steel fluid storage tanks β=1/300 to 1/500

Flexible utility connections s=150mm

Crane operation on rails β=1/300

Drainage of floors β=1/50 to 1/100

Stacking of goods ω=1/100

Operation of machinery β=1/300 to 1/5000 depending on machinery type, 1/750 typical.

Lift and escalator operation ω=1/1200 to 1/2000

<new >

<Drafting note: PT6 will check the compatibility of these values with EN 1990.>

M515.SC7.T2 prEN 1997-1:20xx (E) Draft April v.8.1 WORK

86

Table C-1 — Damage criteria for walls

Damage class

Normal degree of sensitivity

Limiting tensile strain (%)

Description Typical crack widths (mm)

Ease of repair

0 Negligible 0-0.05 Hairline cracks < 0.1

1 Very slight 0.05-0.075 Damage generally restricted to internal wall finishes. Close inspection may reveal some cracks in external brickwork or masonry

≤ 1 Fine cracks that are easily treated during normal redecoration

2 Slight 0.075-0.15 Cracks may be visible externally; doors and windows may stick slightly

2-3 Cracks easily filled. Re-decoration probably required. Recurrent cracks can be masked by suitable linings. Some repointing may be required to ensure water-tightness

3 Moderate 0.15-0.3 Doors and windows sticking; service pipes may fracture; weather-tightness often impaired

Up to 5 locally Cracks require some opening up and can be patched by a mason. Repointing of external brickwork and possibly a small amount of brickwork may be replaced

4 Severe > 0.3 Windows and door frames distorted; floor sloping noticeably; walls leaning or bulging noticeably; some loss of bearing in beams; service pipes disrupted

5-15 Extensive repair work involving breaking-out and replacing sections of walls, especially over doors and windows

5 Very severe Beams lose bearing; walls lean badly and require shoring; windows broken with distortion; danger of instability

Several closely spaced > 3

Requires a major repair job involving partial or complete rebuilding


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(Informative)

Implementation of design during execution

D.1 Use of this Informative Annex

This Informative Annex provides additional guidance to that given in clause 10 for construction supervision and performance monitoring.


D.2 Scope and field of application

This Informative Annex covers measures to be considered for supervision, inspection and monitoring of a geotechnical structure.

NOTE 148. Items that refer to specific aspects of geotechnical engineering or to specific types of works are reported in the normative part of this standard and in EN 1997-3.

D.3 Supervision

D.3.1 General

<RCM> The following should be considered in the supervision plan: − verification of ground conditions; − location and general lay-out of the structure; − movements, yielding, stability of excavation walls and base; − temporary support systems; − effects on nearby buildings and utilities; − measurement of soil pressures on retaining structures; − measurement of groundwater pressure variations resulting from excavation or loading; − safety of workers with due consideration of geotechnical limit states.

<REQ> The design assumptions regarding the descriptions and geotechnical properties of the ground in the zone of influence shall be verified during construction.

<REQ> Fills shall be inspected and tested to ensure that the material, its placement water content and the compaction procedures comply with the design specification.

<REQ> Groundwater levels, groundwater pressures, groundwater flow characteristics and groundwater chemistry shall be checked during construction to ensure that the encountered conditions are compatible with the assumptions made in the design.

<RCM> Indirect evidence of the ground properties should be recorded and used to assist in checking the ground conditions.

NOTE 149. Indirect evidence includes, for example, drilling records, pile driving records, etc

NOTE 150. Table D.1 give guideline on the content of the supervision plan


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Table D.1 Content of supervision plan


Content of supervision plan

GC3 All the items given below for GC2 and, in addition: - measurements during each significant stage of construction

GC2 All the items given below for GC1 and, in addition measurement of: - ground properties; - piezometric levels; - behaviour of the structure.

GC1 All the items given below: - visual inspection, - simple quality controls, - qualitative assessment of the performance of the structure. <EN 1997-1 4.2.2(2)>

D.3.2 Control of ground and fil

<RCM> Table D.2 should be used to check the ground conditions and fill within the zone of influence.

Table D.2 Measures for checking ground and fill within the zone of influence


Ground and fill

GC3 All the items given below for GC2 and, in addition: - a detailed examination of ground and fill conditions, including additional ground investigations, measurements and observations.

GC2 All the items given below for GC1 and, in addition: - Determine ground properties by at least one of the followings:

- Observations; - Measurements; - Ground investigations.

