Sample Disturbance of a Soft Organic Dutch Clay

Sample Disturbance of a SoftOrganic Dutch Clay

CO-710203/20 version 1march 2001

Sample Disturbance of a Soft OrganicDutch Clay

CO-710203/20march 2001

rap.monsterverstoring

By order of :DELFT CLUSTER

STRATEGIC RESEARCH DEPARTMENTGEODELFT

Project manager : dr.ir. E.J. den HaanProject supervisor : ir. J. de Feijter

GeoDelftStieltjesweg 2, 2628 CK DELFT

Postbus 69, 2600 AB DELFTThe Netherlands

Telephone (+31) 15 - 269 35 00Telefax (+31) 15 - 261 08 21

Postal account 234342Bank MeesPierson NVAccount 25.92.35.911

Report no.: CO-710203/20 Date report: march 2001

Department: Strategic Research Department, GeoDelftTitle and subtitle:Sample Disturbance of a Soft OrganicDutch Clay

Project: "Gedrag van Klei en Veen"

Project manager(s): dr.ir. E.J. den HaanOther project members:A. van Slingerlandir. J. Tigchelaardr. Ph. Reiffsteck (L.C.P.C. Paris)

Project supervisor(s): ir. J. de Feijter

Reference client: 10203

Copies sent:

Name and address of client:Delft Cluster

Type report: research Summary of report:Comparative laboratory testing has been performed on Oostvaardersplassen clay which has been sampled by three differentmethods, to establish the relative degree of sample disturbance. The common Dutch tube sampling method, the continuous DelftBegemann sampler and the Laval sampler have been compared. The laboratory tests performed were UU, CIU and CAU triaxial testsand Ko-C.R.S. oedometer tests. Suction was measured in some triaxial samples prior to the testing and also comparatively evaluated.The high quality Laval sampler was taken to produce largely undisturbed behaviour and this was used as benchmark for the Dutchsampling methods.

The tests indicate that the effects of sampling disturbance are limited.This result is not unexpected, as these clays have a high plasticity and it is known that highly plastic clays are less susceptible tosampling disturbance . Nevertheless it is reassuring to establish that the common Dutch sampling methods can be used, not only forroutine testing, but also for advanced fundamental research.

Taking advantage of the large diameter of the Laval samples and the possibility this gives to take subsamples immediately adjacent toeach other, additional issues were addressed: the effect of sample diameter on triaxial test results, and the difference betweenresults for subsamples taken from the perimeter and from the centre respectively. Both effects are significant: smaller diametersubsamples yield higher strength, and the central subsample is weaker than those from the perimeter. However, the latter conclusionneeds more substantiation.

The testing programme yielded as extra spin-off a rather complete set of data on the stress - strain behaviour of natural organicOostvaardersplassen clay. The high angle of internal friction found in earlier tests on such clays was substantiated, and for the firsttime evidence was found for a very low value of normally consolidated K o value in such soils.

Comments:

Keywords:Sample disturbance, soft clay, organicclay, Laval sampler, Begemann sampler,tube sampler, triaxial test, Ko oedometertest, Constant Rate of Strain, suction,structure of clays

Distribution:prof. Verruijt (T.U. Delft),prof. Magnan (L.C.P.C.),ir. A.H. Nooy - van der Kolff (Boskalis),ir. H.L. Bakker (Rijkswaterstaat),drs. A. Bizzarri (Rijkswaterstaat),dr.ir. P. van den Berg (GeoDelft)

Saved:Title: \\DG-SV6\DHA\dha\DelftCluster\Monsterverstoring\rapport710203.20Sample Disturbance of a Soft Organic Dutch Clay.docmonsterverstoring

No. of pages:27

Version: Date: Prepared by: Signature: Checked by: Signature:1 march 2001 E.J. den Haan J. de Feijter

GeoDelft

TABLE OF CONTENTS

1 Introduction 1

2 Site description and soil characteristics 1

3 Sampling methods 23.1 Ackermann tube sampling 23.2 Continuous Begemann (or Delft) sampling 33.3 Laval sampling 3

4 Test programme 54.1 The Ko-C.R.S. oedometer 54.2 U.U. triaxial tests 64.3 C.I.U. triaxial tests 74.4 C.A.U. triaxial tests 7

5 Overview of tests, and general soil properties 7

6 Results and evaluation - suction tests 10

7 Results and evaluation - triaxial tests 13

8 Results and evaluation - Ko-C.R.S. tests 15

9 Effects of Diameter and Sample Position 16

10 General evaluation and conclusion 17

11 References 18

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1 Introduction

In the Netherlands, samples of soft organic clay and peat for laboratory testing are most commonlyobtained from continuous Begemann (Delft) borings or discontinuous Ackermann tube borings. Thesesoils are usually quite plastic and as it is well-known that the effects of sampling disturbance aresmaller in more plastic soil, it has always been thought that sample disturbance in Dutch organic claysis limited and could essentially be ignored. In the project described in this report, this assumption istested by comparative laboratory tests on Begemann, Ackermann and Laval samples taken from anorganic clay in the Oostvaardersplassen near Almere. The Laval samples are taken to represent a highquality with which to benchmark the usual methods.

The laboratory tests performed are the following:- Unconsolidated undrained (U.U.) triaxial tests with measurement of pore pressure- Isotropically and anisotropically consolidated (C.I.U. and C.A.U.) triaxial tests, some with

measurement of initial suction- Ko-C.R.S. oedometer tests

In addition to the comparative tests with regard to different samplers, the large diameter of the Lavalsamples, 20cm, was taken advantage of to investigate the effect of different subsample diameter ontriaxial results. Further, the influence of the location of the subsample within the Laval sample, centreor perimeter, was investigated.

The tests reveal only slight differences between the three sampling methods, and no significantinfluence on the measured strength parameters. For routine testing certainly, and for fundamentalresearch on consolidated samples, the usual Dutch sampling methods suffice.

The testing programme was rather complete in studying the stress - strain behaviour, making itsuitable for evaluation of the geotechnical properties. High initial specific volume v o , high internalfriction angle ϕ´ and low coefficient of lateral stress Ko in the normally consolidated state arepoignant features of the established behaviour.

2 Site description and soil characteristicsThe site which was chosen to obtain the samples of organic clay, is located in the reclaimed polderSouth Flevoland, immediately north of the city of Almere, in a nature reserve namedOostvaardersplassen. The soil layer under study lies between depths of 1.2 and 2.6 m belowgroundlevel, and is a highly organic, slightly silty soft clay. It is covered by a surface layer of 1.2 mthickness of very silty clay. Groundwater level is at approximately 0.85 to 1.0 m below groundlevel.

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A full description of the soil profile is given in GeoDelft report "Project Klei en Veen - VerslagMonstername", nr. CO-710203, july 2000. A geological description of the soft upper layers at the siteis given in GeoDelft Memo "Geologie Oostvaardersplassen site", 12 april 2001 by J. Tigchelaar.

Figure 2.1 shows profiles of bulk density and loss - on - ignition. The samples of the present studywere taken in the depth range from 1.6 to 2.4 m - G.L. Bulk density generally decreases with depth,and loss - on - ignition increases. The natural water content of the samples ranged from 127% to197% ; the bulk density from 1.23 to 1.32 t/m3. Such variations are inevitable in natural organic soils.The values for each test sample are given further on.

