geotechnical engineering handbook - chapter 1-3

1.3 Geotechnical field investigations

Klaus-Jiirgen Melzer and Ulf Bergdahl

1 Basics

1.1 Standards

Section 3 of Eurocode EN 1997 Part 1 (see also Chapter 1.1) covers geotechnical investigations. Section 3.1 contains the requirement that field investigations are to be carried out according to internationally recognised standards and recommendations. Regarding the requirements for equipment and test procedures for laboratory and field investigations, reference is made to Parts 2 and 3 (ENV 1997-2; ENV 1997-3); these documents also demonstrate possibilities and examples for deriving geotechnical parameters from the test results. Besides investigations related to soil and rock mechanics properties, the field investigations have to include explorations relating to the engineering hydrology and hydrogeology and also consider aspects relevant to the environment. The scope of the investigations should be adjusted to the geotechnical category (see Chapter 1.8, Sec- tion 4.4). This has to be supplemented in case unforeseen conditions are encountered.

The geotechnical investigation shall provide all data necessary for determining the ground- structure-system dependent characteristic geotechnical parameters and those relevant to the planning and design of a structure or to determining construction materials.

Only general requirements were given in EN 1997-1 regarding the most commonly used field tests. Thus, preparing Part 3 became difficult because only a very limited number of internationally acknowledged standards for equipment and test procedure exist. For this reason, ENV 1997-3 was prepared not only to describe means of deriving values of geotechnical parameters from the results of field investigations (the original purpose of Part 3 of the code) but also to define essential requirements for the corresponding equipment, test procedures and evaluation (differences to the German status of standardisation are reported in [1, 2]). Existing gaps are filled by complementary national standards in different countries. This has been done in Germany by adjusting the existing established DIN Standards to the corresponding ENV 1997-3 procedures.

The following German standards are relevant to this chapter:

• DIN 4020 Geotechnische Untersuchungen fiir bautechnische Zwecke (Geotechnical investigations for civil engineering purposes)

• DIN 4021 Baugrund - Aufschlul3 durch Schiirfe und Bohrungen sowie Entnahme von Proben (Ground - Exploration by excavation, boring and sampling)

• DIN 4022 Baugrund und Grundwasser (3 Teile) (Subsoil and groundwater, 3 Parts)

52 Klaus-Jtirgen Melzer and Ulf Bergdahl

• DIN 4023 Baugrund- und Wasserbohrungen; Zeichnerische Darstellung der Ergebnisse (Subsoil and water borings; graphic presentation of the results)

• DIN 4030 Beurteilung betonangreifender W~isser, B6den und Gase (2 Teile) (Assessment of water, soil and gases for their aggressiveness to concrete)

In particular DIN 4094, Baugrund - Erkundung durch Sondierungen (Ground - Explo- ration by penetration tests) was re-written as DIN 4094, Baugrund - Felduntersuchungen (Ground - Field investigations):

• DIN 4094-1 Drucksondierungen (CPT) (Cone penetration tests)

• DIN 4094-2 Bohrlochrammsondierung (BDP) (Borehole dynamic probing)

• DIN4094-3 Rammsondierungen (DP) (Dynamic probing)

• DIN4094-4 Fltigelscherversuche (FVT) (Field vane test)

• DIN 4094-5 Bohrlochaufweitungsversuche (PMT) (Borehole deformation tests)

In the meantime, the CEN Technical Committee 341 on Geotechnical Investigation and Testing has been established to develop European Method Standards.

1.2 Preliminary investigations

Preliminary investigations are necessary to decide:

• whether a proposed structure can be constructed at all, at the intended location and to an acceptable cost, with regard to the ground conditions;

• which technical and economic requirements for the design of the foundation, the structure and the construction have to be considered.

In Germany, such preliminary investigations are the basis of the legal procedures for development planning. This means that these preliminary investigations have to also show what influences there are on the vicinity of the construction site, what environmental effects have to be considered and to what extent the ground in the vicinity of the planned structure can be loaded (e. g. by anchors).

The extent of the investigation depends on the existing information available, which especially in densely populated areas, may consist of geological maps, ground maps, ground expert opinions in the vicinity, aerial photography (important to the assessment of war damage), hydrological and geotechnical assessments, historical knowledge (filled cavities, quarries, underground air raid shelters, caverns, cavities in lime stone formations, old slopes or creeping slopes, mining activities etc.) and so on. In all other cases, ground and groundwater conditions have to be determined at least in a coarse grid. Hydrological data should be available for a significant period, generally, at least a full year. The same is applicable for meteorological data if construction in open waters is considered.

1.3 Geotechnical field investigations 53

Preliminary investigations of soil and rock for the purpose of obtaining construction materials should give information on whether, where and to what amount suitable material is available, considering the economic aspects.

1.3 Design investigations

Design investigations are the topic of this chapter. They consist of:

• carrying out excavations, drilling, penetration tests and other tests for the determination of geotechnical parameters (see Chapter 1.2);

• determining the ground strata and all relevant geotechnical properties of the soil and rock necessary for the design, the invitation to bid, the construction and for the geotechnical observation of the behaviour a structure or for deciding on the suitability of materials for construction purposes;

• determining potential difficulties during construction of the chosen foundation; • recovering soil and water samples from excavations and drilling (especially special

samples for laboratory tests for the determination of geotechnical parameters).

Field investigations include, in a wider sense:

• load tests of foundation elements, for example spread foundations (ENV 1997-3, 11), of piles (Chapter 3.2 and ENV 1997-1, 7) or of anchors (Chapter 2.5 and ENV 1997-1, 8). These tests are not covered by this chapter;

• measurements of settlements and deformations which are treated in Chapters 1.11 and 1.12.

Additionally, reference is also made to DIN 4020, Supplement 1, and relevant references [3-5].

It is in the hands of the engineer with geotechnical experience to design the ground investigation program and to select the tests to be carried out in such a way that the selection of tests, equipment or an intelligent combination of different methods results in the best technical and economical solution for the intended purpose. It is not always the "best" test equipment that ensures the most appropriate solution for given boundary conditions and circumstances.

2 Ground investigation by excavation, drilling and sampling

2.1 General

Trial pits, including headings (horizontal or with slight inclination) and shafts (vertical or with steep inclination), drilling and so called small-scale drilling are direct investigation methods which allow an inspection of soil and rock, their sampling and their performance evaluation in the field. Table 1 gives an overview of the suitability of some of the direct investigation methods for soils and rocks.

Trial pits give the best investigation results because details of the ground strata and the soil condition can be clearly identified and high quality sampling is possible. However, the investigation only reaches moderate depths and is in general only possible above the groundwater level. The cost rises considerably with increasing investigation depth because of the need to retain the ground or possible groundwater lowering.

54 Klaus-Jt~rgen Melzer and Ulf Bergdahl

Table 1. Suitability of some direct investigation methods (following DIN 4020, Supplement 1, Table 5)

1 2 3 4

Suitability of direct investigation methods

Investigation Type of soil/rock Weathering, Discontinuities methods strata, density state of loosening, (strata, cleavage, joints)

(in rock)

Existing, inspectable + ÷ ÷ - + explorations

Excavation -i-I-÷ + ÷ .i.÷ down to moderate also width of joints, depth and above filling, roughness, groundwater level smoothness, direction

Shaft ÷ +

4 Heading

5 Rotary core drilling

Percussive core drilling (also with tube or hose)

7 Grab drilling (dry)

8 Flush drilling

÷ ÷ difficult in the presence of groundwater and if immediate lining is necessary

÷ ÷

÷ + in rock +

in stiff cohesive soils

+ ÷ only in soils; narrow strata also detectable, often changes in density and structure

+ in soils at strata thickness of >_ 50 cm; in admixtures of coarse graveol, stones and boulders

_[_m

in conjunction with borehole geophysics: ÷

+ +

+ to judge rock material and filling of joints

+ + also width of joints, filling, roughness, smoothness, direction

+ +

+ in directional drilling, known strata or combination of different drilling directions, with TV probing

+-I- very suitable, partly optimum investigation method + suitable, generally sufficient results

+ - partly sufficient, sufficient only if supplementing by other investigation methods and for special problems

- not sufficient, partial results to be expected in exceptions only


5 6 7 8

Suitability of direct investigation methods

Geological faults Investigation of Borehole/ Remarks groundwater field-tests

d-d- d- -

d-d- d-+ d- Optimum sampling, especially recommendable for investigat- ing weathered/loosened zones in rock

d-d- d--

d-d-

d- often core loss in faults

d - m

only by comparing adjacent boreholes

m

only by comparing adjacent boreholes

only by correlating of boreholes

+ on heading level only

d- in rock d-- in soil

d-d-

d - -

o f t e n difficulties due to water and lack of wall stability

+ + all tests possible

+ + water pressure tests, PBP tests, SPT, BDP measurements of primary stresses

+ permeability tests, SPT, BDP

+ permeability tests, SPT, BDP

+

geophysical borehole measurements

For deep foundations in difficult ground, e.g. subways, power plants

Caverns, large tunnels, reservoir dams, field tests

Most frequent investigation method. In case of complex geological conditions and difficult structures, completed by shafts and headings

High quality drilling method for coarse soils and changing strata, appropriate with difficult structures in such soils

Suitable for coarse soils

Simple deep exploration, groundwater gauge


With drilling, soil and rock as well as water samples can be obtained also from greater depths and in addition, tests can be conducted in the borehole. The drilling itself is not hin- dered in case of groundwater, however, the presence of the groundwater has an influence on the selection of the sampling equipment.

Small-scale drilling requires less sophisticated equipment compared to the normal drilling equipment, however it generally provides only small samples unsuitable for soil mechanics investigations. Samples of higher quality (Table 4) can only seldomly be obtained. Therefore, DIN 4020 and DIN 4021 require that small-scale drilling is used for preliminary investigations under strong restrictions only and the drilling required for design investigations must not be replaced by small-scale drilling. The latter primarily serves the purpose of supplementing other investigation methods and for example of examining the ground at the base level of foundations. A combination of small-scale drilling with sampling and high quality penetration testing may be used as well, for example in certain clays.

The type and extent of the investigation depends on the laboratory and field investigation programme designed by the geotechnical expert and with this on the type and extent of the planned structure. DIN 4020 (Section 6.2.4.3) gives guidelines for the spacing of investigation points (e. g. 20--40 m for high-rise and industrial structures) and for the investigation depth for simple structures, large-area structures (e. g. industrial complexes), linear structures (e. g. roads and airfields), special structures (e. g. bridges) and water retaining structures. The reference level for the investigation depth is the lowest level of the structure or the structural element or of the excavation depth respectively. In cases where the stability of slopes or effects on neighbouring structures have to be considered, the investigations have to be extended beyond the area covered by the structure.

DIN 4021 describes the investigation of the ground by excavations, drilling, small-scale drilling and sampling. In the following reference will be made to major deviations from ENV 1997-3, especially when essential requirements are not met by DIN 4021.

2.2 Investigation of soils

In ENV 1997-2, Table 1, soil samples for laboratory investigations are divided into five quality classes according to soil properties, remaining unchanged during the sampling process and the subsequent treatment (transport etc.). This table was also included in ENV 1997-3, 12. The quality classes are described here in Table 2. Undoubtedly, the quality class of a sample for laboratory tests, obtained by using a certain soil sampling method, will depend on the soil type and also significantly on the design of the sampler and the care taken during sampling, transport, storage and handling in the laboratory. Quality classes 1 to 5 were introduced in DIN4021 for the first time in the early 1970's. The quality class describes what parameters and what properties can be determined from one class of samples. The system is based on six parameters and properties:

• Particle size Z • Water content w • Density • Permeability k • Linear modulus of elasticity Eoed • Shear strength ~f


Table 2. Quality classes of soil samples for laboratory investigations and corresponding sampling categories (after ENV 1997-3, Table 12.1)

Soil properties / quality class

Unchanged soil properties particle size water content density, density index, permeability compressibility, shear strength

Properties that can be determined sequence of layers boundaries of strata, broad boundaries of strata, fine Atterberg limits, particle density, organic content water content density, density index, porosity, permeability compressibility, shear strength

Sampling category to be used

1 2 3 4 5

X X X X

X X X

X X

X

X X X X X

X X X X

X X

X X X X

X X X

X X

X

Samples of the highest quality class (Class 1) retain all the indicated soil properties, most desirably unchanged. The state and composition of samples of the lowest quality class (Class 5) have been changed completely. These samples can only be used to draw conclusions regarding the ground layering. With the introduction of these quality classes, the selection of a suitable drilling and sampling method has improved. Only samples of a particular quality class are necessary to be sampled to allow the correct determination of the required soil parameters.

Table 3 gives an overview of drilling methods appropriate for certain soil types. Table 3 also shows the quality class for laboratory tests that can be reached (column 9) and the soil parameters that can be determined from those samples (column 10). Table 4 shows probable applications of small-scale sampling in soils.

When drilling methods with non-continuous sampling are applied, one sample has to be taken from each separate layer or each meter for layers of considerable thickness. These samples should reflect the composition and state of the actual soil conditions as much as possible.

Contrary to above, ENV 1997-3, 12.2.1 uses an equipment related approach by character- ising the sampling methods by means of the following three sampling categories:

• Category A: By using these methods, the intention is to obtain samples in which no or only slight disturbance of the soil structure has occurred during the sampling procedure or in handling of the samples. The water content and the void ratio of the soil correspond to that in situ. No changes in constituents or in the chemical composition of the soil have occurred.

• Category B: By using these methods, samples contain all the constituents of the soil in situ in their original proportions and the soil has retained its natural water content. The general arrangement of the different soil layers or components can be identified. The structure of the soil has been disturbed.

5 8 Klaus-J t~rgen M e l z e r a n d U l f B e r g d a h l

T a b l e 3. D r i l l i n g m e t h o d s in soi ls ( a f t e r D I N 4021, T a b l e 1)

Column 1 [ 2 ] 3 4

Drilling method

Line Soil Use of Extraction of Drilling loosening flushing sample by technique technique medium

5 6

Equipment

Drilling tool Borehole diameter range t)

Drilling involving continuous coring

1 Rotary No Drilling tool drilling

2 Yes Drilling tool

3 Yes

4 Hammer No driving

5 No

6 Rotary Yes hammer driving

Rotary dry core drilling

Rotary core drilling

Drilling tool Rotary core drilling

Drilling tool Percussive core drilling

Drilling tool Percussive-rotary core drilling

Drilling tool

7 Pneumatic No Drilling tool

Percussive-rotary core drilling

Pneumatic core drilling

Single-tube core barrel

Hollow-stemmed auger

Single-tube core barrel

65 to 200

65 to 300

65 to 200

Double-tube core barrel

Double-tube core barrel 100 to 200 with screwed cutting shoe

Percussive clay cutter with 80 to 200 cutting edge inside; also with sleeve or hose, or hollow- stemmed auger

Percussive clay cutter with 150 to 300 cutting edge outside

Single- or double-tube core barrel

Single-tube core barrel with cutting edge inside, or hollow-stemmed auger

100 to 200

50to 150

Drilling involving continuous recovery of bulk samples

8 Rotary No Drilling tool drilling

9 Percussion No

10 Grabbing No

Rotary drilling

Drilling tool Light cable percussion drilling

Drilling tool Grab drilling

Drill rods with shell auger or worm auger

100 to 2000

Wire line with percussion 150 to 500 shell auger

! Wire line with grab 400 to 2500

1~ G u i d e l i n e va lues .

