advanced foundation design module

COURSE FASCILITATOR:

ASSOC. PROF IR. DR. RAMLI NAZIRPROF. DR. KHAIRUL ANUAR KASSIM

LECTURE MODULE

COURSE FASCILITATOR:

ASSOC. PROF IR. DR. RAMLI NAZIR

SECTION A

LECTURE 1 FOUNDATION ENG. DESIGN PRINCIPLES

1

By

ASSOC. PROF. Ir. DR. HJ. RAMLI NAZIRUNIVERSITI TEKNOLOGI MALAYSIA

1FOUNDATIONENG.DESIGNPRINCIPLES

There is no glory as a Geotechnical Engineer- Terzaghi




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GEOTECHNICAL BRAIN FUNCTION





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A PROFESSIONAL COMPARISON


What is Value Engineering in Foundation Design???

Challenge The Norm Thru Innovation To Excel



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VALUE ENGINEERING.


Stage of Design

Normally there are 3 stages of design i.e

1. PRE DESIGN STAGE

2. CONSTRUCTION STAGE

3. POST DESIGN STAGE


PRE DESIGN STAGE

Accurate and reliable SI data is vital. Type of foundation use for the structure is based from the above. An overall aspect and anticipation during construction has to be

considered especially practical and economics consideration.

During this stage, loading, foundation arrangement and location, bearing capacity and other related practice has been identified.

Anticipation of the problem in foundation construction work should be recognised and overcoming the problem should be readily available.



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DESIGN ANALYSES

Which one to use???

TOTAL STRESS ANALYSISOr

EFFECTIVE STRESS ANALYSIS


TOTAL STRESS ANALYSES

This type of analysis uses the undrained shear strength of the cohesive soil and also known as short term analysis.

The undrained shear strength, cu can be obtained from field such as vane shear and laboratory such as unconfined compression test. If the undrained shear strength is constant throughout the depth then cu = c and =0o. The use of unconsolidated undrained triaxial compression test is also applicable provided that it is saturated plastic soil.

The groundwater does not have an effect in the use of total stress parameters.


EFFECTIVE STRESS ANALYSIS

This type of analysis uses the drained shear strength, c and of the plastic soil.

The drained shear strength could be obtained from triaxialcompression test with pore pressure measurement tested on a fully saturated specimen of the plastic soil.

Also known as long term analysis since the shear-induced pore water pressure (positive or negative) from the loading has dissipated and the hydrostatic pore pressure conditions now prevail in the field.

Thus the location of the water table is significant in considering in the analysis.



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GENESIS OF FOUNDATION DESIGN


PRINCIPLE IN GEOTECHNICAL ENGINEERING DESIGN

SI SOIL PROPERTIES

GROUND CHARACTERIZATION

GROUND BEHAVIOUR

ENGINEERING PERFORMANCE

ENGINEERING PROPERTIES

CHEMICAL PROPERTIES

BASIC & INDEX PROPERTIES

MASS PROPERTIES

TYPICAL & GENERALISED SUBSOIL PROFILE & PROPERTIES OF TYPICAL GEOLOGICAL FORMATIONS, MAN MADE FILL etc..

ENGINEERING GEOLOGY

SOIL & ROCK MECHANICS EFFECTIVE STRESS THEORY SEEPAGE THEORY STRESS DISTRIBUTION LATERAL PRESSUREBEARING CAPACITY COMPRESSIBILITY

INSTRUMENTATION FOR PORE WATER PRESSURE EARTH PRESSURE DISPLACEMENT(SURFACE & SUBSURFACE INTERNAL STRESSES

CODE OF PRACTICES:- FOUNDATION BS 8004ANCHORS BS8081EARTHWORKS BS6031REINFORCED FILLS BS8006GEOGUIDES

INTERPRETATIONJUDGEMENT

MODELLINGPREDICTION

DEFORMATION DISPLACEMENTSTABILITY


THE IMPORTANCE OF SI

To study the general suitability of the site for an engineering project. (FEED Program)- FRONTIER EVALUATION ENGINEERING DEVELOPMENT.

To enable a safe, practical and economic design to be prepared.

To determine the possible difficulties that may be encountered by a specific construction method.

To study the suitability of construction material (soil or rock).



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Cont

SI nowdays has become contracting exercise and we tend to forget that SI is an INVESTIGATION.

As in many INVESTIGATION it is an itterative process. For information to be reliable, adhere to the procedure is very

important.

SI is the most procedure oriented operation within Civil Engineering Discipline.

This is due to the variability of the soil formation millions of years ago The properties of oil assessment or test carried out is affected by the

latter.

Accuracy and correct procedure is of vital important.


The Facts Why SI is needed

This is a part of geotechnical processes.

Lack of geotechnical processes will lead to a:- Failures where many case histories are available. Significant delay and increase in construction costs when the design has

to be revised or ammended.

Generally the elimination of the SI will not safe the cost of the project thus it only comprises from only 0.1% to 5% of the project cost.

In fact most frequent claims in civil engineering contracts are on the basis of inadequate SI or obstructions resulting in extra costs which could not reasonably have been forseen by an experience contractor.




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YOU HAVE TO PAY FOR THE S.I WHETHER YOU LIKE IT OR NOT!!


Method of Site Investigation

JKR PROBE/MACKINTOSH PROBE HAND AUGERING (HA) MOTORISED HAND BORING (MHB) DEEP BORING (DB) TRIAL PITS AND PLATE BEARING TEST DEEP SOUNDING (DS) INSITU VANE SHEAR TEST (IVST) STANDARD PENETRATION TEST (SPT) PRESSUREMETER TEST GROUND WATER INVESTIGATION ROCK CORING



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10

HAND AUGERING



ROTARY WASH BORING



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BEARING PLATE



CONE PENETRATION TEST/ DEEP SOUNDING



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IN SITU VANE SHEAR TEST



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STANDARD PENETRATION TEST (SPT)





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STANDARD PENETRATION TEST (SPT)

This a dynamic field test usually carried out in boreholes.

Test consists of driving a standard split barrel sampler 50.8mm in diameter.

The SPT is read from a 65kg drop hammer fall at a vertical height of 75cm.

The sampler is driven to a total of 45cm into the soil and the number of blows recorded for the last 30cm of penetration (SPT, N-value)


Numbers of BH, POSITION and Depth




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STANDARD PENETRATION TEST VALUE FOR DESIGN

Developed in 1927 and currently the most popular method and economical means to obtain subsurface information.

Currently 85% - 90% of usage in conventional foundation design. Test consist of :-

Drivingthesplitbarrelsampleatadistanceof460mmintothesoilatthebottomofboring.

Countingthenumberofblowstodrivesampleatlasttwo150mmdistancestoobtainNvalue

Using63.5kgdrivingmassfallingfreefromaheightof760mm.

The boring log shows refusal and the test is halted if:- 50blowsarerequiredforany150mmincrement 100blowsareobtainedtodrivetherequired300mm 10successiveblowsproducenoadvance.



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When full test depth cannot be obtained, boring log will show a ratio as 70/100 or 50/100 indicating that 70 or 50 blows resulted in a penetration of 100mm.

The blow count is directly related to the driving energy:-

Substituting Both Equations : m=

v= 2

2gh=Wh

Forstandardtest:E=63.5x9.81x0.762=474.5~475kJ

W= weight of mass or hammer

H = height of fall


Kovac and Salomone ( 1982) found that the actual energy impact to the sampler range about 30% to 80% while Riggs (1983) obtained energy input from 70% to 100%

The discrepancies arises from:- Equipment from different manufacturers Driving hammer configuration Usage of liner inside the barrel Overburden pressure Length of drill rod

Therefore SPT can be standardised to some energy ratio Er such that:-

Er= (Actual hammer energy to sampler (Ea)/ Input Energy (E)) x 100


'p76.95Co

N

Energy input of 70% is normally use since observation is close to the actual energy ratio (Er)

Therefore the standard blow count N70 is measure from N as follows:

N70 = CN x N x x x x

Where i = adjustment factor from tableN70 = Adjusted N

CN = Adjustment for effective overburden pressure

po in kPa



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12r

1r

22r11r

xNEE2N

xNExNE

Note that larger Er decrease the blow count nearly linearlyi.e Er45 gives N=20

Er90 gives N = 10

With Er70 gives N = 13

Energy ratio x blow count should be constant thus :-Say Er1 = 70 thus gives N2 = (70/Er2)xN1

Say N2 for Er45 = 20 = Er2We obtain N1 = 13

If we convert N70 to N60 than N2 = N60 = (70/60)x13 = 15

Using the equation we can readily convert any energy ratio to any other base.