GC1 All the items given below: - Inspection at site - Identification and description of ground units.

D.3.3 Control of water flow and groundwater pressures

<RCM> Table D.3 should be used to check the groundwater conditions within the zone of influence.


89

Table D.3 Measures for checking groundwater conditions within the zone of influence


Groundwater

GC3 All the items given below for GC2 and, in addition: - More detailed examination that includes additional measurements and observations, as required.

GC2 All the items given below for GC1 and, in addition: - Direct observations - Measurements of groundwater levels and groundwater pressures - Measurements of groundwater flow and chemistry, if they affect the method of

construction or the performance of the structure

GC1 All the items given below: - Direct observations - Documented experience from the vicinity of the site - Any other relevant evidence

<RCM>The following items should be considered in the supervision in relation to groundwater: − Groundwater flow and groundwater pressure regime; − effects of dewatering operations on groundwater table; − effectiveness of measures taken to control seepage inflow; − internal erosion processes and piping; − chemical composition of groundwater; corrosion potential; − adequacy of systems to ensure control of groundwater pressures in all aquifers where excess

pressure could affect stability of slopes or base of excavation, including artesian pressures in an aquifer beneath the excavation;

− disposal of water from dewatering systems; depression of groundwater table throughout entire excavation to prevent boiling or quick conditions, piping and disturbance of formation by construction equipment;

− diversion and removal of rainfall or other surface water; − efficient and effective operation of dewatering systems throughout the entire construction period,

considering encrusting of well screens, silting of wells or sumps; wear in pumps; clogging of pumps; − control of dewatering to avoid disturbance of adjoining structures or areas; observations of

piezometric levels; effectiveness, operation and maintenance of water recharge systems, if installed;

− piezometric levels under buildings or in adjoining areas, especially if deep drainage or permanent dewatering systems are installed or if deep basements are constructed;

− effectiveness of sub-horizontal borehole drains; − flow measurements from drains.

D.4 Inspection

<RCM> Inspection should be undertaken under, during and after the execution to ensure quality of the geotechnical structure and limited environmental impact.

<REQ> Inspection shall ensure that the specified acceptance criteria of the product are achieved.

<REQ> Inspection shall ensure that the identity and quality of the products used at the site during execution are in accordance with the specifications from the design.


90

<REQ> Inspection shall be undertaken during the execution to ensure that all safety measures required to ensure a safe working environment are implemented.

D.5 Monitoring

<RCM> Monitoring should be undertaken: − before construction, to establish reference conditions; − during construction, to identify the need for remedial measures, for switching to a different design

method or variant (in the Observational Method) or alterations of the construction sequence; − after construction, to evaluate the long-term performance of the structure.

<RCM> Monitoring should provide knowledge of: − groundwater levels and groundwater pressures in the ground, for effective stress analyses; − lateral and vertical ground movements; − the depth and shape of the moving surface in a developed slide; − rates of movement; − other site-specific data.

<PER> Monitoring may include measurement of the following: − deformations of the ground affected by the structure; − values of actions; − values of contact pressure between ground and structure; − groundwater levels, groundwater pressures and groundwater flow; − forces and displacements (vertical or horizontal movements, rotations or distortions) in structural

members; − vibrations caused by construction activities; − other site-specific data.

NOTE 151. Table D.4 give guideline on the content of the supervision plan

Table D.4 Content of monitoring plan


Content of Monitoring Plan

GC3 All the items given below for GC2 and, in addition: - additional points to confirm prognosis for each significant stage of construction

GC2 All the items given below for GC1 and, in addition measurement in selected points of: - movements - groundwater pressure and flow

GC1 - visual inspection

<REQ> The effect of construction operations on the groundwater regime shall be checked.

NOTE 152. Construction operations that affect the groundwater regime include – for example – dewatering, grouting, and tunnelling.

<RCM> The possibility of leakage or of alterations in the pattern of groundwater flow due to monitoring instruments should be considered.

<RCM> The following items should be checked:


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− settlement at established time intervals of buildings and other structures including those due to effects of vibrations on metastable soils;

− settlement of adjoining structures or areas; − lateral displacement and distortions, especially those related to fills and stockpiles; soil supported

structures, such as buildings or large tanks; deep trenches; − deflection or displacement of retaining structures considering normal backfill loadings; effects of

stockpiles; fills or other surface loadings; water pressures; − water tightness; − vibration measurements.

