Undrained shearing response of loose sand subjected to different strain paths addressing evolution of fabric anisotropy and non-coaxiality

The undrained shearing response of loose sand usually depicts a sudden loss in shear strength due to emergence of liquefaction type solid-fluid instability. For real field cases, such solid-fluid instability leads to catastrophic failure of geotechnical structures resulting in loss of life and property. In such cases, the loading is generally displacement/strain controlled with existence of a generalized strain state. Consequently, consideration of various strain paths becomes crucial while analysing the mechanical response of saturated loose sand subjected to undrained shearing. Furthermore, due to distinct evolution of fabric structure, granular materials like sand exhibits significant variation in its mechanical response when sheared under different loading paths. In this regard, 3D Discrete Element simulations of constant volume true-triaxial test have been carried out on loose sand specimen mimicking the undrained shearing condition at varying intermediate principal strain ratios (bε). The effect of bε on the macro-level response, including stress-strain behavior, stress path and pore-water pressure evolution have been investigated. Further, such macro-level responses are examined in light of the evolving fabric anisotropy. The simulation results indicate a reduction in the liquefaction susceptibility with increasing bε. Additionally, non-coaxiality between macro-level stress, strain and micro-level fabric has also been investigated in the present study.