Difficulty in clarifying the deformation characteristics of deep rocks under a high water pressure environment is a technical bottleneck restricting the safe operation of large hydropower stations. In order to study the effect of reservoir water level changes on the mechanical behavior of deep limestone, a series of mechanical tests were conducted under different dynamic high water pressure environments using a self-developed hydraulic loading test device. The test results show that the unsaturated limestone always undergoes compressive deformation during the linear increase in external water pressure, and the saturated limestone changes its deformation state from compression to expansion during the linear decrease in external water pressure. The stress–strain curve of limestone shows apparent hysteresis characteristics during the cyclic increase and decrease in external water pressure. Overall, the rock strain rate showed a significant negative correlation with the external water pressure, and the rock deformation modulus showed a certain positive correlation with the external water pressure. During hydraulic loading, saturated rocks had a smaller range of variation in the strain rate and deformation modulus and were more resistant to deformation than unsaturated rocks. Limestone was subjected to both external water pressure and internal pore water pressure in a cyclic cycle, where pore water pressure promotes pore creation and expansion, while external water pressure prevents water from degrading the pore structure. The periodic change of water pressure has a significant influence on rock mechanics and deformation behavior, and the rock mass will undergo elastic deformation, plastic deformation, and even fracture. Further study of this deformation rule can provide a more accurate theoretical basis for the safe operation of water conservancy projects.

This study deeply explores the permeation deformation mechanism of limestone cores in deep-water environments. Through a customized test device, the mechanical responses of deep-water rocks under different moisture content conditions are simulated. The device is composed of a pressurization system, a pressure vessel, and a data acquisition system, which can accurately apply high water pressure and monitor the stress and strain changes in the core in real time. The cores used in the experiment were cut to standardized sizes and subjected to strict saturation and drying treatments to ensure the consistency of test conditions and the accuracy of data. The mechanical behaviors of cores under four working conditions of dryness, 50% moisture content, and 100% moisture content are analyzed. Through the cyclic process of pressurization and depressurization, the changes in the strain characteristics of the cores are observed. The research results show that when pressure is applied for the first time, low moisture content cores will absorb water and expand, and the strain will increase and then tend to be stable as the pressure increases. There is no such process for cores with 100% moisture content. Water pressure is positively correlated with the elastic modulus of rocks, negatively correlated with the strain rate during pressurization, and positively correlated during depressurization. Moreover, an increase in moisture content reduces the average strain mutation, reduces the average strain rate amplitude, and increases the elastic modulus. This study provides important theoretical support for the design and construction of deep-water rock engineering and provides a reference for further research in related fields.