Analysis of various drained and undrained instability modes in medium dense sand subjected to biaxial loading conditions

The present study theoretically explores instability behavior of medium dense sand under both drained and undrained biaxial test. The instability analysis has been posed as a plane strain bifurcation problem within a large deformation framework. A generalized pressure-dependent 3D constitutive model has been employed to simulate the drained and undrained biaxial tests on a medium dense sand sample assuming two types of lateral boundaries, namely rigid and flexible. The lateral boundary condition can influence significantly the onset of undrained soild-fluid instability and drained diffused intabilities. Localization gets delayed with increasing lateral confinement for both drained and undrained cases. Elastic parameters have strong impact on the instability onset.