geo-quebec 04 presentation

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11/ 7/ 2004 Prashant and Penumadu. Geo-Quebec 2004 1

INFLUENCE OF SPECIMEN SHAPE ANDINFLUENCE OF SPECIMEN SHAPE AND

TEST BOUNDARY CONDITIONS ON THETEST BOUNDARY CONDITIONS ON THESTRESSSTRESS --STRAIN BEHAVIOUR OF SOILSTRAIN BEHAVIOUR OF SOIL

Amit Prashant and Dayakar PenumaduDepartment of Civil and Environmental Engineering,University of Tennessee, Knoxville, TN 37996, USA

Acknowledgements: Financial support from the National Science Foundation(NSF) through grants CMS-9872618 and CMS-0296111 is gratefully acknowledged.

Any opinions, findings, and conclusions or recommendations expressed in thispresentation are those of authors and do not necessarily reflect the views of NSF.


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Presentation outlinePresentation outline

The need of laboratory testing with different specimen shapes andloading/boundary conditions.

Testing program and the apparatus used to study the shear strengthbehaviour of Kaolin clay

Lubricated end triaxial test on solid cylinder and cubical

specimensTrue triaxial test on cubical specimens

Frictional end triaxial test on hollow cylinder specimen

Experimental results and discussion on the effect of specimenshape and boundary conditions on shear strength behaviour

Conclusions


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Triaxial test on solid cylindersTriaxial test on solid cylinders

Conventionally used method forobtaining the shear strengthparameters for short and long termstability of soil structures.

Controlled drainage conditions.

With lubricated ends, the specimendeformation is uniform along the heightof the specimen

Can be used to study the soil behavioronly under the axistymmetric stress

conditions.


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Combined axialCombined axial --torsional test ontorsional test onhollow cylindershollow cylinders

With all the advantages of conventionaltriaxial system, it can also be used tostudy the effect of principal stressrotation on the mechanical response ofanisotropic soil.

Frictional ends are used to apply thetorsional shear stress for principal stressrotation, which results in non-uniformdeformation.

Usually, the inside and outside cellpressures are equal, and therefore therelative magnitudes of principal stresseshave a constant relationship with therotation of principal stresses.


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True triaxial on cubical specimensTrue triaxial on cubical specimens

Three principal stresses areindependently applied to the specimenfaces. Therefore, this test is used tostudy the effect of the relativemagnitudes of principal stresses.

The specimen boundaries could be allrigid, all flexible, or a combination of rigidand flexible. Depending on the boundarytypes, stress concentrations and/or non-uniform deformations may occur in thespecimen.

This test can not be used for continuousrotation of principal stresses.


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Specimen preparationSpecimen preparation

Kaolin clay mixed at awater content of 155%and consolidated under207 kPa axial pressure.

Cubical specimenconsolidometer

Hollow andsolid cylinderspecimenconsolidometer


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Lubricated end triaxial systemLubricated end triaxial system

Triaxial compression andextension tests on solidcylinders and cubes usinglubricated end platens.

Complete drainage pathprovided using filter paper strips.

End lubrication is providedthrough the use of 0.6 mm thicklatex membranes and a thinlayer of vacuum grease.

Specimen dimensions:Cylindrical 102 mm diameter Prismatic square base with 102 mmdiagonal, 102 mm height


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True triaxial systemTrue triaxial system

Triaxial compression and extension testson cubical specimens using flexibleboundaries. Ref. [1], and [2]

Strain rate controlled using PID basedclosed loop control algorithm.

Specimen dimensions:Cube each side of 102 mm.

[1] Mandeville, D., and Penumadu, D. 2004. True triaxial testing systemfor clay with Proportional-Integral-Differential control. ASTM GeotechnicalTesting Journal, 27(2), GTJ11756: 1-12.

[2] Prashant A. and Penumadu D., 2004. Effect of intermediate principalstress on overconsolidated Kaolin clay. J. Geotech. Geoenv. Engrg.,

ASCE, 130(3), 284-292.


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Triaxial cell for hollow cylinder specimenTriaxial cell for hollow cylinder specimen

Triaxial compression and extensiontests on Hollow cylinders usingfrictional end boundaries.

MTS 858 loading equipment with aSeries 359 Axial-Torsional LoadUnit. Data acquisition and controlusing TEST STAR electronic

interface and TESTWARE-SXsoftware

Hollow cylinder specimen:Height = 230 mmOuter diameter = 102 mmInner diameter = 71.2 mm


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Tests performed in this studyTests performed in this study

TT-EExtension

TT-CCompressionCubicalTrue triaxial test

TH-EExtension

TH-CCompressionHollow Cylinder Frictional end triaxial test

LC-EExtension

LC-CCompressionCubicalLubricated end triaxial test

LS-EExtension

LS-CCompressionSolid Cylinder Lubricated end triaxial test

DesignationLoadingSpecimenTest Method


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StressStress --strain and excess pore pressurestrain and excess pore pressure


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Observed strengthObserved strength behaviourbehaviour

1.540.9936.40.270.156TT-E

1.680.9534.20.240.117TH-E

1.551.0841.10.290.131LC-E

1.601.0539.50.260.132LS-E

1.081.1428.80.310.150TT-C

1.121.3433.10.320.104TH-C1.231.1829.60.290.132LC-C

1.161.2029.90.300.088LS-C

A f MS u / c qTest


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