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.
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.
To reveal the mechanical degradation, damage evolution, and failure mechanism of dense sandstone under varying water content, uniaxial compression tests were conducted on sandstone with different water contents. Combined with acoustic emission monitoring, scanning electron microscopy, and energy evolution analysis, constitutive models of damage evolution in sandstone with different water contents were established. The deformation and failure characteristics of water-bearing sandstone were systematically studied at both macroscopic and microscopic scales. The results show that with increasing water content, the peak strain, compressive strength, and elastic modulus of sandstone generally decrease, and the degradation pattern is initially steep and then gradual. Increasing water content gradually lowers the damage threshold of sandstone, leading to earlier damage evolution. The cumulative acoustic emission count and cumulative energy decrease overall, and moisture has a significant inhibitory effect on crack propagation and energy release. In terms of failure mode, sandstone gradually shifts from shear failure to tensile failure, with the proportion of tensile cracks increasing significantly with increasing water content. Microscopically, the fracture morphology gradually transforms from relatively smooth transgranular fractures in the dry state to rougher intergranular fractures and coupling fractures. These findings can provide a theoretical basis for the analysis of the mechanical properties of deep water-bearing dense sandstone surrounding rocks and their engineering applications.
This study investigates the mechanical behavior and failure characteristics of fly ash concrete under quasi-static to low-to-medium strain rate loading. Uniaxial compression tests were conducted on three specimen sizes under four strain rate conditions (totaling 12 working conditions), analyzing damage evolution and failure patterns across different scales and loading rates. Results indicate that at lower strain rates, uniformly distributed cracks formed on specimen surfaces, with damage concentrated at coarse aggregate-mortar interfaces. In contrast, higher strain rates induced brittle failure characterized by crack propagation along the loading direction and coarse aggregate fracture - particularly evident in smaller specimens. As strain rates increased, the compressive strength of small, medium, and large specimens rose by 48.18%, 38.19%, and 29.07% respectively, demonstrating diminishing strength enhancement and reduced strain rate sensitivity with larger dimensions. Based on Weibull and log-normal statistical models, this study introduces a coupling coefficient accounting for size and strain rate effects, establishing a novel dynamic strength model capable of predicting stress-strain responses within target strain rate ranges. The model provides theoretical support for optimizing fly Ash cement-based materials and offers valuable references for durability assessment in hydraulic and civil engineering structures.
