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

Research on the Stability of Arc-Fractured Rock–Concrete Composites: Mechanical Response and Energy Evolution

To mitigate the violent movement of overlying strata in goaf areas, rock–concrete composite support systems are widely utilized. However, the mechanical behavior of such systems under the influence of complex pre-existing defects, such as arc-shaped fractures, remains insufficiently understood. This study aims to clarify the failure mechanisms and the evolution of stability in these composites by evaluating the influence of fracture inclination angles. A synergistic methodology was adopted, combining laboratory uniaxial compression tests with discrete-element method simulations. Based on energy dissipation theory and the strain equivalence hypothesis, a statistical damage constitutive model was established to bridge the gap between microscopic damage and macroscopic mechanical response. The results demonstrate that fracture inclination significantly dictates the energy partitioning and crack propagation patterns within the composite. The established constitutive model, validated by numerical results ( R 2 > 0.999), effectively quantifies how increasing inclination angles enhance energy absorption efficiency and retard structural damage progression. Due to the high toughness of the concrete component, the composite maintains substantial residual bearing capacity, preventing instantaneous failure. These findings provide a robust theoretical framework and practical guidance for optimizing support designs in deep underground excavations with intricate geological defects.

Fracture evolution of micritic bioclastic limestone under Brazilian splitting: a comparison between natural and water-saturated states

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.

Mechanical response and damage evolution mechanism of multi-layer combined coal mass under static and dynamic loading

During underground excavation, structural instability and failure of coal-rock masses are major causes of engineering accidents. This study focuses on the coal mass ahead of the excavation face and divides into a multi-layer composite structure to systematically analyze the mechanical response characteristics of the combined coal mass under static and dynamic loading. Drop hammer impact tests were conducted to investigate the crack propagation and failure morphology of the combined coal mass. The results show that, under static loading, single-layer coal mainly exhibited X-shaped shear failure, whereas the combined coal mass showed V-shaped layered spalling failure. Under dynamic loading, compressive failure dominated in the central region, while shear failure mainly occurred at the four corners, and the damage was more pronounced along the minor axis direction. Two crack patterns were observed on the coal surface, simple radial cracks and complex intersecting radial and circumferential cracks. Under the combined effects of rectangular geometry and impact loading, the radial cracks of the specimen show a structural tendency to preferentially propagate along the minor axis direction. Under impact loading, the combined coal mass exhibited an overall spindle-shaped failure morphology in the axial direction. In the damage zone, the superposition of tensile stress and energy accumulation made the coal mass more susceptible to failure, resulting in a greater number of radial and circumferential cracks. These findings provide a scientific theoretical basis for revealing the incubation mechanisms of coal-rock dynamic disasters and optimizing disaster prevention and control measures under mining-induced disturbance conditions.

Mechanical response and failure mechanisms of sandstone under water–rock interaction: a multi-scale study and constitutive modeling

Study on Energy Evolution Mechanisms and Damage Mechanisms of Shale under Hydration

: Exploration and production activities targeting shale oil and gas have become an essential part of developing unconventional hydrocarbon resources. To clarify the damage mechanisms and mechanical property evolution of shale under hydration, uniaxial compression tests were conducted on shale specimens with different hydration states. Based on energy dissipation theory, the mechanical response characteristics, failure modes, and energy evolution behaviors of hydrated shale were systematically investigated. The results indicate that hydration leads to substantial reductions in shale peak strength and elastic modulus, which decrease by 60.8% and 49%, respectively, under saturated conditions. Meanwhile, hydration markedly alters the failure mode of shale, causing a gradual transition from brittle failure dominated by the rapid release of elastic strain energy to ductile failure governed by the sustained evolution of dissipated energy. In addition, the fracture surface energy exhibits an overall increasing trend with hydration time, increasing rapidly at the early stage of hydration and then tending to stabilize.

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.