The influence of the intermediate stress on the plane strain strength

A general 3D model is presented that includes the intermediate stress in strength analysis. The model is formulated in triaxial-compression strength parameters and the ratio between triaxial extension strength and triaxial compression strength. The model allows for a smooth transition between the expressions of MatsuokaNakai and Lade-Duncan. Starting from the general 3D model, the equivalent Mohr-Coulomb approach is developed for the commonly used calculation of failure loads for plane strain configurations. The approach includes the effect of the intermediate stress on the strength. The match between the general 3D model and the equivalent Mohr-Coulomb formulation is illustrated with Finite Element Method examples. Strain localisation is shown to be a dominant mechanism in the simulation of failure loads in the case of non-associativity. It is shown that Davis expressions derived from the equivalent Mohr-Coulomb model match the simulations of the general 3D model.