Triaxial creep tests were carried out under seepage pressure by using rock servo-controlled triaxial rheology testing equipment. Based on experimental results, rock rheological properties influenced by seepage-stress coupling were studied, and variations of seepage rate with time in complete creep processes of rock were analyzed. It is shown that, when the applied stress is less than failure stress level, the creep deformation is not obvious, and its main form is steady-state creep. When applied stress level is greater than or less than but close to fracture stress, it is easier to see the increase of creep deformation and the more obvious accelerative creep characteristics. The circumferential creep deformation is obviously higher than the axial creep deformation. At the stage of steady-state creep, the average of seepage flow rate is about 4.7×10-9 rn/s at confining pressure （tr3） of 2 MPa, and is about 3.9×10-9 m/s at a3 of 6 MPa. It is seen that the seepage flow rate at or3 of 2 MPa in this case is obviously larger than that at tr3 of 6 MPa. At the stage of creep acceleration, the seepage flow rate is markedly increased with the increase of time. The variation of rock permeability is directly connected to the growth and evolution of creep crack. It is suggested that the permeability coefficient in complete creep processes of rock is not a constant, but is a function of rock creep strain, confining pressure, damage variable and pore water pressure. The results can be considered to provide a reliable reference for the establishment of rock rheological model and parameter identification.
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.
