Abstract:In order to study mechanical characteristics of the oil sand core of Fengcheng oilfield in Xinjiang Karamay，a consolidated drained triaxial compression tests at room temperature were conducted on MTS 815，and the triaxial mechanics properties of oil sand under varying confining pressure were studied.Results indicated that the typical stress-strain curve of oil sand seems a hump curve，exhibiting strain-softening and shear dilatancy.Test boundary conditions and the confining pressure have significant influences on the mechanical properties of oil sand

which determine the failure modes and the post-peak softening behaviors.The deformation modulus and Poisson’s ratio of oil sand have linear relationship with confining pressure in logarithmic coordinates respectively，and the failure criterion of oil sand at low stresses can be explained approximately with the Mohr-Coulomb criterion.Based on two classical nonlinear constitutive models，by introducing new parameters，the stress-strain constitutive relationship of oil sand in Fengcheng was discussed，which demonstrated that the modified Chengdu Science and Technology University Model seems better to describe the strain-softening properties of oil sand than Nanshui Model，and able to consider shear dilatancy to some extent.