Pre-failure strain softening and pre-failure instability of sand: a comparative study

Chu, Jian; Leong, W K

doi:10.1680/geot.2001.51.4.311

Cited by 64 publications

(25 citation statements)

References 23 publications

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“…Whether pre-failure instability or pre-failure strain-softening will occur in a test is affected by whether the test is conducted under a load-controlled or deformation-controlled loading mode. This observation is consistent with experimental and analytical studies carried out by , , di Prisco & Imposimato (1997), Chu & Leong (2001), Andrade (2009) and Daouadji et al (2010).…”

Section: Load Control Versus Deformation Controlsupporting

confidence: 93%

“…The effective mean stress decreases owing to the increase in pore pressure. As discussed by Chu & Leong (2001), such a stress path points outside the yield surface only when a stress ratio is higher than the stress ratio at the peak point of the yield surface. If the stress ratio where an instability test starts is lower than the stress ratio at the peak point, such a stress path will point inside the yield surface and result in an elastic response.…”

Section: Stress Ratiomentioning

confidence: 95%

“…In this case, strain-softening in the form of a reduction in the deviator stress occurs instead. For more discussion, see Chu & Leong (2001) and Chu & Wanatowski (2009).…”

Section: Types Of Instabilitymentioning

confidence: 99%

“…It has been discussed by Chu & Leong (2001) and Chu & Wanatowski (2009) that the load control mode is one of the main factors affecting the occurrence of instability (or strain-softening) of soils. Although the conditions that lead to strain-softening and instability are the same, the former occurs when a specimen is sheared under a deformationcontrolled loading mode and the latter under a loadcontrolled loading mode.…”

Section: Load Control Versus Deformation Controlmentioning

confidence: 99%

“…Several experimental studies on pre-failure instability behaviour of sand have been reported in the past (Sasitharan et al, 1993;Skopek et al, 1994;Chu & Leong, 2001;Chu et al, 2003;Orense et al, 2004;Sento et al, 2004;Daouadji et al, 2010). However, all the above cited studies were carried out under axisymmetric conditions.…”

Section: Introductionmentioning

confidence: 99%

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Factors affecting pre-failure instability of sand under plane-strain conditions

Wanatowski¹,

Chu²

2012

Géotechnique

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Experimental data obtained from a plane-strain apparatus are presented in this paper to show that a pre-failure instability in the form of a rapid and sustained increase in strain rate can occur for both contractive and dilative sand under fully drained conditions. However, this type of instability is different from the runaway type of instability observed under undrained conditions, and has therefore been called conditional instability. Despite the differences, the conditions for both types of instability are the same for contractive sand. There are also other factors that affect the pre-failure instability of sand observed in the laboratory. These include the stress ratio, void ratio, sand state, load control mode and reduction rate of the effective confining stress. In this paper, these factors are discussed and analysed using experimental data obtained from undrained instability (or creep) tests and constant shear drained (CSD) tests carried out under plane-strain conditions. KEYWORDS: failure; laboratory tests; liquefaction; pore pressures; sands; slopes Cette communication présente des données expérimen-tales obtenues avec un appareil à déformation plane dans le but de démontrer qu'une instabilité pré-rupture, sous forme d'une augmentation rapide et soutenue de la vitesse de déformation, peut se produire pour des sables en contractif et dilatif, en présence d'un drainage inté-gral. Toutefois, ce type d'instabilité se distingue du type d'instabilité galopante relevée en présence de conditions non drainées, et a été dénommé, pour cette raison, instabilité conditionnelle. En dépit des différences, les conditions propres à ces deux types d'instabilité sont les mêmes pour le sable contractif. D'autres facteurs égale-ment affectent l'instabilité pré-rupture du sable, observée en laboratoire. Parmi ceux-ci, indiquons le rapport des contraintes, l'état du sable, le mode de contrôle de la charge, et le taux de réduction des contraintes de confinement efficaces. Dans la présente communication, on discute et on analyse ces facteurs sur la base de données expérimentales obtenues avec des essais d'instabilité non drainée (ou de fluage) et des essais de cisaillement constant drainés (CSD), effectués en présence de déforma-tions planes.

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Section: Load Control Versus Deformation Controlsupporting

confidence: 93%

Section: Stress Ratiomentioning

confidence: 95%

“…In this case, strain-softening in the form of a reduction in the deviator stress occurs instead. For more discussion, see Chu & Leong (2001) and Chu & Wanatowski (2009).…”

Section: Types Of Instabilitymentioning

confidence: 99%

Section: Load Control Versus Deformation Controlmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Factors affecting pre-failure instability of sand under plane-strain conditions

Wanatowski¹,

Chu²

2012

Géotechnique

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Investigating landslide‐related cracks along the edge of two loess platforms in northwest China

Dai

Tham

et al. 2012

Earth Surf Processes Landf

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Cracks are widely developed along the edge of loess platforms in northwest China. Field surveys reveal that these cracks can be grouped into shallow and deeply penetrating ones. The former occur at a small distance from the platform edge, normally penetrate into the top unsaturated loess with the penetration depth being controlled by the joints in loess. The latter penetrate deeper into the saturated loess farther away from the platform edge. These cracks control the inflow and drainage of irrigation water. The shallow penetrating crack can fail as a slide or fall with a volume of up to hundreds of cubic meters. The deeply penetrating crack can fail as a flow-like landslide with a volume of thousands of cubic meters or more. A full-scale field test simulating irrigation on the platform surface was conducted. The two types of crack can be interconnected so that the water applied in the test finally flowed into the deep crack and was discharged from the platform. Analysis of soil stress states and the results of field test show that the deeply-penetrating cracks could have both positive as well as negative effects on slope stability. On the one hand, water can flow more freely in the cracks, and the loess could be saturated and trigger a landslide. On the other hand, the water can drain more easily along the crack and slope stability could be enhanced as the groundwater level is suppressed.

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Undrained shear band in water saturated granular media: A critical revisiting with numerical examples

Guo

2011

Num Anal Meth Geomechanics

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SUMMARYBy taking into account the continuity of stresses and pore pressure across the boundaries of a shear band, it is theoretically shown that incipient localization may take place in saturated loose contractive sand in the regime of decreasing deviator stress under undrained conditions. The undrained shear band orientation primarily depends on the Poisson's ratio and the dilatancy characteristics of the material. However, under strict isochoric constraint, localization is precluded in dense dilative sand with deviator stress increasing only. If any local volume change takes place with a certain mechanism, undrained shear band would be possible in dense sand, most likely in the regime of decreasing friction angle after the peak friction angle is mobilized. Numerical examples are given to demonstrate the variation of shear band inclinations with void ratios and initial consolidation pressures.

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Pre-failure strain softening and pre-failure instability of sand: a comparative study

Cited by 64 publications

References 23 publications

Factors affecting pre-failure instability of sand under plane-strain conditions

Factors affecting pre-failure instability of sand under plane-strain conditions

Investigating landslide‐related cracks along the edge of two loess platforms in northwest China

Undrained shear band in water saturated granular media: A critical revisiting with numerical examples

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