Chang Liu

Foliation-induced anisotropy in phyllite leads to complex deformation and failure responses, making excavation stability analysis and support design particularly challenging for geo-energy and geo-resource applications. To elucidate the influence of foliation angle (β) on mechanical behavior and fracture mechanisms, uniaxial compression tests were conducted and Particle Flow Code numerical simulations were performed on phyllite specimens with seven different foliation angles. The anisotropic mechanical behavior of phyllite under uniaxial compression was systematically analyzed across varying foliation angles. Furthermore, the interaction mechanism between matrix and foliation-induced cracks was investigated based on relevant theoretical frameworks. The foliation angle β has a significant effect on the stress–strain curve of phyllite. The elastic modulus generally increases with increasing β, whereas the peak strength displays an overall U-shaped distribution. As β increases, the macroscopic failure mode shifts from matrix-dominated fracturing to foliation plane-controlled slip/opening, and then trends back toward matrix-dominated fracturing at high β. In the simulations, microcrack type, initiation sequence, and the internal mechanism of instability vary markedly across β. Combined with the energy release rate criterion of fracture mechanics and the compression bar stability theory, the mutual induction mechanism between matrix cracks and foliation cracks is further clarified. The penetration or deflection behavior of matrix cracks near weak planes is jointly controlled by the crack propagation direction and foliation angle. When the foliation plane is parallel to the loading direction, the buckling instability of thin rock flakes resulting from tensile cracking along weak planes constitutes the primary factor contributing to the reduction in the strength of specimens where the foliation plane is normal to the loading direction. This finding clarifies the intrinsic cause of the prediction deviation of the conventional Jaeger weak plane theory and can provide a more accurate theoretical reference for the stability evaluation of layered rock mass engineering.

Intersecting fissures strongly affect stress transfer and crack coalescence in rock, but their coupled effects on mechanical degradation and acoustic emission signatures remain incompletely understood. We conducted uniaxial compression tests with synchronous acoustic emission monitoring on prismatic sandstone specimens containing five intersecting-fissure configurations and on intact controls. The specimens measured 50 mm × 50 mm × 100 mm, and each prefabricated fissure was 30 mm long and 2 mm wide. The central 0–90° configuration produced the greatest degradation: its peak stress, peak strain, and elastic modulus were about 70%, 36%, and 50% lower, respectively, than those of the intact specimen. Acoustic emission ring-down counts captured the transition from early crack activation to unstable coalescence and increased sharply near macroscopic failure. Low-inclination configurations generated predominantly intermediate- and high-frequency signals, consistent with the activation of numerous small tensile cracks. Gaussian mixture model clustering of rise angle and average frequency values further showed that tensile microcracking dominated all fissured specimens, whereas the shear-crack fraction increased with fissure angle α. These findings link fissure geometry, macroscopic weakening, and acoustic emission source characteristics under uniaxial loading, providing a laboratory basis for identifying potentially hazardous intersecting-fissure configurations in underground rock engineering.

In goafs formed by underground mineral resource extraction, the remaining pillars are often subjected to uniaxial loading at different loading rates, and their mechanical responses and failure mechanisms directly affect the long-term stability of the goafs. This study uses rock-like materials to conduct uniaxial compression tests at loading rates ranging from 0.001 mm/min to 0.05 mm/min, combined with acoustic emission (AE) monitoring, to systematically investigate the effects of loading rate on the mechanical properties, energy distribution, constitutive model, and AE characteristics of the material. The results show that an increase in loading rate significantly enhances the stiffness and strength of the material, promotes a transition in failure mode from a shear–tension composite to tension-dominated, intensifies brittle characteristics, and simultaneously inhibits full crack development and fragments generation. In terms of energy evolution, an increased loading rate enhances the pre-peak total strain energy and elastic strain energy storage but reduces the efficiency of energy dissipation, leading to an intensified mismatch between energy storage and dissipation capacities at peak stress. A damage variable induced by loading rate was proposed, and a damage constitutive model considering the loading rate was established, with the theoretical curves showing good agreement with the experimental data. AE characteristic analysis further reveals that an increase in loading rate causes the crack type to transition from shear-dominated to tension-dominated, and the fluctuating increase in the b-value reflects a reduction in pre-peak fracture scale and a decrease in the degree of material fragmentation. The research findings are expected to deepen the understanding of the damage and failure mechanisms of rock materials under different loading rates, thereby laying a research foundation for the stability assessment of goaf pillars and disaster warning.

Uniaxial compression tests were carried out for two stress paths: fixed upper limit and increasing lower limit, and fixed lower limit and increasing upper limit, to study the differences in mechanical behavior, energy evolution patterns, and fractal dimension of simulated deep sandstone under different stress paths. The results show that the strength of the stress path with a fixed lower limit and increasing upper limit is higher than that of the stress path with a fixed upper limit and increasing lower limit. Failure mode occurs in both cases through tension, but the former is more intense. Under cyclic loading and unloading, the evolution of total energy, elastic energy, and dissipated energy highly depends on the stress path. High stress increases the ratio of elastic energy to total energy and the ratio of elastic energy to dissipated energy. When maximum or minimum stress remains unchanged, both ratios decrease with cycling. Both stress paths produce predominantly coarse particles, but the stress path with a fixed lower limit and increasing upper limit results in higher fragmentation and a larger fractal dimension.