<RCM> In addition the following special problems should be considered: − high temperature structures such as boilers, hot ducts: desiccation of clay or silt soils; monitoring

of temperatures; movements; − low temperature structures, such as cryogenic installations or refrigerated areas: monitoring of

temperature; ground freezing; frost heave; effects of subsequent thawing.

<POS> The duration and frequency of post-construction monitoring can be altered as a result of observations made during construction.

<REQ> For structures that impact unfavourably on significant parts of the surrounding environment – or for which failure involves abnormal risks to property or life – monitoring shall be provided for as long as required, as specified in the design.

<RCM> If groundwater pressures change during construction in a way that can affect the performance of the structure, those pressures should be monitored until construction is complete or until those pressures have dissipated to safe values.

<RCM> For structures below groundwater level that are subject to uplift, groundwater pressures should be monitored until adequate resistance against uplift has been established.

D.6 Execution using Observational Method

<REQ> If the Observational Method is used, the Supervision Plan shall address foreseeable ground responses and ground-structure interactions and give required contingency actions for all design variants.


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(normative)

Additional requirements and recommendations for reporting

E.1 Use of this Normative Annex

This Normative Annex provides additional requirements and recommendations to those given in clause 12, concerning the content and extent of reporting.

E.2 Scope and field of application

This Normative Annex covers documentation of the design process from initial desk study and ground investigation to implementation of the design in execution.

This Normative Annex is intended to be used in conjunction with other European standards, that give complementary requirements on documentation for specific phases in the design process, as illustrated in Figure E1.

NOTE 153. The process of geotechnical design and execution generally comprises a number of successive phases. The guidelines for documentation are defined in different standards for these phases, as presented in Figure E1.

Figure E.1 Illustration of interaction between documentation in EN 1997 and complementary European standards.


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E.3 Minimum content of reports

<RCM> For all Geotechnical Categories, the records and documentation should be presented in a clear and accessible way to facilitate external review or revaluation.

<PER> For Geotechnical Category 1, the extent of the documentation for each heading, as defined in E.4 to E.7, may be reduced to a record with bullet-points of what has been done.

NOTE 154. An example of a reduced GDR for GC1 is presented in E.5.5

<RCM> For Geotechnical Category 2, the documentation should cover all critical aspects of the design.

<PER> For Geotechnical Category 2, the extent of the documentation for items that are not critical may be reduced or excluded provided justification is given.

<RCM> For Geotechnical Category 3, more extensive documentation should be included, covering all aspects of the design.

<RCM> For Geotechnical Category 3, the degree of detail should make it possible for a third party to obtain similar results on repeating the design analyses.

E.4 Ground Investigation Report

<REQ>The Ground Investigation Report shall include, but is not limited to, the following information, as applicable:

1. Project name 2. Proposed structure, stage of execution relevant for GIR, scope of investigation 3. Normative references 4. List of available information needed for planning 5. Geotechnical Category (selection for the ground investigation purposes) 6. Site overview (topography, existing structures, vegetation) 7. Location (coordinates) 8. Desk study 9. Field reconnaissance of site and surroundings 10. Geological study 11. Field investigation

a. List of performed investigations and locations b. Dates of field work c. Names of field personnel d. Type of equipment e. Documentation of calibration and certification documents f. Handling of samples g. Environmental conditions during investigation h. Main observations during the investigation

12. Laboratory testing a. List of investigations performed, on which samples b. Dates tests performed c. Names of laboratory personnel d. Documentation of calibration and certification documents e. Main observations during testing (quality, sample content)

13. Groundwater investigations


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a. List of investigations performed and their locations i. Short term

ii. Long term b. Time period for investigation c. Names of field personnel d. Documentation of calibration and certification documents e. Handling of samples f. Main observations during the investigation

14. Derived values of ground properties a. Basic properties (water content, density, plasticity, etc.) b. Strength properties c. Deformation properties d. Groundwater properties e. Other relevant properties

15. Ground Model 16. Review of investigation and results

a. Known limitations of the results b. Important observations from the field and laboratory investigations

<RCM> The following should be added to the GIR as separate annexes or as referenced reports: - Field reports - Laboratory reports - Test reports - Desk studies - Geological studies - Field reconnaissance reports - Evaluated soundings with derived values - Graphical presentations of derived values - Estimates of the coefficient of variation of ground properties

<PER> The following drawings may be added to the GIR: plans, sections and profiles.

<PER> A Building Information Model may be included in the GIR.