2) De is t he i n t e r n a l d i a m e t e r o f t he d r i l l i ng tool .

3) The q u a l i t y c l a s ses g i v e n in b r a c k e t s c an o n l y b e a c h i e v e d in p a r t i c u l a r l y f a v o u r a b l e g r o u n d

cond i t ions .

1.3 G e o t e c h n i c a l f ie ld i n v e s t i g a t i o n s 59

7 8 9 10 11

Applications and limitations Sample quality 3)

Unsuitable for D Preferred method for t) Remarks Probable quality Sample class (cf. Table 2) unaffected for soil as in with respect to column 8

Coarse gravel, cobbles, boulders

Non-cohesive soils, silt

Gravels, cobbles, boulders

soils with a particle size larger than De/3 2)

Dense soils with a particle size larger than De/3

Composite and pure sands with a particle size larger than 0.2 mm, as well as gravels, firm and stiff clays

Boulders, cobbles, gravel, dense sand

Clay, silt, silty fine sand

Clay, silt, sand, organic soil

Clay, clayey and cemented composite soils, boulders

4,(3 to2)

3, (2 to 1)

4, (3 to2)

Z,(w,e)

Z,w, (~, Eoe d, rf, k)

Z, (w, 0)

3, (2 to 1) Z, w, (~, Eoed, rf, k)

Clay, silt 2, (1) Z, w, O, (Eoed, gf)

Clay, silt and soils with a particle size up to De/3

Cohesive soil: 2,(1)

Non-cohesive soil: 3, (2)

Cohesive soil: 2,(1)


Cohesive soil: 2, (1)


Gravel, soils with a particle size up to De/3

Clay, silt, fine sand

Soils with a particle size up to De/5

Z, w, (Q, Eoed,~f,k)

Z,(w)

Z, w, ~, (Eoed, "tf, k)

Z, (w)

Z,w, (Z,w, 0, k)

Z,(Z, w)

Good interior, outside dried out

Plotting of driving chart on the basis of number of impacts

Boulders of size larger than De/3

Gravel above water table, silt, sand and gravel below water table

Firm, cohesive soils, boulders of size larger than De/2

All soils above water table, all cohesive soils below water table

Clay and silt above water table, clay below water table

Gravel, boulders of size less than De/2, cobbles

4, (3)

4, (3)

Above water table: 3

Z, (w), below water table (only from cuttings drilled with large diameter shell auger)

Z,(w)

Z, (w)

Maximum length of auger: 0.5 m

Below water (Z) table: 5, (4)


Table 3 ( c o n t i n u e d )

Column 1 I 2 [ 3 Drilling involving recovery of incomplete samples

11 Yes Direct flushing Rotary drilling

12 Yes

13 Percussion No

14 No Drilling tool/ auxiliary flushing

1) G u i d e l i n e va lues .

2) De is the i n t e r n a l d i a m e t e r o f the d r i l l i ng tool .

4 5 6

Wash boring Drill rods with roler bit, 100 to 500 (rotary drilling) jet bit, step bit, etc.

Reverse flow of Reverse As in line 11, but with hollow 60 to 1000 drilling fluid circulation chisel

drilling

Drilling tool Light cable Wire line with valve auger 100 to 1000 percussion drilling

Drilling by chisels Wire line or drill rods, 100 to 1000 with chisels

Table 4. Methods for small-scale drilling in soils (after DIN 4021, Table 3)

Line Soil Use of : loosening flushing technique medium

Column 1 ] 2 I 3 4

Drilling method 2)

Extraction of sample by

1 Rotary No drilling

2 Hammer No driving

With drilling tool

With drilling tool

3 Pneumatic No With drilling tool

1) Guideline values. 2) See limitations described in subclause 5.3.

Drilling technique

Hand auger drilling

Small-scale hammer driving

Small-scale pneumatic drilling

3) De is the internal diameter of the drilling tool.

5 6

Equipment

Drilling tool

Shell auger, worm auger or spiral auger

Hammer-driving linkage, with tube sampler

Pneumatic linkage, with tube sampler

Borehole diameter range 1)

60 to 80

30 to 80

30 to 40

• Category C: Here, the structure of the soil in the sample has been totally changed. The general a r rangement of the different soil layers or components has been changed so that the in situ layers cannot be identified accurately. The water content may not represent the natural water content of the soil layer sampled.

Table 2 defines which of the three categories A, B or C of the sampling methods should be used in order to obta in a corresponding quality class for labora tory tests. Using this a connect ion to D I N 4021 has been established.


7 8 9 10 11

- All soils (5) Samples unsuit- Limited to pene- able for soil tration of irrele- mechanics tests r an t upper strata

- All soils 5, (4) (Z), Z, if core - pieces are produced

Recovery from above Gravel and sand in water 5, (4) (Z) Can also be used water table in cohesive soils if

water is added

- All soils, to remove 5 Samples unsuit- - obstructions able for soil

mechanics tests

3) T h e q u a l i t y c l a s s e s g i v e n in b r a c k e t s c a n o n l y b e a c h i e v e d in p a r t i c u l a r l y f a v o u r a b l e g r o u n d

c o n d i t i o n s .

7 8 9 10 1 1

Applications and limitations Samples 4l

Unsuitable for D Preferred method for 1) Remarks

Coarse gravel with a particle size larger than De/3 3) and dense soils

Soils with a particle size larger than De/2

Clay to medium gravel above water table; cohesive soils below water table

Soils with a particle size up to De/5

Probable quality class (cf. Table 2) for soil as in column 8

Above water table: 4, (3)

Below water table: 4

Cohesive soil: ~3, (2)


Sample unaffected with respect to

Z, (w)

Z, w, (Q)

z, (w)

Firm and coarse-grained Clay, silt, fine, sand 3, (2) Z, w, (Q) soils

Only to be used for small depths

4) The quality classes given in brackets can only be achieved in particularly favourable conditions.

While DIN 4021 only defines five quality classes that can be obtained, E N V 1997-3, 12 specifies minimum requirements for the sampling equipment - especially for category A - to be used for taking samples of a required quality. On the other hand, DIN 4021 is generally more strict regarding certain dimensions such as inside diameters, cylinder length etc. [1, 2] because the Eurocode states essential requirements only.

For each borehole, a qualified field foreman has to record the results on site in a borehole log according to DIN 4022 Part 1 which reflects the results of the drilling, using the

62 Klaus-JOrgen Melzer and Ulf Bergdahl

nomencla ture for the different soil types specified in this s tandard. D I N 4022 Par t 3 has to be appl ied when dril l ing methods with cont inuous core sample recovery are used because the sample mater ia l can be inspected only after opening the liner or tube. The fine strata also have to be described.

2.3 Invest igat ion o f rocks

The above quali ty classes for soils are not appl icable for drilling in rock because other aspects are re levant to the assessment of rock propert ies, e.g. degree of weathering, discontinuities, joint planes, striping and dipping planes (see E N V 1997-1, 3.3.2). These topics are also deta i led in D I N 4021. Table 5 shows different drilling methods in rock with respect to suitabili ty and results.

Table 5. Drilling methods for rock investigations (after DIN 4021, Table 2)

Column

Line

1 3

Drilling method

Breaking Flush. Extraction of the rock medium samples by

1 Drilling involving continuous coring

I 4 5

Equipment

Drilling technique

Drilling tool

Rotary drilling

Rotary drilling

Rotary drilling

4 Rotary drilling

5 Rotary drilling

Drilling tool Rotary core Single-tube core barrel, attached to drill rods drilling usually with hardfaced

c o r e

Drilling tool Rotary dry Single-tube core barrel, attached to drill rods core drilling with hardfaced core

Drilling tool Rotary core Double-tube core barrel attached to drill rods drilling with hollow bit

Drilling tool Rotary core Triple-tube core barrel attached to drill rods drilling

Drilling tool attached to drill rods, with wireline extractable inner barrel

Wireline core drilling

6 Rotary Drilling tool Percussive hammer attached to drill rods rotary core driving drilling

2 Drilling involving recovery of incomplete samples 7 Rotary yes Drilling tool Rotary open

drilling attached to drill rods hole drilling

1) Guidelines.

Wireline core barrel with hollow bit, or triple-tube barrel

Rotary percussion clay cutter

Solid bit, roller bit


Frequently, rotary open hole drilling is used in rock and also in soils for preliminary investigations, for example to assess the level of rock surfaces, weathered zones in rock, or the occurrence of cobbles or boulders in soils. Besides the penetra t ion resistance (measured in sec/0.2 m of penetration), the following parameters can be recorded using the MWD-technique (Measuring While Drilling): pushing pressure, revolutions/min, applied torque, fluid pressure and fluid volume (1/min). Together with the drill mud flushed up, these parameters give indications of the ground layers penetrated. Based on these results, additional drilling using high-quality drilling methods is planned to determine the ground strata accurately and for core sampling purposes.

Table 6 shows propert ies of rock materials and rock mass that can be determined by drilling. Fifteen mechanical properties of rock materials and rock mass respectively, are listed in the table which can, cannot, or can only partly be determined from drilling or from tests in the borehole.

6 7 8 9 10

Equipment

Borehole outer diameter range 1)

Drilling method less suitable for 1~

Cores 11

Sample

Drill cuttings Remarks

100 to 200 Rock of medium Jointed, soft rock Sieve residue Flushing medium may to high hardness suspended cause disturbance of

matter core material

100 to 200 Rock of medium Soft, erosive, water- None To prevent overheating to high hardness sensitive rock; short of the bit, core runs

core runs shoult not exceed 0.5 m

50 to 200 Erosive, water- All types of rock As 1 - sensitive rock

50 to 200 - All types of rock As 1 -

50 to 200 Erosive, water- All types of rock As 1 - sensitive rock

100 to 200 Rock of medium to high hardness

50 to 200

Medium to hard As 1 With drive device at rock the equipment or as

in-borehole hammer

None As 1 -

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For each borehole, a qualified field foreman has to record the results on site in a borehole log according to DIN 4022 Part 2. The log shall contain all the facts and observations made during the core drilling in rock.

In general, it has to be stated that E NV 1997-3, 13 is more comprehensive than DIN 4021 regarding rock sampling, especially in view of the requirements for sampling equipment and quality control [1, 2]. However, DIN 4021 shows a higher degree of detail in descrip- tions of the drilling methods (Table 5) and the properties of rock materials and rock mass that can be determined from borings (Table 6).

Similar to soil sampling, ENV 1997-3, 13 defines the following methods for rock sampling:

• Category A: By using these sampling methods, the intention is to obtain samples in which no or only slight disturbance of the rock structure has occurred during the sampling procedure or in handling of the samples. The strength and deformation properties, water content, density, porosity and permeability of the rock sample correspond to the in situ values. No change in constituents or in chemical composition of the rock mass has occurred.

• Category B: By using these sampling methods, the samples contain all the constituents of the in situ rock mass in their original proportions and the rock pieces have retained their strength and deformation properties, water content, density, porosity. The discontinuities in the rock mass may be identified. The structure of the rock mass has been disturbed and thereby the strength and deformation properties, water content, density, porosity and permeability of the rock mass itself.

• Category C: By using these sampling methods, the structure of the rock mass and its discontinuities have been totally changed. The rock material may have been crushed. Some changes in constituents or in chemical composition of the rock material may have occurred. The rock type and its matrix, texture and fabric may be identified.

Furthermore, ENV 1997-3, 13.2.3 defines the following parameters for the degree of rock recovery from rotary core drilling that should be evaluated in context, not individually:

• Rock quality designation (RQD): The sum length of all core pieces that are 10 cm and longer, measured along the centre line of the core, expressed as a percentage of the total length of the core run.

• Solid core recovery (SCR): The sum of the length of all core pieces, expressed as a percentage of the total length of the core run. A core piece must possess one full diameter but not necessarily a full circumference.

• Total core recovery (TQR): The total length of core sample recovered, expressed as a percentage of the total length of the core run.

E N V 1997-3, 13.3.2 recommends the following methods as sampling techniques for the categories A-B that are inevitable depending on the structure and the decomposition grade of the rock and on the requirements of the laboratory testing to be performed:

• Category A or B: Rotary core sampling in which a tube with a cutter at its lower end is rotated into the rock mass thereby processing a core sample.

• Category A or B: Drive sampling in which a tube or a split-tube sampler having a sharp cutting edge at its lower end is forced into highly or completely weathered rock mass either by a static thrust or by dynamic impact. Drive samplers are usually piston samplers or open tube samplers.

66 Klaus-J~irgen Melzer and Ulf Bergdahl

• Category C: Shell or auger sampling where the sample is taken from the actual drilling tool.

• Category C: Cuttings sampling in which the rock mass, remoulded or crushed, by cable or rod handled percussion or cutting tools is brought up to the surface by means of a bailer or circulation of a transporting substance.

• Category C: Block sampling made by hand cutting from a trial pit, shaft or heading or by using specially made block samplers.

The selection of the appropriate method is to be made in accordance with the required sample quality for the classification of the rock mass and for the laboratory tests to be performed.

Furthermore, precise requirements are defined for core barrels for sampling according to category A and for sampling with rotary core drilling for the categories A and B: ENV 1997-3, 13.3.3 and 13.4. Regarding rotary core drilling, special attention is drawn to the different requirements on equipment checks and controls before and during sampling operation: ENV 1997-3, 13.4.1.

This move towards improvement of quality assurance is continued in the Eurocode in the requirements for the documentation (ENV 1997-3, 13.5). Here, the requirements of DIN 4021 and of ENV 1997-3 are in agreement regarding the labelling of the core samples. However, in the latter, information on the sampling category and the sampling equipment are added. In addition, a sampling log is required that must contain the usual information also detailed in DIN 4021 and DIN 4022 Part 2 but in addition, the signature of the qualified field foreman or the project manager.

The following details (ENV 1997-3, 13.5.2) have to be reported:

- date of sampling; - position and elevation of drilling location; - borehole direction, inclination and orientation; - whenever possible the depth of the free groundwater level; - the method of pre-drilling if used; - the use of casing and depth of casing tip; - the use of drilling fluid and the level of the drilling fluid in the borehole; - colour and colour shifts of drilling fluid; - loss, if any, of drilling fluid; - drilling fluid pressure and circulated volume; - the specification and type of sampler used; - the diameter or the size of the sample; - the depth (top and bottom of the sample) and the length of the sample; - the core run interval; - pressure on the cutting edge; - the rock mass type, discontinuities and grade of decomposition based on

the visual inspection of the sample by the field foreman and his judgement of the sampling category;

- any obstructions and difficulties encountered during the sampling operation (including unsuccessful sampling attempts).


2.4 Obtaining special samples

Methods for taking special samples are included in category A.

2.4.1 Soils

Special samples of fine-grained soils and sands can be obtained quite simply from the base of construction excavations and roads, foundation base levels, slopes and trial pits by means of thin walled cylinders with sharp cutting edges. This method is particularly suitable in cohesive soils of firm consistency and in fine sands of medium density. The test is standardised in DIN 18125 Part 2. In loose and dense cohesionless and cohesive soils of stiff and very stiff consistency, the equipment for obtaining special samples from trial pits according to DIN 4021 should be used (Fig. 1). Cubes with side length of 10 to 30cm can also be cut out from cohesive soils.

