Study on creep mechanical properties of carbonaceous shale under dry-wet cycle

Abstract The creep mechanical properties of rock under dry-wet cycles are of great significance for studying the long-term aging stability of engineering rock and soil. In the past, there were few studies in this area, and most of the dry-wet cycle tests on rock samples did not conform to the actual stress state of the rock. In view of the shortcomings of these studies, this paper innovatively carried out the dry-wet cycle test of the rock under the continuous state of the stress field, and studied its mechanical properties. The specific method is to take carbonaceous shale as the research object, and use the soft rock shear rheological test system independently developed by our research group to carry out the shear creep test of carbonaceous shale under the action of dry-wet cycle. The test results show that the creep full-time curves of carbonaceous shale under different dry-wet cycles show a step-shaped curve shape. The dry-wet cycle has a significant effect on the deformation characteristics of carbonaceous shale. With the increase of the number of dry-wet cycles, the instantaneous strain of the rock gradually increases, the instantaneous shear modulus decreases from 596.650 MPa at 0 times to 365.199 MPa at 12 times, and the attenuation rate reaches 38.79%. The creep strain and cumulative creep strain become larger, the stress required for accelerated creep decreases from 3.29 MPa to 2.75 MPa, and the accelerated creep time in the third stage increases from 11.892 h to 5.316 h, and the creep effect is more significant. The long-term strength of carbonaceous shale decreases from 3.05 MPa to 2.49 MPa, and the decrease increases with the increase of dry-wet cycles. The more the number of dry-wet cycles, the smaller the undulation of the shear failure section of the carbonaceous shale, and the smoother the surface. The research results have important guiding significance for the long-term aging stability analysis of engineering rock and soil mass subjected to repeated dry-wet cycles.