Mesh Size Sensitivity and Effect of Perturbation Intensity on Coupled Undrained Instability Analysis in Sands

The sudden loss in load carrying capacity of a soil specimen from its homogeneous material response is coined as the onset of instability or bifurcation in geomaterials. A numerical investigation of the coupled undrained (globally undrained, locally drained) transient analysis in Hostun RF sand under biaxial loading has been carried out in ABAQUS along with the implementation of a user defined generalized 3D nonassociative material model. Onset of localization has been probed by inducing material heterogeneity within the numerical framework. This requires a mesh convergence study for a given perturbation intensity. Numerically predicted instability onset strain becomes practically asymptotic to the theoretically predicted value with mesh refinement. The simulations revealed -that increased intensity of material heterogeneity induced in the sand specimens significantly reduced the bifurcation onset strain.