3 !..! b)

= ~100

~96

// 7

t

~ 9 I

c) !L:i i-.).'..:.!:;i.:.{.:.!-.::i;.: ;;::. :": i:ii :7:!.7 ::..:.:..::.i :. i ::.:i: 7::;: .: L! i i:'. 7i:. Fig. 1. Obtaining special samples from trial pits (after DIN 4021) a) Arrangement of sampler, b) Sampler tube, c) Sampling process 1 Percussion drill rods 6 Guide hood 2 Drop weight 7 Sampler tube 3 Anvil 8 Guide plate 4 Driving device 9 End caps (sealed with adhesive tape) 5 Ring mark 10 Metal plate for limiting depth of penetration

68 Klaus-Jargen Melzer and Ulf Bergdahl

Obtaining undisturbed samples from boreholes is more difficult and time consuming because the normal drilling operation has to be interrupted. Nevertheless, it is necessary because only in this way will laboratory investigations of soil properties yield reliable results. However, it is not always possible to obtain completely undisturbed samples from cohesionless soils. In this case, penetration testing is suitable and generally sufficient as a complementary investigation.

Table 6 of DIN 4021 contains details about obtaining special samples, the required equipment, the suitability of various equipment and the achievable laboratory quality classes of the samples obtained with the corresponding equipment.

2.4.2 Rocks

In general, only rotary core drilling is suitable for the ground investigation in rock because only with this method it is possible to obtain sufficiently large and undisturbed core samples, accurate identification of the rock and the determination of the rock properties by strength tests (ENV 1997-3, 13). With rotary open hole and percussion drilling, cuttings are only obtained which are just suitable for the identification of the rock type. In water sensitive strata or in rock with strong discontinuities, double and triple-tube core barrels have to be used to avoid the flushing medium disturbing the core sample.

2.5 Investigation of groundwater conditions

ENV 1997-3,14 contains the corresponding requirements for groundwater measurements. Furthermore, DIN 4021, 8 describes the different types of water in the ground and the problems with groundwater observations during drilling operations. It stresses the point that groundwater gauging stations are necessary to obtain reliable data, and describes their arrangement for short and long-term observations. DIN 4021 also contains guidance for measuring the direction of flow and the flow velocity of the groundwater and describes how to obtain water samples (for pumping tests see Chapter 2.9). It describes the test arrangements using single and double packers necessary for drilling in rock to measure the water pressure in different aquifers, and the associated packer test for determining the permeability of the rock mass. The following Figs. 2 to 7 show some examples.

In the case of more than one aquifer and the borehole being drilled with a single run of casing, it is only possible to get an approximate measurement of the groundwater level or piezometric level in the uppermost aquifer (Fig. 2a-d). In general, an adequate seal along the casing through each aquifer cannot be achieved. Therefore, the measurement of the piezometric level in the lower aquifer can be distorted (Fig. 2c and d). If the piezometric level of a second, lower aquifer is to be measured, the first run of casing has to be sealed by drilling into the aquiclude. A second run of a casing is brought down inside the first and the drilling continued until the lower aquifer has been reached (Fig. 2b) ; the piezometric level of the lower aquifer can then be determined in the second casing.

Packers also have to be installed for measuring the pressure head of groundwater in fissured rock. A single packer seals off the measuring section c, that reaches down to the bottom of the borehole (Fig. 3). Double packers can be used to define the measuring section c between the two packers (Fig. 4). If pressure heads in different joint systems are to measured within one borehole, multiple packers must be used.


oOoOoOi i o : o 2 / = ooo-~U~ o.~_~3

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d)

Fig. 2. Possible effect on water level measurement when drilling through an aquiclude (after DIN 4021) a) Correct measurement of groundwater level b) Correct measurement of the piezometric level of the lower aquifer c) and d) Erroneous measurement of the piezometric level of the lower aquifer 1 Groundwater level 2 Piezometric level of lower aquifer 3 Aquifer 4 Aquiclude (clay layer), measured water level, direction of flow

1 Spreading device 2 Inner tube of packer 3 Outer tube of packer 4 Annular space 5 Rubber sleeve 6 Piezometer 7 Clamps 8 Observation jar 9 Recording pressure gauge

10 Compressed air bottle

c Measuring section

Fig. 3. Arrangement of single packer and air pressure gauge for water pressure measurements (after DIN 4021)

The ar rangement of groundwater gauging stations obviously has to take into account the ground conditions, the hydrological requirements , the engineering task and the length of the observat ion period. A n installat ion plan for each groundwater gauging station has to be documented (Figs. 5 to 7). The p iezometer for a gauging station consists of a sump pipe, a filter pipe and extension pipes that can be closed off at the top whilst allowing for ventilation. The filter pipe is surrounded by filter sand (Fig. 5). Figs. 6 and 7 show examples


2

3

; - 6 • . Z " l

IC

Fig. 4. Double packer arrangement

1 Spreading device 2 Inner tube of packer 3 Outer tube of packer 4 Annular space 5 Rubber sleeve 6 Perforated section of inner and outer tube 7 Clamps

c Measuring section

(after DIN 4021)

1

1 Cap 2 Extension pipe 3 Filter pipe 4 Sump pipe 5 Concrete cover 6 Frost-resistant soil material 7 Seal 8 Drill cuttings 9 Filter gravel

Fig . 5 . Arrangement of a piezometer with free groundwater in the uppermost aquifer. For example above ground level with precautions against frost heave (after DIN 4021)

of various ar rangements of groundwater gauging stations ( top below and above ground level etc.).

Cont rary to D I N 4021, where mainly ground water measurements with open system are t reated, E N V 1997-3, 14 covers in addi t ion measurements of groundwater pressures with closed systems, i. e. the measurement of pore pressure in fine-grained soils.

The requirements for records and the presenta t ion of groundwater gauging station results are given in E N V 1997-3, 14.5 and 14.6 (see also D I N 4020, 8.1). DIN 4023 is re levant for the presenta t ion itself.


~ 1 2

:. ~ 1 3

-~1:7- i: 2:f13

i :

1 Cap 2 Extension pipe 3 Filter pipe 4 Sump pipe 5 Cover 6 Below-ground access pit 7 Sleeve 8 Frost-resistant soil 9 Seal

10 Drill cuttings 11 Filter gravel 12 Aquiclude 13 Aquifer

Fig. 6. Arrangement of a single piezometer below ground level, with a group of aquifers (after DIN 4021)

1 Cap (tightly fitting) 2 Casing 3 Extension pipe 4 Concrete cover 5 Anchor 6 Frost-resistant soil 7 Frost line 8 Seal 9 Dill cuttings

Fig. 7. Arrangement of a groundwater gauging station with the top above ground level and protection against frost heave (after DIN 4021)

3 Ground investigation by penetration testing

3.1 General

For a penet ra t ion test, a thin rod is pushed or driven into the ground or turned around its longitudinal axis. F rom the magni tude of the pene t ra t ion resistance and/or from its variat ion with depth conclusions can be drawn regarding the strength or sequence of the strata. Compared to trial pits, shafts, headings and drillings, pene t ra t ion tests are regarded


as indirect investigations, i. e. direct visual inspection or sampling of the strata is generally not possible.

Penetration tests are indirect investigations which always have to be supplemented by direct investigations (e. g. key boreholes with sampling) for an accurate identification of the ground because the measured value of the "penetration resistance" by itself does not allow any conclusions regarding the soil type. On the other hand, the penetration resistance diagram can be used as additional information to allow the selection of sampling depths.

The derivation of geotechnical parameters has to be viewed carefully Many investigations on the topic of establishing reliable relations between penetration resistance and geotechnical parameters, e. g. cohesion, angle of shearing resistance, modulus of elasticity either directly or indirectly (via consistency or relative density, etc.) have been made. Approaches to find direct relations between bearing capacity of foundation elements, e.g. the skin friction and the pile resistance are also well known. However, the validity and the suitability of such relations has to be evaluated critically for each case and area because of potential superimposing influences. For instance in cohesive soil, the penetration resistance at the penetrometer tip can be relatively constant; it maybe, however, that this result is falsified by skin friction along the rods.

Difficulties can also occur in the interpretation of results obtained in cohesionless soils. For instance, the penetration resistance depends not only on the relative density but also on the degree of uniformity and the compactibility of the soil. In this case, the determination of the relative density is valuable only if the grain size distribution or the maximum and minimum voids respectively, are known [6-10].

Especially in silty cohesionless soils, the measured penetration resistance can be higher than the one corresponding to the actual relative density, due to false cohesion. Peaks also occur in the penetration resistance measured in gravelly soils because of cobble admixtures. These peaks should be disregarded in the evaluation.

The widespread use of penetration testing in practice and numerous research programmes have through the years led to equipment related improvements giving reproducible results at compatible conditions and to reliable relations for the derivation of geotechnical parameters, for example [11-13]. However, it has to be pointed out that all possibilities to derive geotechnical parameters shown in the following sections are examples that are valid only for the corresponding conditions investigated (e. g. soil types etc.), because it is not possible to establish relations which are valid world-wide.

Furthermore, the origin of the individual examples has to be observed. For instance, all equations regarding dynamic probing, cone penetration tests and borehole dynamic probing as quoted from DIN 4094 in the following sections, are deterministic relations taken as conservative estimates. Other examples have been taken from statistical regression analysis or are just tables with a range of geotechnical parameters. Therefore, different safety concepts have to be considered to suit the application. For this reason, it is recommended that the original source is checked for a closer review of the corresponding examples and that any local experience is collected.

In the meantime, the development of some penetrometers and the presentation of the test results are being coordinated on international level [14, 15] and were initially harmonised on European level in the ENV 1997-3. Among other tests, this document contains the essential requirements for the following tests:


• Cone penet ra t ion test (CPT) • Standard pene t ra t ion test (SPT) • Dynamic probing (DP) • Field vane test (FVT) • Weight sounding test (WST)

The German s tandardisat ion work in the newly edi ted D I N 4094 is consistent with these internat ional efforts.

3.2 Dynamic probing

3.2.1 Equipment and test procedures

Dynamic probing as ment ioned in ENV-1, 1.3.3.10.2, and in accordance with D I N 4094 is the in situ measurement of the pene t ra t ion resistance from driving a cone vertically into the ground. A hammer of a given mass at a constant height of fall is used to drive the cone, while the number of blows N10 for a pene t ra t ion depth of 10 cm is counted (ENV 1997-3, 6 also allows N20). The dynamic pene t rome te r consists of a cone and preferable hollow rods. Common pene t rometers are listed in Table 7.

In the new edit ion of DIN 4094-3, only the light pene t rome te r DPL, the heavy pene t rom- eter D P H and the superheavy pene t rome te r D P G (hammer mass = 200 kg, height of fall = 50cm, cone cross section = 50cm 2 [16, 17]) appear in the s tandard itself. The light pene t romete r DPL-5 and the medium heavy pene t romete r s DPM, which are used on a regional level only, appear in an informative annex. E N V 1997-3, 6 agrees general ly with D I N 4094 except in Table 7 above, which contains a D P S H with the dimensions of the s tandard penet ra t ion test instead of the DPL-5. The t rend to pene t romete rs with higher hammer masses can be observed also more recent ly in Japan, Canada and the U.S.A. [18]; the background to this is the desire to be able to also investigate s trata of very high strength e. g. tills, gravels, soft rock etc..

The diameter of the cone is somewhat larger than that of the rod to reduce skin friction, allowing the pene t ra t ion resistance of the cone to be measured more accurately (Fig. 8). Retr ieving the pene t romete r from the ground is easier if it is equipped with a sacrificial cone that is not fixed to the rod instead of a re ta inable cone. The rods have to be turned at least 1,5 revolut ions after each meter of pene t ra t ion to the reduce skin friction and to ensure that the rod threads are kept tight. If a torque measuring wrench is used, the skin friction can be es t imated from the measured torque. To avoid skin friction, a fluid medium (preferable water of drinking quality) can be injected through horizontal or upwards holes in the hollow rods near the cone. Sometimes, a casing is used for the same purpose.

Fig. 8. Cone for dynamic probing (d = 1; after DIN 4094-3)

74 K

laus-Jt~rgen Melzer and U

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3.2.2 Evaluation

3.2.2.1 General

The results of dynamic probing can be evaluated qualitatively if

• strata are investigated by drilling and sampling; • the homogeneity or inhomogeneity, respectively, of the ground, or of a fill, is to be

evaluated; • especially loose or firm layers in fills or the rock surface (with heavy equipment) are to

be investigated; • compaction controls are to be performed, by comparing the penetration resistances

before and after compaction (see also Chapter 2.12 of Volume 2 of this Handbook).

The following investigation depths can normally be reached using the different dynamic probing methods: DPL: 10 m; DPM: 20 m; DPH: 25 m; DPSH: 25 m; DPG: 40 m.

In DIN 4094-3 examples are given of equipment and geotechnical related influences to be observed in the evaluation of the test results. One of these, is that the penetration resistance in cohesionless soils with the same relative density, is lower below the groundwater level than above at the same conditions. Corresponding relations to correct for this influence, are given in DIN 4094-3.

3.2.2.2 Derivation of geotechnical parameters

Shear strength

The results from dynamic probing tests are used mainly to derive the strength and compressibility of primarily cohesionless soils.

First, an example is shown on how to derive indirectly the angle of effective shearing resistance q/ from results of dynamic probing (see also ENV 1997-3, Annex E.1 and DIN 4094-3). Extensive investigations have demonstrated [7] that the following general equation represents the best relationship between the penetration resistance (in this case the number of blows N10 ) and the relative density of cohesionless soils:

ID = al + a2 log N10 (1)

Table 8 contains examples of the coefficients shown in Eq. (1) for different cohesionless soils for both the light (DPL) and heavy (DPH) dynamic penetrometers. The equations are valid for penetration tests performed above the groundwater level and for a depth larger than about I m where this is the critical depth from which under the same conditions, the cone penetration resistance becomes almost constant. Above this depth, the cone penetration resistance increases considerably with depth.

The angle of effective shearing resistance qg' can then be determined from tests or by proven relationships using the relative density ID, predicted from the dynamic probing test results, with the above equations. ENV 1997-3, Annex D.3 contains an example of the relation between ID and q / for silica sands, which are differentiated qualitatively by the degree of uniformity and grain size. A practical example for deriving the angle of shearing resistance of gravelly soils by means of this indirect method, in conjunction with the design of harbour sheet pile walls, is described in [9].


Table 8. Examples of coefficients in Eqs. (1), (3) and (4) for deriving relative density ID and stiffness coefficient v from results of dynamic probing above groundwater level (after ENV 1997-3 and DIN 4094-3)

Soil Conditions Relative density ID Stiffness coefficient v classification (DIN 18196) U 1) If 2~ DPL DPH

SE

SW, GW

TL TM

_<3

>_6

- 0.75-1.30

al

0.15

a2 al

0.260 0.10

- --0.14

a2 bl b2

0.435 71 214

0.550 - -

- 3 0 4

DPL DPH

bl b2

161 249

50 6

1) Degree of uniformity, d60/dl0.2) Consistency, unit: 1

Valid ranges: For the relative density: 3 5 N10 < 50. For the stiffness coefficient in SE: with DPL: 4 _< N10 _< 50; with DPH: 3 _< N10 5 10. For the stiffness coefficient in TL, TM: with DPL: 6 < N10 _< 19; with DPH: 3 _< N10 < 13.

Soil classification according to DIN 18196: SE: poorly graded sands; SW: well graded sands; GW: well graded sand-gravel mixtures; TL: low plasticity clays; TM: medium plasticity clays.

C o m p r e s s i b i l i t y

The following is an example of deriving directly the stress dependent modulus of linear elasticity from results of dynamic probing tests above the groundwater level (ENV 1997-3, Annex E.3 and DIN 4094-3).

