Yielding and Flow Liquefaction of Loose Sand

Imam, Reza; Morgenstern, N. R.; Robertson, P. K.; Chan, Dave

doi:10.3208/sandf.42.3_19

Cited by 44 publications

(13 citation statements)

References 33 publications

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“…The highest IL for loose sand is on or very close to the CSL. Similar observations have also been made by Sladen et al (1985b) and Imam et al (2002).…”

Section: Very Loose Sandsupporting

confidence: 84%

Undrained behaviour of Changi sand in triaxial and plane-strain compression

Wanatowski

Chu

2008

Geomechanics and Geoengineering

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The results of an experimental study of the undrained behaviour of Changi sand under axisymmetric and plane-strain conditions are presented. K 0 consolidated undrained plane-strain tests and K 0 or isotropically consolidated triaxial tests on very loose and medium dense specimens were conducted. The undrained behaviour of sand at very loose and medium dense states under plane-strain conditions was characterised and compared with that under axisymmetric conditions. It was observed that the undrained behaviour of very loose and medium dense sand under plane strain is similar to that under axisymmetric conditions. However, because of the formation of shear bands in plane-strain tests, the post-peak behaviour of medium dense sand in plane strain is different from that in triaxial tests. It was also established that an instability line for plane-strain conditions can be defined in a way similar to that for axisymmetric conditions. Using the state parameter, a unified relationship between the normalised slope of instability line and the state parameters can be established for both axisymmetric and plane-strain conditions. Using this relationship, the instability conditions established under axisymmetric conditions can be used for plane-strain conditions.

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“…The highest IL for loose sand is on or very close to the CSL. Similar observations have also been made by Sladen et al (1985b) and Imam et al (2002).…”

Section: Very Loose Sandsupporting

confidence: 84%

Undrained behaviour of Changi sand in triaxial and plane-strain compression

Wanatowski

Chu

2008

Geomechanics and Geoengineering

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“…9 are consistent with theoretical and analytical investigations published in the literature Lade, 1992;Imam et al, 2002;Chu et al, 2003;Been & Jefferies, 2004;Andrade, 2009). In these studies it has been established that instability of granular materials depends on the state of the soil, although slightly different interpretations have been given by different researchers.…”

Section: Soil Statesupporting

confidence: 79%

“…These conditions are approximately defined by the instability line shown in Figs 3 and 4. Therefore the instability line is associated with the yield surface, and defines the conditions under which large plastic yielding can take place (Lade, 1992;Chu et al, 1993;Imam et al, 2002). Large plastic yielding has to take place when soil becomes unstable: that is, when large plastic strain develops rapidly.…”

Section: Stress Ratiomentioning

confidence: 99%

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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“…12, the initial yield surface f for virgin loose sand sample is pushed outward from the first drained triaxial loading to point C of mobilized stress ratio level g mob . The theoretical yield surface f can be approximated as the shape of the effective stress path [34]. Fig.…”

Section: Initial Gradient Of Effective Stress Pathsmentioning

confidence: 99%

Exploring the undrained induced anisotropy of Hostun RF loose sand

2010

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The effects of recent history on the undrained behaviour of very loose and saturated Hostun RF clean sand are investigated in this paper. From an initial isotropic stress state in the triaxial plane, recent histories are generated by isotropic consolidation followed by standard drained triaxial preshear in compression, up to a desired value of axial strain or mobilized stress ratio, and unloading to an initial stress ratio. Subsequent undrained behaviour in triaxial compression is analysed in detail. This paper contributes to the traits explaining the progressive transformation of a compressive and unstable behaviour of loose sand into a dilative and stable behaviour of dense-like sand by previous history, while remaining in the same state of loose density. Experiments show a large pseudo-elastic domain induced by recent history in terms of effective stress paths, function of the initially mobilized stress ratio level, a unique initial gradient of the effective stress paths depending on the stress ratio at the beginning of the undrained shearing, a progressive appearance of dilatancy and a surprising evolution the undrained behaviour of loose sand. Experimental results evidence the important role of the recent deviatoric strain history, from any initial isotropic or anisotropic stress state. This paper also offers a comprehensive understanding of the history mechanisms created by simple linear stress paths with fixed direction in the classical triaxial plane.

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Yielding and Flow Liquefaction of Loose Sand

Cited by 44 publications

References 33 publications

Undrained behaviour of Changi sand in triaxial and plane-strain compression

Undrained behaviour of Changi sand in triaxial and plane-strain compression

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

Exploring the undrained induced anisotropy of Hostun RF loose sand

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