Given the challenging conditions of high-alpine and high-altitude metal mining, complex factors affecting rock mass quality, and the intricate mechanisms of slope instability, this study focuses on the tuff from the high-alpine and high-altitude region of China. The deformation, strength, and failure characteristics of the tuff specimen were investigated through uniaxial compression tests, stress–seepage coupling triaxial compression tests under low-temperature curing conditions and nuclear magnetic resonance analysis. A damage constitutive model for the tuff specimen considering curing temperature was established. Results show that low temperatures significantly promote the development and interconnection of pores and fissures within the tuff specimen. Low-temperature and stress–seepage coupling increase the number of pores and fissures and drive their growth toward larger sizes. The tuff specimen undergoes compaction, elastic deformation, plastic yielding, and failure under triaxial compression. As temperature decreases, failure transitions from simple shear to combined shear-tensile failure, with extended compaction and shortened plastic yielding phases, leading to enhanced brittleness. A low temperature–load coupling damage variable was introduced based on nuclear magnetic resonance porosity and the Weibull distribution function, effectively modeling the stress–strain relationship and strength characteristics of the tuff specimen under low-temperature and stress–seepage coupling, with a good fit between experimental and theoretical.
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.
Thermal cycling and pre-existing cracks significantly influence the mechanical response and damage evolution of granite in high-temperature rock engineering. To clarify their coupled effects, granite specimens with different prefabricated crack inclination angles (0°, 45°, and 90°) were subjected to different temperature conditions (30-130 °C) and thermal cycle numbers (1-5 cycles), followed by uniaxial compression tests. Characteristic stresses, AE (AE) parameters, AE b-value evolution, fractal dimensions, macroscopic failure patterns, and SEM observations were jointly analyzed to reveal the damage mechanism.The results show that the mechanical and AE responses of cracked granite exhibit clear nonlinear dependence on temperature, thermal cycle number, and crack inclination. Under the same crack inclination, the peak stress, crack initiation stress ratio, AE counts, and cumulative AE energy vary non-monotonically with temperature, and 70 °C appears to be a critical transition temperature for AE activity and damage evolution. Increasing the number of thermal cycles promotes damage accumulation, enhances AE activity, and advances the abrupt drop point of the AE b-value, indicating earlier dominance of large-scale crack propagation and main crack formation. The prefabricated crack inclination further controls the crack propagation path and failure pattern. In particular, 45° cracks are more likely to guide inclined crack coalescence and tensile-shear failure under intensified thermal cycling, whereas 90° cracks tend to maintain tensile-dominated failure. SEM observations and box-counting fractal analysis further confirm that thermal cycling promotes the development of pores and microcracks, especially at 50 °C, 100 °C, and 130 °C. These findings provide a multi-scale understanding of the coupled thermal-mechanical damage mechanism of cracked granite and may support stability evaluation of rock masses subjected to repeated thermal disturbance.
Water significantly modifies rock mechanical performance and fracture characteristics through water content and water distribution. Nevertheless, the evolution laws of rock mechanical properties and underlying fracture mechanisms under variable water conditions remain incompletely clarified. In this study, uniaxial compression tests were carried out on sandstone samples with diverse water immersion durations. Experimental observations reveal that the uniaxial compressive strength (UCS) and elastic modulus of sandstone follow negative exponential attenuation with prolonged immersion time, with maximum reductions of 50.1% and 25.6%, respectively. Under equivalent water contents, samples featuring dry exteriors and wet interiors possess lower strength than those with wet exteriors and dry interiors. A self-developed numerical code incorporating humidity diffusion effects was subsequently adopted to interpret water-controlled sandstone fracture behaviors. Numerical outputs verify that water-induced softening and heterogeneous water distribution exacerbate rock material heterogeneity and internal stress non-uniformity, triggering tensile microcracks along dry–wet interfaces. As the immersion duration rises, the rock failure mode transitions from shear-dominated mixed failure to tension-dominated failure, and finally reverts to shear-dominated mixed failure. Macroscopic rupture is predominantly governed by the gradual coalescence of tension-generated microcracks. This study offers a theoretical foundation to advance the understanding of water-triggered mechanical degradation and fracture mechanisms in sandstone.
The deformation and failure mechanism of deep mudstone under high temperature and high pressure (HTHP) is a critical issue constraining deep-drilling efficiency. Taking an HTHP mudstone formation in the western South China Sea as the research object, this study integrates X-ray diffraction, scanning electron microscopy, nanoindentation, HTHP triaxial compression tests, and FDEM numerical modeling incorporating mineral heterogeneity and Weibull strength distribution. The mudstone is predominantly composed of clay minerals (44.67%) and quartz (32.37%), with low hardness (1.42–2.96 GPa) and moderate elastic modulus (43.9–58.2 GPa). Under ambient conditions, uniaxial compressive strength is approximately 19.5 MPa with axial splitting failure; at 40 MPa confining pressure, strength increases to 121.8 MPa with shear failure; at 150 °C and 40 MPa, peak strength slightly decreases, yield point is delayed, and post-peak decline accelerates. The FDEM model, calibrated against experimental data, reasonably reproduces crack evolution and failure modes. However, due to limited tests (one per condition) and variations in specimen depth, statistical robustness is constrained; thus, this study does not yet establish a generalizable quantitative cross-scale correlation, and the findings are primarily applicable to the specific formation investigated.
