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.

For a long time, one of the important safety problems in open-pit mines is the stability of a large number of high slopes with gently inclined soft interlayer. Rock masses formed after long geological processes generally have some initial damage. Mining works also cause varying degrees of disturbance and damage to rock masses in the mining area during the mining process. This phenomenon means that accurate characterization of the time-dependent creep damage for rock masses under shear load is necessary. The damage variable D is defined based on the spatial and temporal evolution laws of shear modulus and initial level of damage for the rock mass. In addition, a coupling damage equation between the initial damage of the rock mass and shear creep damage is established based on Lemaitre’s strain equivalence assumption. Kachanov’s damage theory is also incorporated to describe the entire process of time-dependent creep damage evolution for rock masses. A creep damage constitutive model that can reasonably reflect the actual mechanical properties of rock masses under multi-stage shear creep loading conditions is established. This takes into account multi-stage shear creep loading conditions, instantaneous creep damage during the shear load phase, staged creep damage and factors influencing the initial damage of rock masses. The reasonableness, reliability and applicability of this model are verified by comparing the results of the multi-stage shear creep test with calculated values from the proposed model. As opposed to the traditional creep damage model, the shear creep model established in this present study takes into account the initial damage of rock masses and can describe the multi-stage shear creep damage characteristics of rock masses more convincingly.

Under field conditions, the moisture content of rock changes with the weather during prolonged creep. In order to investigate the effect of moisture content change on long-term shear strength and deformation behavior, a shear apparatus for intact rock was developed. Since three prefabricated holes are drilled in the upper part of the rock sample, the water injection device and the gas injection device can be used to inject water and gas into the rock sample alternately during the test to adjust the moisture content without removing the normal load and shear load. By using silicone gasket and seals in the shear box, fluid injection at a pressure of 5 MPa was achieved without leakage. Shear creep tests of argillaceous shale were conducted under both constant and dynamic moisture conditions, and the results were described by the Nishihara model. The experimental results revealed that there are significant differences in the long-term shear strength and deformation of argillaceous shale under different moisture content conditions. The proposed rock shear apparatus can advance the quantitative study of the shear creep properties of rock samples during moisture content changes and has certain practical application value for the prediction of engineering rock mass stability during rainfall.