Influence of loading mode and water content on the mechanical properties and deterioration mechanisms of various lithologies: insights from acoustic emission characterization

Damage evolution and microscopic failure characteristics of dense sandstone at different water contents.

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.

Water-rich environments trigger coal instability risks via dynamic energy evolution and microscopic damage mechanisms.

Water-rock interaction significantly influences the mechanical behavior and failure characteristics of coal masses; however, the underlying mechanisms governing the transition of failure modes from dry to saturated conditions remain insufficiently understood. In this study, uniaxial compression tests combined with particle flow numerical simulations were conducted to investigate the mechanical response, crack evolution, force-chain characteristics, and failure mechanisms of coal specimens under dry and water-saturated conditions. The mesoscale evolution of cracks and force-chain networks was quantitatively characterized to elucidate the intrinsic relationship between internal damage development and macroscopic failure patterns. The results indicate that water saturation markedly deteriorates the mechanical properties of coal, leading to pronounced reductions in compressive strength and elastic modulus while accelerating damage accumulation. Dry specimens predominantly exhibit conjugate shear failure characterized by X-shaped shear bands and relatively large fragmented blocks. In contrast, saturated specimens are dominated by tensile failure, with axial cracks initiating from the specimen base and propagating parallel to the loading direction, resulting in more severe fragmentation and higher crack density. Analysis of crack hotspots and force-chain distributions reveals that macroscopic failure is governed by the evolution, rupture, and reorganization of internal force-chain networks. In dry specimens, strong force chains effectively sustain localized shear stress concentrations, promoting shear crack coalescence. Water-rock interaction weakens inter-particle bonding and frictional resistance, redistributes internal stresses, and disrupts force-chain continuity, thereby facilitating the initiation and propagation of tensile microcracks. The formation of force chains oriented obliquely to the loading direction is identified as an important precursor to tensile failure. These findings provide new insights into the mesoscale mechanisms of water-induced weakening and failure-mode transition in coal and offer a theoretical basis for the stability evaluation and disaster prevention of water-bearing coal engineering.

Fracture behavior and constitutive modeling of rock-concrete contact surfaces with different roughness under freeze–thaw cycles

Experimental and Numerical Study of Water Effects on Mechanical and Fracture Behavior of Sandstone: A Case Study

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 failure characteristics of heat-treated sandstone subjected to splitting loading and the pore-crack distribution effects

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.