The definition of the modulus of linear elasticity Eoe d derived from oedometer tests and used for the calculation of the sett lement of spread foundations, is the basis for the determinat ion of compressibility:

! ! W

Eoed = v . pa[(O v + 0.5Op)/Pa]

with:

v = w --

! O V ---~

Op

Pa = Wp = W L =

(2)

stiffness coefficient stiffness exponent; for sands and sand-gravel mixtures: w = 0.5; for slightly plastic clays with low plasticity index (we _< 10; WL < 35): w = 0.6 effective vertical stress at the base of the foundation or at any depth below it due to the overburden of the soil effective vertical stress caused by the structure at the base of the foundation or at any depth below it atmospheric pressure plasticity index liquid limit

If soil shear deformations during the sett lement process are to be considered, the corresponding modulus of l inear elasticity can be assumed to be approximately 0.75 Eoe d.


Corresponding investigations in cohesionless and cohesive soils [7, 19] resulted in the following equations for the determination of the stiffness exponent v of Eq. (2) above.

• For sands and gravelly sands: v = bl + b2 log N10 (3)

• For slightly and medium plastic clays: v ---- bl + b2 - N10 (4)

The stress dependent modulus goed, according to Eq. (2), can then be derived directly using the coefficients from Table 8 for determining v from Eqs. (3) and (4) and with w -- 0.5 for cohesionless soils and w = 0.6 for cohesive soils.

3.2.2.3 Bearing capacity of piles

Results from dynamic probing tests have been used for some time to predict the drive ability of piles and sheet piles, as well as of the bearing capacity of piles (see EN 1997-1, 7 and also [16, 17, 20-22]). This is due to similarities in the driving and testing techniques used.

3.2.2.4 Relations between the results from different penetration tests

It should also be noted that a number of relations have been established between the results from different dynamic probing tests and between these and the results of standard penetration and cone penetration tests, see DIN 4094 and e. g. [7, 19].

It has to be stated that the various types of penetrometers have different penetrability and sensitivity for variations in soil types. It can therefore be appropriate to use different types of penetrometers in parallel for a certain project to obtain the best information about the ground to be investigated in the most economical way possible.

3.3 Standard penetration test


The standard penetration test mentioned in EN 1997-1, 3.3.10.2, covers, according to ENV 1997-3, 5, the determination of the resistance of the soil at the bot tom of a borehole to the dynamic penetration of a split barrel sampler and the recovery of disturbed samples for soil identification purposes.

The test consists in driving the sampler (outer diameter: 51 mm, inner diameter: 35 mm) by dropping a hammer of 63.5 kg mass from a height of 76 cm on to an anvil. The number of blows necessary to achieve a penetration of the sampler of 30 cm (after its penetration under gravity and below a seating drive of 15 cm) is defined as the penetration resistance N (blows/30 cm penetration).

The standard penetration test is the oldest form of dynamic probing [11, 23]. Its first known use goes back to beginning of the 20th century. The original attempts to standardise the equipment stem from the early 1930's in the U.S.A. Even today, the standard penetration test is the most widely used in situ test for bearing capacity and stability investigations [12, 24]; ref. [11] contains a very good survey. The best known standards for SPT are A S T M D 1586 in North America and BS 1377 in Great Britain, which are referred to on a world-wide basis. National standards are also available, for example in Australia, Brasilia, Denmark, India, Japan and Sweden. With the "International Test Procedures

78 Klaus-Jiirgen Melzer and Ulf Bergdahl

for SPT" [14], the Technical Committee TC 16 of ISSMFE succeeded for the first time in harmonising the test on an international level. This document was the basis for ENV 1997-3, 5.

However, difficulties occurred in interpreting the results because the actual value of the energy which is induced in the rods has to be known. In addition, energy losses can occur due to the rods in the borehole not being supported. Today, methods for determining these energy losses or corresponding values from experience are available [11, 24-26], and are induced in various standards, e. g. ASTM D 4633 and ENV 1997-3, 5.

Recent extensions of the equipment and the test procedures include devices for measuring the torque at the rods [23, 27] to obtain additional information about the soil types encountered.

In the early 1950's in Germany, this uncertainty about the energy losses led to an essential modification of the equipment, whilst maintaining the original technical specifications (height of fall etc.), with the following aims:

• transmission of as much of the full energy as possible on to the anvil; • essential reduction of the rod influence.

The equipment was improved [3, 28, 29] by the drive mechanism being encapsulated in a water tight casing directly above the penetrometer (Fig. 9) .The equipment as a whole is lowered into the borehole. The hammer is released by means of an automatic release mechanism. The sampler is closed by a cone (apex angle = 60 °) because disturbed or

v'l Ox

I '

1 Rope 2 Stuffing box 3 Automatic release ]

mechanism | 4 Hammer 5 Water proof casing | 6 Anvil / 7 Penetrometer

3 to 6 Driving device

Fig. 9. Borehole dynamic probing BDP (after DIN 4094)


undisturbed samples (depending on the soil type) can be obtained from the borehole itself between penetration tests.

The use of a closed sampler or solid penetrometer (of about 90 cm length) with a cone (apex angle: 60 ° ) for performing tests in gravelly soils and in soft weathered rock is also current practice in countries like Australia, Great Britain, Portugal, Spain and South Africa [11]. The abbreviation for this test is generally SPT(C) or SPT(cone).

Since the early 1950's, the equipment described in Fig. 9 was standardised in DIN 4094 and also covered by ENV 1997-3, 5. It is defined as follows - Borehole dynamic probing (BDP) is a penetration test where the penetrometer is driven into the ground from the bottom of a borehole for a defined penetration depth. As in the case of SPT, the number of blows N30 is determined for a penetration depth of 30 cm after the penetration under gravity and an initial drive of 15 cm. Recently, the use of additional weights, mounted directly above the penetrometer, are recommended for investigation depths of > 20m below water level (see DIN 4094-2 and [30]).

Special care has to be taken when performing the test in cohesionless soils below the groundwater level - for example, the soil below the bottom of the borehole could be disturbed by the drilling. Using drilling tools causing suction, should be avoided. It is also possible that the penetration test is performed with the casing in soil subjected to buoyancy. The soil would then be constrained between the penetrometer and the casing, leading to an increased number of blows. Therefore, a lowered water level in the casing has to be avoided by for example, maintaining the water or drilling fluid level in the borehole at a sufficiently high level at all times.

The standard penetration test is primarily performed in key boreholes to obtain indications about the strength and deformation properties of the ground.

3.3.2 Evaluation

3.3.2.1 General

The opportunities to applying SPT results for different design purposes is considerable. The test is mostly used for the determination of strength and deformation characteristics of cohesionless soils, however, valuable data can be also determined for other types of soil under certain circumstances, e. g. [31]. Table 9 gives an overview of the current application of SPT results on an international level for geotechnical design. ENV 1997-3, 5 and [11] give examples of corresponding applications.

In applying relations between the SPT results and geotechnical parameters, the following conditions should be considered in addition to the effects of the different performance of the test and the equipment used. The soil type to which a relationship was established has to be described because relative density not only influences the number of blows in cohesionless soils but also the compactibility, the grain size and possible cementing [7, 32]. This of course affects the derivation of geotechnical parameters. The same is also valid for the other penetration test methods covered by this chapter, e. g. [6-9]. It is also necessary to know whether, and by which method, the number of blows used in the relation, has been corrected in respect of said energy losses.

As for the dynamic probing tests (Section 3.2.2.1), the following has to be considered in evaluating the SPT results obtained in cohesionless soils; at the same relative density, the penetration resistance below the groundwater level is smaller than above the groundwater


Table 9. Examples of the application of SPT results in international geotechnical design (following [11])

Derivation of geotechnical parameters

• Angle of shearing resistance of cohesionless soils • Undrained shear strength of clays • Unconfined compressive strength of weak rocks • Modulus of elasticity or stiffness coefficient, respectively, of cohesionless and cohesive soils • Maximum shear modulus

Direct calculations

• Settlements of spread foundations on sand • Acceptable bearing pressure of foundations on sand • Acceptable bearing pressure of rafts on sand • Liquefaction potential of sands • Shaft and end resistance of piles • Sheet pile drive ability

level. DIN4094-2 gives some relat ionships to correct for this effect (see also Section 3.3.2.2).


Shear strength

The following example shows a possible method of deriving indirectly the angle of effective shearing resistance qJ for cohesionless soils. Similarly to Eq. (1), the following general re lat ion between number of blows N30 and relative density ID applies:

ID = Cl + c2 log N30 (5)

Table 10 shows examples for the coefficients Cl and c2 in Eq. (5) for B D P results obta ined in different cohesionless soils above the groundwater level.

Using the relat ive density ID, de te rmined from SPT/BDP results, the angle of effective shearing resistance q~' can be derived. For instance, D I N 1054 and E N V 1997-3, Annex D.3 contain corresponding est imations of qJ for different cohesionless soils. For more deta i led investigations of the relat ion be tween the penet ra t ion resistance of dynamic pene t romete r s and cone pene t romete rs in cohesionless soils on the one hand and their relat ive density and angle of shearing resistance on the other hand, reference is made to [6-11, 28, 33-35]. A good overview of the options to derive the shear parameters for cohesive soils, l imestone and soft rock can be found in [11, p. 83 ff.]t.

Compressibility

Similarly to the evaluat ion of dynamic probing results, the stiffness coefficient v in Eq. (2) can be der ived directly from the number of blows N30 as shown in the following example.

1 In the following text, ref. [11] is the secondary reference; the page numbers refer to the original source.


Table 10. Examples of coefficients in Eqs. (5) to (7) for deriving relative density Io and stiffness coefficient v from BDP results (after DIN 4094'

Soil classification (DIN 18196)

Conditions

U 1) Ic 2) above under GW GW

53 - x -

_<3 - - x

; > 6 -- X --

- 0.75- x - 1.30

SE

SE

SW, GW

TL, TM

Relative Density Stiffness coefficient v I D

cl c2 dl d2

0.10 0.385 146 217

0.18 0.370 -

-0.03 0.455 -

- - 50 4


Valid ranges: For the relative density: 3 < N30 < 50. For the stiffness coefficient: in SE: 3 _< N30 < 25; in TL, TM: 3 _< N30 < 23.


Investigations into cohesionless and cohesive soils [7, 19] resulted in the following equations to determine directly the stiffness coefficient in Eq. (2):

• For sands: v = d l + d2 log N30 (6)

• For slightly and medium plastic clays: v = d t + d2 - N30 (7)

With the coefficients d 1 and d2 from Table 10, the stiffness coefficient v can be derived and by applying w = 0.5 for sands and w = 0.6 for the cohesive soils considered, the stress dependent modulus of elasticity Eoe d is determined.

ENV 1997-3, Annex D.4 gives an example for determining directly the set t lement of spread foundations in cohesionless soils from SPT results.

3.3.2.3 Bear ing capacity o f spread f o u n d a t i o n s and pi les

Spread foundat ions

Numerous attempts have been made since the late 1940's to determine the bearing capacity of spread foundations in cohesionless soils from SPT results. However, these have to be accepted as methods that result in rough estimates only. On the other hand, some methods, developed during the last 25 years, use statistical evaluations of sett lement observations of structures as a basis for determining the relationships between allowable bearing pressure, settlements, foundation geometry and SPT results [11, p. 95 ff.]. Even in these cases however, large deviations can occur. Because of these uncertainties, in ternat ional practice prefers to derive the geotechnical parameters for shear strength and compressibility


from SPT results and use these as input to the design methods when only SPT results are available.

Piles

Boundary condit ions are more favourable for determining the bearing capacity of piles (pile base resistance, shaft resistance) f rom SPT results. Methods are available for cohesive and cohesionless soils, l imestone and soft rocks [11, p. 101 ft.]. These are mainly based on the results from pile load tests on various pile types. The approach is similar to that used in G e r m a n y (Section 3.4.2.3).

3.3.2.4 Relations between the results from different penetration tests

Finally, reference has to be made to relat ionships establ ished between SPT/BDP results and those from dynamic probing and cone penet ra t ion tests in DIN 4094 and refs. [7, 19, 36-38] (see also Section 3.4.2.4).

3.4 Cone penetration test


The cone pene t ra t ion test (CPT) - ment ioned in EN 1997-1, 3.3.10.1 and according to E N V 1997-3, 3 - consists of a pene t rome te r being pushed vertically into the soil at a relat ively constant rate of pene t ra t ion of 2 cm/sec. The pene t romete r comprises a series of rods ending in a pene t romete r tip, consisting of a cone and a cylindrical shaft. During the penet ra t ion , the resistance of the cone and, if possible, the local friction on a sleeve (friction sleeve) located in the cylindrical shaft are measured. The cone resistance qc (pene t ra t ion resistance Qc divided by the cross sectional area of the cone Ac) and the local unit skin friction fs (frictional force Qs acting on the sleeve divided by its area As) are used for further evaluation.

Today the electrical cone is the most used equipment on a world-wide basis. One example of this is shown in Fig. 10. Generally, the cone has a cross sectional area of 10 cm 2. During the recent 10 years, a cone with a cross sectional area of 15 cm 2 (followed by a series of rods with a cross sectional area of 10 cm 2) has also come into use [12] to increase the pene t ra t ion depth and measurement accuracy but also to allow the incorporat ion of other measur ing devices into the cone. Compared to the electrical cone, o ther equipment [12] for example the mechanical ( "Dutch") cone pene t romete r is now only seldomly used.

A t the beginning of the 1970's, the addi t ional measurement of the pore water pressure using the so called piezocone was introduced. According to E N V 1997-3, 3, the cone pene t ra t ion test CPTU is a CPT which includes the measurement of the pore water pressure genera ted at the base of the cone during the penetra t ion. Fig. 11 shows an electrical cone, and Fig. 12 shows the corresponding definitions. Other equipment allows the measurement of the pore water pressure in the middle of the cone and at a defined distance above the friction sleeve [12]. Correct ions and the methods of interpret ing these test results are also given in reference [12].

The widespread use of the cone pene t ra t ion test also outside Europe, which s tar ted in the 1970's, increased the need for internat ional harmonisat ion. Initially, recommendat ions for CPT were made by the Technical Commit tee TC 16 of the ISSMFE [14] which were


1 Cone, Ac = 10cm 2, apex angle = 60 °

2 Load cell 3 Strain gauges 4 Friction sleeve,

As = 150 cm 2 5 Adjustment ring 6 Waterproof cable bushing 7 Signal cable 8 Rod connection

Fig. 10. Tip of the cone penetration test CPT (after DIN 4094)

/ ' k l

1

a

d Q

Push rods

-- Shaft

Gap and seal

Possible Friction sleeve

t -

- - Gap and seal Possible-I Cy ndr ca filter _[" part " - ~ Cone

Conical part _ /

Fig. 11. Scheme ofa piezocone for the cone penetration test CPTU (after ENV 1997-3)

Total area Ac = Net area A N

d c = 35.7 mm Q ~

~" =" t @ a = AN/Ac

qc = Q c / A c qt = Q t /Ac = qc+ u(1 - a )

TOt

Fig. 12. Critical dimensions for a piezocone test CPTU (after ENV 1997-3)

followed recently by recommendat ions for the CPTU [15]. These were also the basis for ENV 1997-3, 3. In addition, there exist a number of comprehensive national standards for example in the Netherlands, Norway, Sweden and the U.S.A. [12]. As the content of DIN4094 was less comprehensive, it made its new edition, DIN4094-1, even more important.

