A kinematic hardening and elastic visco-plastic model of saturated cohesive anisotropic soils

Abstract

Soils have anisotropic kinematic hardening and time-dependent behavior, therefore an anisotropic and kinematic hardening elastic visco-plastic (EVP) model is developed to simulate the anisotropic kinematic hardening and strain rate effects as well as their combined effect. Following the approach of Perzyna’s overstress visco-plasticity and Suklje’s isotaches concept, the anisotropic yield stresses associated with the parameters CΓ and Cvp are used to describe the effect of viscosity on the yield stress. The isotropic and kinematic hardening laws suggested previously by the authors are implemented in the EVP model. With a smart cone-cap connection at critical state points, the EVP model can maintain zero incremental visco-plastic volumetric strains at the intersection points between the Matsuoka-Nakai cone and the associated visco-plastic ellipse cap. Therefore the direction of the visco-plastic strain increment vectors at the cone-cap intersection points is assured unique and numerical calculation is thus convenient. With a deviatoric fabric scalar, zero incremental visco-plastic deviatoric strains can also be kept at the intersection point between the visco-plastic ellipse cap and the anisotropic line. As well, an associated flow rule further assures a smooth transition of the visco-plastic strain increment vectors on the visco-plastic cone-cap limit state surfaces. With the few parameters determined from traditional experiments for the stress element soil sample, numerical analysis is performed to assess the model via CD constant-strain-rate K0 axial and 1/K0 radial triaxial compression, constant-strain-rate traditional CD triaxial compression/extension. Numerical analysis is also performed to validate the model via constant-strain-rate traditional CU triaxial compression tests and constant-strain-rate CD triaxial K = σr′/σa′ = cst compression tests on the anisotropic Berthierville clay. Numerical analysis by the kinematic hardening anisotropic EVP model validates the test results very well, and especially the combined effect is well simulated between strain rate and kinematic hardening on the visco-plastic behavior of the saturated cohesive anisotropic soil. In the future, micro-structure or/and temperature can be further combined with the kinematic hardening anisotropic EVP model introduced in this paper.