The Onset of Strain Localization in Cross-Anisotropic Soils Under True Triaxial Condition

Abstract

The in‰uences of inherent cross-anisotropy on soil strength on the homogeneous deformation and bifurcation characteristic of the stress-strain relationship are studied. By neglecting the cohesion term and employing an elliptical shape function in Mohr-Coulomb failure criterion, a 3D anisotropic failure criterion is proposed to describe the strength of cross-anisotropic sands under true triaxial conditions. Based on the proposed failure criterion, the in‰uence of the anisotropic parameter on the failure curve on the deviatoric plane and the relationship between the peak friction angle and the intermediate principal stress ratio are obtained. The suitability of the criterion is justiˆed by comparing with a series of true triaxial tests on sands without strain localization. The proposed failure criterion is adopted to build a three dimensional anisotropic elasto-plastic model, which allows the bifurcation analysis to be incorporated with the non-coaxial ‰ow rule for the purpose of studying the onset of strain localization. Compared with the true triaxial tests under several intermediate principal stress ratios conditions in the literature, the proposed model and bifurcation analysis is shown to be capable of predicting the in‰uence of inherent cross-anisotropy on the onset of strain localization.

Predicting the initiation of static liquefaction of cross‐anisotropic sands under multiaxial stress conditions

“…The critical state line obtained from triaxial extension tests is lower than that obtained from triaxial compression tests; the high degree of crossanisotropy induces the dropdown of the critical state line. Because the influence of the intermediate principal stress ratio on the stress-strain behavior has been verified by Lu et al [36] under the true triaxial condition, as a modification of that model, the verification here focuses on the influence of loading direction angle δ (the angle between the direction of the major principal stress and the normal of the bedding plane). The tests were simulated by deformation-controlled loading under drained condition with loading angle δ being kept constant.…”

“…Most existing strength criteria, for example, the Lade–Duncan criterion , the spatially mobilized plane criterion , and the modified Mohr–Coulomb criterion , treat soil isotropically. Revising the isotropic criterion's shape function in the deviatoric plane allows it to reflect the influence of the intermediate principal stress ratio on anisotropic shear strength . These criteria are only suitable for the cross‐anisotropic sand subjected to a fixed loading direction without any stress rotation, that is, a true triaxial stress test in which the loading axis is kept parallel or orthogonal to the sedimentation plane.…”

Prediction of plane strain undrained diffuse instability and strain localization with non-coaxial plasticity

“…In order to study the strain localization in plane strain tests as a 3D problem, the original 2D model has been extended to 3D case (Qian et al, 2008). This extended model was further modified by using an elaborated shape function to predict the strain localization on both isotropic and cross-anisotropic soils under true triaxial conditions (Huang et al, 2010;Lu et al, 2011). The influence of non-coaxial flow rule on the failure of soil has been also studied by the numerical modeling of soil element test and real engineering problems (Yang and Yu, 2010;Yang et al, 2011).…”

Bifurcation and Degradation of Geomaterials in the New Millennium

“…Huang et al (2010) using the 3D non-coaxial plasticity to study true triaxial tests and obtain good predictions. Lu et al (2011) studied the onset of strain localization on cross-anisotropic sand under true triaxial conditions. Recently, the non-coaxial plasticity model has been further formulated by Yang et al (2011) and Cai et al (2013), and these models are ready to be used in the bifurcation analysis.…”