A constitutive model for broken ice

Using triaxial test data, a time-independent incremental plasticity model has been developed for normally-consolidated broken ice. For this material, both the yield criterion and potential function are found to depend on the void ratio. The inclination of the incremental plastic-strain vector is approximately constant in the triaxial (p-q) plane. It appears that the initial yield of the broken ice can be approximated by a Mohr-Coulomb-type yield surface with the cohesion and fractional parameters varying with the void ratio of the material. Extrapolating into three-dimensional stress space, a Drucker-Prager-type yield surface may be adopted. The hardening law is assumed to be isotropic and can be described by a unique relationship in the mean normal stress-deviatoric stress-void ratio (p-q-e) space. A plastic potential function is established using the observation that the ratio of the incremental shear strain to the incremental volumetric strain is approximately constant. The analytical solution of these plasticity equations has been used to reproduce several triaxial test results.