E.5 Geotechnical Design Report

E.5.1 General content

<REQ> The Geotechnical Design Report shall include, but is not limited to, the following information, as applicable:

1. Project information a. Project name b. Proposed structure and its use and location (coordinates and reference system) c. Normative references d. Reference to the GIR, Ground Model, and other sources of information

2. Evaluation of available information a. Field and laboratory investigations b. Field reconnaissance reports c. Geological studies d. Desk studies e. Other relevant investigations and studies

3. List/sketch geotechnical structures for evaluation


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a. Geotechnical constructions for consideration b. Evaluation of the alternatives c. Choice of main alternatives, and motive for abandoning the other

4. Design situations a. Geotechnical Design Model, including evaluation of representative values b. Consequence Class, Geotechnical Complexity Class, and Geotechnical Category c. Restrictions (loading, vibration, deformation, etc.) d. Any assumptions or simplifications e. Failure modes f. Verification method with corresponding input parameters, including:

i. Applicable design case and partial factors ii. Validation of chosen calculation model

iii. Reference for the chosen prescriptive measure iv. For numerical models, the chosen constitutive model together with justification

of its applicability 5. Geotechnical Analyses

a. Estimate of the expected range of results b. Documentation of analyses c. Sensitivity analyses d. Evaluation of results e. Analyses of execution phases

6. Specification of the geotechnical structure a. Specification of materials and dimensions b. Requirements on the execution process and description of each execution phase

7. Plan of supervision, inspection, monitoring, and maintenance

E.5.2 Specification of the Geotechnical Design Model

<RCM> The description of the ground conditions compiled in the Geotechnical Design Model should include, but is not limited to:

− the results of the field investigations and laboratory tests evaluated according to EN 1997-2; − statement about data that is excluded from evaluation with justification; − statement about any limitations of the investigation results; − choice of Geotechnical Category, with justification; − a review of the results of the desk study, geological study, field investigation, and laboratory

tests; − a review of topographical data; − a review of the derived values of ground properties.

<RCM> The description of geotechnical units should include, but is not limited to: - Description and classification of ground included within each geotechnical unit; - designation of the material parameters relevant for design; - identification of the data that was used in the selection of representative values of ground

properties; representative values of ground properties.

NOTE Guidance on the specification of geotechnical units is given in EN 1997-2.

<RCM> The geometrical specification should include, but is not limited to: - location of boundaries between different geotechnical units; - location of discontinuities within a geotechnical unit; - spatial trends in the variation of ground properties, particularly with depth.


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NOTE Guidance on the geometric specification is given in EN 1997-2.

<RCM> The specification of groundwater conditions at a site should include, but is not limited to: - identification of any low permeability materials; - specification of water tables, groundwater pressures, and flows relevant to the design; - identification of saturation conditions for all materials in the model; - chemical properties of groundwater; - a statement about the likely drainage response of each permeable saturated material present in

the model.

NOTE Guidance on the specification of groundwater conditions is given in EN 1997-2.

<RCM> The documentation should include, but is not limited to: a. tabulation and graphical presentation of the results of field investigation and laboratory

testing; b. cross-sections of the ground showing relevant geotechnical units and their boundaries

including the groundwater table; c. the process of compiling the Geotechnical Design Model considering the groundwater table,

ground type, drilling and/or sampling method, transport, handling, specimen preparation, local experience, and other sources of information.

E.5.3 Verification of limit states

<RCM> Documentation of verification by prescriptive measures should include, but is not limited to:

− reference to the clause in EN 1997 or its National Annex giving the prescriptive measure; − evaluation of the applicability of the prescriptive measure for the design situation.

<RCM> Documentation of verification by testing should include, but is not limited to: − reference to the appropriate geotechnical test report; − evaluation of the test results and their limitations.

<RCM> Documentation of verification by the partial factor method should include, but is not limited to:

− validation of the calculation model for the used Geotechnical Category; − design values of ground parameters, including justification; − design cases used; − geotechnical design calculations and drawings.

<RCM> Documentation of verification by the Observational Method should include, but is not limited to:

− justification of the applicability of the Observational Method for specific design situations and Geotechnical Category;

− initial design; − variations of the design including alarm levels and planned measures to be activated.

<RCM> In addition to (3) or (4), documentation of design by calculation using numerical methods should include, but is not limited to:

− justification of the applicability of the numerical model used for specific design situations; − statement about the boundary conditions of the model.


