Reloading experimental research on the creep properties of yellow sandstone samples considering pre-peak unloading and cyclic water intrusion damage

To address the long-term stability of water-related slope projects such as water conservancy and hydropower after excavation and unloading, the CDT1305-2 microcomputer-controlled electronic pressure test system and the YAW-3000A electro-hydraulic pressure test system were used to carry out the uniaxial compression and graded load creep tests of yellow sandstone after different pre-peak unloading and cyclic water intrusion. Taking the undamaged state of the rock as the base state, the damage mechanics theory and the principle of strain equivalence after promotion are applied to construct the DUNC, the macroscopic and microscopic coupled damage variable of the rock. The creep properties of the rock reloading under the action of different influencing factors are investigated, and the elastic-visco-plasticity theory is introduced to establish a new type of nonlinear creep damage model. The results show that:(1) After 0.4Rc and 0.55Rc pre-peak unloading, the internal vertical pores of the rock are gradually expanded and the transverse pores are compacted, resulting in the improvement of axial homogeneity, but after 0.65Rc and 0.7Rc pre-peak unloading, the internal vertical and transverse pores are further developed and widened, making the whole inhomogeneity of the rock more significant. (2) The rock creep damage angle α and the cracks gradually increase with the pre-peak unloading point, while the creep deformation shows a tendency to first decrease and then increase, and the level of creep stress increases with the number of cyclic water intrusion. (3) According to the deformation modulus evolution law in the rock creep process, the variables of global damage and local time-varying damage are defined to reveal the rock damage evolution mechanism, then the rock macroscopic and microscopic coupled damage variable are analysed and constructed, taking into account the effects of pre-peak unloading, cyclic water intrusion and creep loading. (4) A nonlinear creep damage constitutive model is established by combining the nonlinear components and damage processing, and the model identification and validation are carried out based on the experimental data, which can not only satisfy the whole creep process damage evolution law, but also accurately describe the nonlinear deformation law in the stage of accelerated creep. The results are of great significance for the prevention and control of creep-type landslide disaster following the excavation and unloading of wading and high steep rocky slopes. © 2024 Academia Sinica. All rights reserved.