ESTIMATION OF LONG-TERM STRENGTH FOR XIANGJIABA SANDSTONE BASED ON CREEP TESTS
Conventional triaxial compression tests and triaxial compression creep tests were carried out on Xiangjiaba sandstone, and the long-term strength of Xiangjiaba sandstone was estimated. To do that, a series of observations were used including isotime curves of strain, relations between steady creep rate and applied stress, relations between applied stress and time to failure, and crack damage stress. Isotime curves of volumetric strain are more sensitive to time and applied stress than isotime curves of axial and lateral strain. The volumetric strain isotime curves have the most obvious turning points, which are considered to be indicators of long-term strength. Relation between axial (lateral) steady-state creep rate and the deviatoric stress can be described by an exponential function. Steady-state creep rate threshold was proposed to determine long-term strength of rock. This method is more reasonable than that using the turning point of steady-state creep rate-stress curve. The long-term strength of rock can also be estimated by isotime curves of crack volumetric strain and the relation between steady-state crackvolumetric strain rate and the deviatoric stress. It is found that crack damage stress can indicate the level of long-term strength of rock, which provides the basis for determining applied stress in multi-stepped creep test.