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

Guo, Peijun

doi:10.1002/nag.1101

Cited by 9 publications

(9 citation statements)

References 54 publications

(129 reference statements)

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“…Although the undrained condition still prevails globally, internal local drainage is allowed at the emergence of such shear bands (Han and Vardoulakis 1991). Moreover, Guo (2013) showed an early initiation of shear band with an increase in permitted local volume change under globally undrained biaxial loading. In this study, the most critical case for localization was considered by analyzing it under locally drained conditions.…”

Section: Problem Statementmentioning

confidence: 96%

“…Bardet and Shiv (1995) and Iai and Bardet (2001) modified the plane-strain bifurcation framework to account for general constitutive response and explored two-phase instabilities in hypoelastic and Mohr-Coulomb-type elastoplastic materials. More recently, Guo (2013) and Guo and Stolle (2013) followed a similar approach to explore undrained shear banding in sand. However, a better representation of the stress-strain relation is required to explain various instability modes that can emerge during undrained testing of sand at different stress states.…”

Section: Introductionmentioning

confidence: 99%

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Instability Analysis of Sand under Undrained Biaxial Loading with Rigid and Flexible Boundary

2017

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The emergence of possible instability modes under undrained biaxial shear of sand was investigated to develop better understanding about the onset of localized and liquefaction-type solid-fluid instability modes using a generalized three-dimensional (3D) material model. These two modes are the primary instability modes that can exist in most cases while conducting undrained biaxial testing of sand at different densities, confining pressures, and boundary conditions. Using a 3D rate-independent and nonassociative constitutive model, the instability analysis was performed as a plane-strain bifurcation problem from a uniform stress-strain state. Large deformation formulation was used to simulate the biaxial test configuration with both rigid and flexible boundaries in the lateral direction. The existing theoretical framework of solid-fluid instability analysis under rigid boundaries was extended to the flexible lateral boundary condition. Interestingly, the onset of solid-fluid instability modes is significantly influenced by the choice of boundary conditions. The trends for the onset of various undrained instability modes were assessed as a function of material state variables.

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Section: Problem Statementmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Instability Analysis of Sand under Undrained Biaxial Loading with Rigid and Flexible Boundary

2017

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“…Due to the lack of experimental evidence, most studies on the locally drained shear bands in the globally undrained sand are limited to theoretical and numerical investigations. [6], [7] and [8] presented the concept of the locally drained shear band under globally undrained conditions. Only this type of instability is possible for dilative dense sand [7,8].…”

Section: Literature Reviewmentioning

confidence: 99%

“…[6], [7] and [8] presented the concept of the locally drained shear band under globally undrained conditions. Only this type of instability is possible for dilative dense sand [7,8]. A local volume change is always accompanied by a water flow associated with a pore pressure gradient.…”

Section: Literature Reviewmentioning

confidence: 99%

“…The onset of the shear band is dictated by the rate of local volume change. [7] theoretically showed it is most likely that a shear band initiates with a minimum deviation from the isochoric constraint, after the peak friction ratio. Because in this region, the jump in local volume change required to trigger a dilative shear band is smaller.…”

Section: Literature Reviewmentioning

confidence: 99%

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A Constitutive Model for Locally Drained Shear Bands in Globally Undrained Dense Sand

Mallikarachchi

Soga

2019

E3S Web Conf.

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When saturated granular materials which are dilative in nature are subjected to the undrained deformation, their strength increases due to the generation of negative excess pore pressure. This phenomenon is known as dilative hardening and can be witnessed in saturated dense sand or rocks during very fast loading. However, experimental evidence of undrained biaxial compression tests of dense sand shows a limit to this dilative hardening due to the formation of shear bands. There is no consensus in the literature about the mechanism which triggers these shear bands in the dense dilative sand under isochoric constraint. The possible theoretical reasoning is the local drainage inside the specimen under the globally undrained condition, which is challenging to be monitored experimentally. Hence, both incept of localisation and post-bifurcation of the saturated undrained dense sand demand further numerical investigation. Pathological mesh dependency hinders the ability of the finite element method to represent the localisation without advanced regularisation methods. This paper attempt to provide a macroscopic constitutive behaviour of the undrained deformation of the saturated dense sand in the presence of a locally drained shear band. Discontinuation of dilatant hardening due to partial drainage between the shear band and the adjacent material is integrated into the constitutive model without changing governing equilibrium equations. Initially, a classical bifurcation analysis is conducted to detect the inception and inclination of the shear band based on the underlying drained deformation. Then a post-bifurcation analysis is carried out assuming an embedded drained or partially drained shear band at gauss points which satisfy bifurcation criterion. The smeared shear band approach is utilised to homogenise the constitutive relationship. It is observed that the dilatant hardening in the saturated undrained dense sand is reduced considerably due to the formation of shear bands.

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A two‐scale constitutive framework for modelling localised deformation in saturated dilative hardening material

Mallikarachchi

Soga

2020

Num Anal Meth Geomechanics

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Summary Undrained deformation of dilative sand generates negative excess pore pressure. It enhances the strength, which is called dilative hardening. This increased suction is not permanent. The heterogeneity at the grain scale triggers localisations causing local volume changes. The negative hydraulic gradient drives fluid into dilating shear zones. It loosens the soil and diminishes the shear strength. It is essential to understand the mechanism behind this internal drainage and to capture it numerically. The purpose of this paper is to develop a macroscopic constitutive relationship for the undrained deformation of saturated dense sand in the presence of a locally fully or partially drained shear band. Separate constitutive relations are generated for the band and intact material. Both time and scale dependence during pore fluid diffusion in saturated sand are captured, eliminating the mesh dependency for finite element implementations. The model is applied to the Gauss points that satisfy the bifurcation criterion. The proposed method is calibrated to recreate the undrained macroscopic response bestowed by an extra‐small mesh. The microscopic behaviours inside and outside shear band predicted by this model are qualitatively in good agreement with individual material point behaviours inside and outside the shear band in the extra‐small mesh. Depending on the loading rate and the shear band thickness, the response inside the band can be fully or partially drained, which governs the ultimate global strength. The calibrated model is exploited to simulate an upscaled biaxial compression test with semipermeable boundaries.

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

Cited by 9 publications

References 54 publications

Instability Analysis of Sand under Undrained Biaxial Loading with Rigid and Flexible Boundary

Instability Analysis of Sand under Undrained Biaxial Loading with Rigid and Flexible Boundary

A Constitutive Model for Locally Drained Shear Bands in Globally Undrained Dense Sand

A two‐scale constitutive framework for modelling localised deformation in saturated dilative hardening material

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