Geological evidence has it that the clay in study is a part of the Almere deposits which were formed inpredominantly fresh water in the period 900 B.C. to 1600 A.D. The Zuiderzee deposit formed afterthis period was subjected to increasingly salt water conditions by the widening of the sea entrance tothe Almere lake. The layers underneath the clay in study are extremely organic and are redepositedremnants of an approximately 3m thick sedge peat layer which covered the area and was erodedduring the formation of the Flevo lake around 1200 A.D. The increasing content of organic matterwith depth in the depth range in study is explained by this redeposition.

3 Sampling methods

3.1 Ackermann tube samplingAckermann tube sampling is one of the most common methods in the Netherlands of obtaining soilsamples for laboratory testing. It consists of hammering a thin-walled tube into the bottom of a holepreviously formed by shell boring. The tube dimensions are: Inner diameter 67mm, wall thickness 0.8mm, length 440mm. The cutting edge is external and is sharpened to approx. 20-25°. The nominalarea ratio is 6.1%. Stainless steel tubes are used to reduce wall friction and increase tube longevity.The cutting edges of used tubes are often bent inwards, which compromises cutting angle, area ratioand sample quality. Used tubes were employed in this project, but it was assured that the cuttingedges were straight.An outward bulging collar 3mm wide is formed in the tube at 47mm from the top end to grip the tubeinto the shell boring equipment. A ball valve is incorporated in the sampler head to allow air andwater to escape during penetration of the tube into the soil. Effective sample length is 300mm.Continuous sampling was used at the site, with the hole carefully being cleaned out by the shell aftereach tube withdrawal. A casing with internal diameter 110mm was used. Water level in the boreholewas kept at slightly below ground level. Sample recovery was virtually 100%. After sampling, thetubes were sealed with plastic caps and transported upright in crates to the conditioned storage facilityat the laboratory.

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3.2 Continuous Begemann (or Delft) samplingThe continuous Begemann sampler was developed by GeoDelft in the 1960's and early 1970's. SeeBegemann (1971) for a full description. It allows continuous samples of soft soil to be obtained in onesingle operation. Sample lengths of 10 - 15m are common. A cross section of the sampler is shown inFigure 3.1. The soil is cut by a cutting shoe at the tip of a thick-walled tube (1) of 90 cm length. Thecutting shoe has an inner diameter of 66 mm and a height of some 58 mm. After being cut, the sampleis immediately enclosed by a specially produced nylon stocking which unfolds from a storagechamber. This chamber is formed between the outer wall and a so-called stocking tube (2). An innerp.v.c. liner (3) receives the enclosed sample. Penetration is stopped every 1m to screw on new lengthsof outer tube and liner. Drilling fluid is applied through the annulus between (2) and (3). It penetratesthrough the holes marked A to form a lubrication layer between the stocking-coated sample and theliner. Often, drilling fluid is also applied into the liner, providing a second pathway to this layer.

Once at the desired depth, a catch (B) is activated which presses into the liner at 90 cm above the tip,to prevent loss of the sample during retraction. The sample is extracted in 1 meter lengths and storedin the p.v.c. liners, which are sealed by plastic caps. The 90 cm length of soil beneath the catch isoften retained and can be used in the same manner as the soil above it. In the laboratory, the samplessimply slide out of the liners and the stocking is cut away. No force whatsoever is applied to thesamples in this stage.

An inside clearance exists between the nylon stocking and the p.v.c. liner of 0.5 - 1%. The area ratioof the Begemann sampler, determined for the maximum cross section, is approximately 160%, and thecutting angle is approximately 11° near the tip. The high area ratio is offset by positive aspects suchas

* during cutting, friction occurs along a length of only 58mm rather than full sample length, andfriction in the liner is minimal,

* no suction is used during cutting (as e.g. is the case with fixed piston sampling),* the suction created during severing of the sample from the soil mass affects sample quality

only in a small length of soil at the tip of the boring which can be rejected if necessary* no force is necessary to recover the sample from its liner.

One less desirable feature is that the sample can swell in the liner by drawing moisture out of thelubrication fluid through the stocking. Even though the nylon stocking is coated, it is still porous andpermeable. The lubrication fluid which forms a film between stocking and liner is probably subject tohydrostatic pressure, so that swelling of the sample could be limited by choosing a fluid with a highdensity.

In this project, the lubrication fluid was given a high density, 1.8 t/m3, in the upper layer of silty clay,and 1.05 t/m3 in the layer of interest.

3.3 Laval samplingThe Laval sampler is described in La Rochelle et al. (1981). It was developed to minimize samplingdisturbance in the sensitive soils of Eastern Canada. It has gained recognition throughout the world as

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an instrument which yields high quality samples, second only to those obtained by the so-calledSherbrooke blocksampler (which also originates from Eastern Canada). Figure 3.2 is a cross sectionthrough the sampler and Figure 3.3 shows its mode of operation. The sampling tube has a diameter of208 mm and a sharp outside cutting edge of 5°. Wall thickness is 5 mm, and no inside clearance isused. Area ratio is 9.8%. The sampling tube is 660mm long. The sampling tube is closed at its head bya head valve which is operated by a steel rod. It is open during penetration into the soil to allow waterand air to exit the sampler, and it is closed before retraction so that suction can develop to aidretention of the sample if it tends to fall out.

After penetration of the sample tube, a coring tube which is concentric with the sample tube is used to"overcore" the sample tube. The coring tube has an external diameter of 273 mm and is operated bymeans of a drilling rod. At the head of the coring tube there is a hook-up device for the sample tube.At the bottom, sharp teeth and cutters are fixed to remould the soil during coring. External andinternal guides are fixed lengthwise to the corer to keep it concentric with the sampler during coring.The external guides and cutting teeth increase the external diameter to 302 mm. The overcoringoperation prevents suction occurring at the bottom of the sample during retraction by providing accessof atmospheric pressure to the tip of the boring.

No drilling fluid other than water is used. The water level in the hole is kept close to ground level.Before retracting the sampler, it is twisted over 90° to separate the sample from the soil below it.

The samples are extracted from the tube immediately after recovery to the ground surface. Samplesare extruded from the tube and cut to the desired length. The sample is placed on a piece of plywoodboard and wrapped by a sample-wrapping technique developed by Laval University. In this techniquethe sample is very thoroughly wrapped, providing complete isolation to air and moisture. It isaccepted as making long storage possible without significant detrimental effects on sample quality. Itconsists of enclosing the sample by a few alternating layers of Saran wrapping foil and a mixture ofparaffin wax and vaseline. The plywood board too is waxed before the sample is placed on it.

The sampling was performed by Laboratoire Central de Ponts et Chaussees of Paris under thesupervision of Dr. Ph. Reiffsteck. A photo report of the sampling in the Oostvaardersplassen area isgiven in Figure 3.4. Figure 3-4a shows the overcoring tube in the foreground and the sampling tube inthe background. In Figure 3-4b a recovered sampling tube is being to carried to a press, Figure 3-4c bywhich the sample is extracted from the tube. The top and bottom sections (some 5 cm length) arediscarded, and a length of approximately 22cm is placed on a plywood board, Figures 3-4d and 3-4e,which has been treated with wax. Figure 3-4f shows the application of wax and foil to the sample andFigure 3-4g shows the samples reading for transport to the laboratory.