SPT CORRELATIONS

20N5.4 70

It can be used in correlation for unit weight relative density, Dr, angle of internal friction angle , undrained compressive strength, qu, bearing capacity and stress-strain modulus.

Angle of internal friction:-Base from Japanese Railway Standard:

Relative DensityBase from Meyerhof(1957) :

where po is in kPa

For OCR > 1 Skempton suggest the following adjustment has been made:-

o2

r

70 'p288.032D

'N

oOCR2

r

70 'pBCAD

'N



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Where A range between 15 to 54B range between 0.306 to 0.204

And

For COCR=1 it relates to normally consolidated clay

Thus Meyerhof estimate:-

A correlation for N versus qu in general form of:-qu = kN

Where k tend to be site dependant.However k = 12 has been used i.e for N70 = 10, qu = 120kPa

OCR

OCR

o

onc

ppC

''

rDo

15o

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DESIGN N-values




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Relationship between Angle of Internal Friction and N-Value

(Sandy Soil)


Hammer TypeSPT

c (t/m2) = 2/3 NN-SPT = Total No. of Blows for spoon sampler to penetrate at a depth of 30cm

SPT (Standard Penetration Test)


Relationship between Cohesion and N-Value (Cohesive soil)

2/3 N



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PRESSUREMETER TEST



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ROCK CORING

To determine the soundness of rock. Sound rock : Rock which ring when struck with a pick or bar. Does not integrate

after exposure to air or water, breaks with a sharp, fresh fracture, in which cracksare unweathered and less than 3mm wide and generally not closer than 1m apart.Core recovery is normally 85%.

Medium rock : Characteristic as for sound rock but the cracks maybe 6mm wideand slightly weathered, generally no closer than 60cm. Core recovery is 50% ormore.

Intermediate rock : Give dull sound when hit by pick or bar. Does not integrateafter exposure to air or water. Broken pieces may show weathered faces. Fracturesup to 25mm wide and space no closer than 30cm. Core recovery generally is 35% orgreater.

Soft rock : Any rock which flakes on exposure to air or water. Give a very dullsound when struck with pick or bar. Core recovery generally is less than 35% orgreater but SPT more than 50.



Strength of Rock Materials

Term Uniaxial Compressive Strength (MN/m2)

Very Weak < 1.25

Depending on moisture , anisotrophy and test procedure

Weak 1.25 5.0

Moderately Weak 5.0 12.5

Moderately Strong 12.5 50.0

Strong 50 - 100

Very Strong 100 - 200

Extremely strong > 200



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SOIL SAMPLING TECHNIQUE

2 TYPES OF SAMPLE :-

Undisturbed : To determine properties such as strength parameters,consolidation, permeability and parameters which need to observed as per sitecondition.

Disturbed : Do determine physical properties such as grain size, colour, texture,compaction properties, remoulded properties and for testing etc.


FIELD IDENTIFICATION AND DESCRIPTION OF SOIL

Soil descriptions are made from washed and disturbed samples recovered from the boreholes.

The soil name is based on particle size distribution and plasticity, which can be readily estimated and measured at the laboratory.


According to BS 5930, soil samples are described with each element of the descriptions having a fixed position within the overall description:- a) Consistency (cohesive) or RD (non cohesive) b) Fabric and Fissuring, if distinguishable c) Colour d) Subsidiary constituent e) Angularity or grading of principal soil type (for coarse grained soil) f) Principal soil type (in capital letter) g) More detailed comments on constituents or fabric.

EG.

Very Stiff (a) Dark Grey (c) CLAY (f)

Dense (a) Brown (c) Fine to Coarse (e) Angular (e) GRAVEL (f)

Very Stiff (a) Greenish blue (c) Sandy (d) CLAY (f) With some rounded gravel (g)



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When soils are desribed at field, it is important to learn how to distinguish between clay and non cohesive soils on the basis of estimated engineering behaviour. (10% of clay can impart an essentially cohesive behaviour. Eg.

A soil containing 50% of silt, 30% of clay and 20% of sand is described as sandy silty CLAY because the soil behaves more like a clay.

Clayey SAND not cohesive, but contains clay

Very clayey SAND or Very sandy CLAY borderline

Sandy CLAY cohesive, but sand may be the major constituents by weight.


CONSTRUCTION STAGE

Engineers should allow or apt with changes during construction of foundation at site.

Alternative design need to be in hand whenever there are changes during this stage.

At this stage a critical, fast and accurate decision need to be done as the delay in making decision will hold or retarding the process of construction.

This is a stage where foundation engineers are really tested in their knowledge integrity.

This is also a stage where reliability of SI data is known.


POST DESIGN STAGE

To validate the design, load test need to be carried out. The designer may choose to have them conducted either before or after the bids are taken.

The first alternative permits development or revision of design and specifications to fit the actual conditions.

The second saves expenses on mobilisation but may lead to delay if the results is unsatisfactorily.



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PILE LOAD TEST AND INTERPRETATION





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LOAD TEST

To ensure the pile workability before and after construction. It is also as a method to determine settlement and ensuring that it does not exceed allowable limit.

Failure of load test according to JKR specification:-1. Residual settlement at working load exceed 6.5mm

2. Total settlement at working load exceed 12.5mm

3. Total settlement exceed 38mm or 10% of pile diameter or width whichever is lower at twice working load.

Methods of statement shall be refer to JKR Specification or BS8004. Pile in granular soil are often tested 24 to 48 hrs when load

arrangement have been made.



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The time lapse is sufficient for excess pore water pressure to dissipates. Pile in cohesive soils should be tested after sufficient lapse for excess

pore water pressure to dissipates.

This time lapse is commonly in the order of 30 to 90 days giving also some additional strength gain from thixotropic effects.



NEW FAILURE INTERPRETATION

i) The total residual settlement after removal of the test load at working load exceeds ((diameter of pile or diagonal width for non-circular pile / 120) + 4) mm or 12.50 mm whichever is the lower value.

ii) The total settlement under twice the Working Load exceeds 38.0 mm, or 10% of pile diameter / width whichever is the lower value.



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2DL

LOAD

sett

lem

ent

DL

6.5m

m

12.5

mm

38mm


Failure Load Definition

1. NAVFAC Method

2. Van Weele

3. Chin Fung Kee Method

4. DeBeer Method

5. Mazurkiewicz Method


NAVFAC Method



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Van Weele Method


From point O to a the capacity is based on the skin resistance plus any small point contribution. From point a to b the load capacity is the sum of the limiting skin resistance plus the point

capacity.

From point b the curves becomes vertical as the ultimate point capacity is reached. Often the vertical asymptote is anticipated and the test terminated before a vertical curve branch is established.

250kN

1600-250 = 1350kN



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Chin Fung Kee Method



De Beer Method



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Load (Log Scale)

Sett

lem

ent

(Log

Sca

le)

The load settlement curve is plotted in log-log plot and the point of intersection of the two straight lines thus obtained is the failure load.


Mazurkiewicz Method


Load

Sett

lem

ent

45o He assumed that the loadsettlement curve is parabolic afteran initial straight portion . Theultimate load can be obtained bygeometric construction. After theinitial straight portion, draw setsof equal settlement lines tointersect the load settlementcurve. Draw vertical line loadsfrom this intersection to intersectthe load axis. Draw 45o line tointersect the next load line. Theintersection fall in a line whichcuts the load axis at the ultimateload.



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STARTING POINT OF FOUNDATION DESIGN

Following steps are the minimum requirement for designing a foundation.

1. Locate the site and the position of the load

2. Physical inspect the site for any geological or other evidence that may indicate potential design problems

3. Establish the field exploration program for design parameters

4. Determine necessary design parameters base on integration of test data, scientific principles and engineering judgement.

5. Design the foundation using the latter and it should be economical and be able to be built by the available construction personnel.


GENERAL REQUIREMENT

TWO MOST IMPORTANT QUESTION FOR DESIGNER!!!

WHAT LOADS ARE TO BE SUPPORTED.

HOW FAR MAY THE FOUNDATION SETTLE IN RESPONSE TO THESE LOAD.


