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 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.
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.
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.
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.
Zuguo Mo, Maojun Huang, Yong Wu et al.· Frontiers in Built Environme...· 0 citations