Figure 3-4h shows a Laval sample cut through. Spoiled soil is to be seen on top, which illustrates thatcare is necessary to ensure a completely clean borehole before sampling. Another obvious feature ofthe photograph is the slanted layering and the different colours. The samples therefore are nothomogeneous, and this alone would result in variation in measured results from different samples,quite apart from the effects of sampling method.

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4 Test programme

The comparative tests performed on the three kinds of samples were* Ko-C.R.S. oedometer tests* U.U. triaxial tests* C.I.U. triaxial tests at a consolidation pressure of 25 kPa* C.A.U. triaxial tests at vertical consolidation pressures of 50 and 100 kPa, and K o ratios of 0.5Most tests were performed in duplicate. Suction was measured in some C.A.U. tests prior to thetriaxial testing. Suction was also evaluated for the U.U. tests and both sets of suction values were alsocomparatively evaluated to establish the influence of sampling method.

Further, advantage was taken of the availability of the large Laval samples to investigate* the influence of subsample diameter on the behaviour in C.A.U. tests* the influence of subsample location within the sample, i.e. perimeter or centre.Sample diameters of 38mm, 50mm and 65mm were tested in C.A.U. tests at 100 kPa consolidationpressure. Most samples were taken from a single Laval block, making direct comparison of the resultspossible. One sample of 50mm diameter taken from the centre of this block allowed to investigate thepossible influence of position of the sample within the block.

4.1 The Ko-C.R.S. oedometerThe Ko-C.R.S. oedometer is shown in detail in Figure 4.1 and more schematically in Figure 4.2. It wasdeveloped at GeoDelft in a project funded by Rijkswaterstaat, Dienst Weg- en Waterbouwkunde, andhas been improved for the current project. It measures the coefficient of lateral effective stress K o

during Constant Rate of Strain. Ko is defined as

´´

v

hoK

σσ

=

where σ´,h is effective horizontal stress, and σ´,v is effective vertical stress.

The sample (diameter 63mm, initial height 20mm) is placed in an oedometer ring made of titanium.The ring has a wall thickness of 5mm, but is turned down to 0.6mm over a section of 7mm length.This section is instrumented on its outer surface with strain gauges to pick up the deformation due tothe lateral stress in the sample. The strain gauge readings are translated to lateral stress by calibrationwith air pressure in the ring, for which a special device was made. This device fits in the ring andforms an air-tight chamber within it which can be pressurized.

The sample/ring assembly is placed in a triaxial cell. Load on the piston can be controlled in variousways, and constant rate of displacement is used in the Ko tests. This has come to be termed ConstantRate of Strain (C.R.S.) although Constant Rate of Deformation would be more accurate. It would berelatively easy to adopt true Constant Rate of Strain by feedback control of the rate of deformation,adjusting (decreasing) rate of deformation as deformation increases.

An internal load cell measures applied vertical load. A second load cell is placed under the sample tobe able to deduce wall friction on the oedometer ring. The sample drains upward to the triaxial cell

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during compression, and a back pressure is applied to the cell fluid to improve sample saturation. Porepressures are measured at the base of the sample.

The thin measuring section of the oedometer ring is placed at midheight of the sample. This allows32.5% vertical strain before the sample compresses below the thin section and the calibrationbecomes uncertain. By assuming a parabolic distribution of excess pore pressure, the average porepressure on the thin section can be determined. This is subtracted from the lateral stress read by thestrain gauges to obtain σ´,h . The total vertical stress σv is determined from the average of the upperand lower load cell readings, and σ´,v is obtained by subtracting the excess pore pressure at the thinmeasuring section from σv .

To minimize sample disturbance by trimming into the ring, the ring is placed in a specially madecutter with a sharp cutting edge. Top and bottom faces are trimmed in the cutter and the porousdrainage stones placed on either end. Lateral stress, the force on the lower load cell and suction aremeasured from the moment the ring/sample assembly is placed on the pedestal. Later on, cell pressureand the upper load cell are measured from the moment they come into play.

The oedometer ring rests on a vertically adjustable ring, which makes it possible to achieve goodcontact between the sample and the pedestal. The weight of the ring can be conducted away from thepedestal.

4.2 U.U. triaxial testsIn the U.U. (unconsolidated, undrained) triaxial tests, the cell pressure was first raised in 4 steps ofeach 25 kPa to a value of 100 kPa.Then the samples were sheared. Undrained conditions were maintained throughout.

Both stages - undrained application of cell pressure and undrained shear - provide information whichallows for comparative evaluation. During the undrained raising of the cell pressure in 4 steps, theresponse of the pore pressure indicates the degree of saturation. The cell pressure is applied in steps:25, 50, 75 and 100 kPa. Each step is maintained until equilibrium of the pore pressure is reached. AB-value can be determined from the results. An initial suction of the sample is found by back-extrapolation to zero cell pressure of the relation between the applied cell pressure and the porepressure. Both B and initial suction us can be used as a comparative parameter of the various samplingtechniques.

The suction pressure remaining in the samples is an indication of the amount of sampling disturbance.In soft, contractive soils, suction is considerably less than the in-situ isotropic effective stress

´iosu σ<<where the index o indicates in-situ conditions. Not only the release of total isotropic and deviatoricstress plays a role, but also the disturbance due to sampling and sample handling.

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The resulting effective pressure at the cell pressure of 100 kPa depends on the initial suction and theB-value according to

)(100)1(´3 kPaBus −+=σThis pressure determines the initial condition for the shear stage and influences the shear strength.The undrained shear stage is performed at a rate of axial strain of 5% per hour. The effective stresspath, shear strength and stress - strain behaviour can all be evaluated comparatively.

4.3 C.I.U. triaxial testsIsotropically consolidated undrained triaxial tests were performed at a consolidation pressure of 25kPa. The rate of shear in the undrained shearphase was 5% axial strain per hour.

4.4 C.A.U. triaxial testsAnisotropically consolidated triaxial tests were performed at vertical effective consolidation stressesof 50 kPa and 100 kPa. A Ko value of 0.5 was chosen for the anisotropic condition. This value wasassumed to represent the normally consolidated condition in the clay. It was eventually establishedthat this value is too high.

Prior to the triaxial testing, the suction in a number of the C.A.U. samples was measured. This wasdone simply by placing the sample on the pedestal which is equipped with a saturated porous stoneconnected to a pressure measuring device. The porous stone and pore water measuring system is filledwith de-aired water, and care is taken to achieve a good connection between sample and stone. Nofree water is allowed to stand on the porous stone before placing the sample, to avoid unnecessarywetting and loss of suction of the sample. The level of water in the porous stone is chosen just underits surface. The air entry value of the porous stone is at least 100 kPa and is amply sufficient toprevent entry of air from the sample into the measuring system at the suction values encountered.