Generally the proper design requires the following:-1. Determine the building purpose, probable service life

loading, type of framing, soil profile, construction methods and construction cost.

2. Determine the client owner and client needs.

3. Making the design, but ensuring that it does not successively degrade the environment and provide a margin of safety that

produces a tolerable risk level to all parties, the public, the owner and the engineer.



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ADDITIONAL CONSIDERATION IN FOUNDATION DESIGN

Adequate depth Depth of foundation to be below seasonal change Considering problematic soil Compressive strength consideration Protection of foundation against natural causes Sustainable to changes Buildable or limitation. Apt to local environment standard.


CHOICE OF FOUNDATION TYPE

Based from Neoh C.A, the choice of the foundation designs are considered from:

1. Loads per column

2. Bearing type either end or skin

3. Bearing layer

4. Type of Intermediate layer

5. Location of water level.


Assess Foundation Base

Assess Ground Conditions and Type of Structures

Are pile necessary Choose

Shallow Foundation Types

Technical Considerations for Different Pile Types:-

1. Ground Condition

2. Loading Condition

3. Environmental Considerations

4. Site and Plant Considerations

5. Safety

List all technically feasible pile types and rank them in order of suitability based on technical consideration.

Assess cost of each suitable pile type and rank them based on cost consideration.

Assess construction programme for each suitable pile type and rank them based on program consideration

Make overall ranking of each pile type based on technical, cost and programme considerations

Submit individual and overall rankings of each pile type to client and make recommendation on most suitable pile type.

NOYES

PROCEDURE FOR THE CHOICE OF FOUNDATION TYPE FOR A SITE



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Myths in Piling

Myth Dynamic Formulae such as Hileys Formula Tells us the Capacity of

the Pile

The Truth

Pile Capacity can only be verified by using: (i) Maintained (Static) Load Tests (ii)Pile Dynamic Analyser (PDA) Tests


Continue

Myth: Pile Achieves Capacity When It is Set. Truth: Pile May Only Set on Intermediate Hard Layer BUT May Still Not

Achieve Required Capacity within Allowable Settlement.

Myth:

Pile settlement at 2 times working load must be less than certain magnitude (e.g. 38mm)

Truth: Pile designed to Factor of Safety of 2.0. Therefore, at 2 times working

load:

- Pile expected to fail unless capacity under- predicted significantly



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Continue

Myth Load test can opt not to be done since the pile has all set. Truth Load test need to be done since it is part of Geotechnical Design

process i.e to verify. Pile set does not mean that it has reach its allowable capacity at designated settlement.





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THE END


LECTURE 2 APPLICATION OF EUROCODE IN GEOTECHNICAL DESIGN

1

APPLICATION OF EUROCODE IN GEOTECHNICAL DESIGN

ASSOC. PROF. Ir. DR. HJ. RAMLI NAZIRDEPT. OF GEOTECHNIC AND TRANSPORTATION,

UNIVERSITI TEKNOLOGI MALAYSIA

INSPIRING CREATIVE AND INNOVATIVE MINDS

Lecture 2

UNDERSTANDING THE DESIGN USING EUROCODE (EN-7 (MALAYSIAN ANNEXE))


INTRODUCTION

The Eurocode system consists of :

1. EN1990 Eurocode 0 Basis of Design2. EN1991 Eurocode 1 Actions on Structure3. EN1992 Eurocode 2 Design of Concrete Structures 4. EN1993 Eurocode 3 Design of Steel Structures5. EN1994 Eurocode 4 Design of Composite Steel and

Concrete Structures6. EN1995 Eurocode 5 Design of Timber Structures.7. EN1996 Eurocode 6 Design of Masonry Structures8. EN1997 Eurocode 7 Geotechnical Design9. EN1998 Eurocode 8 Design of Structure for Earthquake

Resistance10. EN1999 Eurocode 9 Design of Aluminium Alloy

Structures.Other related documents : CEN and ISO


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OBJECTIVES OF THE EUROCODES

As a mean to prove compliance of building and civil engineering works with the essential requirements of mechanical resistance and stability and safety in case of fire.

A basis for specifying contracts for construction works and related engineering services.

A framework for drawing up harmonised technical specs for construction products.

Improve the functioning of a single market for products and engineering services by removing obstacles arising from different nationality codified practices for the assessment of structural liabilities.

Improve the competitiveness of the European construction industry and its professionals and industries, in countries outside the European Union.

Eurocode Design Method

All the Eurocodes are all based on a common design method The common design method is presented in EN 1990 A common loading code for all the Eurocodes is presented in EN1991- Actions The Eurocodes share a common terminology and symbols The common design method for the verification of safety and serviceability involves

The limit state design method Partial factors Characteristic actions and material parameters or resistances Reliability based


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Q: Why do we need a change?

Eurocode 7 draws geotechnical design into a framework common to other aspects of civil and structural engineering.

In the past, differences in design approach have arisen due to the properties of soil and rock being fundamentally different and more difficult to predict than other engineering materials.

In order to overcome difficulties in prediction and uncertainty of material behaviour, designers have often adopted large factors of safety under working loads to ensure serviceability.

However, to avoid problems, designers need to grasp fundamental geotechnical principles, including overall stability, hydraulic uplift and piping.

Contd

Eurocode 7 may be seen by some as an unnecessary complication, it introduces the concepts of limit state design to geotechnical calculations.

This will be second nature to most structural engineers who will not find any difficulty with the concepts.

The currently accepted methods of analysis of geotechnical problems remain largely unchanged.

The real advantage in its application lies in a common framework for design, including overall stability, and uplift.

The Eurocodes adopt, for all civil and building engineering materials and structures, a common design philosophy based on the use of separate limit states and partial factors rather than global factor of safety.

The intended are to ensure safe structures, so they will be use both by the designers and the checkers of the design.

COMPARISON BETWEEN CONVENTIONAL DESIGN AND EUROCODES

Advantages :

Conventional Design EurocodeUsing Global FOS and simple

applications Using PFOS and harmonic design

Accustomed to use Type of load has different levels of uncertaintyUniform Level of Safety

Risk Assessment


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COMPARISON BETWEEN CONVENTIONAL DESIGN AND EUROCODES

Disadvantages :

Conventional Design EurocodeInadequate amount of variability More ComplexStress is not a good measure of

resistance Old Habits

FOS is subjective Requires availability of statistical dataNo risk assessment Resistance Factor varies

Whereabout in Eurocodes ?

The suite of primary structural Eurocodes

Numbers Name SubjectEN1990 Basis of structural designEN1991 Eurocode 1 Action on structuresEN1992 Eurocode 2 Design of concrete stucturesEN1993 Eurocode 3 Design of steel structuresEN1994 Eurocode 4 Design of composite steel and concrete

structuresEN1995 Eurocode 5 Design of timber structuresEN1996 Eurocode 6 Design of masonry structuresEN1997 Eurocode 7 Geotechnical DesignEN1998 Eurocode 8 Design of structures for earthquake

resistanceEN1999 Eurocode 9 Design of aluminium sructures.


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EN1990

EN1990

EN 1990 describes the Principles and requirements for safety, serviceability and durability of structures.

It is based on the limit state concept used in conjunction with a partial factor method. For the design of new structures, EN 1990 is intended to be used, for direct application,

together with Eurocodes EN 1991 to 1999. EN 1990 also gives guidelines for the aspects of structural reliability relating to safety,

serviceability and durability: for design cases not covered by EN 1991 to EN 1999 (other actions, structures not treated,

other materials) ; to serve as a reference document for other CEN TCs concerning structural matters.

EN1990

EN 1990 is intended for use by : committees drafting standards for structural design and related product, testing and execution

standards ; clients (e.g. for the formulation of their specific requirements on reliability levels and

durability) ; designers and constructors ; relevant authorities.

EN 1990 may be used, when relevant, as a guidance document for the design of structures outside the scope of the Eurocodes EN 1991 to EN 1999, for :

assessing other actions and their combinations ; modelling material and structural behaviour ; assessing numerical values of the reliability format


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EN1990

This standard gives alternative procedures, values and recommendations for classes with notes indicating where national choices may have to be made.

