Mohr-Coulomb Strength Theory for Anisotropic Soils

A general adaptation of the Mohr-Coulomb strength criterion is developed to include all probable variations for the effective stress strength parameters anticipated for normally and lightly overconsolidated transversely isotropic cohesive soils. The orientation of the failure plane is shown to depend on both the magnitude of the minor principal stress and the orientation of the principal stresses, and an important relationship is establishied between principal stress strengths and failure plane strengths. The mathematical formulation is based on a cylindrical coordinate reference system, which, from a conceptual point of view, is found to be more useful than the conventional Mohr-Coulomb diagram when dealing with anisotropic soils. The derived strength equation represents a closed mathematical solution for the shear resistance along a particular plane, and the analytical results of this study provide a rational basis for interpreting the effective stress strength anisotropy found in many natural and compacted soils. In addition, certain physical implications are considered with relation to strength testing of soils, and several numerical examples are given.