During the last 30 years, the cone penetrat ion test has gone through an enormous development not only because of its widespread use outside Europe, but also because of changes to the equipment. Ref. [12] 2 gives an excellent overview of the current situation and [39] summarises the state of the art for aspects like earthquake and environmental engineering. Today the standard penetrat ion test is perhaps still the leading test used world-wide.

2 In the following text, [12] is the secondary reference; the page number refers to the original source.


However, the cone penetration test has reached or even passed it for many applications because of a higher accuracy in the interpretation of the test results and the numerous possibilities it offers in equipment and operations. This has also intensified the investigations on comparisons of the results from the two tests methods [40], to transfer the SPT know how to the evaluation of the cone penetration test results (and vice versa). In the long run, the application of the two test methods will most probably follow the trend in Germany during the last 50 years: Within a ground investigation project, the cone penetration test (or if applicable, a corresponding dynamic probing test) will be used as the main test, and the SPT will be used as a valuable supplement in the key boreholes, including sampling as for example required by DIN 4094 or EN 1997-1, 3.

The state of development of the technical equipment is as follows: Generally, a dead- weight of up to 100 kN is sufficient to overcome the total penetration resistance. The dead weight is usually obtained by self-propelled thrust machines (mostly trucks). For light weight machines the counterweight can be increased by using screw anchors. A corresponding measuring capacity of the cone of 50 MPa is usually sufficient to measure the cone penetration resistance. There is also off-shore equipment now available, with dead-weights up to 200 kN, for penetrations of very stiff and very dense grounds (tertiary clays, glacial sands, soft rock). The corresponding cones possess measuring capacities of up to 120 MPa [12, p. 8 ff., 41]. By comparison, the cone penetration resistance is usually low in cohesive soils; a value of 5 MPa can already characterise a soil of very stiff consistency [42] and values of qc < 1.5 MPa could indicate a firm to stiff consistency [33]. This means, however, that an "all-purpose cone" [41] would need to have a measuring capacity from 1.5-120 MPa which is hardly feasible. Therefore, [15] recommends cone classes of different measuring capacities depending on the required use.

While the electrical cones with and without the capability to measure pore water pressure, belong to today's standard equipment, the following additional measuring devices made possible by fast sensor development, were introduced for practical applications during the last ten years:

• Cones for measuring lateral stresses [12, p. 172 ff.] • Cones with pressuremeters [12, p. 175 ff., 43, 44] • Cones for seismic measurements [12, p. 179 ff., 45] • Acoustic cones [12, p. 190 ff., 46, 47] • Cones for measuring permeability [12, p. 80 f., 48] • Cones with liquid samplers to obtain pore fluid for chemical investigations

[12, p. 199 ft., 49, 50] • Cone for measuring electrical conductivity/resistivity [12, p. 193 f., 49, 50] • Cones for radiometric measurements [12, p. 186 ft., 51-53] • Cones with build-in cameras [54, 55] • Vibratory cones [12, p. 132]

3.4.2 Evaluation

3.4.2.1 General

The aim of the evaluation of cone penetrometer test results is principally the same as that for the results from the dynamic probing and the standard penetration test. The primary aim is a qualitative evaluation of the ground strata (together with the results from key boreholes). However, in this case the sensitivity is larger than from the dynamic penetrometers.


The ability to measure the local unit side friction fs on the friction sleeve, in addition to the cone penetration resistance qc, has already led early to the use of the parameters qc and fs as a means to classify the penetrated soil strata [56, 57]. Fig. 13 shows such an example. Further investigations demonstrated [12, p. 51 ft., 58, 59] that the accuracy of the prediction can be improved by using the corrected cone penetration resistance qt (Fig. 12) and/or the pore water pressure itself instead of qc. This had led to the recommendat ion in ENV 1997-3, 3 to use the results from investigations with the CPTU for soil classification purposes. Further improvements were obtained using refined statistical evaluations [59], additional evaluation methods (e. g. Fuzzi logic) [60] or by using cameras in the cone.

There is no doubt that classification systems, as the example in Fig. 13 shows, can be a valuable tool in identifying the penetrated soil strata. However, it must be stated that such a system established for a certain geographic/geological region cannot necessarily be applied in other areas without additional calibration [61]. This fact was confirmed by recent comparisons of different classification systems [58]. Therefore, DIN 4094-1 and E N V 1997-3 insist that in addition to indirect ground investigations (here: cone penetration tests), direct ground investigations (e. g. key boreholes) with sampling and laboratory investigations are also performed.

Thanks to the variety in available measuring techniques, a considerable number of parameters representative of different soil properties can now be quantitatively determined. Table 1 in [12] presents a good overview of what can be obtained with common field testing. Besides the consolidation ratio, sensitivity, permeability etc., the following evaluation options should be mentioned: the description of in situ stress conditions including the coefficient of earth pressure [12, p. 61f., 88 f., 172ff.], seismic properties [43], soil liquefaction [12, p. 166 f., 39, 62-64], porewater pressure distribution [12, p. 74 ft.] and with increasing investigations of soil contamination, the quality of pore liquid, electrical resistivity and conductivity [12, p. 194 ft., 49, 50]. The application of cone penetration test

o o 100 ' o ° o ' ' 0 _ 0 I

20 ' o o ~,:

~t 0,5

8

0,2

0,1 0 1

!, I I I - Friction ratio Rf = fs/qc" 100

: ~ , . _-_-_ _-_-_ -_ -_ - -_ -_ - -_-_~ -_-_~

2 3 4 6 7 8 9 10 Friction ratio, %

Fig. 13. Example of a semi-logarithmic relation between the cone penetration resistance and the friction ratio in various soils (designation after DIN 4022) from measurements by the GEOSOND company


results in geotechnical design has, on an internat ional level, at least reached and maybe even passed, the appl icat ion of SPT results (see Table 9). Advanced measuring techniques and numerous basic investigations in test chambers [12, p. 291 ff., 65, 66] have both con- t r ibuted to this fact. In these tests, the influences of individual parameters , such as in situ stress conditions, have been invest igated systematically. This has contr ibuted essentially, at least qualitatively, to the clarification of the penet ra t ion processes around the cone. However , the results cannot be directly t ransferred to real i ty because of l imited test conditions (part ial ly too small chambers; "non-grown" soils) [12, p. 291 ft., 39] al though the transfer was possible in some isolated cases as descr ibed in [67].


Shear strength

In the following sections, some examples are presented for deriving geotechnical parameters from CPT results. Firstly, there are two examples of the indirect de terminat ion of the angle of effective shearing resistance qf of cohesionless soils. In these cases, the relative density ID is initially der ived and, by the means of this parameter , q0' can be de te rmined from a corresponding relationship.

F rom Eqs. (1) and (5), confirmed by recent investigations [12, p. 81 if.I, DIN4094 gives the following general equat ion as an example of the der ivat ion of the relative density ID from the cone pene t ra t ion resistance qc:

ID = el + e2 log qc (8)

Table 11 contains examples of the coefficients ez and e2 for sands and sand-gravel mixtures for CPT with a 10-cm 2 cone. These relat ions are valid for CPT per formed above the groundwater level and for a depth larger than about 1 m where this is the critical depth

Table 11. Examples of coefficients in Eqs. (8), (13) and (14) for deriving relative density ID and stiffness coefficient v from cone penetration resistance qc (in MPa; 10-cm2-cone) above groundwater level (after DIN 4094)


SE

SW

SW, GW

TL, TM

U 1 )

_<3

>6

>_6

Conditions Relative density ID

Ic 2) el e2

- -0.33 0.73

- 0.25 0.31

0.75-1.30 - -

Stiffness coefficient v

fl f2

113 167

-13 463

50 15.2


Valid ranges (in MPa): For the relative density: 3 _< qc < 30. For the stiffness coefficient: in SE, SW: 5 _< qc _< 30; in TL, TM: 0.6 _< qc _< 3.5.


1.3 Geotechnical field investigations

Table 12. Example of a relation between cone penetration resistance qc (10-cm 2-cone) and relative density ID for naturally moist medium sands (after [68-70])

87

Cone penetration resistance Relative density Designation qc, MPa ID

<2.5 2.5-7.5 7.5-15.0 15.0-25.0

> 25.0

<0.15 0.15-0.35 0.35~9.65 0.65--0.85

> 0.85

Very loose Loose

Medium dense Dense

Very dense

from which under the same conditions, the cone penetration resistance becomes almost constant. Above this depth, the cone penetration resistance increases considerably with depth.

The second example (Table 12) shows in tabular form, the relation between cone penetration resistance qc and relative density I D for moist uniform medium sands ("Berlin Sands") based on numerous tests [68-70]. With comparable boundary conditions, this relation could be used also for deriving indirectly COl from qc via ID.

Comparative penetration tests have shown that the cone penetration resistance in non- uniform cohesionless soils is smaller than in uniform soils at the same relative density [6, 7]. This is due to the higher compactibility = (emax - emin)/emin of the non-uniform soils. Additional investigations [7, 8] revealed that not only the compactibility, but also the average grain size, influences the cone penetration resistance at the same relative density (Section 3.1). This means that an absolute determination of the relative density from the cone penetration resistance itself is not possible. For this, the grain size distribution and the maximum and minimum void ratios must be known. In addition, the existence of groundwater has a certain influence on the penetration resistance. Conse- quently, DIN 4094 differentiates between cases of "with and without groundwater" in the correlations for deriving ID (see also Tables 8, 10 and 11). The tables also show the boundary conditions (soil types etc.) for which the correlations have been established. In case of the CPT, however, the influence of the ground water may often be negligible.

A number of theoretical and empirical investigations of the relationship between the relative density ID and the angle of effective shearing resistance CO' are also available in [9, 12, p. 90 ff., 35, 39] and E N V 1997-3. Most of these relations are dependent on the type of cohesionless soil investigated. The stress dependency of c 0' is also increasingly being considered.

Some examples for deriving the angle of effective shearing resistance cO' directly, are given below. The similarity of a cone penetration test with a deep foundation led to attempts to derive cO~ empirically as well theoretically from the cone penetration resistance, as can be seen from a number of investigations [12, p. 90 ff., 39]. Some of the references refer again to the stress dependency of cO~. The dependency on the type of cohesionless soil is also mentioned.

Table 13 shows a tabular relationship between cone penetration resistance qc and the angle of shearing resistance cO' for natural quartz and feldspar sands according to [71] which was also included in E NV 1997-3.

Another example is the approximated relation between qc and cO' for different sands according to [72] which was additionally confirmed for a sand (U = 2.2) and a sand-


Table 13. Example of a relation for deriving the angle of shearing resistance cp' and the drained Young's modulus Em from cone penetration resistance qc for natural cohesionless soils (quartz- and feldspar sands) (after [71])

Cone penetration resistance Angle of shearing Drained Young's modulus 2) qc,MPa resistance 1) cp', deg. Era, MPa

0-2.5 2.5-5.0 5.0-10.0

10.0~0.0 >20.0

29-32 32-35 35-37 37~,0 4042

<10 10-20 20-30 30-60 60-90

i) The values are valid for sands. For silty soils a reduction of 3 ° should be made. For gravels 2 ° should be added. 2) Em is approximated by the stress and time dependent secant modulus. Values given for the drained modulus correspond to settlements for 10 years. They are obtained assuming that the vertical stress distribution follows the 2:1 approximation [71, p. 64ff.]. Furthermore, some investigations indicate that these values can be 50 % lower in silty soils and 50 % higher in gravelly soils. In overconsolidated cohesionless soils the modulus can be considerably higher. When calculating settlements for ground pressures greater than 2/3 of the design bearing pressures in ultimate limit state, the modulus should be set to half of the values given in this table.

gravel mix ture (U = 5.7) [10, 70, 73, 74]. This re la t ion can be descr ibed by the following e q u a t i o n with a valid range of 6.9 M P a < qc < 42.5 MPa:

q)' = 26.8 + 4.5 In qc ± 1 ° (9)

with qc in MPa.

The t r end and order of m a g n i t u d e agree with the de terminis t ic equa t ion in D I N 4094-1 for na r rowly graded sands (SE, U _< 3) wi th in the range of 5 M P a _< qc _< 28 MPa:

q0' = 23 + 13.5 log qc (10)

with qc in MPa.

Theore t ica l and empir ica l inves t igat ions are also avai lable for the der iva t ion of the u n d r a i n e d shear s t rength Cu in cohesive soils [12, p. 63 ft., 33, 39, 75]. As examples, the two fol lowing equa t ions are m e n t i o n e d , which were also inc luded in E N V 1997-3, 3.

With qc f rom CPT:

Cu = (qc - Ovo)/Nk (11)

Bu t pre fe rab ly with qt f rom C P T U :

Cu = (qt -- Ovo)/Nkt (12)

where: Ovo = total vert ical stress (due to o v e r b u r d e n ) Nk, Nkt = factors to be es t imated f rom local exper ience

Nk can take values b e t w e e n 11 and 19 and Nkt be tween 8 and 20 respect ively d e p e n d i n g on the actual cohesive soil and its plasticity index [12, S. 64 ft., 75]


Compressibility

Especially in international practice, the Young's modulus Em is frequently used as a geotechnical design parameter . Investigations under controlled laboratory conditions indicate that Em in sand under drained conditions depends primarily on the relative density, the consolidation ratio and the actual stress condition. Consequently, the methods for the determination of Em from the cone penetrat ion resistance qc reflect this fact [12, p. 93]. A simple example is given in Table 13 [71] (see also E N V 1997-3, Annex B.1). The Eurocode contains further examples for set t lement calculations of spread foundations in sands (ENV 1997-3, Annex B.2 and [12, p. 158 f.]). For similar investigations in cohesive soils reference is made to [12, p. 71 f.] and [33].

In Germany, the modulus Eoe d f rom oedometer tests is primarily used for set t lement calculations. The same type of investigations, as used for the dynamic penetrat ion tests in cohesionless and cohesive soils [7, 19], resulted in the following equations for deriving the stiffness coefficient v in Eq. (2) directly f rom the cone penetrat ion resistance qc (in MPa):

• For sands: v = f l + f2 • log qc (13)

• For slightly and medium plastic clays: v = fl q- f2 " qc (14)

Examples of the coefficients fl and f2 are given in Table 11. Using w = 0.5 for the investigated sands and w = 0.6 for the corresponding cohesive soils, the stress dependent modulus Eoed can be derived directly.

On the other hand, a direct correlation between the modulus of elasticity Eoed f rom sett lement measurements (e.g. f rom plate loading tests with model foundations) and the cone penetrat ion qc is not possible because parameters such as loading conditions, shape and size of the foundation and thickness of the compressible layer beneath the foundation, have an additional influence [10]. The well known relation E o e d = aqc (for values of c~ see [33] and E N V 1997-3, Annex B.3) should therefore be considered as a rough approximation only.

3.4.2.3 Bearing capacity of spread foundations and piles

Spread foundations As already ment ioned when discussing the relation between cone penetrat ion resistance and angle of shearing resistance (Section 3.4.2.2), it was obvious to correlate theoretically the coefficients in the equation for calculating the bearing resistance of spread foundations with qc because of the similarity of a cone penetrat ing the ground.

In practice however, early successful at tempts were made to estimate the bearing resistance of spread foundation directly f rom CPT results [12, p. 157 f.]. In Germany, the evaluation of numerous large-scale load tests showed that cone penetrat ion resistance and bearing resistance are directly proport ional to each other [10, 70, 73, 74]. This method for direct application in the design of spread foundations is reflected in the standardisation (see D I N 1054).