Therefore the National Standard implementing EN 1990 should 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 1990 through : A1.1(1) A1.2.1(1) A1.2.2 (Table A1.1) A1.3.1(1) (Tables A1.2(A) to (C)) A1.3.1(5) A1.3.2 (Table A1.3) A1.4.2(2)

ASSUMPTIONS

The general assumptions of EN 1990 are : the choice of the structural system and the design of the structure is made by

appropriately qualified and experienced personnel; execution is carried out by personnel having the appropriate skill and experience; adequate supervision and quality control is provided during execution of the work, i.e. in

design offices, factories, plants, and on site; the construction materials and products are used as specified in EN 1990 or in EN 1991

to EN 1999 or in the relevant execution standards, or reference material or product specifications;

the structure will be adequately maintained; the structure will be used in accordance with the design assumptions.

TERMS USED

Principles are mandatory (Normative) requirements; Principle clauses in the Code are identified by a P after the clause number and contain the word shall.

All other clauses are Application Rules that indicate the manner in which the design may be shown to comply with the Principles.

Application Rules are Informative (i.e. not mandatory and for Information only) and use words such as should and may.


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EN1997

What is the structure of the new code?

Eurocode 7 consists of two Parts: Part 1 (EN 1997-1) Geotechnical design General rules and Part 2 (EN 1997-2) - Ground investigation and testing.

It is important to appreciate that EN 1997-1 is not a detailed geotechnical design manual but is intended to provide a framework for design and for checking that a design will perform satisfactorily; that is, that the structure will not reach a limiting condition in prescribed design situations.

The Code therefore provides, in outline, all the general requirements for conducting and checking design.

It provides only limited assistance or information on how to perform design calculations and further detail may be required from other texts, such as standard soil mechanics books and industry publications.

EN1997

Part 2 covers Ground Investigation and Testing. The application of the code in the Malaysia requires reference to the Malaysia National

Annexes which provide the partial factors prescribed for use in the Malaysia. The Malaysia National Annex for Part 1 will be available in 2012 and the National Annex

for Part 2 is expected to be published after that since it is still in progress. A series of geotechnical execution standards covering geotechnical processes such as

piling works and grouting also exist; these are primarily of interest to construction, but are also of general interest to designers.


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EN1997

It describes the general Principles and Application Rules for geotechnical design, primarily to ensure safety (adequate strength and stability), serviceability (acceptable movement and deformation) and durability of supported structures, that is of buildings and civil engineering works , founded on soil or rock.

Principles are mandatory (Normative) requirements; Principle clauses in the Code are identified by a P after the clause number and contain the word shall.

All other clauses are Application Rules that indicate the manner in which the design may be shown to comply with the Principles.

Application Rules are Informative (i.e. not mandatory and for information only) and use words such as should and may.

Content of EN1997-1

BS EN 1997-1 contains the following Sections: Section 1 General Section 2 Basis of geotechnical design Section 3 Geotechnical data Section 4 Supervision of construction, monitoring and maintenance Section 5 Fill, dewatering, ground improvement and reinforcement Section 6 Spread foundations Section 7 Pile foundations Section 8 Anchorages (Still not Apply in Malaysia) Section 9 Retaining structures Section 10 Hydraulic failure Section 11 Site stability Section 12 Embankments.

Annexes

The Annex is informative which means that the partial factors listed must be used; however, the values of these factors are a matter for national determination and the values shown in the Annex are thus only recommended

Annex A Annex A is used with Sections 6 to 12, as it gives the relevant partial and correlation factors,

and their recommended values, for ultimate limit state design. Annex A is normative , which means that it is an integral part of the standard and the factors

in it must be used, although their values are informative and may therefore be modified in the National Annex.

Annex B Annex B gives some background information on the three alternative Design Approaches

permitted by EN 1990 and given in EN 1997-1


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Annex C - H Annexes C to G provide examples of internationally recognised calculation methods for the

design of foundations or retaining structures; Annexes C to J are informative , which means that in principle, they may be superseded in the

National Annex

SUMMARY OF ANNEXES

DESIGN PHILOSOPHY IN EN1997-1


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Traditional Design Philosophies

FOS on the materials is applied in the choice of the stresses used in the design of the piles and pile caps as structural members.

When pile considered single, the working load shall not exceed the allowable bearing capacity. The ultimate value shall be obtain from load tests whenever practicable. In general a value of 2 to 3 is normally used.

Settlement or differential settlement at working load shall not be greater than can be tolerated by the structure.

When settlement is not critical a smaller FOS can be employed. The basis of design will be use allowable value and check the settlement.

Limit state design

An understanding of limit state design can be obtained by contrasting it with working state design

Working state design : Analyse the expected, working state, then apply margin of safety.

Limit state design : Analyse the unexpected states at which the structure has reach an unacceptable limit.

Make sure the limit states are unrealistic or at least unlikely.

DESIGN PHILOSOPHY IN EN1997-1

EN 1997-1 is a limit state design code; this means that a design that complies with it will prevent the occurrence of a limit state

A limit state could, for example, be: an unsafe situation damage to the structure economic loss.

While there are, in theory, many limit states that can be envisaged, it has been found convenient to identify two fundamentally different types of limit state, each of them having its own design requirements: ultimate limit states (ULS); serviceability limit states (SLS).


11

Ultimate Limit Stress

ULSs are defined as states associated with collapse or with other similar forms of structural failure (e.g. failure of the foundation due to insufficient bearing resistance).

In geotechnical design, ULSs include: failure by excessive deformation, loss of stability of the structure or any part of it.

Hence, a state in which part of a structure becomes unsafe because of foundation settlement or other ground movements should be regarded as a ULS even if the ground itself has not reached the limit of its strength.

Contd.

Ultimate limit states of full collapse or failure of geotechnical structures are fortunately quite rare.

However, an ultimate state may develop in the supported structure because of large displacement of a foundation, which has itself not failed.

This means, for example, that a foundation may be stable, after initially settling (it hasnt exceeded a ULS or failed), but part of the supported structure may have failed (for example, a beam has lost its bearing and collapsed owing to substantial deformation in the structure).

What is the general approach to design?

The principal emphasis of Eurocode 7 is in the definition and application of partial factors of safety.

Factors are applied to characteristic actions, nominal dimensions and characteristic material properties.

These are considered through calculation with a view to ensuring that the design effects are less than or equal to the design resistances.

Where relevant, the code requires a total of five different ultimate states to be considered.


12

Contd

EQU: the loss of equilibrium of the structure or the ground, considered as a rigid body, in which the strengths of structural materials and the ground are insignificant in providing resistance;

STR: internal failure or excessive deformation of the structure or structural elements, including footings, piles, basement walls, etc, in which the strength of structural materials is significant in providing resistance;

GEO: failure or excessive deformation of the ground, in which the strength of soil or rock is significant in providing resistance (e.g. overall stability, bearing resistance of spread foundations or pile foundations);

UPL: loss of equilibrium of the structure or the ground due to uplift by water pressure (buoyancy) or other vertical actions;

HYD: hydraulic heave, internal erosion and piping in the ground caused by hydraulic gradients.


13

Contd

An exception to the application of partial factors is made in relation to water pressure.

It is recognized that the application of partial factors to water pressure can, in some circumstances, lead to unrealistically high water pressure. In this case, it is suggested that a suitable margin of safety be applied to characteristic water levels.

Three basic design approaches are permitted in the assessment of ultimate limit states and are applied according to local practice.

What limit states need to be considered?

For most simple geotechnical design situations, the GEO limit state will be critical to the sizing of foundations and structural members.

The sections of the code covering specific design issues, such as pile foundations and spread footings etc., give advice on the limit states that need to be considered.

Where groundwater is present in excavations or cuttings, the UPL and HYD limit states need to be considered.

The STR limit state is less well defined, but is nevertheless very important in some design situations.

The STR case might become critical where imposed loading causes deformation of some part of the structure or deformation of the ground imposes deformation on a structural member.

Which frequently used ?

For most of the design problems likely to be encountered the STR and GEO ultimate limit states are the ones that will apply, as they cover the routine design of shallow and pile foundations and other common geotechnical structures.

The EQU ULS is intended to cater for the rare occasion when, for example, a rigid retaining wall, bearing on a rigid rock foundation, could rotate about one edge of its base.

The UPL and HYD ULSs, while more common than EQU, are generally beyond the routine


14

Unrealistic possibility

Serviceability Limit States

SLSs are defined as states that correspond to conditions beyond which specified service requirements for a structure or structural member are no longer met (e.g. settlement that is excessive for the purposes of the structure).