5 Overview of tests, and general soil properties

Table 1 lists all tests and gives particulars such as type of sampler used, depth of sample belowground level, diameter and height of the samples as they were tested, initial total density ρO (t/m3) andvarious determinations of water content. The value wo is found from cuttings left over from trimming,and is not accurate because of the large variation in water content in this soil. The value w c iscalculated from wo and takes account of the loss of moisture during consolidation in the triaxialapparatus. The value wf is determined on the sample after testing and removal from the apparatus.This is done fairly quickly, so it can be taken as the water content during the undrained shear stage.The value wo,corr is backcalculated from wf using wc and wo:

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Table 1 Overview of tests and general sample properties

Test type Sampler Boring - Depth Diameter ρo wo wc wfinal wo,corr vo vc

Block/ m - G.L. - Height t/m3 - - - - - -

Sample nr mm

UU Laval 7-38A 1-85 - 2.10 65 -150 1.266 1.627 1.627 1.706 1.706 4.998 4.998

UU Laval 7-38B 1-85 - 2.10 65 -150 1.265 1.651 1.651 1.693 1.693 4.984 4.984

UU Tube 1-21A 2.20 - 2.40 65 -150 1.244 1.962 1.962 1.843 1.843 5.272 5.272

UU Tube 2-26A 2.20 - 2.40 65 -150 1.239 1.973 1.973 1.888 1.888 5.351 5.351

UU Begemann 2-7C 2.25 - 2.42 65 -150 1.237 1.789 1.789 1.902 1.902 5.377 5.377

UU Begemann 3-14C 2.21 - 2.41 65 -150 1.226 1.931 1.931 1.962 1.962 5.503 5.503

CIU 25 Laval 7-38C 1-85 - 2.10 65 -150 1.262 1.628 1.466 1.545 1.712 5.019 4.774

CIU 25 Tube 1-20A 1.80 - 1.95 65 -150 1.272 1.670 1.513 1.390 1.539 4.742 4.524

CIU 25 Begemann 2-7A 1.81 - 1.98 65 -150 1.320 1.624 1.501 1.281 1.394 4.370 4.214

CAU50 Laval 7-38D 1-85 - 2.10 65 -150 1.264 1.602 1.278 1.366 1.703 5.001 4.508

CAU50 Laval 7-38E* 1-85 - 2.10 65 -150 1.272 1.535 1.253 1.271 1.555 4.767 4.350

CAU50 Tube 2-25B* 1.95 - 2.10 65 -150 1.261 1.679 1.364 1.381 1.698 5.006 4.541

CAU50 Tube 1-20B 1.95 - 2.10 65 -150 1.269 1.724 1.327 1.296 1.687 4.958 4.389

CAU50 Begemann 3-14B* 1.96 - 2.11 65 -150 1.237 1.621 1.279 1.251 1.588 4.949 4.427

CAU50 Begemann 2-7B* 1.98 - 2.15 65 -150 1.267 1.581 1.256 1.379 1.721 5.014 4.516

CAU100 Laval 7-37A* 1.60 - 1.85 65 -150 1.295 1.472 0.948 0.978 1.510 4.620 3.864

CAU100 Laval 7-37E* 1.60 - 1.85 65 -150 1.296 1.455 0.952 1.018 1.538 4.652 3.917

CAU100 Tube 2-25A* 1.80 - 1.95 65 -150 1.314 1.372 0.912 0.977 1.453 4.472 3.812

CAU100 Begemann 3-14A* 1.81 - 1.96 65 -150 1.298 1.535 1.111 1.094 1.515 4.615 4.020

CAU100 Laval 7-37B* 1.60 - 1.85 50 - 100 1.313 1.482 1.031 1.012 1.458 4.482 3.862

CAU100 Laval 7-37C*x 1.60 - 1.85 50 - 100 1.305 1.477 1.013 1.035 1.504 4.575 3.917

CAU100 Laval 7-37D* 1.85 - 2.10 50 - 100 1.311 1.447 0.996 1.000 1.452 4.480 3.850

CAU100 Laval 7-37F 1.60 - 1.85 38 - 85 1.302 1.468 0.981 1.003 1.495 4.572 3.880

CAU100 Laval 7-37G 1.85 - 2.10 38 - 85 1.302 1.478 1.013 1.006 1.469 4.536 3.882

Ko-CRS Laval 38 63 1.276 1.548 0.788 1.461 4.617

Ko-CRS Laval 34 63 1.310 1.274 0.982 1.464 4.501

Ko-CRS Tube 21B 2.15 - 2.20 63 1.251 1.794 0.968 1.841 5.237

Ko-CRS Tube 26B 2.15 - 2.20 63 1.246 1.846 1.076 1.824 5.235

Ko-CRS Begemann 7B 2.20 - 2.25 63 1.244 1.831 1.035 2.006 5.482

Ko-CRS Begemann 14B 2.16 - 2.21 63 1.230 1.820 0.908 1.642 5.053

* Suction measured prior to testx From centre of Laval Sample

c

cofofcorro w

wwwwww

+−++

=1,

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On Laval block sample nr. 34, determinations of specific gravity , loss on ignition and CaCO 3 contentwere made

Gs = 2.463L.O.I. = 14.33%CaCO3 content 11.1%

The Gs determination was by means of helium displacement. L.O.I. was determined by heating at500°C during 4 hours. The L.O.I. test is followed by heating at 900°C during 2 hours. The associatedloss of mass is ascribed to CO2 , from which the CaCO3 content is calculated.

Note that Figure 2-1 shows L.O.I. and γtot to vary with depth. Individual values of L.O.I. were notdetermined for all samples. Use can be made of the correlation of L.O.I. with either γtot or wo . Suchcorrelations were produced for this project by J. Tigchelaar jr. on the basis of very intensivemeasurements. γtot , wo , L.O.I. and Gs were determined every 8cm on a Begemann boring. Thecorrelation

Gs = 2.73 - 0.23 wo [t/m3]

was found, with a regression factor R2 of 0.88. Using this correlation, the initial specific volume vo

(i.e. voids ratio eo+1) can be estimated. Further, vc after consolidation in the triaxial tests, which holdsduring the undrained shearing stage, can be found. Both values are given in the table.

Figure 2.1 shows an approximately linear decrease with depth of bulk density:

2.6mz ][kN/m 52.23.18 3 ≤∀−= ztotγ

so that

2.6mz ][kN/m 26.13.18 22 ≤∀−= zzvσ

Effective stresses vary with the fluctuation in ground water table. An equilibrium level at 0.8 m belowg.l. is assumed. In the investigated range between 1.6 and 2.4 m-G.L., this gives:

Table 2: Approximate bulk density and vertical in-situ stresses

depth γtot σv σv´m-G.L. kN/m3 kPa kPa

1.60 14.3 26.1 18.22.40 12.3 36.7 21.0

Comparing the estimated range of bulk density with that of the tests, it will be seen the latter aregenerally somewhat smaller. The stresses in Table 2 may therefore slightly overestimate the truevalues.

