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

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.

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

Fissured limestone in the gorge-section hydro-fluctuation belt of the Three Gorges Reservoir (TGR) is continuously affected by wet-dry cycles and overburden self-weight stress, and its progressive deterioration markedly increases geohazard risk. However, the multiscale damage evolution mechanism of fissured limestone involving axial stress remains insufficiently understood. This study investigated damage evolution under coupled effects through wet-dry cycle-axial stress deterioration tests, uniaxial compression tests, and XRD, SEM, CT, and AE analyses. Based on elemental conservation, stoichiometric porosity was proposed to improve microscopic damage characterization. The results show that the deformation and failure process includes compaction, stable microcrack propagation, unstable microcrack propagation, and failure stages. With increasing wet-dry cycles and axial stress, the mass loss rate, saturated water absorption rate, and pore parameters continuously increase, while the proportion of tensile cracks decreases and the shear component increases. Under wet-dry cycle-axial stress coupling, calcite dissolution dominates mineral deterioration, grain cementation progressively weakens, the specimen surface evolves from a dense morphology to a honeycomb-like structure, and internal pore-fissure structures continue to develop. Overall, wet-dry cycling is the fundamental driver of damage deterioration, whereas axial stress promotes pore-fissure propagation and aggravates structural damage. The average difference between stoichiometric porosity and CT porosity is approximately 4.07%, indicating that the proposed index can support quantitative evaluation of microscopic damage in fractured limestone under acidic cycling. These findings deepen the understanding of damage evolution in fractured limestone within the gorge-section hydro-fluctuation belt in TGR.

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.

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

Macro- and micro-scale mechanical properties and energy evolution analysis during unidirectional freeze-thaw cycling of sandstone.

This study investigates the microstructural effects, energy evolution, and damage progression of sandstone under uniaxial cyclic freeze-thaw (F-T) conditions. Using the roof sandstone from Shuangma No. 1 Mine, uniaxial compression tests were performed on samples subjected to varying numbers of F-T cycles. PFC3D simulations were employed to reproduce the failure process and analyze microcrack evolution.Results show that both the compressive strength and elastic modulus of sandstone decrease with increasing F-T cycles. When loaded perpendicular to the freeze-thaw direction, the elastic modulus of sandstone is significantly higher than that under parallel loading; conversely, the peak strain and compressive strength show the opposite trend. Post-failure analysis reveals an increase in the total number of cracks, tensile cracks, and shear cracks with more F-T cycles for both loading directions. However, the total and tensile crack counts in the parallel direction remain consistently higher than in the perpendicular direction.Energy analysis indicates that the proportion of elastic energy at peak stress continuously decreases with more F-T cycles, though it remains higher in the parallel direction. A rebound occurs at 140 cycles. The cumulative elastic energy ratio also decreases with increasing cycles, with the parallel direction consistently exhibiting higher values. Damage evolution equations, derived from the principle of minimum energy dissipation, show that the damage threshold in the parallel direction continuously increases and stays higher than in the perpendicular direction, where it first decreases and then increases. Final damage values in both directions initially rise and then decline, with transition points at 140 and 110 cycles, respectively. These findings provide theoretical guidance for rock engineering in cold regions.

Cyclic Thermal Shock‐Induced Permeability Enhancement in Tight Lithologies: Microstructural Controls and Elastic‐Wave Monitoring

Enhanced geothermal systems rely on increasing permeability and pore surface area in rock. Cyclic thermal shocking can achieve both by inducing thermal cracks through repeated rapid cooling. Laboratory experiments subjected micritic limestone, granodiorite, and trachybasalt to up to 10 thermal shock cycles, while tracking crack evolution qualitatively using time‐lapse electron microscopy and quantifying pressure‐dependent permeability and elastic wave velocities. This work advances prior efforts focused primarily on crack initiation by demonstrating how lithology‐specific microstructures govern the cyclic evolution, persistence, and efficiency of pressure‐dependent permeability enhancement during cyclic thermal shocking. This reframes microstructure as a key design variable controlling permeability enhancement and monitoring during geothermal stimulation. Contrasting mineral thermal properties, large mineral grains, and irregular vugs promote the greatest permeability enhancement. Velocity reductions were most pronounced <10 MPa effective pressure (Peff) and diminished with increasing cycle number, indicating that velocity‐based monitoring in geothermal systems must account for Peff and cycle number.