Study on the damage evolution of red-bed soft rock in foundation pits under the coupled influence of drying-wetting cycles and cyclic disturbance

Mesoscopic Damage Evolution of Water-Bearing Mudstone Under Low-Strain-Rate Cyclic Dynamic Loading: A Particle-Flow Simulation Study

Groundwater-related weakening and repeated low-strain-rate disturbances can jointly affect the long-term stability of soft surrounding rock. In this study, a PFC3D model was developed by combining a cumulative residual-strain damage variable with a Weibull statistical damage variable. Water effects were represented indirectly through water-content-dependent mesoscopic parameters and contact-strength degradation, thereby linking macroscopic irreversible deformation to progressive mesoscopic bond degradation. The cyclic responses of mudstone specimens with water contents of 0%, 3%, 5%, and 7.04% were simulated under a roadway-like three-directional, five-face boundary condition, consisting of axial loading, lateral pressure, one laterally constrained side, and one free face. The model reproduced the main stress–strain trends and failure characteristics. From the dry to saturated state, the experimental and simulated peak strengths decreased by 68.51% and 67.44%, respectively. Increasing water content also promoted earlier crack initiation, weakened strong force-chain continuity, and shifted failure from localized shear instability to distributed tensile–shear damage. Energy dissipation became increasingly important as water content increased. These findings clarify the mesoscopic damage mechanism of water-bearing mudstone under coupled water-induced softening and low-strain-rate cyclic loading, providing a reference for stability assessment and support design in underground soft-rock engineering.

Dynamic Progressive Failure and Energy-Driven Damage Evolution of Coal–Sandstone Composite Specimens Under Impact Loading: Coupling Effects of Component Ratio

Overburden rotation and mining disturbance promote deep coal fracture and spalling, potentially inducing dynamic hazards, while the coal–rock thickness ratio largely governs the composite’s dynamic response and failure severity. Based on the geological conditions of a typical deep coal mine, SHPB tests were performed on coal–sandstone composite specimens with four systematically varied coal-to-rock ratios (C:R = 1:0, 2:1, 1:1, and 1:2). High-speed photography and the digital speckle correlation method (DIC) were integrated to capture displacement, strain, energy, and fragmentation fields throughout progressive dynamic compression. Experimental data revealed four findings: (1) Crack development follows a sequential evolution process of initiation, propagation, and failure. Higher impact air pressure accelerates crack development and coalescence, resulting in a higher degree of specimen fragmentation and fewer large blocks. Within the tested range of coal–rock ratios, an increase in the rock proportion accelerates coal fracture, which is attributed to the significantly higher density and hardness of rock compared to coal. (2) Energy evolution consistently follows three stages: absorption, accumulation, and dissipation. Under identical impact pressure, a higher rock ratio elevates equivalent stiffness and wave impedance, leading to monotonic increases in peak stress, peak strain, absorbed energy, and dissipated energy. (3) The fragmentation degree exhibits a pronounced dependence on impact pressure. Specifically, for the pure coal specimen (C:R = 1:0), when the impact pressure increases from 0.3 MPa to 0.7 MPa, the mass percentage of coarse debris (>30 mm) drops from 73.37% to 18.57%, whereas that of fine particles (<4 mm) rises from 15.69% to 35.24%. (4) Under identical impact conditions, a higher rock proportion leads to increasing trends in all measured indicators, including peak stress, strain, and energy accumulation and dissipation, which are consistent with the superior mechanical properties of the rock. Based on these observations, it can be inferred that the wave impedance mismatch and stiffness ratio at the coal–rock interface play a key role in controlling stress wave transmission/reflection and strain incompatibility; however, the individual contribution of each factor warrants further dedicated investigation.