It is a non technical statement (i)P The limit states that concern :-

- The functioning of the structures or structural members under normal use;- The comfort of people;- The appearance of the construction works- Shall be classified as serviceability limit states (SLS)

Inconvenience, disappointments and more manageable costs.

Should be rare, but it might be uneconomic to eliminate them completely.

SERVICEABILITY FAILURE


15

Who should carry out geotechnical design?

Part 1 provides a useful, although optional, definition of categories of geotechnical structures.

Geotechnical Category 1 (GC1) includes relatively straightforward structures in which routine methods, including prescriptive methods, may be used.

While the code makes no attempt to define levels of competency, experienced civil and structural engineers should be capable of preparing the geotechnical design basis for Category 1 structures.

A designer should be capable of judging whether a design situation is not more complex than allowed within the Geotechnical Category.

Contd

Structures that involve excavation below the water table, but otherwise conventional structures without unusual risk, are defined as Geotechnical Category 2 (CG2).

Such structures normally require some form of geotechnical characterisation based on field or laboratory testing.

The terms geotechnical engineer, geotechnical specialist and geotechnical advisor are defined.

It was suggested that design work on CG2 structures should be carried out by an experienced civil or structural engineer.

Contd

Geotechnical Category 3 (GC3) covers situations that are considered unusual or are associated with high risk.

GC3 projects will typically involve advanced field or laboratory testing and numerical analysis.

The Association of Geotechnical Specialists advocates the role of Geotechnical Advisors in establishing the design strategy of large projects, and this would seem to be appropriate to GC3 structures.


16

En1990 fundamental equation for ULSs

Fundamental limit states requirement

Design values of action

6.3.1 Design values of actions(1) The design value Fd of an action F can be expressed in general terms as:

Fd=FFrepwith

Frep=FKWhere F = Partial Factor of Safety for the action which takes account the possibility of

unfavourable deviations of the action values from the representatives value.Frep= The relevant representative values for the actionFK = The characteristic values of the action is either 1.0 or


17

Contd

Contd..

Design values of material or product properties


18

Contd..

Design values of geometrical data

Basis of geotechnical design

Refer details to EN7: Geotechnical Design Part 1 : General Rules Section 2 page 19 onwards.

2.1 Design requirement2.2 Design situations2.3 Durability2.4 Geotechnical Design by Calculation2.5 Design by prescriptive measures2.6 Load tests and tests on experimental models2.7 Observational method2.8 Geotechnical Design Report.


19

DESIGN APPROACH

Generally EN1997 provides 3 Design Approach for the application of partial factor of Safety.

The Design Approach is know as DA-1/1, DA-1/2 (Design Approach 1),DA 2 (Design Approach 2) and DA-3(Design Approach 3)

MALAYSIA PRACTICE USE ONLY DESIGN APPROACH 1 FOR STR and EQU IN THE DESIGN.

What combinations of partial factors to use?

Combination 1 involves the consideration of factored actions and unfactored material properties and resistances.

Combination 2 considers unfactored actions, except unfavourable variable actions, and factored material properties.

Difficulties arise with the application of numerical methods, such as finite element, in the assessment of ultimate state.

In this case, the factoring of soil strength or stiffness can lead to the generation of inappropriate mechanisms in the analysis.

Contd

Uncertainty can also be experienced in assessing slope stability, where it can be difficult to separate favourable and unfavourable actions, and in the design of ground anchors where the design and execution codes provide conflicting advice.

Serviceability states are usually assessed by adopting unfactored actions and material properties.

In this area, numerical analysis provides a useful tool for GC2 and GC3 projects.


20

DESIGN APPROACH 1 (MSIA PRACTICE)

National choice is permitted in the use of a Design Approach for the STR and GEO limitstates (see MS EN 1997-1:2012, 2.4.7.3.4.1(1)P).

As indicated in Table NA1, only Design Approach 1 is to be used in Malaysia.

Table NA1 of this national annex lists the clauses in MS EN 1997-1:2012 where national choice may be exercised in respect of factor values for design in Malaysia.

Where choice applies, Table NA1 indicates where values are given, or states a value to be used, or describes the procedure for specifying the factor.

The values given in the Tables in Annex A of this national annex replace the recommended values in Annex A of MS EN 1997-1:2012.

ONLY FOR DESIGN APPROACH 1 - STR AND GEOClause 2.4.7.3.4.2

Other than pile and anchor use Combination 1 : A1 + M1 + R1Combination 2 : A2 + M2 + R1

For Axially loaded Pile and AnchorCombination 1 : A1 + M1 + R1Combination 2 : A2 + (M1 or M2) + R4

where M2 is for calculating any unfavourable actions such as negative skin or transverse loading.


DESIGN APPROACH 1 (MSIA PRACTICE)

SUMMARY FOR FACTOR OF SAFETY

Refer only to Design Approach 1


21

SUMMARY OF GEOTECHNICAL DESIGN BY CALCULATIONCHARACTERISTIC MATERIALS PROPERTIES

DIVIDED BY M VALUES

DESIGN MATERIALS PROPERTIES

VERIFY Ed Rd

DESIGN RESISTANCE, RdDESIGN EFFECT ANALYSIS, Ed

REPRESENTATIVE ACTION, Fk

MULTIPLIED BY F VALUES

DESIGN ACTION, Fd

Geotechnical Design Analysis

THE DESIGN IS ALL ABOUT

Actions:(loads, forces etc.) and Material Properties (c, tan , etc)

DESIGN VALUES OF ACTIONS

CHARACTERISTICACTIONS, Fk

DESIGN EFFECT OF ACTION, Ed

REPRESENTATIVE ACTION, Frep

DESIGN ACTION, Fd

Correlation Factor, rep Partial Factor of Safety, rep

ENGINEERING STUDENT


22

GEOTECHNICAL ENGINEERING STUDENT

CIVIL ENGINEERS

DESIGN ENGINEERS RATIONAL


23

FINALLY - HOW TO LOOK SMART FOR ENGINEERS

THE END

LECTURE 3 Shallow Foundation

1

DESIGN OF SHALLOW FOUNDATION

ASSOC. PROF. Ir. DR. RAMLI NAZIR

TEL : 013 7927925

OFF: 07 5531722


Lecture 3

DESIGN OF SHALLOW FOUNDATION


Brief Revision


2

Basic Consideration in designing the shallow footings are:-

1. Significance and use

2. Settlement limitations

3. Total Settlement

4. Differential settlement

5. Bearing Capacity

Stability ProblemBearing Capacity Failure

How do we estimate the maximum bearing pressure that the soil can withstand before failure occurs?

DESIGN REQUIREMENT

The design must meet two principle requirement of the Limit State:-1. Capacity is sufficient to support loads

2. Avoiding excess settlement which might lead t a loss of function.

This limit state is known as Ultimate Limit State and Serviceability Limit State.

Both states must always be considered in the design. This philosophies is the basis of Eurocode 7. The concept related to shallow foundation design can be shown in the

figure below.


3

Bearing Capacity and Limit Analysis

Types/Modes of Failure

general shear failure local shear failure punching shear failure

Typical Mode of Failure


4

Mode (a)

As the pressure increase towards failure value, qf, a state of plastic equilibrium is reached initially in the soil around the edges of footing.

As the soil is not perfectly level , the soil movement will accompany with tilting and heaving to one side of the footing.

This mode is typical for low compressibility soil where the peak value is significant.

Ultimately the state of plastic equilibrium is fully developed throughout the soil above the failure surface.

This type of failure is called a general shear failure.

Mode (b)

There is a significant compression of the soil under the footing and only partial development of the state of plastic equilibrium.

The failure surfaces does not reach the ground surface and only slight heaving occurs.

Tilting of foundation will less been expected. The ultimate bearing capacity is not well defined. This mode is associated with high compressibility and is called Local

Shear Failure.

Mode (c)

Relatively to high compression of soil under the footing. This will accompanied by shearing in a vertical direction around the

footing.

No heaving occurs on the ground surface away from the edges of footing and no tilting occurs.

Large settlement is the main characteristic of this mode. The bearing capacity is not well defined. In general, he mode of failure depend on the compressibility of the soil

and the depth of foundation related to the breadth.


5

Model Tests by Vesic (1973)

General Guidelines

Footings in clays - general shear

Footings in Dense sands( > 67%)-general shear

Footings in Loose to Medium dense (30%< < 67%) - Local Shear

Footings in Very Loose Sand ( < 30%)- punching shearrD

rD

rD

The bearing capacity problem can be considered in terms of plastic theory.

