ISC2 Session 1: Mechanical in-situ testing methods

Marcelo. Devincenzi Igeotest, SL, Spain.

John J. M. Powell Centre for Structural and Geotechnical Engineering, Building Research Establishment, Watford, United Kingdom.

Nuno Cruz Mota-Engil, Engenharia e Construes, SA; Faculdade de Cincias e Tecnologia da Universidade de Coimbra, Portugal.

Keywords: in situ test, characterisation, investigation programme, standards

ABSTRACT: The objective of this report is to introduce ISC2 Session 1 Mechanical in-situ testing meth-ods. A general prologue is made stressing the potential of geotechnical/geoenvironmental in situ testing andthe importance of global standards that will ensure that tests are carried out with consistency, a subject ofprime importance to transfer experience from one country to another or develop generic correlations. A widerange of parameters can be reliably obtained from in situ testing and it is noticeable that the ratings of sometests have improved as the database of experience has built up, but others have declined as the initial predic-tions of their capability have been found to be wanting. Effort is required in order to improve the situation and get the best from existing tests. The papers presentedto Session 1 are an example of this fact. The 20 papers, from 13 different countries around the world, cover awide range of topics and uses of in situ tests and this variability is a good example of their versatility and use-fulness for a ground investigation programme provided the right test is selected for the situation and the equipment and procedures allow repeatable and quality data to be obtained.

1 INTRODUCTION

Successful geotechnical design and construction re-quire a good knowledge of the mechanical behaviour of the ground including its spatial variability. The requisite information is gathered as part of a ground investigation programme.

The objective of any subsurface exploration pro-gramme is to determine the following:

1. Nature and sequence of the subsurface strata

(geological regime) 2. Groundwater conditions (hydrogeological re-

gime) 3. Physical and mechanical properties of the sub-

surface strata (engineering regime) For geo-environmental site investigations of

ground contamination there is the additional re-quirement to determine the

4. Distribution and composition of contaminants

(geoenvironmental regime)

These requirements vary in volumetric extent de-pending on the nature of the proposed project and the perceived ground related risks. There are many

techniques available to meet the objectives of a ground investigation and these include both field and laboratory testing of the ground. Laboratory tests include those that test elements of the ground, such as triaxial tests and those that test prototype models, such as centrifuge tests. Field tests include drilling, sampling, in-situ testing, full-scale testing and geo-physical tests.

An ideal ground investigation (GI) should include a combination of laboratory tests, primarily to clas-sify the ground, and field tests, primarily to deter-mine engineering parameters.

Field and laboratory techniques should be viewed as complementary rather than competitive. In situ tests can, however, often offer significant advan-tages over laboratory tests, for example:

they can be quicker, easier and cheaper than sam-

pling and laboratory testing, the soil can be assessed in its natural environment

without the potential problems of sample distur-bance,

and the spatial variability of the deposit can be more fully investigated. Table 1 (from Lunne et al 1997) is an updated

version of a table originally devised in the early

Preprint : ISC2, 2nd International Conference on Geotechnical Site

Characterization, Porto, Sept. 2004

Table 1: The applicability and usefulness of in situ tests. Lunne et al., 1997

Soil Parameters Ground type

Gro

up

Device

Soil

Type

Prof

ile

u *

Su

I D

mv c v k G

0

h

OC

R

Har

d ro

ck

Soft

rock

Gra

vel

Sand

Silt

Cla

y

Peat

Dynamic C B - C C C - - - C - C - - C B A B B B Mechanical A A/B - C C B C- - - C C C - - C C A A A A

Electric (CPT) B A - C B A/B C - - B B/C B - - C C A A A A Piezocone (CPTU) A A A B B A/B B AB B B B/C B C - C - A A A A

Seismic (SCPT/SCPTU) A A A B A/B A/B B AB B A B B B - C - A A A A Flat Dilatometer (DMT) B A C B B C B - - B B B C C C - A A A A

Standard (SPT) A B - C C B - - - C - C - - C B A A A A

Pene

trom

eter

s

Resistivity probe B B - B C A C - - - - - - - C - A A A A Pre-Bored (PBP) B B - C B C B C - B C C C A A B B B A B Self boring (SBP) B B A1 B B B B A1 B A2 A/B B AB2 - B - B B A B

Pres

sure

-m

eter

s

Full displacement (FDP) B B - C B C C C - A2 C C C - C - B B A A Vane (FVT) B C - - A - - - - - - B/C B - - - - - A B Plate load C - - C B B B C C A C B B B A B B A A A

Screw plate C C - C B B B C C A C B - - - - A A A A Borehole permeability C - A - - - - B A - - - - A A A A A A B

