Elastoplastic Two-Surface Model for Unsaturated Cohesive Soils under Cyclic Loading

This paper presents an elastoplastic two-surface model for the description of the stress-strain behavior of unsaturated cohesive soils under suction-controlled cyclic loading conditions. First, the model was developed within the framework of plastic incremental flow theory combining Barcelona Basic Model (BBM) with two-surface model. Second, by extending the Masing's rule to a general multiaxial case, the point at which the stress path reverses is taken as the memory center. Third, a bounding surface and a geometrically similar loading surface evolved in stress space through the plastic hardening criterion suggested by the corresponding author. The characteristics of nonlinear, cyclic plasticity, and deformation accumulation of unsaturated cohesive soils under cyclic loading can be described by the evolution of the constant-suction cross-sections of the bounding and loading surface in the stress space. Model simulations of the stress-strain response taking into consideration the effect of suction, net cell confining pressure and dynamic stress amplitude are compared with the results obtained from a number of suction-controlled laboratory monotonic and cyclic triaxial shear tests. In addition, typical predictions are described and compared with characteristic trends of the behavior of unsaturated soils. The comparisons indicate that the elastoplastic two-surface model can simulate the mechanical behavior of unsaturated soil under cyclic loading.