Experimental evaluation of multiscale damage evolution in fissured limestone under different wet-dry cycles and axial stress.

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.

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

Taking argillaceous sandstone collected from foundation pits as the research object, laboratory tests including drying-wetting cycles, uniaxial compression, cyclic disturbance, and acoustic emission (AE) monitoring were conducted to investigate the deterioration and fatigue damage evolution laws. The results show that, under the influence of drying–wetting cycles, the compressive strength and elastic modulus of argillaceous sandstone both decline following a power-function attenuation trend, while the ultimate fatigue strain under cyclic disturbance rises, and the spatial distribution of AE events grows more scattered. In contrast, a higher upper-limit stress ratio yields a lower ultimate fatigue strain and induces more significant spatial clustering of AE events along the shear failure plane. After being subjected to drying-wetting cycles, the fatigue failure threshold of argillaceous sandstone remains stable within the range of 75%–80% σ . Fatigue life presents a log-linear correlation with the upper-limit stress ratio, and varies in accordance with a power function against the number of drying-wetting cycles. On this basis, a three-dimensional quantitative model was established to characterize the fatigue damage evolution of argillaceous sandstone. The research findings can provide a scientific basis for the design, construction, and stability control of foundation pits in red-bed soft rock.

Fracture evolution of micritic bioclastic limestone under Brazilian splitting: a comparison between natural and water-saturated states

The tensile strength properties and the initiation and propagation of tensile cracks within micritic bioclastic limestone–which forms the surrounding rock mass at the tunnel exit of the Altash Water Conservancy Project–pose a threat to engineering stability. To investigate the differences in tensile strength and stress-induced crack evolution under natural and water-saturated conditions, a comparative experimental study was conducted using Brazilian splitting tests coupled with acoustic emission (AE) monitoring. The results demonstrate that, compared with natural specimens, saturated limestone exhibits a 16.54% reduction in tensile strength. The failure process can be categorized into three distinct stages: compaction, quasi-linear elasticity, and unstable crack propagation. Furthermore, AE analysis indicates that while overall AE activity decreases following water saturation, the proportion of tensile cracks increases from 92.30% to 95.14%. Conversely, under natural conditions, shear cracks are more active and initiate earlier. Microscopically, the high content of bioclasts and associated complex interconnected pores (e.g., body cavity and secondary dissolution pores) endow the rock with remarkable hydrophilic and water-retention characteristics. Coupled with the presence of the abundant hydrophilic mineral illite, these factors collectively exacerbate water-rock interactions, driving the significant degradation of the rock’s mechanical properties from both material and structural perspectives.

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.

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.

Experimental study on freezing-dynamic deterioration damage characteristics of joint-filled rock samples of cold regional open-pit slope