Research on the Macro‐Micro Energy Evolution Law and Segmented Damage Constitutive Model of Sandstone Under Dry‐Wet Cycles

The periodic fluctuation of reservoir water levels induces dry‐wet cycles, deteriorating sandy rock slope stability and potentially triggering collapses. This study investigates the degradation mechanism of Three Gorges Reservoir fine sandstone through uniaxial compression tests and PFC2D simulations under varying dry‐wet cycles. Key findings include: (1) Increasing cycles reduce uniaxial compressive strength and elastic modulus (showing “V‐shaped” and “N‐shaped” degradation trends), while permeability and porosity rise, and P‐wave velocity declines. (2) Crack growth is nonlinear, dominated by shear cracks and high‐angle microcracks, with force chains aligning with the loading direction. (3) Dissipation energy rate follows a “W‐shaped” trend, while elastic energy rate exhibits an “M‐shaped” pattern; both energies at crack initiation, damage, and peak stress correlate exponentially with cycle count ( K sd being more sensitive). (4) Dry‐wet cycles weaken intergranular bonds, reduce elastic energy storage ( U e ), increase dissipated energy ( U d ), lower M ‐value stability, and shift failure from brittle to ductile. (5) A Weibull‐based segmented damage model effectively simulates sandstone behavior under cyclic conditions. These insights enhance understanding of reservoir slope stability under hydrological fluctuations.

Study on mechanical response and damage models of sandstone-shale interbedding under different cyclic loading modes

Experimental investigation on damage and seepage characteristics of layered slate under cyclic loading and unloading of stress

To investigate the damage deterioration and seepage evolution of bedded slate under cyclic axial loading–unloading, triaxial tests were conducted on specimens with bedding angles of 0°, 30°, 45°, 60° and 90° under 10 MPa confining pressure and 5 MPa pore pressure. The study systematically analyzed the influence of bedding structure on rock strength, deformation, damage accumulation, and permeability. Consequently, a damage constitutive model and a permeability evolution model were developed, incorporating bedding angle, cyclic fatigue, loading path, and effective stress. Results indicate that bedded slate exhibits pronounced nonlinear deformation, hysteresis, and stiffness degradation under cyclic loading, with responses strongly dependent on bedding angle. Peak strength follows a “U-shaped” distribution, where specimens near 45° show the greatest damage due to combined shear-tensile failure along bedding planes. Permeability initially decreases due to fracture compaction but subsequently increases as stress exceeds the historical maximum, facilitating fracture interconnection. This evolution shows distinct anisotropy; intermediate bedding angles promote more efficient seepage channel formation, leading to larger permeability increments. The proposed models accurately reproduce the experimental stress–strain and permeability behaviors across different angles. These findings provide a theoretical framework for stability analysis and seepage hazard mitigation in stratified rock masses subjected to cyclic disturbances and fluid flow.

Mechanical Properties of Limestone Under Different Confining Pressures and Wet–Dry Cycles

During the operation of large reservoirs, slope rock masses at different elevations are subjected to confining pressure variation and alternating wet–dry cycles induced by water-level fluctuations, resulting in the evolution of their mechanical properties. To investigate this issue, conventional triaxial compression tests were conducted on limestone from Badong County in the Three Gorges Reservoir area under confining pressures of 5–20 MPa and 0–50 wet–dry cycles. The results show that confining pressure significantly enhances limestone strength, whereas wet–dry cycles induce a progressive deterioration in mechanical properties. Under the same confining pressure, the deterioration exhibits a staged characteristic, with a rapid decrease at the early stage followed by a slower decline. Higher confining pressure effectively suppresses crack propagation and mitigates the degradation caused by wet–dry cycling. Meanwhile, wet–dry cycles promote the transition of the failure mode from single-fracture failure to multi-fracture fragmentation. The elastic modulus, cohesion, and internal friction angle all decrease exponentially with increasing wet–dry cycles. Based on damage mechanics theory, a constitutive relationship considering wet–dry cycle effects was established to characterize rock stiffness degradation and its influence on the overall mechanical response. The proposed model effectively describes the evolution of mechanical parameters and deformation characteristics under wet–dry cycling conditions. This study provides an experimental and theoretical basis for evaluating the long-term stability of reservoir slopes.