Effects of end restraint and strain rate in triaxial tests

Sheng, Daichao; Westerberg, Bo; Mattsson, Hans; Axelsson, Kennet

doi:10.1016/s0266-352x(97)00021-9

Cited by 39 publications

(29 citation statements)

References 5 publications

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“…Global deviatoric stresses obtained for the cases with rough contact are about 65 and 60% of those given by the case with smooth contact for the Natural Calcarenite and Corinth Canal Marl, respectively, when the applied axial strain is 0.5. These global trends are similar to the trends observed by Sheng et al ͑1997͒ in the response of Norrköping clay predicted using the Modified Cam Clay model.…”

Section: Inhomogeneities In Natural Calcarenite and Corinth Canal Marsupporting

confidence: 84%

“…Behavior similar to this has been observed by Sheng et al ͑1997͒ in numerical studies carried out using the Modified Cam Clay model. The reason is that the calculated global stresses are affected by the deformation pattern of the triaxial specimen as well as by the constitutive law of the material.…”

Section: Inhomogeneities In Natural Calcarenite and Corinth Canal Marsupporting

confidence: 81%

“…Some of these studies adopted the Modified Cam Clay model ͑e.g. , Carter 1982;Airey 1991;and Sheng et al 1997͒ while others assumed linear-elastic-perfectly-plastic models ͑e.g., Schanz and Gussman 1994͒. Predictions of the values of shear, radial, and tangential stresses vary depending on how well the boundary conditions have been satisfied.…”

Section: Introductionmentioning

confidence: 99%

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Numerical Modeling of Nonhomogeneous Behavior of Structured Soils during Triaxial Tests

2005

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Abstract:The nonhomogeneous behavior of structured soils during triaxial tests has been studied using a finite element model based on the Structured Cam Clay constitutive model with Biot-type consolidation. The effect of inhomogeneities caused by the end restraint is studied by simulating drained triaxial tests for samples with a height to diameter ratio of 2. It was discovered that with the increase in degree of soil structure with respect to the same soil at the reconstituted state, the inhomogeineities caused by the end restraint will increase. By loading the sample at different strain rates and assuming different hydraulic boundary conditions, inhomogeneities caused by partial drainage were investigated. It was found that if drainage is allowed from all faces of the specimen, fully drained tests can be carried out at strain rates about ten times higher than those required when the drainage is allowed only in the vertical direction at the top and bottom of the specimen, confirming the findings of previous studies. Both end restraint and partial drainage can cause bulging of the triaxial specimen around mid-height. Inhomogeneities due to partial drainage influence the stress-strain behavior during destructuring, a characteristic feature of a structured soil. With an increase in the strain rate, the change in voids ratio during destructuration reduces, but, in contrast, the mean effective stress at which destructuration commences was found to increase. It is shown that the stress-strain behavior of the soil calculated for a triaxial specimen with inhomogeneities, based on global measurements of the triaxial response, does not represent the true constitutive behavior of the soil inside the test specimen. For most soils analyzed, the deviatoric stress based on the global measurements is about 25% less than that for the soil inside the test specimen, when the applied axial strain is about 30%. Therefore it can be concluded that the conventional global measurements of the sample response may not accurately reflect the true stress-strain behavior of a structured soil. This finding has major implications for the interpretation of laboratory triaxial tests on structured soils.

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Section: Inhomogeneities In Natural Calcarenite and Corinth Canal Marsupporting

confidence: 84%

Section: Inhomogeneities In Natural Calcarenite and Corinth Canal Marsupporting

confidence: 81%

Section: Introductionmentioning

confidence: 99%

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Numerical Modeling of Nonhomogeneous Behavior of Structured Soils during Triaxial Tests

2005

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“…Owing to the geometry of a classical triaxial cell, some authors have acknowledged the importance of frictional effects at the piston/sample interfaces. However, these effects mostly have been documented in soil mechanic (LEE, 1978;FOURIE and XIAOBI, 1991;SHENG et al, 1997) rather than for consolidated geomaterials. Recently, KORSNES et al (2006) have investigated the influence of these end effects on permeability of both chalks and sandstones using a modified core sleeve, which allows pore pressure sampling in a region distant from the interfaces where frictional effects take place.…”

Section: Introductionmentioning

confidence: 99%

Axial and Radial Permeability Evolutions of Compressed Sandstones: End Effects and Shear-band Induced Permeability Anisotropy

Dautriat

Gland

Guélard

et al. 2009

Pure appl. geophys.

