Non-associative constitutive laws for low porosity rocks

Two simple constitutive laws appropriate for elastic–plastic deformation up to peak load of low porosity rocks are presented. Both laws account for mean stress dependence of yield hardening between yield and peak strength and non‐associative plastic straining. The two constitutive laws are based on the Mohr–Coulomb and the Mises–Schleicher yield criteria. The yield criteria are matched at axisymmetric compression and the relationships among the constitutive parameters are given. The parameters are then evaluated for two evaporite rocks anhydrite and polyhalite based on axisymmetric compression data. Comparison of predicted stress–strain laws with those measured in the laboratory show that these laws can be used for engineering analysis.