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Figure 5-1 shows the depth profiles of initial specific volume vo and initial uncorrected water contentwo of all test samples, as function of the sampling method. There is a general trend for increasing v o

and wo with depth, and there is no clear difference between the three sampling methods visible. Thevariability at a given depth can be established from the Laval samples taken from a single block. It isquite large, and lies on the high side of the variability found from different sampling methods.

A tendency is seen in Figure 5-1(b) for the tube samples to yield high uncorrected water content. Thecorrected water content profiles wo,corr are different and are more akin to those of vo . There is too littledata to conclude that the tube samples are indeed generally wetter.

6 Results and evaluation - suction testsThe results and evaluation of the suction measured in the test samples prior to the triaxial testing areshown in Figures 6.1 - 6.4. In Table 1 the C.A.U. tests are indicated with an asterisk in which thesuction was measured directly by the pore pressure measurement system after the sample was placedon the pedestal. The results are shown in Figure 6.1. The remaining figures pertain to the evaluationof suction and B-factor in the U.U. tests, in which the suction us was determined by backextrapolation to zero cell pressure of the cell pressure - pore pressure relationship found during the 4stepwise increases of the cell pressure: 25, 50, 75 and 100 kPa. Note that direct measurement ofsuction did not take place in the U.U. tests.

Figure 6.1(a) shows the development of suction in a number of C.A.U. triaxial test samples. The largescatter in values both for a given test and between different tests is obvious. The test was notperformed under temperature control, and Figure 6.1(b) shows the variation of suction with thetemperature of a water bath placed in the testing room, of Laval sample 38E. The dots indicate fulldays after start of measurement. Temperatures fluctuate by approx. 3°C per day, and there is atendency toward the development of a fixed hysteresis loop, after the suction has fully developed.Approximately 70 h are necessary (see Figure 6.1(a)) for the full development of suction.

The tests on the tube samples were terminated earlier than those on the other samples and the finalvalue of suction in these samples is unsure. They could possibly be lower, as the rate of developmentup to the end of the test is on the low side of the measured range. There are no evident differences inthe rate of development or the magnitude of measured suction between Laval and the Begemannsamples.

During the initial stages of the U.U. tests, cell pressure was applied undrained in 4 steps of 25 kPaeach. Figure 6.2(a) shows the applied cell pressure and the measured response of pore water pressure(termed "drain pressure" as it is measured on the sample drainage line, albeit in undrained state) forLaval sample 38A. 5 stages of cell pressure occur: the initial stage after filling the cell with water, andthe application of 4 pressure steps of each 25 kPa. The response of pore water pressure is notcompletely equal to the applied cell pressure, indicating a slightly unsaturated condition of thesample. In Figure 6.2(b) the equilibrium values of cell pressure and drain pressure are plotted for thesame sample. The 5 data points define a linear relationship given by

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)(3 kPaBuu s σ+=

where u is pore pressure, σ3 is cell pressure and us and B are the linear constants. us is an estimate ofthe initial suction present in the sample, and B is one of the Skempton pore pressure coefficients. B isan indication of the degree of saturation, being 1 in completely saturated (soft) soil. The linearconstants have been determined by linear regression for all the U.U. samples, see Figure 6-3. Theobtained us and B values per sample are correlated in Figure 6-4(a). It appears that this correlation ismore or less linear.

In comparing the range of inferred suction values in Figure 6-4(a) with the range of directly measuredvalues in Figure 6-1(a), the duration of the cell pressure increments in the U.U. tests, approx. 1 h,must be taken into account. After 1 h the values in Figure 6-1(a) are still increasing, and the rangeafter 1 h, approx. 1 - 3 kPa, increases to a final range of 2 - 5 kPa. Figure 6-4(a) shows a range of 1 -4.7 kPa after 1 h. This corresponds more or less to the final range of initial suction, and the appliedperiod of 1 h to equilibrium in Figure 6-2(a) is considered sufficient.

Comparatively, in the U.U. test samples, Laval samples have high saturation and high initial suction.The Begemann samples can be either high or low, while the tube samples have low saturation and lowinitial suction. If the parameter B is used as a relative indication of sample quality, Figure 6-4(a)shows the Laval samples are superior, and the tube samples inferior. The Begemann samples arevariable and can have values in the range of the Laval samples as well as falling close to the tubesamples.

Evaluation of Skempton's B-parameterB is a measure of sample saturation. It presumably approaches 1 in-situ, although gasses will bepresent due to decomposition of organic material and the close proximity to the ground water table. Alower value in the samples would not be a result of sampling itself, as in these contractant clays, thestresses associated with sampling should, if anything, compact the clay and increase water content.Sample handling is the most likely cause of any differences. The Laval samples are very well sealed,and this is probably the cause of their high B-value. Begemann samples are not sealed but remain inthe stocking until being processed in the laboratory, after which they are stored in cling foil. In thestocking, both swelling (samples attract moisture from the lubrication fluid through the stocking) anddessication can occur. Some dessication can occur during processing. Processing of the Begemannsamples involved geological description of the layers, bulk weight determination per m 1, and otheractivities, and dessication could have been larger than for the other methods. This may explain thevariability of B in the Begemann samples. The tube samples are not well sealed. Only a plastic cap isapplied to the sampling tube. Some dessication could well occur.

Correlation of us and BAs B indicates the degree of saturation, the apparent correlation of u s and B in Figure 6-4(b) wouldexpress that us decreases with decreasing saturation. This requires consideration, as the oppositemight also be expected. The suction in a sample develops as a result of the following processes:a. release of in-situ deviatoric stressb. release of in-situ isotropic total stressc. insertion (soil displacement) of the sampler

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d. friction forces exerted on the soil by the samplere. stresses during sample handling and trimmingf. dessication or swelling after sampling, dependent on ambient moisture condition.The factors a. and b. result in a pore pressure through Skempton's pore pressure equation:

)}({ hvh ABu σσσ ∆−∆+∆=∆where ∆u is the change in pore pressure, A and B are Skempton's pore pressure parameters, and ∆σv

and ∆σh are the change of the vertical and horizontal total stresses. Knowing

ovo

oho

v

ho

hoh

vov

os

uuK

uuu

−−

=′′

=

−=∆−=∆

∆+=

σσ

σσ

σσσσ

then

''

)1()}1({vo

ooo

vo

s uBKAKBuσσ−

−−+=−

B is usually put to one in most literature where this equation is derived, leaving

' )1( oovo

s KAKu

σ−+=

−

The B value to be inserted in this equation is the in-situ value, which need not be the same as thatmeasured in the U.U. tests. "Perfect sampling" is a term used to express the influences of processes a.and b. on sample suction, and the above equations quantify perfect sampling. These processes shouldnot lead to differences between the various sampling methods.

Adding to this the effects of process c., an "Ideal" sample is obtained. In soft soil, which is usuallycontractant, the processes c., d. and e. usually result in decreased suction. Dessication will increasesuction, and swelling will decrease it.

Summarizing, differences in B in the samples results from dessication/swelling, and differences in us

in the samples result from ideal sampling and friction effects, stresses during handling and trimming,and dessication/swelling. Dessication/swelling produce lower/higher B and higher/lower u s , while theobtained correlation shows lower B correlates with lower u s . The only logical remaining conclusion isthat the low suction in the tube samples is due to the effects of ideal sampling, friction, handling andtrimming which more than offset the increase of suction due to the dessication which must also occurgiven the low value of B. For Laval samples the situation is reversed, and Begemann samples can goeither way. There seems to be no logical basis for the apparent correlation of u s and B in Figures 6-4(a).

