Large-scale roof collapse is a major dynamic hazard threatening the safe coal mine operations. Understanding the deformation and failure characteristics of overburden rock strata, as well as deciphering the stress evolution mechanism of overburden rock structure in mining stopes, is of great theoretical advancement and engineering applications in roof disasters prevention. This study employs a theoretical derivation to systematically analyze the characteristics of overburden roof deformation and caving behavior during the coal seam mining. By modeling the trapezoidal caving zone in the overburden roof strata as a complex functional system, the stress distribution within the caving zone and adjacent intact strata was mathematically characterized. Stress evolution patterns of overburden strata at different caving stages were derived under both elastic and elastoplastic deformation conditions, accompanied by the demarcation of elastic-plastic zones. In addition, the critical length for the first caving and periodic caving of overburden are theoretically determined. To validate the proposed analytical framework, comprehensive numerical simulation and physical model tests are conducted to investigate the overburden roof caving characteristics during coal seam mining. Quantitative comparisons between experimental, numerical results and theoretical analyses were performed in terms of the caving range of roof strata, the critical length for the roof strata caving and stress distribution. The consistencies among different approaches confirms the reliability of the theoretical model, providing a robust foundation for optimizing mining designs and implementing effective roof control strategies.

Borehole sonic dispersion analysis is a technique that provides valuable insights into the realm of borehole sonic interpretation. This research involves an analysis of shear-wave anisotropy and ultrasonic image logs to differentiate between types of fractures and their orientations. Evaluating fractures relies on core samples and image logs are limited. This highlights the need for a more affordable and efficient way to analyse fractures. A challenge in the wellbore is distinguishing natural fractures from those caused by drilling. Using oil-based mud often makes it hard to find signs indicating the direction of in-situ stress. A new method has been created to reliably identify natural fractures when image logs are insufficient for mapping fracture networks. The cross-dipole data reveals five main zones exhibiting shear-wave splitting. Higher anisotropy is observed at shallower depths, while the deeper interval shows low porosity accompanied by considerable inhomogeneity, highlighting potential areas of concern. The dominant directions of anisotropy are aligned with NW-SE, WNW-ESE, and N-S orientations. Slowness frequency analysis of rotated flexural waves identifies fracture types. Dispersion profiles show natural and induced fractures, with cross-over patterns indicating stress-induced anisotropy. Significant inhomogeneity is observed in the bottom interval, where the differences between maximum and minimum energy level are pronounced. Wider dispersion curves suggest breakouts are slowing high-frequency flexural waves, indicating mechanical damage. The maximum stress direction is determined by the fast-shear azimuth. In conclusion, this study demonstrates that by integrating acoustic shear dispersion, shear anisotropy, Stoneley analysis, and image log data, fractures within the borehole wall can be effectively investigated.

Anchor-shotcrete support has been widely applied in underground rock mass engineering globally, where the anchoring of bolts plays a crucial role in stabilizing the mortar-rock interface. In this study, triaxial compression tests were conducted on anchored mortar-rock composite specimens under varying confining pressures, and the failure mechanisms of the anchored mortar-rock composites were investigated using acoustic emission (AE) and three-dimensional morphology scanning techniques. The results indicate that the bolt inclination angle significantly influences the plastic deformation and compressive strength of the mortar-rock composites during triaxial compression tests. The composite specimens with a bolt inclination angle of 90° between the bolt and the mortar-rock interface exhibited the optimal load-bearing performance. As the confining pressure increased, the anchored mortar-rock composites primarily underwent plastic deformation, reducing the property differences caused by varying bolt angles. The bolt angles led to four distinct failure modes in the mortar-rock composites. The acoustic emission (AE) signals during the tests demonstrated that the mortar-rock composites with a bolt inclination angle of 90° exhibited the highest stability. Additionally, the study revealed that the morphological parameters of the mortar-rock interface varied positively with the bolt inclination angle. Finally, a strength model for the anchored mortar-rock composites under triaxial compression was derived. The reliability of the strength model was validated by comparing the experimental results with the model predictions under four different confining pressures.

