An Elastic-Viscoplastic Model for Time-Dependent Behavior of Soft Clay and Its Application on Rheological Consolidation

To describe the time-dependent behavior of soft clay, this paper extended one-dimensional Nishihara model to three-dimensional stress state based on the framework of Perzyna’s overstress theory and modified cam-clay model. The yield criterion of modified cam-clay model was used to describe the plastic properties of soft clay, and the overstress theory was used to describe the strain rate effect. Triaxial rheological tests were carried out on Ningbo soft clay and the rheological characteristics were studied. Based on laboratory results, the parameters of proposed model were determined by curve fitting, which show that this model is suitable for the rheological characteristics of Ningbo soft clay. The analysis of parameters shows that, the value of parameters changes slightly with different deviatoric stress when the confining pressure was constant, but changes notably with the increase of confining pressure. A user material subroutine of the proposed constitutive mode was coded on the platform of the FEM software ABAQUS and verified by triaxial compression of soil column. A plain strain problem was computed to analyze the rheological consolidation properties of soft clay, in which the rheological effect and the finite strain effect were considered.