In order to study the mechanical characteristics and cracking behavior of jointed rock mass under hydro-mechanical coupling, a series of uniaxial compression tests and triaxial compression tests were carried out on cylinder gypsum specimens with a single pre-existing flaw. Under different confining pressures, water pressure was injected on the pre-existing flaw surface through a water injection channel. The geometrical morphology and tensile or shear properties of the cracks were determined by X-ray computed tomography (CT) and scanning electron microscope (SEM). Based on the macro and micro observation, nine types of cracks that caused the specimen failure are summarized. The results of mechanical properties and crack behavior showed that the confining pressure inhibited the tensile cracks, and shear failure occurred under high confining pressure. The water pressure facilitated the initiation and extension of tensile crack, which made the specimens prone to tensile failure. However, under the condition of high confining pressure and low water pressure, the lubrication effect had a significant effect on the failure pattern, under which the specimens were prone to shear failure. This experimental research on mechanical properties and cracking behavior under hydro-mechanical coupling is expected to increase its fundamental understanding.

Determining the safe burial depth is crucial for ensuring the long-term stability of compressed air energy storage chambers throughout their operational cycle. This study proposes a safe burial depth solution based on elastic and elastoplastic theories, with the safety criterion being the prevention of plastic zone formation in the surrounding rock. An approximate method is used to calculate the boundary of the plastic zone, and a closed-form safe burial depth range solution is determined by ensuring that the plastic zone remains contained within the chamber boundary. The study demonstrates that both overly shallow and overly deep burial depths can result in the formation of plastic zones, whereas no plastic zone occurs in the surrounding rock when the burial depth is within the range solution. The validation through comparison with previous physical model experiments and numerical simulation methods proves the effectiveness of the solution. The study further reveals that the range of safe burial depths is wider and more suitable for air storage when the lateral pressure coefficient is closer to 1 and the shear strength of the surrounding rock is higher. The solution is applicable to surrounding rocks of Class II and above, and can be quickly solved using the maximum air pressure determined by engineering requirements and the geomechanical parameters of the rock mass obtained from geotechnical investigations. The solution provides high computational efficiency and accuracy and offers significant engineering value for site selection and the design of burial depth in CAES chambers.

Heterogeneity at the grain scale strongly influences hydraulic fracturing in crystalline rock; however, systematic studies quantifying its impacts on the evolution of injection pressure and crack propagation remain limited. To address this gap, we employ a hydro-mechanical phase-field model incorporating Voronoi-based microstructures to systematically quantify the effects of grain-scale heterogeneity on hydraulic fracturing. Two numerical experimental programs are designed to examine the effects of (i) mean grain size and (ii) mineral distribution under different axial stresses. The simulations reveal a close coupling between injection pressure and crack-length evolution, and both responses are strongly governed by grain-scale heterogeneity. When the fracture enters weak minerals, it advances rapidly and pressure drops; when it encounters on strong minerals, growth slows or arrests and pressure builds until a threshold triggers the next advance. Moreover, peak pressure statistics further indicate that mineral distribution dominates the response scatter, while axial stress plays a secondary role. Specifically, the mean peak pressures at 0 and 10 MPa are similar (about 14.31 and 14.21 MPa), whereas rearranging minerals within the same Voronoi tessellation changes peak pressure by more than 4 MPa. Higher peaks occur when strong minerals lie ahead of the initial crack tip, increasing resistance to initiation and early growth. Finally, the stress state modulates fracture trajectories: under low axial stress, fractures preferentially follow mineral boundaries, whereas higher axial stress strengthens macroscopic stress guidance and shifts the path toward a direction closer to being perpendicular to the maximum principal stress. This trend is consistent with energy minimization, since interface detouring under high axial stress incurs a larger elastic free energy penalty.