Piles

The determination of pile bearing resistance (see also EN 1997-1, 7.6.2.3) can be viewed as the original intention of quantitative evaluation of the cone penetration test results because the transferability of the results appeared to be obvious. Consequently, there are more empirical approaches, mainly validated by pile load tests, available today than theoretical methods. State of the art methods are detailed in [12, p. 151, 76] respectively. There are, however, indications that the empirical use of CPTU results is more accurate [77]. E N V 1997-3, Annex B.4 gives an example of a common method that stems from the early use of deriving pile bearing resistance from CPT.

Germany primarily followed the approach to correlate the results from pile load tests with the CPT results. This was based on a large number of related parameters (ultimate pile base bearing resistance, normalised settlement = settlement/pile diameter) from pile load test results in cohesionless soils with known cone penetration resistances qc from which conservative estimates were taken [78]. These comprehensive investigations are reflected in the German standardisation codes (DIN 1054, DIN EN 1536). These standards contain required minimum values of cone penetration resistances in the ground in the case of the bearing resistance of driven displacement piles. For bored piles, values for pile base resistance and skin friction are given as a function of the cone penetration resistance from CPT within a range of 10 MPa < qc < 25 Mpa. For the pile base resistance, the normalised settlement of the pile head is given as additional parameter.

3.4.2.4 Relations between results from different penetration tests

The opportunity to derive the bearing capacity of foundations directly from the results of cone penetration tests, has led to numerous relationships between the results from different penetration test methods (e. g. SPT and CPT), see [7, 12, p. 149 ff., 36-38, 40]. These efforts were enforced to utilise and to complement the comprehensive existing knowledge for the future. Table 14 shows examples of some of these relationships.

3.5 Field vane test


The field vane test (FVT) is an in situ test (ENV 1997-3, 8); it is performed with a rec- tangular vane, consisting of four plates fixed at 90 ° angles to each other, pushed from the bot tom of a borehole (or excavation pit) to the desired depth and then rotated (loaded by torque). The ratio of the height H of the vanes to the diameter D must be 2:1. The vane should be equipped with a device that allows the torque of the vane to be separated from that of the extension rods. A casing or a slip coupling can be used for this purpose.

The test is used in very soft to very stiff cohesive soils to determine the undrained shear strength and sensitivity. It maybe used also to determine the undrained shear strength of silts and clayey glacier deposits. The reliability of the test results varies with soil type.

In Germany, the field vane test has been standardised in DIN 4096, which was adapted to suit E N V 1997-3, 8 by the new edition DIN 4094-4. The equipment consists of the vane apparatus i.e. the vane and shaft (with protective sleeve, if appropriate), the rotating device, the extension rods (if appropriate) and the measuring device for measuring the torque and the angle of rotation (if appropriate) (Fig. 14).


Table 14. Examples of the average ratios of cone penetration resistance qc (in MPa) to number of blows N30 and N10, respectively, for some cohesionless and cohesive soils above groundwater level (following DIN 4094 and [19])


Ratios of penetration test results

Cohesionless soils Cohesive soils

BDP qc/N30

DPH

qc/Nlo

DPL

qc/Nlo

BDP

qc/N30

DPH

qc/Nlo

DPL qc/Nao

SE 0.5 0.7 0.25 - -

SW, SI 0.7 1.0 0.35 - -

GE, GW, GI 1.1 1.5 - - -

TL, TM l) - - - 0.55 1.00 0.36

1) For Ic = 0.75 - 1.30.

Valid ranges:

BDP: in SE: 3 _< N30 _< 50; in SW, SI: 3 < N30 _< 40; in GE, GW, GI: 3 _< N30 < 30;

in TL, TM: 3 < N30 < 14. DPH: in SE, SW, SI: 3 _< N]0 _< 30; in TL, TM: 3 _< N10 _< 19.

DPL: in SE: 3 _< N10 < 60; in SW, SI: 3 < N10 _< 25; in TL, TM: 9 < N10 < 60.

Soil classification according to DIN 18196:

SE: poorly graded sands; SW: well graded sands; SI: poorly graded sands with some grain diameter missing;

GE: poorly graded sand and gravel; GW: well graded sand and gravel; GI: poorly graded sand and gravel with some grain diameter missing;

TL: low plasticity clays; TM: medium plasticity clays.

Top v iew

Rotation ~ ~ ,~-J Spring for torque angle "7 I ~ I~ measurement:

J i r,~ T = 2 P - a Initial / 1 I position - -

Casing

r N / Position before test

I _1_ _-> 50

_ t _ _ Position during test H->_20

~ -- Vane (top view) Fig. 14. Scheme of the field vane test

92 Klaus-J0rgen Melzer and Ulf Bergdahl

The vane height/diameter ratios are H / D = 100mm/50mm (FVT 50) and H / D = 150 mm/75 mm (FVT 75). The selection of the vane dimensions depends on the strength of the soil. For example FVT 75 is for low consistency and FVT 50 is for higher consistency. The vane apparatus is pushed into the soil until the required depth is reached; driving, vibrating or rotating are not allowed during the push-in process. When a casing is used to reduce skin friction, the apparatus is pushed into the soil only after the casing has reached a required depth; then, the apparatus is rotated; the required depth should be _> 5 D but at least 0.3 m below the bot tom of the borehole/pit.

The rate of rotation should be 0.5°/sec in soft soils at low sensitivity and 0.1-0.2°/sec in soils with high sensitivity respectively. The maximum torque Tmax, u required to shear the soil along the undisturbed cylindrical soil surface for the first time, is measured (the angle of rotation is also recorded on occasions to obtain additional information about the shear behaviour of the soil). After the initial shearing process and the recording of Tmax,u, the vane is rotated at least ten times with a rate of rotation of 10°/sec. After that, the above shearing procedure is repeated and the maximum torque Tmax for this remoulded condition is recorded.

3.5.2 Evaluation

3.5.2.1 General

The maximum shearing resistance is determined by the following formula from the measured torque, with D as vane diameter, assuming a simplified stress distribution along the failure surfaces of the sheared soil cylinder [3, 79]:

Cfv = 0.273 Tmax,u/D 3 (15)

where: cry = maximum shearing resistance of the soil during the initial shearing process Tmax,u = maximum torque during the initial shearing process D = vane diameter

For the determination of the shearing resistance for the remoulded condition Crv, Trnax,u is replaced by Tmax:

Crv = 0.273 Tmax/D 3 (16)

The sensitivity Sty determined from the field vane test is defined as the ratio Cfv/Crv.


The measured shearing resistance cannot be separated into effective friction and cohesion because the effective horizontal stress conditions in the soil being investigated are not known. Therefore, the field vane test can only be applied where the soil can be assumed to be frictionless for undrained conditions, i. e. in saturated normally consolidated cohesive soils of soft to stiff consistency. The shearing resistance Cry can then be determined from the FVT as equivalent to the shear strength Cfu during soil failure under undrained conditions (for normal clays).

At low shear stresses - for example creep movements in slopes - the shear strength of high plasticity clays is smaller [80]. Therefore, the shearing resistance obtained from FVT has to be corrected by means of empirical factors:

Cfu = ~ ' Cfv (17)


The correction factor ~ has to be determined from local experience. In general, it is correlated to the plasticity index or the liquid limit and perhaps to the effective normal stress. The correction factor increases in the case of overconsolidated clays with increasing plasticity index [81-83] or in the case of normally consolidated clays with decreasing liquid limit [84]. In other cases - for example earth pressure calculations - the derived Cfu values are considered as minimum values because they were measured primarily in vertical failure planes, where they are under normal conditions smaller than in horizontal or inclined planes. In these cases, C~u can be increased [81].

Examples of the correction factor ~ are given in E N V 1997-3, Annex G and in DIN 4094-4. In fissured clays and in heavily silty or sandy clays, the correction factor ~ has sometimes to be reduced to as low as 0.3.

The undrained shear strength cfu derived from the results of field vane tests is mainly used for the calculation of bearing resistance of spread foundations and piles or for stability analyses of slopes using analytical methods. The use of common field tests in environmental investigations (see also Section 3.4.1) has also led to the first applications of the field vane test in this area of site investigations [85].

3.6 Weight sounding test


The weight sounding test (WST) mentioned in EN 1997-1, 3.3.10.3 was developed by the geotechnical department of the Swedish Railway Administration in about 1915 and became a national standard by 1917. Today, the method is the most commonly used penetration test in Scandinavia and Finland. The weight sounding test is normally used for preliminary investigations in differing soils. The test results could also be used for design and inspection investigations in most common soils but are primarily applied in very soft to stiff cohesive soils and very loose to dense cohesionless soils. In very dense sand and gravel and tills pre-drilling could be necessary. The results are generally used to evaluate the thickness and extent of different soil layers but also for the assessment of the design parameters for spread foundations and piles.

The first international harmonisation of the weight sounding test took place in 1989 [14]. The method was also included in the European standardisation (ENV 1997-3, 7).

The weight penetrometer in its original form consists of a screw shaped point (diameter: 25 mm), a set of weights (1 x 5 kg, 2 x 10 kg and 3 x 25 kg), a number of rods (diameter: 22 ram) and a handle (Fig. 15). The point is manufactured from a 25 mm square steel bar with a total length of 200 mm. The bar has an 80 mm long pyramidal tip and is twisted one turn to the left over a length of 130mm (see E N V 1997-3, Fig. 7.1). It is used in general as a static penetrometer in very soft and very loose soils where the penetration resistance is less than 1 kN (corresponding to a total load of 100 kg). The weight sounding test can be performed manually or mechanically. Today, most tests are performed mechanically (by hydraulic machines) and the recording of loads and number of halfturns is made automatically by means of electrical sensors.

In the static phase of the test, the penetrometer should be loaded in stages as follows: 0.05 kN, 0.15 kN, 0.25 kN, 0.50kN, 0.75kN and 1.00kN. The load is then adjusted from these standard loads to keep the penetration rate at about 50 mm/sec. If the penetration resistance is greater than 1.00 kN or the penetration rate is less than about 20 mm/sec the


1.00m

O.80m

I 0.20 m

1

_•_ Connection Handle

~ Weights 25 kg Weights 10 kg Clamp 5 kg Wood

- ~ S c r a p e r

Rod, diameter: 22 mm

/ _ _ _ / Screw-shaped cone

Fig. 15. Test equipment for the manual weight sounding test

o

1

2

3

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6

7

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1 Z

Z

Z

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C-" l " , - , . , J

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0 20 40 60

ht/O,2 m

Fig. 16. WST results presentation

WST 22: Weight sounding test, Rod diameter: 22 mm

ht/0.2 m: Revolution per 0.2 m penetration fb(SpQ80): Pre-boring to the designated depth

(encrusted surface layer); diameter: 80 mm

penetrometer has to be rotated. The load of 1.00 kN is then maintained and the number of halfturns required to give a 0.2 m of penetration is recorded.

The weight sounding test is terminated at a depth when a certain penetration resistance is reached or when the penetrometer cannot be driven any deeper, i. e. the so called "firm bot tom" for the weight penetrometer is reached. The criteria chosen for the termination of a weight sounding test depends on the ground conditions and the purpose of the investigations. When the so called "firm bot tom" criteria is used, the final resistance should be checked by sledgehammering on top of the penetrometer, by blows using the weights or by a percussion machine to ensure the "firm bot tom" has actually been reached. The chosen procedure must be recorded in the test report.

The results from a weight sounding test are presented in diagrams showing the penetration resistance versus depth (Fig. 16).

3 . 6 . 2 E v a l u a t i o n

3 . 6 . 2 . 1 G e n e r a l

When considering the evaluation of the weight sounding diagrams, both the magnitude of resistance and its variations are used. One has to remember that the variations of the resistance can also depend on the variations in the soil layer sequence. In very soft to firm


clays the penetrat ion resistance is often less than 1 kN or the resistance against turning is rather constant and low with less than 10 halfturns/0.2 m of penetration. As the sensitivity of the clay also influences the penetrat ion resistance, the strength of the clay cannot be determined directly from the penetrat ion resistance without a separate calibration from each site.

In very loose to loose sediments of silt and sand rather low and constant penetra t ion resistances are also obtained. In medium dense to dense silts and fine sands higher (10-30 halfturns/0.2 m of penetrat ion) resistances are obtained, which remain rather constant with depth. In sand and gravel sediments, the variation in penetrat ion resistance increases with the grain size. When evaluating the weight sounding test results from silty sands and coarse gravel, one should note that a high penetrat ion resistance does not always correspond to higher density or strength and deformation properties.

The soil layer sequence evaluated from the weight sounding tests and any additional sampling on a site, including the "firm bot tom" criteria, is used for the evaluation of the suitability of a site for a certain structure, for the evaluation of the type of foundat ion (spread or pile foundation) and for the derivation of geotechnical parameters.


Weight sounding test results are used as the basis for the design of foundations in cohesionless soils. In [71], it is shown how shear strength and deformation properties can be derived from weight sounding test results and can be used as input for the design methods used for spread foundations (Table 15).

Infine-grained silts and clayey cohesionless soils, geotechnical parameters should be determined by specific tests - for example by in situ pressuremeter tests or in the laboratory using good quality samples.

Table 15. Example of a relation for deriving the angle of shearing resistance q91 and the drained Young's modulus Em for natural cohesionless soils (quartz- and feldspar sands) from the results of weight sounding tests (after [71])

Weight sounding test, Angle of shearing Drained Young's modulus 2) half revolutions/0,2 m resistance 1) q/, deg. Em, MPa

0-10 10-30 20-50 40-90 >90

29-32 32-35 35-37 37-40 40-42

<10 10-20 20-30 30~50 60-90

1) The values are valid for sands. For silty soils a reduction of 3 ° should be made. For gravels 2 ° should be added. 2) Em is approximated by the stress and time dependent secant modulus. Values given for the drained modulus correspond to settlements for 10 years. They are obtained assuming that the vertical stress distribution follows the 2:1 approximation [71, p. 64ff.]. Furthermore, some investigations indicate that these values can be 50 % lower in silty soils and 50 % higher in gravelly soils. In overconsolidated cohesionless soils the modulus can be considerably higher. When calculating settlements for ground pressures greater than 2/3 of the design bearing pressures in ultimate limit state, the modulus should be set to half of the values given in this table.


3.6.2.3 Bearing capacity of piles

The weight sounding test results can also be used directly for pile design [86].

The required length of end bearing concrete piles can be determined from the so called "firm bottom" criteria where the tests have been terminated. Normally, the required end bearing pressure is achieved at the "firm bottom" or up to 2 m deeper. However, dynamic probing is considered to be a more accurate method in determining the length of such piles.

Norwegian experience with friction piles indicates how the average weight sounding resistance along the pile length can also be used to calculate the magnitude of the skin friction (bearing capacity of the pile) in sands.

4 Lateral pressure tests in boreholes

4.1 Equipment and test procedures

The equipment for lateral pressure tests in boreholes (see also ENV 1997-3, 10.4) can generally be defined as follows [87]: The equipment normally consists of a cylindrical device that can apply a uniform pressure to the pocket wall in soil and rock; the pocket is created specially for the test. The term "pocket" is intentionally used rather than borehole to distinguish between the pocket created specially for the lateral pressure test and the borehole created for advancing between test positions. The borehole diameter should be either equal or larger than the pocket diameter. Methods for creating the pocket are summarised in Table 2 of [87]. During the test, the volume change and the radial or lateral displacement of the cylindrical device are measured. From the results, strength and deformation properties of soils and rock, as well as for fills (quality control), can be derived.

