Martí Lloret-Cabot

Numerical Implementation of a Critical State Model for Soft Rocks

This paper details the basic tasks for the numerical implementation of a simple elasto-plastic critical state model for bonded materials (i.e. soft rocks-hard soils) into the finite element program SNAC developed at the University of Newcastle in Australia. The first task described focusses on the derivation of the incremental constitutive relationships used to represent the mechanical response of a bonded/cemented material under saturated conditions. The second task presents how these stress-strain relations can be numerically integrated using an explicit substepping scheme with automatic error control. The third task concentrates on the verification of the substepping algorithm proposed. The model used to represent the saturated mechanical response of a bonded material combines the modified Cam clay with the constitutive relationships for cemented materials proposed in Gens & Nova (1993), but incorporates some flexibility on the degradation law adopted. The role of suction and other relevant aspects of unsaturated behaviour are also discussed at the end of the paper.

Normal Compression Planar Surfaces for Specific Volume and Degree of Saturation

The glasgow coupled model (GCM) predicts unique unsaturated normal compression planar surfaces for specific volume and degree of saturation when the soil states are at the intersection of the mechanical (M) and wetting retention (WR) yield curves. More generally, the model predictions for any stress path where plastic volumetric strains (compression) and plastic increases of degree of saturation occur simultaneously correspond to stress states on these two planar surfaces. The existence and form of these planar surfaces has been only validated against isotropic compression data on unsaturated samples of compacted Speswhite kaolin, but their suitability to represent one-dimensional (1D) loading conditions remains unclear. This paper investigates this aspect by deriving equivalent expressions for 1D normal compression conditions and then comparing them against the experimental response of unsaturated samples of compacted Jossigny silt subjected to 1D compression paths at different constant values of matric suction.