It can be assumed that the stress-strain behaviour of the soil can be represented by the rigid-perfectly plastic idealization.

Shear Strain

Shea

r Stre

ss Y Both yielding and shear failure occur

at the same state of stress. Unrestricted plastic flow takes place

at this stress level. A soil mass is said to be in a state of

plastic equilibrium if the shear stress at every point within the mass reaches the value represented by Y.


6

The plastic collapse will occur after plastic equilibrium has reach in part of the soil mass.

This will result in the formation of unstable mechanism ( The par of the soil mass slip)

The applied load including body forces is called collapse load. Determination of the collapse load is achieved using the limit theorem of

plasticity known as limit analysis to calculate LOWER and UPPER BOUND to the true collapse load.

LOWER BOUND THEOREM

If the state of stress can be found which at no point exceeds the failure criterion for the soil and is in equilibrium with the external load system, than there will be no collapse.

Therefore the external load system constitute a lower bound to the true collapse since a more efficient stress distribution may exit, which would be in equilibrium with higher external loads.

UPPER BOUND THEOREM

If a kinematically admissible mechanism ( the motion of a sliding massmust remain continuous and be compatible with any boundary restriction)of plastic collapse is postulated and if, in an increment of displacement,the work done by the system of external loads is equal to the dissipation ofenergy by the internal stresses, then collapse will occurs.

The external load system constitute an upper bound to the true collapseloads since more efficient mechanism may exist resulting in collapseunder lower external loads.


7

BEARING CAPACITY IN UNDRAINED MATERIALS

UPPER BOUND APPROACH MECHANISM UB-1

For undrained condition the failure mechanism within the soil mass should be a slip lines which are either a straight line or a circular arcs or both.

For simplification a straight line is used to identify the three sliding block of a soil under vertical loading.

The load will push downwards and the blocks will have to move to form a mechanism and therefore be kinematically admissible.

As a result a slip line shown OA, OB, OC,AB and BC which are the results of energy dissipation along this line.

The energy line is shown as in the velocity diagram known a hodograph.

It is use to determine the velocities along the slip line

Starting with the known vertical displacement (v) of a footing, the point f is known. Block A must move 45o horizontal to the stationary soil. The vertical component of this motion must equal to vso the soil and footing will remain contact.

Two construction line may be added to the hodograph to represent the two limiting conditions.

The crossing line will meet at point a and form velocity vOA. Similar to Block B where it moves horizontally with respect to O and at 45o with respect to A. the process continuously move which is therefore a kinematically admissible.

The energy dissipated (Ei) due to shearing at relative velocity vi along a slip line of Length Li is given by :

Total energy dissipated in the soil can then be found by summing Ei for all

slip lines.

Slip Line Stress, f Length, LiRelative velocity,

vi

Energy Dissipated,

Ei

OA cu2 2 cuBv

OB cu B 2v 2cuBv

OC cu2 2 cuBv

AB cu2 2 cuBv

BC cu2 2 cuBv

Total Energy, Ei 6cuBv


8

The work done Wi by a pressure qi acting over an area per unit length Bi moving at velocity vi is given by :-

For qf, the pressure acting downward while for Block C as the motionmove upwards, the surcharge pressure will tend to move against gravity.This is negative work. Therefore the work done for surcharge (q) will be:

Summing W for all component:

Therefore, for mechanism UB-1, for undrained materials the bearing capacity qf is :

=

UPPER BOUND APPROACH, MECHANISM UB-2

Another mechanism approach is by replacing Block B with a number of smaller

wedges. These wedges describe a circular arc of Radius, R between the rigid block A and block C which is known as shear fan.

Block A and C will move in the same direction and b the same magnitude.

The velocity around the edge of the circular arc will be constant as its rotates around point X.

Since Li is circular length then Li = R Thus giving :

The next energy dissipated due to theshearing occurrence between each wedgeis similarlyfound and given as:-

,


9

The total amount of energy disipated is by summing all amount of energy across all wedges.

If the wedges angle is small, this summation becomes an integral over a full internal angle of the zone ().

,

Slip Line Stress, f Length, Li Relative velocity, vi Energy Dissipated, EiOA

cu2

2 cuBv

Fan Zone (/2) cu R = vfan = 2 cuBvOC

cu2

2 cuBv

Total Energy, Ei =

Applying the same equation as previous for UB-1 it yields :

The results in UB-2 is lower than UB-1, so UB-2 present the true collapse load by upper boundtheorem.

LOWER BOUND APPROACH STRESS STATE LB-1

In undrained condition the yield criterion are satisfied without considering mode of deformation thus f = cu.

For equilibrium purposes, 1 in zone 2 must be equal to 3 in zone 1.

The major principal stress at any point in zone 1 is :

The minor principal stress in zone 2 issmilarly :

If the soil is undrained with shear strength

cu, it is in the state of plastic yielding andthe diameter of each circle is 2cu.

At the point where the circle meet : =


10

Lower Bound Approach, Stress State LB-2

A more realistic stress state forming a fan zone which gradually rotate the major principle stress from vertical beneath the footing to horizontal outside.

The change in direction of major principle stress across a frictional discontinuity depend on the frictional strength along the discontinuity , d.

In crossing the discontinuity, the major principle stress will rotate by an amount

And the radius of the Mohr circles are cu;

;

=

For a fan zone of frictional discontinuities substended to an angle , the equation can be integrated as follow across the fan angle fan:-

The principal stress rotation required in the fan is :

, giving :-

This value is higher than for LB-1 so LB-2 represent a better estimate of the true collapse load by the lower bound theorem.

BEARING CAPACITY FACTOR (Undrained Materials)

General Equation : (refer pg. 157, App. D, EN7-1)

For the case of footing surrounded bysurcharge pressure q, Nc = 5.14 where Nc isbearing capacity factor for strip footing underundrained conditions (f = cu)

Skempton (1951) provided figure by the sidewith included value(solid line) suggested bySalgado et.al. (2004) given that :-

. (Eqn 8.18)Where d : footing depth and B : footing width.

For general rectangular footing dimension B x L,Eurocode 7 recommends that shape factor :

. (Eqn 8.19)Nc for circular may be obtain by taking squarefooting (B/L = 1) and should not exceed 9 fordeeply embedded square (sc=1) or circular(sc=2)foundation.


11

Footing in Layered Undrained Soil

Values of Nc obtained previously may be usedfor stratified deposits, provided the value of cufor a particular stratum is not greater than theaverage value for all strata within thesignificant depth by more than 50% of theaverage value.

Merifield et al. (1999) presented upper andlower bound values for Nc for strip footingresting on a two cohesive layer as a functionof thickness H on upper layer of strength cu1overlying deep deposit materials with strengthcu2.

Proposed design value Nc as suggested ingeneral terms from Figure(a) is valid if the undrained shear strngth ofthe upper layer is used in the latter equation.(cu = cu1)

The resulting shape factor for square footingB/L=1 is given as in Figure (b).

Footing Associated With Slopes

For foundation constructed close to the slope, inevitably the bearing capacity will reduced.

Georgiaids (2010), proposed charts for Nc for strip footing set back from the crest of the slope with angle by a multiple of the foundation width.

These are based on upper bound analyses in which an optimal failure mechanism was found giving the lowest upper bound.

Thus it is important to include both local and global failure mechanism.

The value of Nc reduces with the slope increment.

If the foundation is set far enough back from the crest of the slope (l>2B), then the slope will have no effect on the bearing capacity and consider as a level ground (Nc = 2 + )

Variation of cu with Depth

Davies and Booker(1973) conducted upper and lower bound plasticity analyses for soil with linear variation of undrained shear strength with depth z below founding plane :-

Where cu0 is the undrained shear strength at z = 0 and C is the gradient of the cu-z relationship.

The general expression is the given as:

If C=0, then Fz=1 giving Nc=5.14.


12

BEARING CAPACITY IN DRAINED MATERIALS

Upper Bound Theorem

The slip surface within the kinematicallyadmissible failure mechanism is either straight lines or spiral log curves or both.

Normally for drained materials it is a cohesionless soil where c = 0 and will exhibit some amount of dilatancy ( ).

In special case where ( ), the direction of movement will be perpendicular to resultant force, Rs.