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E.5.4 Minimum content of supervision, inspection, monitoring, and maintenance plans

<REQ> The Geotechnical Design Report shall include: − a Supervision Plan, covering construction supervision; − an Inspection Plan, covering inspection of execution and construction control, including

workmanship; − a Monitoring Plan, covering required monitoring of the performance of the structure during

and after construction; − a Maintenance Plan, covering required maintenance.

E.5.5 Simplification for Geotechnical Category 1

<PER>For Geotechnical Category 1, the lists above may be reduced to the following information, as applicable:

1. Project information a. Project name b. Proposed structure and its use c. Reference to the GIR and other sources of information

2. Evaluation of available information, summarised in a simplified Geotechnical Design Model 3. Design situations

a. Consequence Class, Geotechnical Complexity Class, and Geotechnical Category b. Restrictions (loading, vibration, deformation, etc.) c. Failure modes d. Any assumptions and simplifications

4. Geotechnical Analyses, one or more of these might be included: a. Prescriptive measures with justification b. Documentation of calculation model used (with reference of validation)

5. Specification of the geotechnical structure a. Specification of materials and dimensions b. Requirements on the execution process and description of each execution phase c. Drawings

6. Supervision, inspection, monitoring, and maintenance plans

E.6 Geotechnical Construction Record

E.6.1 General content

<REQ> The Geotechnical Construction Record shall include, but is not limited to, the following, as relevant:

1. Project information a. Project name b. Completed structure, its intended use and location (coordinates and reference system) c. Normative references d. Reference to the GIR and GDR and to construction drawings and specifications

2. Construction record a. Sequence of construction operations assumed in the design including any deviations from

it during construction. b. Encountered deviations from the design base including Geotechnical Design Model c. Measures applied d. Deviations from construction specification and structure specification made during

construction including justifications.


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e. Temporary work f. Requirements for on-going monitoring g. As-built drawings

3. Supervision record a. Evaluation of results from supervision, including testing of structure and complementary

ground investigation b. Revision of the Geotechnical Design Model c. Measures applied d. Deviations from the plan

4. Monitoring record a. Evaluation of monitoring results b. Measures applied c. Deviations from the plan

5. Inspection record a. Evaluation of inspection reports b. Measures applied c. Deviations from the plan

6. Consideration for future maintenance a. Summary of observation made during the construction b. Record of items with special consideration for future maintenance

<PER> Test reports, inspection records, and drawings may be added to the GCR.

<PER> A Building Information Model may be used to compile part of the GCR.

E.6.2 Record of construction

<RCM> The record of construction should include, but is not limited to: − a general description of the works, including ground and groundwater conditions encountered; − instability problems, unusual ground conditions, and groundwater problems, including

measures to overcome them; − contaminated and hazardous material encountered on site and the location of disposal, both on

and off site; − temporary works and foundation treatment, including drainage measures and treatment of soft

areas and their effectiveness; − types of imported and site-won materials and their use; − any aspect of the specification or standards used that should be reviewed in view of problems

encountered on site; − any unexpected ground conditions that required changes to design; − problems not envisaged in the Geotechnical Design Report and the solutions to them. <NEW:

R18>

<PER> For geotechnical structures in Geotechnical Category 1, a formal construction schedule may be omitted from the Geotechnical Construction record

E.6.3 Record of supervision, monitoring and inspection

<RCM> The record of supervision, monitoring, and inspection should include, but is not limited to: − evaluation of results from tests on the geotechnical structure or parts of it − the impact of such tests on the execution and built structure; − evaluation of results from complementary geotechnical investigations − the impact of such investigation on the execution and built structure; − alteration of the Geotechnical Design Model;


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− deviations from the supervision, monitoring, and inspection plans; − summary of observations made during supervision, monitoring, and inspection.

E.7 Geotechnical test report

<REQ>The factual account in a geotechnical test report shall include, but is not limited to, as applicable:

1. Project information a. Project name b. Purpose of testing c. List of tests performed and their locations (coordinates) d. Normative reference (if applicable) e. Date and time of tests f. Environmental conditions on site during testing g. Name of field personnel h. Equipment used i. Documentation of calibration and certification documents j. Test methodology

2. Details of tested structural parts a. Type of ground, structure and/or structural parts b. Locations (drawing and/or coordinates) c. Dates of installation

3. Test results a. Measured values b. Derived values (with any correlations used, including justification) c. Remarks on specific test results

4. Review of testing and results a. Problems encountered during the test that could affect the results b. Known limitations of the results c. ..