Hydraulic fracture - - B - - - - C C - B - - B B - - C A C

Oth

ers

Crosshole /Downhole / Surface seismic C C - - - - - - - A - B - A A A A A A A

Applicability: A = high, B = moderate, C = low, -= none * = will depend on soil type; 1 = only when pore pressure sensor fitted; 2 = only when displacement sensor fitted. u = in situ static pore pressure; = effective internal friction angle; su = undrained shear strength; mv = constrained modulus; cv = coefficient of consolidation; k = coefficient of permeability; G0 = shear modulus at small strains; OCR = overconsolidation ratio; - = stress-strain relationship; ID = density index

1980s and presents a list of some of the major in-situ tests and their applicability for use in different ground conditions. If this table were compared with the earlier versions it would be noticeable that the ratings of some tests have improved as the database of experience has built up, but others have declined as the initial predictions of their capability have been found to be wanting. There is little doubt that the levels of applicability given in Table 1 can now be attained or exceeded provided the tests are selected and used correctly. This applies to all levels of in situ testing from the simplest basic tests such as dy-namic probing and the SPT, through tests such as the CPT and piezocone (CPTU), to the more complex devices such as the self-boring pressuremeter (SBP). Table 1 shows that a wide range of parameters can be reliably obtained from in situ testing. Ideally we would want all assessments in Table 1 to be A and researchers and others continue to strive to raise the levels of applicability however this may not always be achievable if there is a fundamental weakness in the appropriateness of the test.

It would appear that many practitioners have felt that too often the capabilities of in situ tests have been over-sold or inappropriately applied. This has resulted in dissatisfaction when the tests failed to

deliver what was promised. The fact that we continue to see papers with more and more correlations for in situ devices often does little to improve this feeling; however it is often not the test that is as fault but its operation and application. Before anything else the results from and in situ test must be repeatable within the bounds of ground variability. There must be consistency in both equipment and operation wherever it is specified and used not just in one country but around the world and this is particularly important if we are to transfer experience from one country to another or develop generic correlations.

We have seen with the CPT how the realisation of the effects of porewater pressure on measured cone resistance has enabled both consistency of results between devices and reduced scatter in developed correlations.

In the SPT we have over the years seen how the results can show significant scatter resulting not simply from the simplicity of the test and operator influences but more importantly from how equipment variations, and particularly the energy input from different equipment, influences the results. Several papers covering this specific topic are presented in Session 1 and commented upon

below. The latest CEN/ISO specification for the test now requires knowledge of the actual energy being delivered by the equipment not just a theoretical value.

2 REALISING THE FULL POTENTIAL OF IN SITU TESTING

So how can we improve the situation and get the best from existing tests without developing new ones? Firstly, whoever is specifying a ground investiga-

tion programme should always consider in situ testing.

they should at least have a basic understanding of the various tests and their strengths (and weak-nesses or limitations).

they should be able to select the right test for the situation and once a decision has been made then be able to specify the correct equipment and pro-cedures for achieving the desired results. They need standards available to them that will ensure that the tests are carried out with consistency (NB. For confidence in the results there must al-ways be a way of checking the quality of the data determined).

they should also consider whether additional in-formation might be required later, for example as a result of design changes. (It may well cost very little extra to gather that data at the same time thus avoiding having to make the best of the original data or incurring remobilisation costs later). We are seeing increasingly in some countries and

in CEN and ISO standards currently in preparation, that specifications for test procedures are now trying to help guide the specifier, for example having various specified classes of accuracy for CPT based on soil type and data use (profiling or soil parameters). Furthermore, we should be encouraging accreditation procedures for in situ testing. If current practice has resulted in cost cutting and bad practice, then this should be firmly discouraged even if some small additional costs are incurred. Two detailed papers dealing with ISO/CEN standards are presented in Session 1 and commented upon below.

With in situ testing we have at our disposal very powerful tools that can yield a great deal of valuable information as part of a well planned GI provided they are specified and used correctly. We should not be specifying them without due thought to the end result and the reliability we can put on the data gathered. The lessons learnt from the past must be used to ensure that as other in situ tests are developed they are validated with reliable databases and that specifications and procedures allow their full potential to be developed.

We do not all have to be experts in in situ testing but a sound understanding of the test methods and equipment, coupled with improved specifications and better guidance will ensure that the engineer is able to realise the full potential of these tests.

By selecting the right configuration of tests, in situ testing will give 4 main advantages over the traditional combination of borings, sampling and other testing, namely:

1. continuous or near continuous data 2. repeatable and reliable data 3. speed of operation (potential for shorter GI time-

scales) 4. cost savings.

It should also be remembered that the power of in

situ tests is not restricted to soil parameter determination; there are also many examples of their use in indirect design applications where parameters unique to a particular test type can be used directly in design procedures.