Response time of suction measurementThe large response time in Figure 6-1(a) of suction is considered not to be a result of air which maybe entrapped between the sample and the porous disc. A needle-piezometer has been developed atGeoDelft which consists of a hollow needle (diameter approx. 1mm) and a connected piezometer. Itcan be pressed into the soil to measure pore pressures. Suction of Oostvaardersplassen clay measuredwith this device had a quick response time, but comparable final values to Figure 6-1(a). The large

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volume of soil involved in the suction measurement in Figure 6-1(a) is considered to be the mainreason for the slow adaptation.

Pore pressure response in U.U. testsFigure 6-4(b) shows the final pore pressure developed in the U.U. samples after application of a cellpressure of 100 kPa (red squares). These values can be predicted from the linear regressions shown onFigure 6-3. They all fall in the (small) range 5.5 - 7 kPa, which is a curious consequence of theequilibrating effect of us and (1-B) in the equation

)(100)1(´3 kPaBus −+=σThe close range of initial effective lateral stress allows the U.U. tests also to be compared in the shearstage.

7 Results and evaluation - triaxial testsAll triaxial test results are presented in Figures 7-1 and 7-2. They give the effective stress paths in t -s´ plots in Figure 7-1 and t - εax and u - εax plots in Figure 7-2.

pressure water pore excess isu strain axial is

2

231

31

ax

t

s

ε

σσ

σσ

′−′=

′+′=′

The stress paths shown in Figure 7-1(a) include the U.U. tests starting from approximately s´ = 5.5 - 7kPa on the horizontal axis, the C.I.U. tests starting from s´ = 25 kPa on the horizontal axis, a group ofC.A.U. tests starting from approximately σ´,1 = 50 kPa and σ´,3 = 25 kPa (s´=37.5 kPa, t=12.5 kPa),and a group of C.A.U. tests starting from approximately σ´,1 = 100 kPa and σ´,3 = 50 kPa (s´=75 kPa,t=25 kPa).

U.U. testsThe initial stress in the U.U. tests has been discussed in the previous chapter. Initial stresses are closetogether, allowing direct comparison of the effects of the various sampling techniques. Figure 7-1(b)details the U.U. effective stress paths. An evident feature is that differences between the 3 samplingmethods are small but nevertheless evident. The Laval samples develop the highest effective isotropicstresses, i.e. the lowest excess pore pressures. Next in this order are the tube samples, and theBegemann samples develop the highest pore pressures. The order of Laval relative to tube samples isnot unexpected. It agrees with the lower B values found for the tube samples during the application ofthe cell pressure.

All paths reach the tension cut-off, where effective horizontal stress σ´,3 = 0. All samples initiallycontract in response to shearing, and eventually switch to dilatant response (∆t/∆s´=3:1). TheBegemann samples have the lowest initial stresses and reach the tension cut-off first. Their stress

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paths even pass the cut-off, which would indicate a tensional effective horizontal stress. The triaxialmachine is incapable of applying effective tension to a sample, and the path above the cut-off is due tomeasurement errors and lack of homogeneity of the stresses in the sample. However, a clear changeoccurs in the path above the cut-off: the path steepens, reflecting a response to the zero horizontaleffective stress condition now acting.

The clear reaction of the sample to the σ´,3 = 0 condition shows that this condition is accuratelymeasured. This indicates that errors due to membrane and filter-paper resistance are small orotherwise are directed along the cut-off itself.

Initial pore pressure and pore pressure development are slightly higher in the Begemann samples(compared to both tube and Laval). The differences in initial pore pressure are small and can beregarded as a fortuitous circumstance. The stronger development of pore pressure during shearindicates an influence of sampling method on Skempton's A-parameter. The differences establishedfor the B-parameter in the pressuring stage of the U.U. tests is too small to explain the differences instress paths. Water content and specific volume differences between the samples indicate that theBegemann samples are the wettest and most porous, followed by the tube samples and the Lavalsamples in order. Perhaps then differences in soil properties are the main factor governing thedifferences in pore pressure build-up in the shear stage of the U.U. tests.

C.I.U. triaxial testsSingle C.I.U. tests were performed with a consolidation pressure of 25 kPa, on a tube, a Begemannand a Laval sample. Very little difference is found for the stress path and stress - strain response ofthe C.I.U. tests on Laval, tube and Begemann samples. This is evidenced by the close match of thecurves in Figures 7-1(a), 7-2(a) and 7-2(b). The axial strain in the latter figures includes that acquiredduring consolidation at 25 kPa. The tube sample acquires slightly more strain in this stage than theother samples. (Corrected) Water contents are highest for Begemann, lower for tube and lowest in theLaval sample. The differences are quite significant, but they have little effect on the measuredbehaviour.

C.A.U. triaxial testsTwo sets of C.A.U. triaxial tests were performed, on Begemann, tube and Laval samples. One set wasat a vertical effective consolidation stress of 50 kPa, the other at 100 kPa. A K o value of 0.5 waschosen to determined the lateral stress. Repeat tests were performed for the first set of tests and forthe Laval samples in the second set.

No significant differences could be established between the various sampling techniques. Onedifference lies in the axial strain acquired during consolidation. This is higher for one tube sample inthe first set, and for both Laval samples in the second set. No consistent explanation of thesedifferences can be based on water content differences of the samples. Correcting the axial strain forthe part developed during consolidation, the remaining strain is very similar for all tests in Figures 7-2(a) and (b).

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8 Results and evaluation - Ko-C.R.S. testsDuplicate tests were performed on Laval, Begemann and tube samples in the Ko - C.R.S. oedometer.One test on a Laval sample failed. The results are shown in Figures 8-1 - 8-3. Figure 8-1(a) illustratesthe data that can be gained from the test, for a tube sample. First a continuous curve of verticaleffective stress versus vertical strain is obtained. This curve clearly delineates the overconsolidatedregion and the normally consolidated region, separated at the preconsolidation pressure σ´,vc . The Ko

value is shown versus σ´,v as are the friction, and the excess pore pressure relative to the verticalstress. Both uav/σ´,v av and ubase/σbase are shown.

The Ko value is initially above 1, due to the swelling taking place early in the test. It decreasesgradually to a value of approximately 0.35. After a strain of 32.5% the top of the sample passes underthe top of the Ko membrane and the Ko values become unreliable. This effect is limited for the testshown, but is much more evident in Figure 8-3(b).

The friction remains small in Figure 8-1(a) well into the normally consolidated region. It increasesafter 20% strain to some 7%. This is still quite low. The relative pore pressure increases to about 5%(in terms of effective stresses) and is also quite low. Both friction and pore pressure increase sharplyafter 20% strain.