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The influence of hydrostatic and uniaxial stress states on the porosity and permeability of sandstones has been investigated. The experimental procedure uses a special triaxial cell which allows permeability measurements in the axial and radial directions. The core sleeve is equipped with two pressure samplers placed distant from the ends. They provide mid-length axial permeability measure as opposed to the overall permeability measure, which is based on the flow imposed through the pistons of the triaxial cell. The core sleeve is also equipped to perform flows in two directions transverse to the axis of the sample. Two independent measures of axial and complementary radial permeability are thus obtained. Both Fontainebleau sandstone specimens with a porosity of about 5.8% to 8% and low permeability ranging from 2.5 mD to 30 mD and Bentheimer sandstone with a porosity of 24% and a high permeability of 3D have been tested. The initial axial permeability values obtained by each method are in good agreement for the Fontainebleau sandstone. The Bentheimer sandstone samples present an axial mid-length permeability 1.6 times higher than the overall permeability. A similar discrepancy is also observed in the radial direction, also it relates essentially to the shape of flow lines induced by the radial flow. All the tested samples have shown a higher stress dependency of overall and radial permeability than mid-length permeability. The effect of compaction damage at the pistons/sample and radial ports/sample interfaces is discussed. The relevance of directional permeability measurements during continuous uniaxial compression loadings has been shown on the Bentheimer sandstone until the failure of the sample. We can efficiently measure the influence of brittle failure associated to dilatant regime on the permeability: It tends to increase in the failure propagation direction and to decrease strongly in the transverse direction.

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“…Then, it is no longer necessary to neglect boundary e!ects that can have substantial in#uences on the obtained result, see e.g. Reference [20] where e!ects of end restraint and strain rate in triaxial testing is discussed. However, optimization at the sample level can be expected to be quite computationally expensive.…”

Section: Discussionmentioning

confidence: 99%

Optimization routine for identification of model parameters in soil plasticity

Mattsson

Klisinski

Axelsson

2001

Num Anal Meth Geomechanics

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SUMMARYThe paper presents an optimization routine especially developed for the identi"cation of model parameters in soil plasticity on the basis of di!erent soil tests. Main focus is put on the mathematical aspects and the experience from application of this optimization routine. Mathematically, for the optimization, an objective function and a search strategy are needed. Some alternative expressions for the objective function are formulated. They capture the overall soil behaviour and can be used in a simultaneous optimization against several laboratory tests. Two di!erent search strategies, Rosenbrock's method and the Simplex method, both belonging to the category of direct search methods, are utilized in the routine. Direct search methods have generally proved to be reliable and their relative simplicity make them quite easy to program into workable codes. The Rosenbrock and simplex methods are modi"ed to make the search strategies as e$cient and user-friendly as possible for the type of optimization problem addressed here. Since these search strategies are of a heuristic nature, which makes it di$cult (or even impossible) to analyse their performance in a theoretical way, representative optimization examples against both simulated experimental results as well as performed triaxial tests are presented to show the e$ciency of the optimization routine. From these examples, it has been concluded that the optimization routine is able to locate a minimum with a good accuracy, fast enough to be a very useful tool for identi"cation of model parameters in soil plasticity.

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Effects of end restraint and strain rate in triaxial tests

Cited by 39 publications

References 5 publications

Numerical Modeling of Nonhomogeneous Behavior of Structured Soils during Triaxial Tests

Numerical Modeling of Nonhomogeneous Behavior of Structured Soils during Triaxial Tests

Axial and Radial Permeability Evolutions of Compressed Sandstones: End Effects and Shear-band Induced Permeability Anisotropy

Optimization routine for identification of model parameters in soil plasticity

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