3 REVIEW OF PAPERS

Twenty papers from 13 different countries are pre-sented in Session 1 covering a wide range of topics and uses of in situ tests as can be seen in Table 2. This breadth is a good example of their versatility and usefulness for a ground investigation pro-gramme. Some of the more relevant items are pre-sented below. 3.1 International and European Standards International and European standards currently in preparation are the main subject of two papers pre-sented to Session 1. As stated above, international standardisation is of prime importance in order to harmonise the quality requirements for equipment as well as methodologies in order to enable comparable results to be obtained. Table 3 briefly summarises the Technical Committees involved in CEN and ISO and the ongoing standards and technical specifica-tions (TS) they are producing.

The paper by Eitner et al. describes in detail the general framework of committees belonging to the International Organisation for Standardisation (ISO) and the European Committee for Standardisation (CEN) and their labours to prepare common standards on equipment and methods used for soil and rock identification, drilling, sampling, field and laboratory testing as well as groundwater measurements for geo-engineering practice. The paper by Stlben et al. deals exclusively with standards on sampling by drilling and groundwater measurements.

Table 2: Session 1 by tests & subject summary of papers

3.2 Standard Penetration Test As can be seen in Table 2, special interest is paid by several papers to the instrumentation of the SPT test in order to determine the energy transmitted from the falling hammer, which is in accordance with the current CEN ISO procedures (EN ISO 22476, Part 4 in Table 3).

3.2.1 Instrumentation of SPT: Energy Efficiency Transmitted energy to the rods by SPT hammer blows is highly dependent on different aspects such as the type of hammer, rod length, blow rate and en-ergy calculation methods. Three papers to ISC2 two from Brazil and one from Korea- report investigations in this field using nearly the same

Test N of papers Authors Main subject & Notes

V. Eitner, R. Katzenbach & F. Stlben

ISO & EN standards on Geotechnical investigation and testing for site characterisation: current framework in European countries. See Table 3.

Standards 2

F. Stlben, V. Eitner & H. Hoffmann

ISO & EN Standards on Geotechnical investigation and testing for site characterisation: sampling by drilling and groundwater measurements. See Table 3.

E. Odebrecht, F. Schnaid, M.M. Rocha & G.P. Bernardes

Energy ratio with instrumentation of system. Different location of sen-sors. Effect of rod length analysed. New approach to define Energy effi-ciency. See Table 4.

Dong-Soo Kim, Won-Seok Seo & Eun Scok Bang

Energy ratio with instrumentation of system. Different hammers. Force waveforms and factors affecting efficiency analysed. See Table 4..

E.H. Cavalcante, F.A.B. Dan-ziger & B.R. Danziger

Energy ratio with instrumentation of system. Manual donut hammer. Dif-ferent ranges of Nspt blow count with different behaviours. See Table 4.

A.S.P. Peixoto, D. de Carvalho & H.L. Giacheti

CPT-T: CPT with torque measurement. Electrical torquemeter. State of the art in Brazilian practice. Suggestion of test procedure. Comparison of 4 methods to predict pile capacity based on CPT-T.

SPT 5

C.R. Daniel, J.A. Howie, R.G. Campanella & A. Sy

Characterisation of SPT grain size effects in gravels.

V. Whenham, N. Huybrechts, M. De Vos, J. Maertens, G. Simon & G. Van Alboom

CPT case study with comparative analysis of results using 3 types of me-chanical cones (mantle cone, Begemann cone and simple cone with clos-ing nut) and electrical cone. Ratios of cone resistance qc mech / qc elec pre-sented.

S.G. Fityus & L. Bates CPT case study assessing parameters on expansive residual clay at Mary-land, where others data available. Thickness and identification of expan-sive soil as well as degree of weathering of basal rock.

D.J. Balbi & F. Saboya Jr. CPTU case study with statistical treatment of data to identify soil groups in Quaternary soils north Rio de Janeiro. Cluster analysis using Bq and Qt (normalised net qT) as variables as Hegazy & Mayne (2003).

M.F. Silva & M.D. Bolton Centrifuge model to investigate sensitivity of CPTU to layering effects and grain size at different penetration rates under different loading condi-tions & permeabilities.

S.M. Fairuz, J. Rohani & T. Lunne

CPTU off shore case study. Characterisation of sands, NC clays and OC clays at four locations in South China Sea. Nkt of fine grained soils 15 to 20 recommended.

CPT 6

F.A. Trevor & P.W. Mayne CPTU & lab tests case study in marine clays in Southeast Asia to esti-mate OCR and Su using Mayne (1991) method based on cavity expan-sion theory and critical state concepts. Determination of correction fac-tors for this method.