The first investigations of this type were described by KOgler [88, 89]. In the 1930's, he developed a lateral pressure device (borehole jacking probe) where two cylindrical half- shells are pressed mechanically against the pocket wall. This device was later replaced by a cylindrical probe closed on all sides by a rubber membrane with steel plates at the top and the bottom of the cylinder. The probe was inflated by air pressure [90, 91]. In the 1950's, this method was developed further by M~nard into the three-cell pressuremeter test (upper guard cell, test cell, lower guard cell). The lateral pressure device developed by Goodman for application in rock [92] should also be noted.

After this, the world-wide dissemination of the "prebored pressuremeter" (PBP) of the M6nard type and of other devices began. In France [93] and Great Britain [94], "self-boring pressuremeters" (SBP) for applications in soil and rock were developed independent of each other, to reduce, as far as possible, the disturbance of the pocket walls during drilling and lowering of the probe, with the drilling device integrated into the probe. Finally, offshore application initiated a third generation of lateral pressure tests: the "pushed-in" or "full displacement pressuremeter" (FDP) [43, 44, 95]. In this case, the pressuremeter is incorporated with the cone in a cone penetrometer. In the broadest sense, the NGI dilatometer, as further development of the flat dilatometer (DMT) by Marchetti, belongs to this group of tests [96, 97]. An overview of the present state of development of lateral pressure tests in boreholes can be found in [87].


A number of countries have now standardised certain devices such as the prebored pressuremeter. The best known are probably the French Standard NF P94-110 and the Amer- ican ASTM D 4719. Other standards for self-boring pressuremeters are in preparation. The first international harmonisation on an European level is described in ENV 1997-3, 4, where the essential requirements for the equipment and test procedures are defined. Sub- sequently, DIN 4094-5 was written to cover the equipment commonly used in Germany (PBP). Whilst internationally the equipment is divided into the three methods of bringing the probes into place (see above), DIN 4094-5 describes the equipment commonly used in Germany (PBP) as follows:

The dilatometer (Fig. 17) is a cylindrical device where a flexible rubber membrane is used to apply uniform pressure (by gas or fluid) to the walls of the pocket (borehole). The displacement of the pocket is measured by displacement transducers in selected radial directions. The applied pressure is measured at the same time.

The pressuremeter (Fig. 18) is a cylindrical device where a flexible rubber membrane is also used to apply uniform pressure to the walls of the pocket (borehole). The displacement of the pocket is determined by measuring the volume of fluid injected into the test cell The applied pressure is measured at the same time.

The borehole jacking probe (Fig. 19) is a device where two half-shells made of steel are pressed diametrically against the pocket walls (borehole) by hydraulic pressure. The expansion between the half-shells is measured by displacement transducers. The applied pressure is measured at the same time.

The types and operational possibilities for these pressuremeters are summarised in Table 16.

Recent experiences with some of the equipment are published in [19, 98-101]. Table 17 gives an overview of some data for self-boring and full displacement pressuremeters. For instance in [104-107] and [43, 44] comparable investigations with these two types of equipment are presented.

Guide rod

l

Data acquisition Pressure source (displacement and pressure) Pressure control

', 00" i EZZ] ~ [] Cable

Pressure ose

J Sediment catcher

~ Dilatometer

~ , Fig. 17. Scheme of the dilatometer equipment (after DIN 4094-5)


Measuring and control unit

Coaxial hose Pressurized gas

1 Pressuremeter

- - Guard cell - - Test cell

- - Guard cell Fig. 18. Scheme of the pressuremeter equipment (after DIN 4094-5)

Guide rod

\ Data acquisition Pressure control

C S ~ D ( ~ Hydraulicpump Cable J

Pressure hose ] I

Borehole jacking probe Fig. 19. Scheme of the borehole jacking test equipment (after DIN 4994-5)

The special case of the flat d i la tometer (DMT) - see also ENV 1997-3, 9 and [96, 97] - includes the de te rmina t ion of the ground strata (supplemented by key boreholes) , in situ stress conditions, the shear strength and deformat ion proper t ies of cohesive soils and sand with a b lade-shaped probe (Fig. 20). The flat d i la tometer has a thin circular steel membrane mounted on the outside of one side of the blade. The test is especially suitable for use in soils where part icles are small compared to the size of the membrane (e. g. clays, silts, sands).

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Fig. 20. Scheme of the DMT equipment and the measuring principle (after ENV 1997-3)

The basic the test method is as follows. The blade is pushed vertically into the soil by a thrust machine (for example, as used in cone penetration tests). At the selected test depth, the contact pressure P0 is initially measured while the membrane is just about to lift off the blade. Subsequently, the pressure Pl (applied by gas) which is necessary to deform the membrane for 1.10 mm is measured. Fig. 20 shows the equipment and the measuring principle. Recent examples of investigations are published in [108-112].

The parameters obtained from these lateral pressure tests, such as the modulus of elasticity EM from the MPT (Table 16 and Section 4.2), are not real geotechnical parameters but equipment specific parameters. Therefore, it should be noted that the tests have to be performed and evaluated exactly in accordance with the standard procedures for each test in order to obtain reproducible and reliable results [87]. In addition, it is important to gain local experience with the test to be able to use the results for design purposes.

Depending on the particular equipment, the main steps of the test procedures are:

1. Calibration before the test (pressure or measuring system, volume or displacement transducer system, system compliance, correction factor for membrane stiffness).

102 Klaus-Jfirgen Melzer and Ulf Bergdahl

2. Preparation of the test pocket (pre-drilling, special drilling of the pocket or push-in) and insertion of the probe minimising the disturbances of the pocket walls.

3. Performance of the test and the corresponding data acquisition, pressure application in constant load steps (stress control) or the creation of stages of constant pocket deformation (strain control), initial load and unload-reload cycles.

4. Recording of the test results (raw data). 5. Evaluation and correction of the measured values (hydrostatic pressure, membrane

stiffness, system compliance, pore water pressure). 6. Reporting (number of the borehole and the test, equipment and component types

used, borehole log etc., see also ENV 1997-3, 4.6). 7. Calibration after each test series (see step 1).

4.2 Evaluation

4.2.1 General

The determination of equipment specific parameters from each test is far more complex than in the case of all other field tests treated in this Chapter. For example, the evaluation of the test data of a pressuremeter test (MPT) are summarised below (see also ENV 1997- 3, 4 and DIN 4094-5).

The M6nard modulus of elasticity Em and the limit pressure PLM are determined from the corrected test results according to Fig. 21. The diagram shows the injected fluid volume V versus the applied pressure p (upper part of Fig. 21) and AV/Ap versus p (lower part of

oT, / -

V c + V r

E M = 2 ,66 & V "V

& (V =Vc+ V r ) v i

- - I I I I I

Prl I IPLM i

I App l ied pressure Ap ;--I -¢

E ~ ~ l m . . . . I-- . . . . . . . 1,2 min

- -- rain Pr

Fig. 21. Determination of EM and PLM from the results of a pressuremeter test (after DIN 4094-5)

Appl ied pressure


Table 18. Examples of the determination of the modulus of elasticity Eoed from different lateral pressure tests

Test Test results

RDT

MPT

BJT

DMT

Modulus of elasticity: ED = (1 + v) • d/Ad. Apd

Creep index: kD = (d2 - d l ) / log(t2/tl)

Modulus of elasticity: EM = 2.66V. Ap/AV

Limit pressure: PLM from Fig. 21 or

PLM = 1.7 pf -- 0.7 OIlS

Modulus of elasticity: EB = f. d • Ap/Ad

Creep index: kD = (d2 - d l ) / log(t2/tl)

Materialindex: IDMT = (Pl -- Po)/(Po -- Uo)

Horizontal stressindex: KDMT = (po--Uo)/O~o

Eoe d --

Eoe d --

Modulus of elasticity

Eoed Eq. no.

EDU(I -- v) (18)

(1 + v)(1 - 2v)

Eoed = EM/a (19)

EBU(1 -- v) (20)

(1 + v)(1 - 2v)

Eoe d = RmEDMT (21)

Explanations in

ENV 1997-3; DIN 4094-5

ENV 1997-3; DIN 4049-5

DIN 4094-5

ENV 1997-3

Fig. 21). The limit pressure pLM is defined as the pressure required to double the volume of the test cell and corresponds to the injected fluid volume of V = Vc -I- Vr where Vc is the deflated volume of the probe and Vr is the injected volume measured at Pr, the latter being the pressure where AV/Ap is a minimum.

Table 18 contains the essential test results from some types of equipment. For further details reference should be made to the relevant standards.

Due to the wide variety of the types of equipment, which enables the user to test soils and rock, and due to the almost 50 years of experience in this area, a number of parameters can nowadays be derived from the test results which represent certain soil properties (see Table 1.1 in [12], Table 10 in [87]). Among others, these are: the consolidation ratio, relative density, soil l iquefaction, horizontal stress conditions, stress-strain relations, pore water pressure and permeability.

The results of lateral pressure tests at internat ional level are applied to the geotechnical design for spread and pile foundations. Series of large-scale tests and rigorous standardisation, e.g. [98] and Fascicule 62, together with detailed laboratory investigations, i.e. [113], have contributed to this fact. The applications of the test results in the design of sheet pile walls, in slope stability analyses and in tunnel design are also well known [87].

Principally, one has to distinguish, as in the case of penetrat ion test results, between two methods of application [87]: on the one hand empirical or theoretical derivation of geotechnical parameters serving as input to design methods or on the other hand empirical or semi-empirical methods, where the test results serve directly as input into the design methods. However, it has to be noted that for of all empirical and semi-empirical methods local experience plays a decisive role.


4.2.2 Derivation of geotechnical parameters

Shear strength For the determination of the angle of effective shearing resistance qJ of sands using these methods, the approach is generally to develop a model for the behaviour of the sample soil and adjust it according to the test results, q9' then can be derived from this semi- empirical model. Examples for empirical and semi-empirical methods are given in [44, 87, 113, 114]. Only results from SBP tests are generally used for this approach and not many examples are available today [87]. In addition, the SBP methods strongly depend on the local conditions for which they were specifically developed.

The undrained shear strength Cu in cohesive soils can be determined directly from the upper part of the pressure-deformation diagram of an SBP test. However, empirical and semi-empirical methods are used in the case of results from PBP tests. For instance, the limit pressure PLM is correlated with Cu from laboratory tests or in situ field vane tests [87, 99, 101]. Eq. (22) from ref. [99], where further relations are given, is an example for deriving Cu from MPT results in clays:

Cu = 25 + (PLM -- a h ) / 1 0 (22)

where: PLM = limit pressure according to Fig. 21 oh = horizontal stress at the tested depth

Eq. (23) is an example of the derivation of Cu from DMT results according to E N V 1997-7, 9:

Cu = 0.22O~o(0.5 KDMT) 1"25 (23)

where: ' = average normal stress at the tested depth before insertion of the probe Ovo

KDMT = horizontal stress index (Table 18)

Pressuremeter tests are suitable for the determination of the shear modulus for soils and also for rocks during initial and cyclic loading [43, 44, 100, 101, 106]. According to the relevant evaluations procedures (e. g. NF P94-110, ASTM D 4719), the shear modulus for the initial loading condition is determined from the middle, almost linear elastic part of the curve of the test results (Fig. 21):

GM = (Vo + V m ) A p / A V (24)

where: Vo = volume of the test cell before loading Vm = average value of the volume in the almost linear elastic part of the test curve

A modified evaluation method is suggested in [100] to make the results from MPT and SBP tests compatible.

Compressibility

In Table 18, equations for deriving the modulus Eoed from the results of tests are summarised (Eqs. 18-21). Eqs. (19) and (21) for MPT and DMT are empirical relations. The values for ct in Eq. (19) and Rm in Eq. (21) are given in ENV 1997-3, 4.


While deriving the modulus Eoe d from R D T and BJT results (Table 18), the following should be noted (see DIN 4094-5, Fig. D.1). Exper ience shows that the moduli for unloading condit ions EDU and EBU, respectively, de te rmined as the secant modulus from the middle section of the unloading curve, are close to the Young's modulus Em of the mater ia l being investigated. The middle section is defined as the par t of the pressure-deformat ion curve from 30 to 70 % of the pressure be tween the upper turning point of the cycle and the full unloading pressure (represent ing 0 %). Assuming that rock and soil exhibit l inear elastic, homogeneous and isotropic behaviour, Eoe d can be der ived from Eqs. (18) and (20), respectively.

4.2.3 Bearing capacity of spread foundations and piles

Spread foundations The direct appl icat ion of MPT results in the calculation of the bearing resistance of spread foundat ions is an excellent example of how a semi-empir ical calculation method can be systematically conver ted into a s tandard method, see Fascicule 62 and [98]. For instance, the bearing resistance under vertical loads can be de te rmined in accordance with E N V 1997-3, Annex C.1 by the following equation:

R / A ' = ovo + k(PLM -- Po)

where: R = A ' = Ovo =

PLM = Po =

k =

g ~--

L = De =

(25)

resistance of the foundat ion to vertical loads effective base area total initial vertical stress at the level of the foundat ion base representa t ive value of the M6nard limit pressures benea th the foundat ion base Ko(ov - u) + u; with Ko normal ly equal to 0.5, Ov as the total vertical stress at test level and u as the pore pressure at the same depth bear ing resistance factor depending on soil type and PLM; given in E N V 1997-3, Table C.1 as a function of B, L and De width of the foundat ion length of the foundat ion equivalent depth of the foundat ion

ENV 1997-3, Annex C.2 also gives an example for MPT results serving as input to a method for calculating sett lements, which is of special impor tance for spread foundat ion design.

Piles

The bear ing resistance Q of piles can also be de te rmined based on MPT results as follows (ENV 1997-3, Annex C.3):

Q = A - k(PLM -- Po) + PE(qsi • zi) (26)

where: A = base area of the pile equal to the actual area for closed ended piles and par t of

that area for open ended piles PLM = representa t ive value of the limit pressure at the base of the pile correc ted for any

weak layers below

106 Klaus-Jfirgen Melzer and Ulf Bergdahl

Po = Ko(ov - u) + u; with Ko normally equal to 0.5, Ov as the total vertical stress at the test level and u as the pore pressure at the same depth

k = bearing resistance factor depending on soil type, PLM and pile type; given in ENV 1997-3, Table C.4

P = pile perimeter qsi = unit shaft resistance for the soil layer i, given by Fig. C.1 and Table C.5; for both

see ENV 1997-3, Annex C.3 zi = thickness of soil layer i

There are also methods available for estimating the settlement of pile foundations [87, 115]. Furthermore, it is important to note that a series of well-tried methods is available for determining the horizontal resistance of piles [87, 116].

4.2.4 Comparison with the results from other field tests

If the results from lateral pressure tests in accordance with Tables 16 and 17 (including DMT) are used in conventional design, it has to be shown that the geotechnical parameters derived from these results correspond to those parameters used in traditional design methods. This has led to series of investigations to compare geotechnical parameters from lateral pressure tests with those determined from common laboratory tests (e. g. triaxial tests) and from other field tests (e. g. DR SPT, CPT). Examples are given in [43, 99-109, 111].