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(Informative)

Ground properties

F.1 Use of this Informative Annex

This Informative Annex provides complementary guidance to that given in clauses 4 and 5, on ground properties.

This informative Annex can only be used, when allowed for by the National Annex


F.2 Scope and field of application

This Informative Annex provides indicative values of ground properties.

F.3 General

<PER> Values of ground properties may be selected on the basis of the description and classification of grounds.

NOTE 156. Indicative values of ground properties are given in Table F.1 (NDP) unless the National Annex gives different values.

NOTE 157. The format of Table F1 is Nationally determined.


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(Informative)

Qualification and professional experience

<Drafting note: This Annex was originally prepared by a group within ISSMGE, chaired by F. Buggy. A draft version was discussed at the Oslo meeting. It was decided that a revised version should be included in the October draft of EN 1997-1. Based on comments from SC7 WG1/TG2, SC7 WG1/TG3 and the ISSMGE group this annex has been revised by SC7.PT2.

In addition to this Annex G, it has been proposed that the material that has been prepared by the ISSMGE group, that is not included in the Annex G, should be published as a Joint Research Paper. Referred to as JRP X in the draft.

The ISSMGE group have assist PT2 to prepare this final draft of this Annex. To ensure a broad acceptance of this informative annex, there will be further discussion during phase 4. >

<Drafting note: This annex is informative. The REQ/REC in the Annex are optional, there is no need to comply with these requirements to claim compliance with the Code. The REQ/REC will only be endorsed if the National Body decide so. Based on IR3 >

G.1 Use of this Informative Annex

This Informative Annex provides additional guidance to that given in clause 1 .3 Assumptions

This Informative Annex establishes one possible way for verifying the assumption that the design and collection of information is performed by competent persons.


G.2 Scope and field of application

This Informative Annex provides guidelines on requirements for competence of persons responsible for either geotechnical design or ground investigation process.

This Informative Annex is intended to be used in conjunction with other national legislation that gives complementary requirements on competence.

G.3 Guideline

<RCM> The persons responsible for Ground Investigation and Geotechnical Design should have appropriate qualifications and experience within their respective field that includes:

− A university diploma demonstrating successful completion of tertiary studies in a relevant field; − Professional experience in ground engineering; − Continuous Professional Development (CPD) in ground engineering; − Membership of a relevant Professional Register, if available or required in individual countries.

NOTE 159. NOTE 1: The recommended minimum requirements for qualifications and experience are given in Table G-1 (NDP) unless the National Annex gives different requirements. Examples of current and proposed requirements for countries can be found in JRP X1


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NOTE 160. European Commission Directive 2005/36/EC on mutual recognition of professional qualifications acknowledges that engineers are organised differently in various EU member states.

NOTE 161. The minimum requirements in Table G-1 are applicable for geotechnical structures that fall within Geotechnical Category 2.

NOTE 162. The National Annex can stipulate which professional titles or levels of registration meet the minimum requirements in Table G-1.

Table G.1. (NDP) Minimum requirements for qualifications and professional experience to fulfil the assumptions of clause 1.3 for Geotechnical Category 2 structures a

(1) (2) (3) (4) (5)

Educational qualification (ECTS credit

points)

Professional experience

Continuous Professional Development

(CPD)

Professional Competence

Remarks Registration

Professional qualifications and application

NOTE 1 NOTE 2 NOTE 3 NOTE 4 and 5

B Sc / B Eng (180 – 240) Dipl. Ing. / M Sc / M Eng (300)

B Sc / B Eng 5 years – GC 2 Dipl. Ing. / M Sc / M Eng 3 years – GC 2

and demonstrated appropriate competence

≥ 20 hours /year

General requirements are defined in Note 5.

National requirements for registration may be enforced by private or public law. Applications for professional registration should be documented, subject to independent assessment and include a statement of professional competency and curriculum vitae.

a This table is an NDP and the NSB can clarify the following for its application. - Additional requirements for Geotechnical Category 3 structures - Additional acceptable academic qualification and associated professional experience - Specification of criteria for CPD - Additional general requirements on professional competence - Specific requirements on professional competence for different technical areas

NOTE 163. Core subjects such as soil / rock mechanics, foundation engineering and engineering geology are required as part of university studies.

NOTE 164. The professional experience is measured in number of years demonstrating appropriate competence in the application of the relevant clauses of EN 1997.

NOTE 165. The criteria for valid CPD hours varies nationally. Learned Societies can give input to the specification.

