A variational Cam-clay theory of plasticity

We present a finite deformation constitutive theory for non-cohesive granular media. The material model falls in the family of the so-called Cam-clay theories. As typical of Cam-clay models, soil is assumed to be frictional with a logarithmic-type compression. The same state boundary surface-described by ellipses-is taken as yield and plastic potential surface. Hardening is related only to plastic volumetric strains. The large deformation theory is based on the multiplicative decomposition of the deformation gradient into elastic and inelastic parts. We extend the stress update algorithms from small-strain plasticity to finite plasticity through the logarithmic and exponential mappings and adopt a fully variational characterization of the visco-plastic constitutive updates. (C) 2004 Elsevier B.V. All rights reserved.