5 D e t e r m i n a t i o n o f density

5.1 Sampling methods

Field tests for determining the density are important, especially in cohesionless soils, because it is not possible to obtain undisturbed samples from boreholes (see Section 2.4). In Germany, the required tests are standardised in DIN 18125-2. Essentially, all tests follow the same principle: a defined volume of soil is measured in situ and its mass weight is determined. From this the density is given by:

9 = m / V (27)

where: m = mass weight of the sample (moist or dry) V = volume of the sample

Whilst the determination of the mass by weighing is relatively simple, the selection of the method for determining the volume depends on the soil type encountered. For instance, recovering undisturbed samples is possible with sampler tubes from trial pits and the base of excavations, roads, foundations etc. if the soil does not contain gravel, i. e. particles a diameter larger than 2 mm. In this case, the replacement methods should be used, i.e. the cavity produced by the sampling procedure is filled with a standardised replacement material in a standardised way. The volume of the cavity is then determined by the volume of the replacement material necessary to fill the cavity. The different tests are defined by the means of determining the volume of the cavity. Table 19 contains an overview of the different methods.


Table 19. Designation and suitability of tests for volume determination (following DIN 18125-2)

Code Method

A

G

Sch

Designation of test

after DIN 18125-2

Applicable in

Cohesive soils Cohesionless Stones and soils boulders 1)

Cutting DIN 18125-2-F-A Without coarse Fine to medium sands - cylinder grain

Balloon DIN 18125-2-F-B All Fine to medium sands, - gravel-sand mixtures, gravel with little sand

Replacement DIN 18125-2-F-F All Fine to medium sands, - by fluid gravel-sand mixtures,

gravel with little sand

Replacement DIN 18125-2-F-G All Fine to medium sands, - by gypsum gravel-sand mixtures,

gravel with little sand

Replacement DIN 18125-2-F-S All Fine to medium sands, - by sand gravel-sand mixtures

Trial pit DIN 18125-2-F-Sch All Fine to medium sands, All gravel-sand mixtures

1) With little admixtures.

In cases where soils have to be investigated in depths that cannot be reached by the above close to surface methods, the density could be determined by radiometric methods (see Section 5.2), by dynamic probing (including SPT) or by cone penetrat ion tests (see Sections 3.2 to 3.4).

5.2 Radiometric methods

In radiometric methods, the radiation of radioactive isotopes is measured by Geiger coun- ters and the results are correlated to the density and the moisture content of the soil (it was for this reason that the method was formerly called the "isotope penetrometer test"). Two types of radiation methods are used:

1. Gamma radiation (,/radiation), consisting of electromagnetic waves of high energy or gamma particles ('l-7 penetrometer) .

2. Neutron radiation (n radiation), consisting of electrical neutral particles with the mass number i (neutron penetrometer) .

The equipment consists of a radiation source, a detector for measuring the radiation intensity and an impulse counter. The combinat ion of the radiation source and the detector is called a radiometric probe. Two main types of equipment are used: devices for close- to-surface operations, e.g. compaction control ("close-to-surface probes"), and probes


g

o

~o

D0

Dimensions in mm

I ~ o

Q _ _

L Geiger-MiJIler J [ counter

o

Lead shield

I Bortrifluoride ---.~ ] [ counter I -

t Re-Be source--@ ---b-- Ra source /

~o

Fig. 22, Example of a ~,-¥ penetrometer (left hand side) and a neutron penetrometer (right hand side) without radiation protection (after [7])

used for deep investigations of the ground ("depth-probes"). Fig. 22 shows the arrangement of the components for a y-¥ penetrometer and of a neutron penetrometer as depth- probes.

The use of radiometric methods is subjected to legal regulations and legal permission has to be obtained. Regulations for radiation protection control, transport, storage and calibration of the radiometric probes apparently still restrict their use. DIN 18125-2 refers to [117] where the methods are described in detail (definitions, terminology, equipment, calibration, performance of measurements, radiation protection etc.).

Radiometric devices for use at greater depths are sometimes already integrated within the cones of cone penetration penetrometers [12, p. 186 ft., 51-53,118]. For the evaluation, the density p, the water content w and the dry density Pd are plotted against depth (Fig. 23). Their application for the compaction control of fills is well established. The combination with key borings and for example, cone penetration tests [119] results in valuable information about the ground strata of natural soils and their properties. This type of application


Measuring point P25 Water content w 0 0.1 0.2 0.3 0.4 0.,'

° Density [) 1.0 1.5 2.0 w''' ~1.0 and ~d

. 1 .00 Q

o Gravelly sand - - -w

o ~ + G W 2.00

P28

o o.1 0.2 03 0.4 o£

1,511 I ~.0" ' " - '

I I I I

w 'Q'

\

II~t

[ill

Fig. 23. Results of gamma radiation and neutron measurements for determining the natural density 9, the water content w and the dry density Pd

has gained importance recently by combining the radiometric device with CPTU equipment. In general, radiometric methods are suitable for use in cohesionless soils [54, 118]. Examples of their use in clayey soils are reported in [53].

6 Geophysical methods

6.1 General

Geophysical investigation methods can be used in conjunction with key boreholes

• in preliminary investigations of large-scale projects for determining the stratification of the top layers;

• in design investigations, to complement the geotechnical investigation; • for locating geological joints, discontinuities and anomalies in the strata; • for locating historical or unknown objects and cavities in the ground; • for locating seepage and gradients in the groundwater flow; • for determining geophysical parameters; • for controlling contaminated groundwater fronts, salt water fronts etc.

Tables 6 and 7 of Supplement 1 of DIN 4020 give overviews of surface and borehole methods and their characteristics. The interpretation of the test results requires experience and special knowledge. In numerous practical applications it has proven appropriate to combine different independent methods to avoid misinterpretations [120-123]; the cost remains justifiable because the requirements for equipment and personnel are relatively small for most of the available methods.

In Germany, common geophysical methods were investigated on a scientific basis within the framework of an extensive research programme "Methods for the ground investigation and description of landfills and toxic waste deposits". The results were published in [124]. A theoretical study is also available from Finland [125].


"Geophysics" on the Internet:

• Deutsche Geophysikalische Gesellschaft (DGG): http://www-seismo-hannover.bgr.de/dgg/dgg.html

• DMT-Gesellschaft ftir Forschung und Prtffung, Essen: http://www.fp.dmt.de

• Harbour Dom, K61n: http://www.harbourdom.de

• GeoPager: http://www.geopager.de

• Deutsche WWW-Server-Liste der Geologie Clausthal: http://www.inggeo.tu-clausthal.de/geo-server/geoserver-germany.html

6.2 Brief descript ions o f s o m e m e t h o d s

• Soil dynamics and soil seismic testing: see Chapter 1.8 and [12, p. 179, 126]

• Gravimetric methods: the measurement of anomalous deviations, unit is mgal, to explore underground close-to-surface hidden objects or cavities in sufficiently level terrain. The application of gravimetrics should always be combined with other geophysical methods.

• Radiometric methods: see Section 5.2.

• Geo-electric methods: by pushing two electrodes into the ground at a set distance a, a direct current field is created in the soil. Using this field, the specific electric resistivity in [f2m] is determined from the potential difference in a soil mass reaching to a depth of about a/4. Approximate values for the resistivity are given in [127[: rock, solid: > 5000 f2m, rock, weathered: 100-1000 f2m, sand, moist: > 100 S2m, sand, wet: > 50 f2m, silt, moist: > 20 S2m, fresh water: 20 ~2m. An extension of this method consists of pro- gressively increasing the distance of the electrodes outside the measuring probes.

• Geo-radar: Uses a transmitter/receiver antenna (transducer) pulled over the ground surface inducing electromagnetic impulses into the ground. The signals reflected from, for example, the strata boundaries in the ground, are registered. The wave propaga- tion depends primarily on the dielectric properties and conductivity of the ground. At discontinuities, the signal is spread, reflected, inflected and partially absorbed. Approx- imate values for penetration depths in soils: up to 10 m [127].

• Geomagnetic methods: The measurement of anomalies in the ground's magnetic field, caused by a ferromagnetic rock mass or other objects (for example, unexploded bombs, cables etc.). With magnetometers (sensors set at two different heights above the ground; F6rster probe or proton-magnetometer) the intensity and gradient in a vertical plane are measured. A depth of only about 4 m can be reached because measurable values caused by objects decrease with the third power of the depth.

• Electromagnetic methods (TEM): Using a mobile probe, an artificial (reacting to all metals) electromagnetic field is created. After turning off the transmitted current, the voltage induced into a receiver spool is registered. The method is characterised by high measuring speed and insensitivity against technical disturbances. Obtainable measuring depths are similar to those for geomagnetic methods.


• S o i l t h e r m i o n i c s : The m e a s u r e m e n t o f t e m p e r a t u r e anomal i e s be low a dep th of 1.5 m with t e m p e r a t u r e sensors (at dep th inc remen t s of abou t 1 m) p laced in d r iven ho l low rods. Measu r ing accuracy is to 4- 0.1 ° [128, 129]. The p r imary appl ica t ion of this m e t h o d is the loca t ion of leakages in the ground.

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[112] Totani, M., Calabrese, M.: In situ determination of ch by flat dilatometer (DMT). Proc. 1st IC on Site Characterization, Atlanta 1998, Vol. 2, 883-888.

[113] Biarez, J., Gambin, M., Gomes-Correia, A., Flavigny, E., Branque, D.: Using pressuremeter to obtain parameters to elastic-plastic models for sand. 1st IC on Site Characterization, Atlanta 1998, Vol. 2, 747-752.

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Klaus-Jtirgen Melzer and Ulf Bergdahl

Fukagawa, R., Muro, T., Hata, K., Hino, N.: A new method to estimate the angle of internal friction using a pressuremeter test. 1st IC on Site Characterization, Atlanta 1998, Vol. 2, 771-775.

[115] Fujiyasu, Y, Orihara, K.: Elastic modulus of weathered rock of Jurong Formation in Singapore. Proc. 5th Int. Symp. Field Measurements, Singapore 1999, 183-186.

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[117] Forschungsgesellschaft fiir das Stragenwesen: Anwendung radiometrischer Verfahren zur Bes- timmung der Dichte und des Wassergehaltes von B6den. Technische Prtifvorschrift TP B-STB, Part B.4.3, K61n 1999.

[118] Shrivastava, A.K., Mimura, M.: Radio-isotope cone penetrometers and the assessment of foundation improvement. 1st IC on Site Characterization, Atlanta 1998, Vol. 1,601-706.

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[120] Niedermeyer, S., Rahn, W., Effenberger, K.: Ingenieurgeophysikalische Untersuchungen ftir Tun- nelbauwerke an der Neubaustrecke Hannover-Wtirzburg der Deutschen Bundesbahn. DGEG- Symposium Messtechnik im Grundbau, Mtinchen 1993, 4348.

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[122] Gelbke, C., Riikers, E., Swoboda, U: Hochaufl6sende Baugruben- und Baugrunderkundung mit kombinierten geophysikalischen Verfahren im zentralen Bereich Berlin. Vortr~ige Baugrund- tagung Stuttgart 1998, 167-177. Deutsche Gesellschaft ftir Geotechnik, Essen.

[123] Lehmann, B., Falk, C., Dickmann, T.: Neue Entwicklungen zur Baugrunderkundung ftir die 4. R6hre Elbtunnel - Bericht tiber ein Forschungsvorhaben. Vortr~ige Baugrundtagung Stuttgart 1998, 189-200. Deutsche Gesellschaft ftir Geotechnik, Essen.

[124] KnOdel, K., Krummel, H., Lange, G.: Handbuch zur Erkundung des Untergrundes von Deponien und Altlasten, Vol. 3: Geophysik. Springer-Verlag, Heidelberg 1997.

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8 Standards

ASTM D 1586-84: Standard test method for penetration test and split barrel sampling of soils. Amer- ican Society for Testing and Materials, Philadelphia 1992.

ASTM D 4633-86: Standard test method for stress wave energy measurements for dynamic penetrometer testing systems. American Society for Testing and Materials, Philadelphia 1986.

ASTM D 4719-94: Standard test method far pressuremeter testing in soils. American Society for Test- ing and Materials, Philadelphia 1994.


BS 1377: Part 9: British standard methods of test for soils for civil engineering purposes. Part 9: In situ tests. British Standards Insitution, London 1990.

DIN 1054: Baugrund - Sicherheitsnachweise im Erd- und Grundbau. Draft, 2000.

DIN EN 1536: Ausftihrung von besonderen geotechnischen Arbei ten (Spezialtiefbau) - Bohrpf/~hle, 2000.

DIN4020: Geotechnische Untersuchungen ftir bautechnische Zwecke; einschl. Beiblatt 1: Anwen- dungshilfen, Erl~iuterungen, 1990 (New edition in preparation).

DIN 4021: Baugrund - AufschluB durch Schiirfe und Bohrungen sowie Entnahme von Bodenproben, 1990 (New edition in preparation).

DIN 4022-1: Baugrund und Grundwasser - Benennen und Beschreiben von Boden und Fels; Schicht- enverzeichnis ftir Bohrungen ohne durchgehende Gewinnung von gekernten Proben im Boden und Fels, 1987.

DIN 4022-2: Baugrund und Grundwasser - Benennen und Beschreiben von Boden und Fels; Schicht- enverzeichnis far Bohrungen im Fels (Festgestein), 1981.

DIN 4022-3: Baugrund und Grundwasser - Benennen und Beschreiben von Boden und Fels; Schicht- enverzeichnis fiir Bohrungen mit durchgehender Gewinnung von gekernten Proben im Boden (Lock- ergestein), 1982.

DIN 4023: Baugrund - und Wasserbohrungen; Zeichnerische Darstellung der Ergebnisse, 1984.

DIN 4030: Beurteilung betonangreifender W/~sser, B6den und Gase (2 Teile), 1991.

DIN4094: Baugrund - Erkundung durch Sondierungen, einschl. Beiblatt 1: Anwendungshilfen, Erkl~irungen, 1990.

DIN 4094-1: Baugrund - Felduntersuchungen, Teil 1: Drucksondierungen. Draft, 2001.

DIN 4094-2: Baugrund - Felduntersuchungen, Teil 2: Bohrlochrammsondierung. Draft, 2002.

DIN 4094-3: Baugrund - Felduntersuchungen, Teil 3: Rammsondierungen. Draft, 2001.

DIN 4094-4: Baugrund - Felduntersuchungen, Teil 4: Flagelscherversuche. Draft, 2001.

DIN 4094-5: Baugrund - Felduntersuchungen, Teil 5: Bohrlochaufweitungsversuche, 2001.

DIN 4096: Baugrund - Flfigelsondierung; Mage des Ger~tes, Arbeitsweise, Auswertung, 1980.

DIN 18125-2: Baugrund - Untersuchung yon Bodenproben, Bestimmung der Dichte des Bodens, Part 2: Feldversuche, 1999.

DIN 18196: Erd- und Grundbau - Bodenklassifizierung far bautechnische Zwecke, 1988.

EN 1997-1: Eurocode 7, Geotechnical Des ign- Part 1: General Rules (in preparation for 2002; German edition: DIN EN 1997-1).

ENV 1997-2: Eurocode 7, Geotechnical Design - Part 2: Design Assisted by Laboratory Testing, 1999 (German edition: DIN V ENV 1997-2).

ENV 1997-3: Eurocode 7, Geotechnical Design - Part 3: Design Assisted by Field Testing, 1999 (German edition: DIN V ENV 1997-3).

Fascicule 62: R~gles sur techniques de conception et de calcul des foundation des ouvrages du g~nie civil. Fascicule 62 Titre V, 1993. Minist~re de l 'Equipment, du Logement et des Transport, Paris.

NF P94-110: Essai pressiom6trique M6nard, AFNOR, Paris la Defense, 1998.

geotechnical engineering handbook - chapter 1-3

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