Experimental and numerical analyses of failure in very loose sands

Daouadji, Ali; Darve, Félix; Gali, Hussein Al; Lejeune, Arnaud; Jrad, Mohamad

doi:10.3166/ejece.13.149-165

Cited by 2 publications

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“… and Daouadji et al . , among others. We herein look at constant shear test behaviours in both drained (CSD) and undrained (QCSU) conditions starting from approximately the same initial void ratio ( e 0 ≅ 0.9) that were explored at various initial effective consolidation pressures, that is, σ c ' = 100, 300 and 750 kPa.…”

Section: Experimental Studies Of Diffuse Failurementioning

confidence: 96%

Diffuse instabilities with transition to localization in loose granular materials

Wan

Pinheiro

Daouadji

et al. 2012

Num Anal Meth Geomechanics

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International audienceThis paper is concerned with diffuse and other ensuing failure modes in geomaterials when tested under homogeneous states of shearing in various loading programs and drainage conditions. Material instability is indeed the basic property that accounts for the instability of an initially homogeneous deformation field leading to diffuse failure and strain localization in geomaterials. The former is normally characterized by a runaway type of failure accompanied with a sudden and violent collapse of the material in the absence of any localization phenomena. Against this backdrop, we present a brief overview of material instability in elastoplastic solids where one finds a rich source of theoretical concepts including bifurcation, strain localization, diffuse failure and second-order work, as well as a considerable body of experiments. Some compelling laboratory experimental studies of material instability with focus to diffuse failure are then presented and interpreted based on the second-order work. Finally, various material instability analyses using an elastoplastic constitutive and a general finite element analysis of the above-mentioned laboratory experimental tests are presented as a boundary value problem. It is shown that instability can be captured from otherwise uniform stress, density and hydraulic states, whereas uniform deviatoric loads are being applied on the external boundaries of a specimen. Although the numerical simulations reproduce well the laboratory experimental results, they also highlight the hierarchy of failure modes where localization phenomena emerge in the post-bifurcation regime as a result of a degradation of homogeneity starting from a diffuse mode signalled by a zero second-order work

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Section: Experimental Studies Of Diffuse Failurementioning

confidence: 96%

Diffuse instabilities with transition to localization in loose granular materials

Wan

Pinheiro

Daouadji

et al. 2012

Num Anal Meth Geomechanics

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“…In three dimensions, monitored increases in water pore pressure lead to q ‐constant drained paths. There are some experimental evidences of diffuse failure before the Mohr–Coulomb criterion along such paths for loose sands . Theoretically, this type of paths were discussed in , for example, using the second‐order work criterion.…”

Section: τ‐Constant Loading Pathsmentioning

confidence: 99%

Material stability analysis of rock joints

Duriez

Darve

Donzé³

et al. 2012

Num Anal Meth Geomechanics

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SUMMARYFor prediction of rockfalls, the failure of rock joints is studied. Considering these failures as constitutive instabilities, a second-order work criterion is used because it explains all divergence instabilities (flutter instabilities are excluded). The bifurcation domain and the loading directions of instabilities, which fulfill the criterion, are determined for any piecewise linear constitutive relation. The instability of rock joints appears to be ruled by coupling features of the behavior (e.g., dilatancy). Depending on the loading parameters, instabilities can lead to failure, even before the plastic limit criterion. Results for two given constitutive relations illustrate the approach. Some given loading paths are especially considered. Constant volume (undrained) shear and -constant paths are stable or not depending on the link between the deviatoric stress and strain along undrained paths, as found for soils. Some unstable loading paths are illustrated. Along these paths, failure before the plastic limit criterion is possible. The corresponding failure rules are determined. Copyright © 2012 John Wiley & Sons, Ltd. Rock slopes present different types of defects at all scale. We call rock joints the discontinuities (e.g., in mechanical properties) at macroscopic scale, and we assume that rock joints have the greatest influence on the stabilities of rock slopes. This is why geomechanical stability analyses need to represent accurately rock joints' failures. We thus focus on the mechanical behavior of such joints, and in the framework of a 2D assumption, only four scalar variables will be used to describe the corresponding mechanical state. Two stress components are considered: one normal, denoted (considered positive in compression), and one tangential, denoted . On the other hand, relative displacements occurring along the joint are considered, with a normal component u (positive in compression) and a tangential component .We define here, as in the general plasticity theory, that failure is obtained when relative displacements along the joint (that we can call 'deformation', from a general point of view) go on under a constant loading, by the existence of limit stress states. Failure of rock joint is obtained for example during constant normal load shearings, defined by a constant value of , once reaches a peak or a plateau [1][2][3][4]: under these conditions, increases continuously, whereas stresses are constant. This situation in a rock slope would trigger rockfalls. Such analysis of failure introduces directly the concept of limit stress states, for which stresses do not vary anymore, E d D .d , d / D E 0, whereas relative displacements still evolve, E

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Experimental and numerical analyses of failure in very loose sands

Cited by 2 publications

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Diffuse instabilities with transition to localization in loose granular materials

Diffuse instabilities with transition to localization in loose granular materials

Material stability analysis of rock joints

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