Creep failure mode and criterion of Xiangjiaba sandstone

Based on the results of conventional triaxial compression tests and triaxial compression creep tests on Xiangjiaba sandstone, the failure modes in short-term tests and creep tests, fractography of sandstone after creep failure, short-term and creep failure criterion are analyzed. In the short-term tests and creep tests, the sandstone samples fail in a mix mode consisting of shear failure in a single main plane and tensile failure. Confining pressure can restrict brittle failure and enhance the ductility of sandstone. In the creep tests, brittle fracture is reduced and plastic deformation can fully be developed compared to the condition of short-term tests. And the shear fracture surfaces are flat and they are covered by small particles as a result of friction. When confining pressure increases, particle size decreases while the degree of friction on shear plane increases. On the tensile failure plane, the tensile trace and direction of tearing could be clearly observed. There are obvious tearing steps on the tensile failure plane and tearing laminated structure on the front edge of tearing fracture. The same criterion can be used for the short-term and creep behavior, and the fitting effect using the MOGI criterion is better than the DRUCKER-PRAGER criterion. The cohesion and friction angle calculated by the MOGI criterion are in good accordance with those calculated by the MOHR-COULOMB criterion.