The condition is known as normality principle and it represent an associative flow rules.

Figure (a) shows a failure mechanism in a weightless cohesionless soil (=c=0) with a friction angle which is similar to UB-2 but log spiral replacing circular fan.

To determine the geometry of the mechanism, the equation describe the log spiral must be first found.

Thus :-

Which may be integrated from ro at =0 to r at .


13

Appling r where ro = LAB, r = LBC and = /2, for associative rule = ;

Length of the spiral log with known foundation width B and wedge angle of

are :-

The area per unit length over which the surcharge acts on the mechanism L can be define as :-

.

As a results of normality principle, there is no energy dissipated by shearing within soil mass which gives = 0.

As for undrained case, the footing and surcharges pressure still do work and the computations for the drain case are as shown:-

Lower Bound Analysis

The change in the direction of the major principle stresses across a frictional discontinuity depends on the frictional strength along the discontinuity as before (td).

For the drained case, the envelope bounding the Mohr circle in zone 1 and zone 2 form:-

and where is the mobilised friction angle along the discontinuity.

The major principle stress will rotate at an amount of whereas the mean effective stress in each zone is represented by s which gives:

2


14

The radii of the Mohr circles (tA and tB) for cohesionless soil can be describe by : thus it means that

.

Substitute into the latter equations gives :-

Setting sB = s as mob approach the above equation can be written as:-

For small

For a fan zone of frictional stress discontinuities subtending an angle qfan, the latter equation can be integrated from zone 1 to zone 2:-

Since in zone 1 and in zone 2 the principle stress rotaion required if the fan is or 90o will give the above equation as:-

.

Bearing Capacity Factor

Bearing capacity in drained materials is generally expressed as:-

N : Bearing Capacity Factor related to self weightNc : Bearing Capacity Factor related to cohesion

s and sc : Shape factor

Value of Nq is found by limit analysis and given in closed-form by :-


15

Parameter Nc can be derived for soil with non-zero c to give :

The final bearing capacity factor N is difficult to determine analytically as it is influence by the roughness of the base and soil interaction. In MSEN7, supersedes by N given in Annex D the following expression is proposed :-

.

The sample method given in MS EN 1997-1:2012, Annex D omits depth and ground inclination factors which are commonly found in bearing resistance formulations.

The omission of the depth factor errs on the side of safety, but the omission of the ground inclination factor does not.

To determine the ground inclination factor, one of the methods which may be considered is described in Foundations and Earth Structures Design Manual [NAVFAC DM 7.02 pp 7.2-135] which will be mentioned in the next topic.

Bearing Capacity Factor Chart (MSEN7)

1

10

100

1000

0 5 10 15 20 25 30 35 40 45 50

Bea

ring

Cap

acity

Fac

tor

' (DEGREE)

Nc

Nq N (MSEN7)

Lyamin et al. (2007) present rectangular shape factor derived from rigorous limit analyses. The results is as shown in Fig. a.

However, sq recommended by EC7 are:

for a rectangular shape for a square and circular shape

s recommended by EC7 are:

. for a rectangular shape . for a square and circular shape

sc recommended by EC7 is :-


16

Water Condition

It is vital that the appropriate values of unit weight are used in the bearing capacity equation. In an effective stress analysis, three different situation must be considered:-

1. If the water table is below the foundation plane, the bulk unit weight is to be used in the first and second terms of the equation.

2. If the water table is at the foundation plane, the buoyant unit weight () must be used in the second term of the equation. The bulk unit weight shall be used in the first term of the equation.

3. If the water table is at ground surface or above, the effective unit weight must be used in the first and second term of the equation.

Partial Factor of Safety for MSEN7-2012

ULS PARTIAL FOS FOR STR AND GEO Symbol

DESIGN APPROACH 1

COMBINATION 1 COMBINATION 2

A1 M1 R1 A2 M2 M2* R4 R4

ACTION (F , E)Permanent

UnfavourableG

1.35 1.00

Othe

r tha

n sl

opes

and

em

bank

men

t

Slop

es a

nd e

mba

nkm

ent

With

out e

xplic

it ve

rific

atio

n of

SL

S(A)

With

exp

lixit

verif

icat

ion

of S

LS(A

)

Favourable 1.00 1.00

VariablesUnfavourable

Q1.50 1.30

Favourable 0.00 0.00

SOIL (M)

tan ' ' 1.00 1.25 1.35

Effective cohesion c' 1.00 1.25 1.35

Undrained strength cu 1.00 1.40 1.50

Unconfined Strength qu 1.00 1.40 1.50

Weight density ' 1.00 1.00 1.00

Spread Footing

Bearing R;v 1.00

Sliding R;h 1.00

Calculation Procedure for Shallow Foundation on Undrained and Drained Materials Using

Limit State Design

Total Stress or Effective Stress analysis : Determine the shear strength parameter or effective stress parameters and unit weight of the underlying soil to determine the bearing capacity factors.

Groundwater Table: For an effective stress analysis, the groundwater table will give an impact to bearing capacity.

Ultimate Limit State Evaluation : Depend on type of footing and analysis using Design Approach 1 only. Determine the size of footing initially.

Check the respond of action against the effect of action together with the model factor of 1.4 or 1.2.

Combination 1 : A1 + M1 + R1 Combination 2 : A2 + M2 + R1 Check on Serviceability Limit States : The allowable bearing capacity may have

to be downgraded due to local building code of practice or lower bearing pressure to avoid excessive settlement allowed.


17

Shallow Foundation Under Combined Loads

Undrained Materials

In some cases apart from vertical loads, foundation can experience horizontal loads and moments.

If the horizontal loads is small in comparison to vertical load, than the horizontal load and moment may be disregard.

For the foundation loaded by action V, H and M, the following limits state must be met:

1. The resultant vertical action must not exceed the bearing resistance of supported soil.

2. Sliding must not occurs due to the resultant of H

3. Overturning must not occurs due to resultant action of M.

The foundation movement due to any settlement must not cause undue distress or lost of function in the supported structures.

Foundation Stability from ULS

Similar to lower bound limit analysis techniques, the addition of horizontal load, H will induced an additional stress f=H/Af at the footing surface as shown.

It is assume that the surface of footing is rough and rotate the major principle stress direction in zone 1.

In undrained materials, the rotation will be = /2. from the vertical.

Overall rotation of principal stresses across the fan zone is now fan = /2 /2.

Therefore From Figure :

In zone 2, , while in

zone1 Thus giving:


18

For all possible value of H (0 H/Afcu it can be found from

;

and V/Afcu ( = bearing capacity Nc) can be found from

When H/Afcu = 0 (purely vertical load) , =0 and V/Afcu= 2 + . When H/Afcu , the shear stress u = cu.

The footing will slide horizontally, irrespective of V.

The resulting curves representing the yield surface for the foundation under V-H loading. Combination of V-H which lie within the yield surface will be stable while those lying outside the yield surface will be unstable.

If V>>H, failure will be in bearing while if V


19

When M , the yield surface becomes 3 dimension (a function of V,H and M).

The contour of V/R for combinations of H and M under general loading are use in ULS design as shown in Figure (b).

The presence of moment allow fot rotation of the foundation when M>>V,H.

The yield surface assumes that tension cannot be sustained along the soil footing interface. This will due to uplift if the overturning effect is strong.

Provided that the combination of V, H and M is within the yield surface, the foundation will satisfy in terms of bearing, sliding and overturning.

Drained Materials

Using a lower bound analysis, it gives:

From the Mohr circle, the rotation of the major principal stress direction in zone 1 is =(+)/2 from vertical.

The stress condition in zone 2 are unchanged as shown in Fig.(a).

Overall rotation of principal stresses across the an zone is now :

Thus

From Fig. (b) :

In zone 2, s2 = q + s2sin while in zone 1, s1 = qf + s1sin cos() as in Figure (b).

Substituting the equation previously gives:

Value of can be found in any combination of V

and H with and Nq from the latter equations. The value is plotted as in the Figure shown. If the footing is perfectly rough (=), sliding will

occur if H/Vtan Similar to undrained case the EC7 apply

additional inclinaion factor in the equation by :

Valid when H/V to account for slidingFot the case of strip footing on cohesionless soil (c=0)


20

Butterfield and Gottardi (1994) presented a yield surface of a general case of V-H-M loading on drained soil:

. .

.