CPT&DMT 1 P.W. Mayne & T. Liao CPT-DMT interrelationships in Piedemont Residum: ID f(FR%), ED f(qT). Equivalent CPT method developed for obtaining constrained modulus.

DMT 1 A. Arulrajah, M.W. Bo & H. Nikraz

DMT test case study in soft marine clays under pre-load improvement treatment. Dissipation testing with DMT to determine ch and kh as a tool to evaluate degree of consolidation of pre-loaded area using Bo et al. (1977) method.

A. Fakher & M. Khodaparast Dynamic penetration in cohesive soft soils. Correlation N E. DP 2 A.M. Rahim & K.P. George Dynamic penetration to estimate subgrade resilient modulus.

DP & PLT 1 A. Arbaoui, R. Gourvs, Ph. Bressolette, L. Bod

Determination of in situ deformation modulus with a penetrometer. Method. Deformation, at depth load test described.

PBP & PLT 1 A. Agharazi & M. Moradi Comparison between plate load test results and dilatometer test results. FVT 1 H. hnberg, R. Larsson & C.

Berglund Influence of vane size and equipment on the results of field vane tests. Method. Different equipment used and commented. Disturbance effects.

Table 3: ISO and CEN framework standards in geotechnical site investigation. Compiled after Eitner et al. and Stlben et al. Technical Committees (TC) &Sub-committees

(SC) Goals Standards

ISO/TC 182/SC 1 Geo-technical Investigation and Testing

Prepares standards on identification, de-scription and classification of soils and rocks. International mirror of CEN/TC 341.

ISO 14688-1 to 3 Geotechnical investigation and testing Identification, description and classification of soil

Part 1: Identification and description. 2002. Part 2: Classification principles. 2003. Part 3: Electronic exchange of data of identification and description of soil. Technical Specification: TS. Under development

ISO 14689-1 to 2 Geotechnical investigation and testing Identification and classification of rock

Part 1: Identification and description. 2003. Part 2: Electronic exchange of data of identification and description of rock. Technical Specification (TS): Under development.

CEN/TC 341 Geotechni-cal Investigation and Test-ing

Standardization in equipment and methods used for drilling, sampling, field and laboratory testing of rock and soil as well as groundwater measurements. In co-operation with ISO/TC 182/SC 1. Five working groups: Drilling and sampling methods and

groundwater measurements. Germany (DIN). See Stlben et al.

Cone and piezocone penetration Tests. Netherlands (NEN)

Dynamic probing and SPT. Germany (DIN)

Testing of geotechnical structures. France (AFNOR)

Borehole expansion tests. France (AF-NOR)

Several standards on field investigation in preparation will be published: EN ISO 22475-1 to 3 Geotechnical investigation and testing Sampling by drilling and excavation and groundwater measurements

Part 1: Technical principles for execution Part 2: Technical qualification criteria for enterprises and personnel Part 3: Conformity assessment of enterprise and per-sonnel

EN ISO 22476 1 to 16 Geotechnical investigation and testing Field testing

Part 1: Electrical cone and piezocone penetration tests Part 2: Dynamic probing Part 3: Standard penetration test Part 4: Mnard pressuremeter test Part 5: Flexible dilatometer test Part 6: Self-boring pressuremeter test Part 7: Borehole jack test Part 8: Full displacement pressuremeter test Part 9: Field vane test Part 10: Weight sounding test (TS) Part 11: Flat dilatometer test (TS) Part 12: Lefranc permeability tests Part 13: Water pressure tests Part 14: Pumping tests Part 15: Mechanical cone penetration test Part 16: Plate loading tests

CEN/TC 250/SC 7 Geo-technical Design

Eurocode 7, the base code for geotechnical design. Test results are used for evaluation and interpretation leading to derived values.

ENV 1997-1 (European pre-standard), soon available as EN. ENV 1997-2, design assisted by laboratory tests. ENV 1997-3, design assisted by field-testing.

Figure 1: Configuration of instrumented SPT test. Dong-Soo Kim et al.

instrumentation consisting of strain gauges & accel-erometers with a data acquisition system to measure force and velocity in order to evaluate the maximum energy delivered to the rods. Typical configuration is shown in Figure 1. Table 4 summarises the main topics of these investigations.