Figure 8-1(a) is illustrative of all the performed tests. Comparisons are made in the remaining figuresfor stress - strain curves, σ´,h - σ´,v and Ko - σ´,v . The stress - strain curves are shown on variousdeformation scales in Figures 8-1(b), 8-2(a) and 8-2(b). In Figure 8-1(b) engineering strain is used.There is some scatter between the various curves. Most striking is that the Laval sample appears toexhibit more structure than the other tests, in that it falls more steeply after σ´,vc . It also stiffens moreat higher stresses. Both tube samples appear to exhibit more compression in the over-consolidatedrange and stiffen more in the normally consolidated range, and this behaviour is an indication ofsample disturbance.

Figure 8-2(a) shows the stress - strain curves with natural strain as the measure of strain. Thenormally consolidated region is effectively linearized by using natural strain, but this is not true forthe Laval sample. The formulation given by Den Haan (1992) can describe both kinds of curve in thisfigure.

In Figure 8-2(b), the specific volume is used as measure of deformation. It is immediately apparentthat the Laval sample is significantly more dense than the other samples, and this agrees with thedifferences in water content. The difference is large, and makes comparison of the results unreliable.The apparently structured behaviour of the Laval sample may well correlate with its lower watercontent.

In Figure 8-3(a) the development of the lateral stress σ´,h is shown against σ´,v . Only smalldifferences occur amongst the various samples. This also applies to the K o values in Figure 8-3(b). Avalue in the normally consolidated region of Ko = 0.34 - 0.36 is found for all samples.

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9 Effects of Diameter and Sample Position

The large diameter and high quality of the Laval samples was made use of to investigate the effects ofdiameter on triaxial results, and the position of the subsample within the Laval sample. Laval samplenr. 37 was used for these tests. The vo value in Table 1 for the seven tests performed on this samplevary only slightly: between 3.85 and 3.92 and this indicates that the natural variability between thesetests is small.

C.A.U. triaxial tests were performed from a vertical effective stress of 100 kPa and a K o value of 0.5.Subsample diameters of 65mm, 50mm and 38mm were tested in duplicate. The height/diameter ratiowas approximately 2.25 for the 65mm and 38mm samples but 2.0 in the case of the 50mm samples.This difference in H/D ratio was an oversight and impairs the comparison. All these subsamples weretaken from the perimeter of the Laval sample. A single test was performed on material from the centreof the Laval sample, with a diameter of 50mm and a H/D ratio of 2.

Figure 9.1 shows the results of the tests in terms of effective stress paths. A consistent order betweenthe tests related to subsample diameter does not emerge, but it is clear the 38mm samples lie relativelyhigh in the plot and have higher strength. The 50mm subsamples lie lower than the 38mm samples.One 66mm subsample lies close to the two 38mm curves; the other 66mm curve is the lowest of all.This wide divergence of the results for one diameter makes it impossible to confidently state thatsubsample diameter is an important factor. It might also be due to the natural variability, although asdiscussed above this is expected to be small.

However, all curves together in Figure 9-1 show more divergence than the curves in Figure 7-1(a)which pertain to the same sample diameter but to different sampling methods. This remains true evenif the most divergent test, the lower curve for the 66mm subsample, is removed. This fact is an, albeitweak, indication that subsample diameter is an important factor. Triaxial testing practice (e.g. in theNetherlands) should therefore use as much as possible the same sample size. Standardization shouldprovide for this. The variability of organic material directs the choice of a standard sample diameter tothe large end of possible values: e.g. 65mm in preference to 38mm.Alternatively, statistical comparisons of large databases could be employed to discover a possibleeffect of sample diameter. This might be a viable approach if two greatly different diameters are incommon use, e.g. 66m and 38mm.

In Figure 9-1 a curve is shown for the 50mm subsample taken from the centre of the Laval sample. Itis very divergent from the other curves, including the 50mm subsamples taken from the perimeter ofthe Laval sample. Nessecarily, only one sample could be tested, and again the divergence could beattributed to natural variability, although this is considered unlikely.As far as is known, the effect of subsample position within a large sample has not hitherto beeninvestigated. The present finding is an indication that this effect is large. No thoughts will be recordedhere as to the possible causes of such an effect.

Note that all tests converge on approximately the same effective stress strength envelope. c´ and ϕ´would not be influenced significantly by subsample diameter or location. Peak and large strain ϕ´(c´=0) approximately coincide at approximately 53°.

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10 General evaluation and conclusionA general evaluation of the geotechnical properties of the Oostvaardersplassen clay is possible on thebasis of the present test results. Test 14B on a Begemann sample is taken as being representative ofthe one-dimensional compression behaviour. Parameters for this sample are:

depth below groudlevel: 2.2mσ´,v o ≈ 20 kPawo = 182%ρο = 1.23 t/m3

vo = 5.05v1 = 11.61a = 0.012b = 0.238maximum curvature of ln(v) - lnσ´,v curve at 39 kPaσ´,v c = 48 kPa (by Casagrande's construction)O.C.R. = 2.4Ko = 0.34

Figure 7-1(a), which plots all measured effective stress paths, can be used to evaluate the effectivestress strength parameters. At low confining stresses, the tension cut-off is reached (U.U. tests). Atconfining stresses above the preconsolidation pressure, the large strain angle of internal friction ϕ´ isapproximately 50°. An effective stress path has been drawn in the figure from the in-situ normallyconsolidated state which is scaled down from a Laval CAU50 test. This path approximately separatesnormally consolidated and overconsolidated states. Around this state, ϕ´≈60° is found if no cohesionintercept is applied. These ϕ´ values are extremely high and are not intuitively expected in such a softsoil. Den Haan (1995) has pointed to this fact and similar behaviour has been found in other similarsoft organic soils.

Shown on the stress paths in the figure are the points at which axial strains (in the shear stage) of 1, 2,5, and 10% are reached. The blue points in Figure 7-1 apply to clay samples with an approximate bulkdensity of 1.25 t/m3 taken from organic clay layers in the course of the Betuwelijn freight railway.They apply to an axial strain of 5%. There is good agreement between the present tests and theBetuwelijn tests. The Betuwelijn samples together covered a distance of some 30 km. It can beconcluded that high friction angles are a general occurrence in soft organic clay. Den Haan (1999) hasshown that friction angle increases with increasing plasticity and increasing water content is suchsoils, which is the opposite of what is found in inorganic clays.

The value of Ko,n,c, ≈ 0.34 is exceptionally low. Values of 0.5-0.7 are more usual in clays, and againthe intuitive expectation would be in exactly the other direction, namely that the value would behigher in softer soil. Using Jâky's well known Ko,n,c, = 1 - sinϕ´ rule, ϕ´ would be 43°. This is alreadyquite high, but the measured value is higher still.

In conclusion, this study has shown that the common sampling methods in the Netherlands, tubesampling (also known as Ackermann or "Delftse Bus" sampling) and Begemann or Delft sampling,when applied to soft organic clay, yield samples which after consolidation at stresses of 10 kPa or

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higher, exhibit behaviour that is not distinguishable from high quality Laval samples. The commonmethods may therefore be considered adequate, not only for routine testing, but also for fundamentalresearch. Sample diameter may be a more important factor than sampling method.

11 References

H.K.S.Ph. Begemann (1971). Soil sampler for taking an undisturbed sample 66mm in diameter andwith a maximum length of 17 metres. 4th Asian Conference, ISSMFE, Bangkok. p. 54-57.