Crack inclination angle (α) plays a critical role in the dynamic failure and thermo-mechanical coupling of granite, which is vital for rockburst monitoring and prevention. In this study, granite specimens with various prefabricated crack inclinations (α = 0°, 30°, 60°, 90°) were tested using a split Hopkinson pressure bar (SHPB) system. Transient crack tip temperatures were monitored in real time by high-speed infrared thermography, and crack propagation was analyzed using digital image correlation (DIC). The results show that: 1) Propagation mode and mechanical properties: Increasing crack inclination causes a transition from pure tensile propagation to tension-shear mixed modes. At α = 60°, enhanced shear promotes branching cracks, while at α = 90°, crack closure suppresses propagation and induces localized damage. 2) Strength characteristics: Peak stress exhibits a "U-shaped" trend with respect to α, reaching the lowest value at α = 60°. 3) Thermal response: Crack tip temperature rise is strongly dependent on inclination. The maximum rise (up to 9.266 ℃) occurs at α = 30° and 60° due to pronounced tension-shear coupling and frictional slip, whereas α = 0° and 90° show smaller increases. 4) Two-stage temperature evolution: Before peak stress, ~80% of the temperature rise originates from plastic work; after peak stress, crack slip and friction dominate, leading to accelerated heating. 5) Crack tip temperature rise serves as a sensitive indicator of local energy concentration and disaster risk, providing theoretical support for monitoring and prevention strategies in deep mining.

The mechanical properties of coal pillars are crucial for evaluating the stability of underground water reservoirs in coal mines. This article examines the fracture mechanical behavior of coal in response to mine water immersion, layer direction, and loading rate. Eight types of specimens were studied, featuring inclination angles between the applied force and the bedding plane of 0°, 15°, 30°, 45°, 60°, 75°, 90°, and the Divider type. The loading rates (V) tested were 0.005 kN/s, 0.02 kN/s, 0.05 kN/s, and 0.1 kN/s. The results indicated that after immersion in mine water for 30 days, the Brazilian splitting strength (BSS), splitting modulus (E_m), and absorbed energy (U_a) of coal decreased by 51.35%, 52.37%, and 44.60%, respectively, compared to the non-immersion samples. The primary reason for this phenomenon is that the production rate of micropores and small pores resulting from mine water immersion surpasses their conversion rate to mesopores and macropores. This imbalance leads to the fragmentation of the internal structure of coal and the interconnection of pore fracture zones, thereby significantly weakening its bearing capacity. It has been observed that the relative proportions of failure mechanisms along and across the bedding plane directly influence the variations in coal mechanical properties at different θ values. Additionally, BSS, E_m, and U_a of coal gradually increase with an increase in loading rate, which is due to the reduced duration of coal damage development and evolution, subsequently lowering the probability of activating weak structures.

Tunnel boring machines (TBMs) are considered a reliable and fast method for boring long tunnels. However, the wear and failure of disc cutters in hard rock influences the efficiency of equipment, ultimate timeline, and project cost. Therefore, estimating the cutter life under different geomechanical conditions is crucial for TBM manufacturers and tunnel engineers. This study investigates the influence of geomechanical factors, including elastic modulus (E), uniaxial compressive strength (σ_c), confining stresses, and TBM operational parameters such as penetration rate (P) and disc cutter inclination angle (ϕ), on disc cutter wear using the explicit finite element method. The results revealed that the uniaxial compressive strength, disc cutter inclination angle, rock elastic modulus, and confining stresses, in that order, had the greatest impact on the cutter wear rate. Such that an increase in compressive strength from 31 MPa to 137.9 MPa caused a 2.4-fold reduction in cutter life. Meanwhile, the cutter life in the rock without confining stress was only 15% greater than in the sample under 15 MPa of confining stress. Additionally, to achieve the most optimal and economical drilling conditions, the penetration depth of the disc cutters should be optimized based on the existing conditions. Since the installation location of the disc cutters, their spacing and rotational trajectory significantly influence wear levels, a full-scale simulation of a TBM is conducted according to a real case study. The comparison of results indicated that the proposed method has high capability in estimating the cutter life under various geomechanical conditions.