Odebrecht et al. observe that the theoretical maximum potential energy PEh+r* delivered to the soil should be expressed as a function of the nomi-nal potential energy (E* = 0.76.Mh.g = 0.76m*63.5kg*9.801m/s = 474J), the permanent sampler penetration and the weight of both hammer and rods, that is:

gMgMPE rhrh ++=+ )76.0(* (1)

Table 4: Instrumented SPT for energy ratio assessment

Author Odebrecht, Schnaid, Rocha & Bernardes Cavalcante, Danziger & Danziger Dong-Soo Kim, Won-Seok Seo & Eun Scok Bang

Type of instrumenta-tion

Load cell with 4 strain gauges sensitive to axial strains only. 2 accelerometers of different range

Strain gauges and piezoelectric accelerometers

8 strain gauges in full bridge and 2 accelerometers

Analysed parameters Force and acceleration (integrated to velocities)

Force and velocity Force and velocity

Location of sensors Just below the anvil Above the sampler Attached to rod, middle position between anvil & sampler

0,5 m below the anvil some near the sampler

Just below the anvil

Computational method FV FV FV & V2 compared Type of hammer Manual pin guided Donut hand operated with rope 4 types compared:

donut hydraulically lifted (WD) chain automatic (CA) manual safety w/rope (RS) manual donut w/rope (RD)

Theoretical energy 478 J 478 J 474 J Type of soil Granular with different DR% Different types 10 to 15 m of weathered soil Nspt blow range 10 to 60 1 to 60 Main results / findings / contributions

Instrumentation at depth, above the sampler. Energy delivered to the spoon is influenced by both test depth and actual penetration. New concept and definition of ef-ficiency accounted by 3 empirical coefficients, 1, 2, 3, being 1 function of rod length and in-versely proportional to the length of the rods

Transmitted energy to the rod fount to be 83% of 474 J nominal energy (ISSMFE, 1989). Previous works in Brazil showed 70% ef-ficiency (energy ratio). Ranges of Nspt with different be-haviour found, 1-6, 7-16, 18-60. Correlations Ncorr/N for these values.

Wave shapes of each hammer. Effects of rod length & blow speed. Energy ratios for each hammer type. Energy ratios from FV method larger than F2 one: 70% and 60% respectively for CA ham-mer. Efficiency depends on type of hammer, rod length, blow rate and energy calculation method.

where Mh is the hammer weight, Mr the rod weight, g the gravity acceleration and sampler penetra-tion under one blow.

The first part of equation (1) represents the ham-mer potential energy (nominal + additional) and sec-ond the rod potential energy. In other words, both length of the rods and permanent spoon penetration contribute to the theoretical energy delivered to the sampler. This becomes significant in loose soils where is high. This factor is independent of the length of the rods.

Energy losses take place during the penetration process. The energy ratio ERr or efficiency is tradi-tionally defined as the ratio between the actual maximum delivered energy Er (i.e. instrumentation) and the nominal potential energy, E*:

*EEER rr = (2)

It is generally accepted to correct the Nspt result

to a reference energy value of 60% of the potential nominal energy of the SPT hammer using standard correction factors (Seed et al., 1985; Skempton, 1986; ISSMFE 1989). However, these corrections assume a theoretical energy input and by using in-strumented tests the correct adjustment of the meas-

ured Nspt value to the value with a reference energy ratio such as N60 can be made.

A new concept of efficiency is postulated by Odebrecht et al. These authors present experimental results of energy measurement in SPT tests carried out under controlled boundary conditions in a cali-bration chamber and the effective energy measured at the top and the bottom of the rods during impact of hammer. They conclude that efficiency is ac-counted for by three coefficients, 1, 2, 3 using:

[ ]gMgMPE rhrh ++=+ 213 )76.0( (3)

where 1, the hammer efficiency, is obtained from measurement at the top of the rod stem, 2 can be assumed as unity and 3, the energy efficiency, is expressed as a function of the length of the rods l, being inversely proportional to them:

l0042.013 = (4)

3.2.2 SPT-T procedure & practice The state of the art in Brazilian practice and proce-dure suggestion for SPT-T test is presented by Peixoto et al. The use of the SPT with torque meas-urement, that required to turn the sampler, was pro-

posed by Ranzini (1988), being the torque as a kind of static component of a dynamic test. The torque is empirically used to estimate pile skin friction mainly for driven piles, being the T/Nspt ratio an in-teresting index for practical purposes, though spe-cific local correlations are needed.

General suggestions for test procedure are re-viewed in Table 5; Figure 2 presents an example of a test with an electric device and data acquisition sys-tem. Oscillations in the curves are due to lateral movements of the rods.

Four methods for predicting bearing capacity of piles based on SPT-T are summarised and discussed by Peixoto et al. (Decourt, 1996; Alonso, 1996a, 1996b; Carvalho et al., 1998 and Peixoto, 2001).

Table 5: SPT-T test general procedure according Peixoto et al. Topic Recommendations Notes Procedure After penetration,

an adapter is placed on the anvil for the torquemeter to twist. A centralising de-vice needed to avoid rod lateral movements.

Torquemeter of proper capacity must be used. Torquemeter hori-zontal during rota-tion. Alignment of rods during applica-tion of torque im-portant key.

Measurements Maximum and re-sidual torque must be logged.