NOTE 166. The required professional competence, including level of competence, depends on which clauses of EN 1997 a person will apply. Specific requirements for different technical areas can vary. Examples of relevant technical areas include planning of field and laboratory investigation, evaluation of ground investigation results, pile design, ground reinforcement, numerical methods. The professional competence also includes general professional competence related to documentation, project management, risk management, and communication.


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NOTE 167. The General requirements are defined in the following statement. “Competence is the ability to carry out a task to an effective standard. To achieve competence requires the right level of knowledge, understanding and skill, and a professional attitude. Competence is developed by a combination of formal and informal learning, and training and experience, generally known as initial professional development. However, these elements are not necessarily separate or sequential and they may not always be formally structured. There are five generic areas of competence and commitment for all ground engineering professionals, broadly covering: A) Knowledge and understanding; B) Design and development of ground engineering processes, systems, services and products; C) Responsibility, management or leadership; D) Communication and inter-personal skills; E) Professional commitment

NOTE 168. 1 JPR x is a planned paper that will give more guideline. JRP X is expected to be largely based on a publication by Buggy et al (2018) “Registration of Ground Engineering Professionals – a European Perspective”, 13th IAEG Congress, San Francisco, Ca. USA 15 – 23 September 2018


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(Informative)

Observational method

<Drafting note: The content of this annex will be elaborated (probably merged into EN 1997 part 3) with the clause texts for retaining walls to make it coherent. For other geotechnical structures OM according EN 1997-1 clause 4.7 is sufficient.

H.1 Use of this Informative Annex

This Informative Annex provides additional guidance to that given in 4.7, on the Observational Method for retaining walls in soils only.


H.2 Scope and field of application

This Annex covers aspects of the application of the Observational Method in the design of geotechnical retaining wall structures in soil.

For other geotechnical structures only OM according EN 1997-1 4.7 shall be followed.

H.3 General

<PER> The design of geotechnical structures may be undertaken using the Observational Method as described in 4.7.

<PER> This Method can be applied ab initio (before construction starts as a planned design procedure) or ipso tempore (applied to a structure during construction that has been designed by another method, usually by calculation).

- the Method offers many potential advantages: - more economic design in terms of materials and programme; - improved safety control; - control of design uncertainties; - stronger connection between designers and constructor; - improved construction control and management; - greater motivation for the project team; - providing databases for benchmarking.

This Method requires more design effort to consider a range of possible behaviours, improved characterisation of the ground and ground water conditions, enhanced instrumentation and monitoring systems and greater involvement of the designer during the construction period.

The extra costs associated with these enhancements is typically adequately offset by economies in construction.


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H.4 Analytical approach

When adopting this Method, the design is required to consider a range of possible behaviours including:

- the ground (and groundwater); - the structure; - the surrounding area (for example, the construction site).

To implement this Method, for each set of assumed behaviour:

An appropriate analysis and construction sequence should be fully developed, satisfying ULS and SLS requirements;

- A set of appropriate measurements or observations should be set to enable the designer to determine which set of assumptions are realised during construction (for example, movements, pore water pressure, or forces).

- An instrumentation and monitoring scheme is required that will provide the required observations required above in a timely, robust and reliable fashion. Redundancy in the instrumentation and monitoring scheme should also be considered.

H.5 Framework

A range of approaches and definitions have been applied to the use of this Method since its formalisation in 1969. Four possible approaches are summarised in Table G.1.

Alternative assumptions about ground behaviour can also be considered.

Table H.1 — Possible approaches for applying the Observational Method

Approach A B C D

Optimistically pro-active

Cautiously pro-active Pro-active modifications

Reactive corrections

Timing Ab initio (from the start) Ipso tempore (in the moment) When implemented

Observational Method is planned from project inception

Starts with conventional design with no explicit intention of applying the Observational Method

Back analysis requirements

Necessary before construction starts from available reliable and relevant case history data

Preferable, but not essential

Necessary – from assessment of initial construction stages

Analysis assumptions for design of the geotechnical structure

Design and construction sequence in accordance with “design by calculation” method

Parameters adopted for initial design

Most probable Representative Representative

Implementation Most probable design and associated construction

Characteristic design and associated construction sequence implemented on site

Monitoring, observations and back analysis during construction show structure

Monitoring and observations during construction show structure not performing in


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Approach A B C D

Optimistically pro-active

Cautiously pro-active Pro-active modifications

Reactive corrections

Timing Ab initio (from the start) Ipso tempore (in the moment) sequence implemented on site. Alternative construction sequence fully developed in accordance with “design by calculation” adopting representative parameters for use as contingency, depending upon the actual performance of the structure