As a weak mineral overlying subduction-zone faults, the widespread presence of antigorite can markedly affect subduction-zone dynamics. To better understand the mechanical properties of antigorite-bearing faults, we conducted frictional sliding experiments on antigorite under hydrothermal conditions. The experimental setup involved a constant confining pressure of 100 MPa, a low pore fluid pressure of 30 MPa, and temperatures ranging from 100 ℃ to 500 ℃. We varied the axial loading rate between 0.04, 0.2, and 1.0 μm/s to examine the velocity dependence of the friction coefficient. The results showed that the friction coefficient of antigorite exhibited a significant temperature dependence. Between 100 ℃ and 400 ℃, the friction coefficient decreased from 0.66 to 0.54 as the temperature increased. Above 400 ℃, the friction coefficient increased, reaching 0.7. The velocity dependence of antigorite exhibited velocity strengthening (a - b > 0) throughout the entire experimental temperature range (100 ℃-500 ℃). The impact of pore-fluid pressure on the frictional behavior of antigorite was also significant. Under low pore-fluid pressure (30 MPa), the frictional strength increases above 400 ℃, associated with dehydration hardening. In contrast, at high pore fluid pressure, frictional weakening continues at elevated temperatures, indicating that pore fluid pressure plays a crucial role in regulating the frictional stability of antigorite. Our experimental results demonstrate that the pore fluid pressure plays a key role in regulating the temperature-dependent frictional behavior of antigorite, highlighting the need for further investigation under varying fluid pressure conditions.

Understanding cement grout diffusion in rock fractures is crucial for rock engineering, yet grouting faces significant challenges due to fracture network heterogeneity and grout's complex non-Newtonian rheology. This study critically reviews recent theoretical, experimental, and numerical advancements to comprehensively understand cement grout diffusion mechanisms within rock fractures. It begins by discussing theoretical foundations, encompassing both continuum and particulate views in single fractures, while also highlighting limitations in extending these simplified concepts to fracture networks and defining robust stop criteria. Subsequently, the article details developments in experiments, including novel apparatus and advanced monitoring techniques. These enable controlled observation of grout diffusion in artificial or simulated fractures, providing crucial insights into the impact of fracture complexities (e.g., fracture roughness, two-phase flow) on grout patterns and sealing efficiency. These laboratory tests also inform the development of practical stop criteria by revealing actual grout behaviour under various conditions. Complementary numerical methods offer a distinct advantage by providing dynamic, continuous solutions for complex fracture networks that are otherwise intractable. Collectively, these diverse approaches bridge critical knowledge gaps, from fundamental principles to real-world complexities, and facilitate cross-scale validation. The review concludes by identifying persistent challenges, such as integrating multi-scale descriptions and simulating true field complexities, and outlines future research directions to understand grout diffusion mechanisms.

Three-dimensional (3D) seismic velocity imaging is crucial for understanding rock mass stress and structures in mining. Conventional straight-ray tomography suffers from ray-path mismatches with true wavefield propagation in complex media, leading to reduced velocity model accuracy. To address this, we propose a 3D velocity imaging method that integrates the Fast Marching Method (FMM) for bent-ray tracing with the Algebraic Reconstruction Technique (ART) for velocity inversion. The proposed approach was validated through checkerboard tests, recovery tests, and laboratory Lead-Break experiments. Results show that FMM-based ray tracing significantly improves inversion accuracy, achieving root-mean-square (RMS) travel-time residuals of 1.39 ms and 28.66 ms in recovery and field tests, corresponding to reductions of 76.6% and 18.6% compared with straight ray tracing-based methods. Application in the Yongshaba mine, Guizhou Province, China, revealed a distinct low-velocity zone surrounded by high-velocity regions, which is consistent with mining activities and excavation plans. This study demonstrates that the FMM-ART framework provides a robust and accurate tool for mine-scale velocity imaging, with implications for monitoring stress evolution, improving safety, and potential integration with real-time monitoring.

The interaction between cemented laminae and induced fractures plays a critical role in hydraulic fracture propagation within laminated shale reservoirs. By combining mode-I fracture mechanics experiment conducted on semi-circular bend (SCB) specimens of black carbonaceous shale from the marine Longmaxi Formation with numerical simulations, this study systematically investigates the effects of three key geological parameters: (1) bond strength, (2) vein stiffness, and (3) approach angle on fracture propagation characteristics. The key findings are summarized as follows: (1) Increasing the parallel bond strength promotes fracture crossing behavior. When the vein fracture toughness was reduced to 0.3, 0.2, and 0.1 times that of the shale matrix, fractures exhibited increased deflection tendency along the vein, creating longer stepped propagation paths. (2) For stiffer veins, induced fracture divert into the vein and propagate over longer distances; Additionally, more micro-cracks form within the vein before fracture-vein interaction occurs. (3) Fracture-vein interaction exhibits significant angular dependence: At approach angles between 60° and 90°, fractures predominantly penetrated laminae without deflection; Below 60°, fractures initially diverted into the vein but subsequently re-entered the matrix before reaching the vein terminus. This bifurcation pattern closely resembles laboratory observations of weakly cemented or pre-damaged vein specimens.