Mechanical creep-ing pointer torque-meter provides enough information.Readings immedi-ately after driving sampler.

Rotation speed 5 turns/minute

Figure 2: SPT-T plot after Peixoto et al.

3.3 Dynamic penetration Fakher & Khodaparast present a study about the re-peatability of Mackintosh probe at three sites in Iran. This equipment is a lightweight portable handy penetrometer which is still widely used. The authors also present a local correlation between N10cm and su. (errata: they do however incorrectly quote the corre-lation of Butcher et al, quoting the relationship be-tween su dynamic point resistance for stiff clays and not soft). Their correlation is lower than Butchers i.e. more blows for the same shear strength and this

may be the result of torque and friction not being eliminated with this simple device. It should be noted that the Mackintosh probe is not covered by the new dynamic probing standard in Table 3.

Another paper by Rahim & George presents a correlation to obtain subgrade resilient modulus from N. 3.4 CPT and DMT tests A total of 8 papers dealing with CPT(u), flat dila-tometer (DMT) and CPT-DMT combined investiga-tion are presented to Session 1 (Table 1).

3.4.1 Mechanical CPT Although electrical CPT(u) is nowadays more com-monly used -and recommended by current stan-dards- mechanical devices are still in use in some countries. Whenham et al. present a comparative analysis in Belgium soils establishing ratios qc mech/qc elec for different mechanical devices (mantle cone, friction sleeve mantle cone and simple cone) and different types of soils. Care is needed in extrapola-tion to other electrical cones and soil types as qc is used and not qt and so the results from the electrical cone in clays will be specific to that cone type as they are not corrected for pore pressure effects (Lunne et al 1997).

3.4.2 Soil profile interpretation The excellent profiling capability of the CPT(u) test is a well recognised feature in the Geotechnical industry. Recent research has also shown that the CPT(u) is a powerful tool for the sedimentological study of delta sediments, even allowing an under-standing of how climatic changes and associated sea level changes during Late Quaternary took place (Amorosi & Marchi., 1999; Devincenzi et al., 2003, 2004).

Three papers related to this subject are presented to Session 1 describing investigations on statistical analysis as a helpful tool to use in layered strata, lo-cation and depth of expansive soils and evaluation of the degree of weathering in residual massifs.

Balby & Saboya present a case study using the statistical method based on similarity criteria on normalised Q and Bq (Hegazy & Mayne, 2003) to identify soil groups in Quaternary soils. The inter-pretation is based on cluster analysis, which has a better capacity in detecting changes that could not be detected by direct observation or classification charts, having three important advantages:

1. Organise soils by similarity. 2. Locate boundaries between layers. 3. Identify lenses and mixed soils. 4. Identify systematic errors as rod changes or cas-

ual pauses during the test.

Fytius and Bates present another interesting ap-plication of CPT in residual expansive clays. In fact, residual soils have a characteristic behaviour, which is not yet well understood. However, characterisa-tion of these soils usually is no more than the basic one. The data usually required for foundation design in expansive soils are:

1. Thickness and position of the layers. 2. Swell potential. 3. Depths of suction and cracks (active layer). 4. Magnitude of suction.

In the proposed approach the CPT results are

used to give either direct or indirect estimates of the thickness of the top soil, the position and thickness of expansive clay layers and the depth and degree of weathering of underlying rock.

3.4.3 Centrifuge penetration Silva & Bolton present research on the use of CPTu tests carried out in centrifuge models to observe the effect of layering of sand layers at different penetra-tion rates and under different loading conditions and permeabilities. The data are used to discuss the methodology of characteristic grain size interpreta-tion and the use of viscous fluid in centrifuge tests.

3.4.4 Assessing undrained shear strength and OCR of marine clays from CPTu

Trevor & Mayne present a modification of Maynes 1991 method based on cavity expansion theory and critical state concepts to predict both the overcon-solidation ratio (OCR) and undrained shear strength from CPTu tests.

The predicted values of su and OCR for marine clays soils using Mayne (1991) method are higher than reference triaxial compression tests values, though the interpreted CPTu profiles and the labora-tory test profiles show similar trends.

The correction factors to improve the piezocone data interpretation method incorporating the critical state parameter (M) were derived by Trevor (2001) on the basis of statistical evaluation and are desig-nated as:

OCR = (0.029+0.409M) and : SU = (0.56+0.095M) Modified equations that can be used to predict

OCR and su in these soils from CPTu tests can be written as:

33.1

'0

2

195.112

+=

v

tOCR

uqM

OCR

(5)

1 10 100Overconsolidation ratio (OCR)

26

24

22

20

18

16

14

12

10

8

6

4

2

0

Dep

th (

m)

past pressure estimateMayne 1991oedometers pile areaoedometers eng props cpt 0.3 normalised coneTrevor and Mayne 2004

20 502 5

Figure 3. OCR profile for glacial till site using Trevor and Mayne method.