Alternative construction sequence fully developed in accordance with “design by calculation” method adopting “most probable” parameters for use on site, depending on actual performance of the structure

performing better than anticipated. Ground, material and structural parameters and ground and analytical models recalibrated on this basis. Construction sequence modified and fully developed in accordance with “design by calculation” method

accordance with design predictions Additional measures put in place to prevent breach of a limit state e.g. damage to nearby structures or to prevent catastrophic collapse

Parameters adopted for revised design

Representative Most probable Recalibrated -

Advantages and possible savings

Maximum potential for savings in materials and construction programme duration

Savings in construction programme duration but no material savings, although some savings in materials may be possible due to reduced requirements

Possible savings in during execution by modifying construction sequence requirements. Only likely to be feasible on large projects with long construction duration

Provides a systematic approach to implementation of remedial contingency measures/actions

H.6 Application of the ab initio approaches (A and B)

H.6.1 Parameter selection

A number of assumed behaviours are determined based on the available ground investigation data. These can be represented by adopting “representative” or “most probable” parameters for design.

In addition to the choice of design values for soil strength and stiffness, the behaviour of the ground (for example, drained or undrained) could be considered as well as ground water level and structural behaviour.

H.6.2 Calculation

The design and analysis of the geotechnical structures are undertaken for each of the sets of assumed behaviour.

Structures that cannot easily be changed once constructed have to be considered in all analyses and only the construction sequence is modified.


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H.6.3 Alarm values and contingency measures

Based on the serviceability analyses for each of the sets of assumed behaviour, a set of alarm values can be set against which the performance of the geotechnical structure is compared.

The choice of parameters that are monitored depends on the type of structure.

H.6.4 Construction phase

It is imperative that the designer is involved during the construction phase and is integral to the review of monitoring data and the decision-making process on the implementation of planned contingencies or modifications.

At each construction stage, the monitoring data is compared to the trigger limits and an appraisal made of the performance of the structure. Opportunities to consider future construction stages and whether contingencies or modifications will or will not be needed should be taken when possible.

H.7 Application of the ipso tempore approaches (C and D)

H.7.1 Evaluation of the structure’s performance and calibration of parameters

Following initiation of this Method ipso tempore, an audit of the geotechnical structures performance should be undertaken.

Monitoring data and observations from the construction site should be used to back analyse the structure to obtain recalibrated parameters and assumptions.

H.7.2 Calculation

The recalibrated parameters and assumptions should be used to forward predict the remaining construction stages and redefine the design or construction sequence.

H.7.3 Alarm values and contingency measures

The same procedure defined for ab initio (see H.6.3) should be used to define alarm values based on the recalibrated parameters and assumptions.

H.7.4 Monitoring system

The monitoring system installed at the start of construction may require augmentation following initiation of the Method ipso tempore approach.

H.7.5 Remaining construction stages

For the remaining construction stages, the performance of the geotechnical structure should be compared to the alarm values defined in H.7.3 to ensure the contingency or modification are having the intended effect.

Further recalibration may be required during the remaining construction stages.


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(Informative) Bibliography

Non-normative references

POWDERHAM (1994), An overview of the observational method: development in cut and cover and bored tunnelling projects, Geotechnique, vol 44, no 4, pp 619-636

NICHOLSON, D, TSE, C and PENNY, C (1999) The Observational Method in ground engineering – principles and applications, Report 185, CIRIA, London

GABA, A, HARDY, S, DOUGHTY, L, POWRIE, W, SELEMETAS D (2017) Guidance on embedded retaining wall design, Report C760, CIRIA, London.

PHOON et al. (2016), Uncertainty representation of geotechnical design parameters, Chapter 3 in Reliability of geotechnical structures in ISO2394, K.K. Phoon & Retief (eds) CRC Press

PHOON, K, KULLHAWY, F (1999), Characterisation of geotechnical variability, Canadian Geotechnical Journal, 36(4): 612-624

BURLAND, J, Wroth, C (1977), Settlement of buildings and associated damage,

CIRIA Report C731 (2013), The International Levee Handbook

Wang et al. 2015

<Drafting note: These non-normative references need to be updated and reviewed by PT6, it to be included or not>

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