Observations on Mohr-Coulomb plasticity under plane strain.

Linear elastic-perfect plasticity using the Mohr-Coulomb yield surface is one of the most widely used pressure-sensitive constitutive models in engineering practice. In the area of geotechnical engineering a number of problems, such as cavity expansion, embankment stability and footing bearing capacity, can be examined using this model together with the simplifying assumption of plane-strain. This paper clarifies the situation regarding the direction of the intermediate principal stress in such an analysis and reveals a unique relationship between hydrostatic pressure and the principal stress ratio for Mohr-Coulomb and Tresca perfect plasticity under those plane-strain conditions. The rational relationship and direction of the intermediate principal stress are illustrated through both material point and finite-element simulations. The latter involves the analysis of a rigid strip footing bearing onto a weightless soil and the finite deformation expansion of a cylindrical cavity