+

=

19.122

MuqMs tsuu (6)

These corrections imply limited sensitivity to M

for the correction for su, the range is 0.48 0.43 as changes from 20 to 35o, whilst for OCR the change is more significant ranging from 0.35 0.61. Powell (2001) showed very good agreement for OCR with the original equation i.e. a correction fac-tor of 1, but Figure 3 shows results for a glacial till site (Powell and Butcher, 2002) with both the old and new correlations. It can be seen that the correc-tion improves the predicted OCR profile but is still too high; the use of a simplified normalised cone re-sistance approach is seen to give a very good fit . Trevor and Mayne recommended to re-evaluate the proposed correction factors for other types of soil and this will be important in understanding when to apply it.

3.4.5 CPTu DMT interrelationships The main advantages of tests like CPT/CPTU and DMT are related to cost effectiveness and fast col-lection of data which permits statistical and numeri-cal analysis. Thus, it is possible to quickly get in-

formation to be used in the powerful numerical models with good enough quality to give a compati-ble input to the models that does not lower their effi-ciency.

It should be stressed that combined (DMT+CPT/U) characterisation campaigns offer an approach to new possibilities to explore situations unresolved by each test in isolation, both in sedi-mentary and residual soils. Both tests, when used to-gether in regular campaigns, can offer an improve-ment both in geological and geotechnical determinations. The combination of both tests pre-sents the following advantages:

1. Cross checking of the same parameters. 2. Complementary data resulting from both tests. 3. Combination of basic parameters from both tests,

offering the possibility of assessing data that oth-erwise could not be deduced. With regards to geotechnical information, the

combined tests can allow the determination of pa-rameters related to stress history, strength and de-formability, permeability and consolidation proper-ties, liquefaction potential, etc. in a continuous manner.

The quantity and quality of information obtained from both tests leads to a better knowledge of soil characteristics, as well as numerical information for design practice.

Interrelationships between CPTu and flat dila-tometer (DMT) in Piedemont residual soils that are comprised of silty fine sands to fine sandy silts are investigated by Mayne & Liao who propose:

tD qE 5= (7)

and

%14.00.2 FRI D = (8)

ED being the dilatometer modulus and ID the mate-rial index obtained with DMT test.

The same subject was studied in a research pro-gram based on the results from 7 investigations per-formed in the region between Porto and Braga (Por-tugal), with a total of 30 borings, 22 CPTU profiles and 23 DMT profiles (Cruz et al, 2004). The region under study is characterized by granitic residual saprolitic soils with a flocculated structure, loose to medium compacted and with a grain size distribution that varies from sandy silts to sands (very similar to Mayne experimental site). The results obtained led to the following conclusions, related to this subject:

M/qt (where M is the constrained modulus calcu-lated from the DMT as M = RM ED) seems to have more potential than ED/qt, since the RM (cor-relation factor between ED and M could be seen as a selection parameter for the type of soil; in

fact, M parameter is calculated based on 3 basic DMT test parameters, i.e. the calculation is de-pendent on the type of soil (ID) and on KD (which seems to reflect the cementation structure), be-sides the dilatometer modulus ED; this seems to be very helpful to work with a wider range of soil types;

M/qt is not a constant value, but tends to increase with the cementation structure in a similar man-ner to the one proposed by Marchetti (1997) to distinguish NC (M/qc = 5 -12) from OC sands (M/qc = 12 24); Cruz et al (2004) found two dif-ferent M/qt correlations in residual soils when working on NC and OC sides equal to 6,4 and 16,8, respectively; of course these can be sub-divided, but this is a basic well known fron-tier of mechanical behaviours, which can be used as a reference (Figure 4);

The overall ED data in the study ranges from 0,1 to 6,0 MPa, while ED/qt falls within the interval 1 20; in general ED/qt around 5 to 6 represents the division between NC OC; Analysing data indi-vidually (from each of the 7 experimental sites) it becomes clear that the relation ED/qt changes with the level of cementation, as well as M/qt, and the results range from 2 to 7;

In conclusion it could be said that both relations are clearly not a constant value but increases with the strength due to cementation effects; the relation M/qt shows a high correlation factor when used to deduce cohesive intercept due to cementation struc-ture (Cruz et al, 2004). In that sense Maynes data would be a local correlation that reflects a particular level of cementation structure. The use of M/qt seems to have a higher potential than ED/qt since in-tegrates the numerical definition of type of soil through identification index from DMT (ID).