For value of V/R at any value of H/V the value of Nq from the latter equation will be divided by the value of Nq at H/V=0; and that H/R=(H/V) x

(V/R) thus the value of qf and Nq in latter equation can be expressed in terms of V/R and H/R for case M=0.

Figure (a) compares the lower bound solution , EC7 and the full yield stress surface for the case of V-H loading (M=0)

When M the yield surface will become 3 dimensiona surface which shows a contour of V/R for combinations of H and M under general loading for uae in ULS design from equation by Butterfield and Gottardi (1994).

In EC7 also accounted for the moments effect through the use of B=B-2e where e = M/V.

For strip footing, the footing soil contact area is B per meter length under V-H-M loading and:

Under pure ;oading V (where V = R at bearing

capacity failure)

Dividing the above equations and substituting for iq, B and e gives:

Foundation in Two way Eccentricity


21

Considering the foundation is subjected to Vertical Loading and Moment M.

The moment component is determine in 2 direction namely Mx and My. This condition is equivalent to the load Qult placed eccentrically on the

foundation with x = eB and y = eL

Since then : eB = and eL =

R = qf A A = effective area B x L

When determine effective area (A) four possible case may arise.

Case 1 :

Where

. .

L is the larger of two dimension that is B1 or L1.

B = A/L

Case II : eL/L


22

Case III : eL/L < 1/6 and 0< eB/B< 0.5

Magnitude of B1 and B2 can be determine from Figure (b)

The effective width is :

The effective length is :

L = L

Case 1 :

With effective width B = A/L

The effective Length L = L

BEARING CAPACITY FROM CPT


23

The bearing capacity use from Terzaghis equation can be estimated using:

0.8Nq ~ 0.8N ~ qcWhere qc is the average over depth interval from B/2 to 1.1B below the footing base. The application should be use for D/B


24

Widely use to obtain the bearing capacity of soil directly. Meyerhof use for computing the allowable bearing capacity for a 25mm

settlement.

qa = allowable bearing pressure for Ho = 25mm

d23

2a

d1

a

KBFB

FNq

KFNq

33.1BD33.01Kd

B F4

FACTORS F AS FOLLOWSCorrected SPT N55 N70

F1 0.05 0.04

F2 0.08 0.06

F3 0.3 same

F4 1.2 same


25

From equation :-N is the statistical average value for the footing influence zone about 0.5B

above footing base to at least 2B below. This is taken into account somewhat for mats where Meyerhof obtain qa = (N/F) x Kd

In this equations the allowable soil pressure is for an assumed 25mm settlement.

In general the allowable pressure for any settlement Hj is

Where Ho = 25mm. And Hj is the actual settlement that can be tolerated in mm

ao

ja q

HH'q

Allowable Bearing Capacity of Sand

Parry (1977) proposed allowable bearing capacity of sand as:

qa = 30N55 kPa (D


26

END

LECTURE 4 DEEP FOUNDATION

1

DEEP FOUNDATION(LECTURE 4)

ASSOC. PROF. Ir. DR. RAMLI NAZIR

TEL : 013 7927925

OFF: 07 5531722


DRIVEN PILE


2

Successful Engineering Failure


3


4

Effect of Installing Driven Pile

Pile in clay have been classified into 4 major categories:-a) Remoulding or partial structural alteration of the soil surrounding the pile.

b) Alteration of the stress state in the soil in the vicinity of the pile.

c) Dissipation of the excess pore pressures developed around the pile.

d) Long Term phenomena of strength-regain in soil.

ESTIMATION OF PORE PRESSURE

fvo

uo

vo

m A'c2)K1(

'u

Within the failure zone of the soil surrounding the pile, the pore pressure were at maximum and constant.

Driving of adjacent pile will only increase the pore pressure slightly.

Outside failure zone, the pore pressure decrease rapidly with distance and was negligible at about 16 diameters from the pile.

Raduis of failure zone is about 4 pile radii. Dappolonia and Lambe (1971) derived the maximum excess

pore pressure during pile driving as:


5

Rra

Where : um = maximum excess pore pressureKo = Insitu coefficient of earth pressure at restcu = Undrained shear strengthAf = Pore pressure coefficient at failurevo = Initial vertical effective stress in soil As a rapid, practical means of estimating the excess pore pressure distribution, the

following procedure is suggested :a) The equation is used to obtain maximum pore pressure from the surface of the pile to

distance R. R varies from 3 pile diameter to 4 pile diameter for insensitive clay and 8 pile diameter for sensitive clays.

a

R

Assume Limit of

Failure zone

2

m

2ruu

b. Beyond the distance R, the excess pore pressure is assumed to vary inversely as the square of the distance r from the pile i.e :

c. For group piles, pore pressure distributions around individual pile may be superimposed, except that pore pressure cannot exceed um.

For pile installed in sand, driving has distinct advantages compare to boring. Densification occurs due to displacement and vibration which resulting in

permanent rearrangement and some crushing of the particles. The amount of compaction near the tip is greater than the top of the pile. Kishida(1967) assume the diameter of compacted zone around the pile is 7 pile

diameter.

Within the zone he assumes that the angle of friction changes linearly with distance from the original values of at a radius r = 3.5d to a maximum value of at the pile tip where :-

When = 40o , no change in relative density due to pile driving. Pile groups driven into a loose sand will highlt compact the soil

around and in between the pile.

If the pile spacing is closed i.e < 6 pile diameter, the efficiency > 1.0

However if pile is driven in very dense sand, adverse effect may occurs.

2

40''

o1

2


6

LOAD TRANSFER OF SINGLE DRIVEN PILE

DEFINITION OF FAILURE LOAD ON PILES

Generally failure load is taken as the load causing ultimate failure of a pile. In engineering sense, failure may have occurred long before reading the

ultimate load since the settlement of the structure will have exceeded the tolerable limits.

Allowable loads on piles would be one which would enable engineer to predict load settlement relationship up to the point of failure, for any given type of size of pile in any soil or rock conditions.

In most cases, the procedure is to calculate the ultimate bearing of the isolated pile and to divide this value by a safety factor which experience has shown will limit the settlement and the working load to a value which is tolerable to the structural designer.

DESIGN PHILOSOPHIES

The design of pile should comply with the following requirements throughout their service life :

There should be adequate safety against ultimate limit state failure of the ground. The FOS depends on the important of the structure, consequences of the failure, reliability and adequacy of information on ground conditions, sensitivity of the structure, nature of the loading, local experience, design methodologies, number of representative preliminary pile load test.

There should be adequate margin against excessive pile movements which would impair the Ultimate Serviceability Limits of the structure.


7

SINGLE PILE ANALYSIS BASE FROM MSEN7

MODE OF FAILURE FOR SINGLE PILE

General Equation for axially loaded single pile:

or

Qs = Shaft skin frictionQp = End bearings = PFOS for skinb = PFOS for baset = PFOS for totalf = PFOS for Action

Qb

Qs

f Q Rd ..

l


8

Model Factor

MS EN 1997-1:2012, 2.4.7.1(6) states that model factors may be applied to the design value of a resistance or the effect of an action to ensure that the results of the design calculation model are either accurate or err on the safe side.

Model factors required in pile design are provided in A3.3.2 and A3.3.3

A3.3.2 Partial resistance factors for pile foundations

The values of factors provided here are considered to be generally applicable forpile foundations. However, variation of these factors is permitted in particularcircumstances when justified by thorough consideration and documentedexperience, and after being agreed, where appropriate, with the relevantauthorities. The value of the model factor should be 1.4, except that it maybe reduced to 1.2 if the resistance is verified by a maintained load testtaken to the calculated, unfactored ultimate resistance

A3.3.3 Correlation factors for pile foundationsFor the verifications of Structural (STR) and Geotechnical (GEO) limit states, the following corelation factors should be applied to derive the characteristic resistance of axially loaded piles:1 on the mean values of the measured resistances in static load tests;2 on the minimum value of the measured resistances in static load tests;3 on the mean values of the calculated resistances from ground test results;4 on the minimum value of the calculated resistances from ground test results;5 on the mean values of the measured resistances in dynamic load tests;6 on the minimum value of the measured resistances in dynamic load tests.

END BEARING


9

End Bearing in Undrained Soil

For piles in undrained condition where = 0

advanced foundation design module

Documents

design principles1byassoc

foundation arrangement

type of foundation use

undrained shear strength

foundation construction

stages of design i

pre design stage2

type of analysis