A simple bounding surface elasto-viscoplasticity model for marine clays under monotonic and cyclic loading

Abstract

This paper develops a bounding surface elasto-viscoplasticity model to consider the viscous behaviors of saturated clays. Consisting of a bounding surface, a dynamic loading surface, and a static loading surface, the model is formulated by combining the elasto-viscoplasticity overstress theory with the bounding surface framework. An overstress function defined by the static and dynamic loading surfaces is adopted, allowing the existence of viscoplastic strains for stress states inside the bounding surface. Enhanced by a static loading surface relocation strategy, the model enables capturing the accumulation of viscoplastic deformations of cyclically loaded clays. A rotated bounding surface is adopted to consider the initial anisotropic condition of natural clays. Besides, the hardening parameter is assumed to be associated with the accumulated viscoplastic deviatoric strain to better simulate the clay cyclic behaviors. The model is implemented into ABAQUS finite element program by using the two-step Euler method with sub-stepping techniques. The model is quantitatively validated by comparing the simulation results of several element tests to the available experimental data. Performance of the developed model in reproducing the secondary compression behaviors at various over-consolidation ratios and the loading frequency dependency of undrained cyclic responses is also examined qualitatively.