0.0

40.0

80.0

120.0

160.0

0.0 5.0 10.0 15.0 20.0

qt (MPa)

M (M

Pa)

NC OC Potncia (NC) Potncia (OC)

Figure 4: M/qt for NC and OC (Cruz et al, 2004). Considering the ID - Fr relation, the general data

given by Cruz et al. (2004) are not as well fitting as Mayne & Liaos. Nevertheless, results seem to con-verge, since the global analysis gives 1,92 0,05 Fr and if intersection is forced to 2 then it is 2 0,06 Fr. Analysing data separately and forcing the inter-section at 2, then 3 of the experimental sites show a

variation of Fr dependent term varying between 0,06 and 0,1. At other sites it is not possible to find any particular trend line.

Data from OC clays slightly cemented in Girona (Spain) also show a good agreement with Mayne & Liaos ID-Fr proposed relationship, OCR ranging from to 3 to 6 and M/qt 25.

On the contrary, no relation could be found be-tween ID and Fr in Quaternary pro-delta silty clays (OCR 1.1) with silt intercalations as can be seen in Fig. 5. It must be stressed that these sediments are not of the same nature as those studied by Mayne & Liao.

0

1

1

2

2

3

3

4

4

0 1 2 3 4 5 6FR%

I D

Figure 5: ID vs. Fr in Quaternary pro-delta silty clays in Barce-lona, Spain.

3.5 Influence of Vane size on results of vane tests Vane test results are affected by several factors such as the effect of disturbance at insertion, the effect of waiting before starting the test, the shape of the rup-ture surface, influences of the rate of rotation, the length of the vane shaft protruding below the casing for the vane, the number of blades and the relation between height and diameter of the vane, among other aspects

Research on the influence of the size of the vane on the results of the vane test -an important fact that has no effect on the standards yet- and a comparative analysis of different equipment available on the market today are presented by hnberg et al. A de-tailed listing of different factors affecting the results is also outlined.

The results of the investigation showed that for tests in clay the larger the vane size, the higher the shear strength, provided that the thickness of the shafts and wings are the same. The small vane (55x110mm2) showed shear strengths that were only about 85% of those obtained with the normal vane (65x130mm2). Figure 6 shows the comparison.

This can be related to the fact that the relative in-fluence of the disturbance at installation of the vane increases with decreasing vane size.

Figure 6: example of results from parallel vane tests in clay with different vane sizes. hnberg et al.

This effect is counteracted in organic soil owing to the fibre content, this may result in the opposite trend. 3.6 Deformability tests Arbaoui et al. present an experimental device which permits performing static loading tests when the penetration is paused. The test allows the establish-ment of monotonic or cyclic stress-displacement curves to obtain deformation modulus.

A case study making a comparative analysis of plate load tests (PLT) and dilatometer (i.e. rock pressuremeter) tests results in rock masses are pre-sented by Agharazi & Moradi. These two methods, the two prevailing for rock deformability assess-ment, do not result in an equal value of deformation modulus. The authors present empirical ratios be-tween them.

4 CONCLUSIONS

Successful geotechnical design requires a good knowledge of the mechanical behaviour of the ground and in situ tests are no doubt powerful tools that can yield a great deal of valuable information. A wide range of parameters can be reliably obtained from in situ testing and it is noticeable that the rat-ings of some tests have improved as the database of experience has built up, but others have declined as the initial predictions of their capability have been found to be wanting.

Effort is required in order to improve the situation and get the best from existing tests. International (i.e. global) standards are a subject of prime impor-tance that will ensure that tests are carried out with consistency in order to enable comparable results to be obtained, a key matter to transfer experience from one country to another or develop generic correla-tions. There must be consistency in both equipment and operation wherever it is specified and used not just in one country but around the world. Session 1 detailed the present efforts being made by the Inter-national Organization for Standardisation (ISO) and the European Committee for Standardisation (CEN).

Furthermore, we should be encouraging accredi-tation procedures for in situ testing. If current prac-tice has resulted in cost cutting and bad practice, then this should be firmly discouraged even if some small additional costs are incurred.

On the other hand, it would appear that many practitioners have felt that too often the capabilities of in situ tests have been over-sold or inappropri-ately applied. This has resulted in dissatisfaction when the tests failed to deliver what was promised. The fact that we continue to see papers with more and more correlations for in situ devices often does little to improve this feeling. However it is often not the test that is as fault but its operation and applica-tion.

The papers presented to Session 1, from 13 dif-ferent countries around the world, cover a wide range of topics and uses of in situ tests. This wide range is a good example of their versatility and use-fulness for a ground investigation programme pro-vided the right test is selected for the situation and the equipment and procedures allow repeatable and quality data to be obtained.

The papers have shown that there is still value in improving our understanding and operation of exist-ing tests before indulging in evermore sophisticated techniques.

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