E.J. den Haan (1992). The formulation of virgin compression of soils. Géotechnique, 3:465-483

E.J. den Haan (1995). Theme report on Special Problem Soils - Peats and Organic Soils. Proc. 11 th

ECSMFE, Copenhagen, 9:139-156

E.J. den Haan (1999). Celproef of Triaxiaalproef? Geotechniek, 1:1-5.

P. La Rochelle, J. Sarrailh, F. Tavenas, M. Roy & S. Leroueil (1981). Causes of sampling disturbanceand design of a new sampler for sensitive soils. Canadian Geotechnical Journal, 18, 52-66 (1981)

J. Tigchelaar CO-710203/15 november 2000 "Voortgangsrapportage juli - november 2000.Werkzaamheden ten behoeve van project "Klei en Veen".

GeoDelft report "Project Klei en Veen - Verslag Monstername", nr. CO-710203, july 2000.

GeoDelft Memo "Geologie Oostvaardersplassen site", 12 april 2001 by J. Tigchelaar.

APPENDICES

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22.04.2001Sample Disturbance in Dutch Organic Oostvaardersplassen Clay

Soil Profiles

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0

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Delft Continuous Begemann Sampler (diameter 66mm) - Cross Section

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Laval Sampler (diameter 200mm) - Cross Section

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Laval Sampler - Mode of operation

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Laval Sampling - Photo Report

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Ko-C.R.S. oedometer - Schematic

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upperload cell

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Ko-C.R.S. oedometer - Cross Section

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(a) Influence of sampling method on specific volume vo

(b) Influence of sampling method on water content wo

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Influence of sampling method on wo and vo

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4.0

4.2

4.4

4.6

4.8

5.0

5.2

5.4

5.6

1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4

depth m-G.L.

v oBgmLavaltube

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(a) Development of suction prior to consolidation

(b) Influence of temperature on developed suction, Laval sample 38E

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Measured suction prior to triaxial tests

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-0.06

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time in hours

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T-effect on suctionLaval sample 38e

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T [°C]

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(a) Undrained application of cell pressure in 4 steps up to 100 kPa, Laval sample 38A

(b) Backextrapolation to obtain suction, Laval sample 38A

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Response of pore pressure to undrained increase of cell pressureLaval sample 38a

-0.2

0

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0 5000 10000 15000 20000 25000

time [sec]

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sure

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Cell pressureDrain pressure

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75 kPa

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Determining initial sample suction by back extrapolationLaval sample 38a

y = 0.9795x - 4.7173

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20

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100

0 20 40 60 80 100 120

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Cell pressure - pore pressure, all UU test samples

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Relation between B value and suction, UU tests

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"Ideal" Suction All samples

0

1

2

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4

5

6

7

8

9

0.94 0.95 0.96 0.97 0.98 0.99 1

B- factor

Suct

ion

[kPa

]

"Ideal" Suction 7.2 kPa

TT

L

L

B

B

Effective stress at 100 kPa external pressure Lower suction compensated due to lower B-factor

0

1

2

3

4

5

6

7

8

9

0.94 0.95 0.96 0.97 0.98 0.99 1

B- factor

Suct

ion

[kPa

]

TT

L

L

B

B

(a) Comparative UU, CIU and CAU tests

(b) Detail, UU tests

date get.

22.03.2001Sample Disturbance in Dutch Organic Oostvaardersplassen Claytriaxial tests

Effective stress paths

CO - 710203/20

Figure 7-1

gez.

form.

A4



0

10

20

30

40

50

0 10 20 30 40 50 60 70 80

s' [kPa]

t [k

Pa]

estimated normally consolidated test from yield stressLavalTubeBegemannBetuwelijn clay 1.25 t/m3 at 5% axial strain1% strain2% strain5% strain10% strain

90°

50°

ϕ'=30°

60°

σp'~45 kPaKO~0.35

Unconsolidated Undrained Triaxial Testsat 100 kPa cell pressure

0

10

0 2 4 6 8 10 12 14

s' [kPa]

t [k

Pa]

Laval

Tube

Begemann

ϕ'=90°

(a) t-ε, comparative UU, CIU and CAU tests

(b) uexcess-ε, comparative UU, CIU and CAU tests

date get.

22.03.2001Sample Disturbance in Dutch Organic Oostvaardersplassen Claytriaxial tests

½ deviator stress and pore pressure vs. axial strain

CO - 710203/20

Figure 7-2

gez.

form.

A4



0

10

20

30

40

50

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40

vertical strain ε

t [k

Pa]

LavalTubeBegemann

0

10

20

30

40

50

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40

vertical strain ε

u [k

Pa]

LavalTubeBegemann

(a) Example of a full test result, Tube sample 26B

(b) Stress - strain curves, all tests

date get.

22.03.2001Sample Disturbance in Dutch Organic Oostvaardersplassen ClayKo-C.R.S. tests

General test results

CO - 710203/20

Figure 8-1

gez.

form.

A4



-0.1

0.0

0.1

0.2

0.3

0.4

0.5

1 10 100 1000 σv' kPa

ε [−]

-0.20-0.15-0.10-0.050.000.050.100.150.200.250.300.350.400.450.500.550.600.650.700.750.800.850.900.951.00

strainKofrictionu_av/sig_v_effu/sig_bottom

Tube sample 26BBoring B3-2; Depth 2.15-2.20 m-G.L.

0.0

0.1

0.2

0.3

0.4

0.5

0.6

1 10 100 1000 σv' kPa

ε [-]

Laval 34Tube 21BTube 26BBegemann 1Begemann 2

Bulk DensityLaval 38 1.276Laval 34 1.310Tube 1-21B 1.251Tube 2-26B 1.246Bgm 2-7B 1.244Bgm 3-14B 1.230

(a) natural strain

(b) specific volume

date get.


Stress - strain curves on different scales

CO - 710203/20

Figure 8-2

gez.

form.

A4



0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

1 10 100 1000 σv' kPa

εΗ [

-] (n

atur

al st

rain

)

Laval 34Tube 21BTube 26BBegemann 14BBegemann 7B


2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

1 10 100 1000 σv' kPa

spec

ific

volu

me

v [-

]



(a) horizontal effective stress - vertical effective stress, all tests

(b) Ko - vertical effective stress, all tests

date get.


Relation between horizontal and vertical stress

CO - 710203/20

Figure 8-3

gez.

form.

A4



0

20

40

60

80

100

120

140

160

180

0 100 200 300 400 500 600

σv' kPa

σh ́ kPa



0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1 10 100 1000 σv' kPa

Κο



Effective stress paths for subsamples with various diameters and position within a single Laval sample (nr 37)

date get.


Effect of sample diameter and position

CO - 710203/20

Figure 9-1

gez.

form.

A4



0

5

10

15

20

25

30

35

40

45

50

0 10 20 30 40 50 60 70 80

s' [kPa]

t [k

Pa]

66mm Perimeter 166mm Perimeter 250mm Perimeter 150mm Perimeter 238mm Perimeter 138mm Perimeter 250mm Centre

Documents

Sample Disturbance of a Soft Organic Dutch Clay