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.

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.

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.

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.

Repetitive mining in multi-seam conditions induces cumulative damage to surrounding rock, significantly increasing the risk of roadway instability. Taking the roadway in the extra-thick coal seam fully mechanized top-coal caving face as the research object, this study innovatively developed a modified damage evolution characteristic model that considers the residual strength of rock mass to quantify the regulatory effect of damage variable D on roof fracture span: damage to the main roof reduces the initial and periodic fracture spans, significantly increasing the probability of sliding and rotational instability of the voussoir beam structure. On this basis, a three-dimensional discrete element method (3D DEM) model was established, and orthogonal tests were designed to reveal the coupling mechanism of the spatial position of fracture lines and coal pillar width on rock mass damage. The results show that when the coal pillar width increases from 8 m to 16 m, the peak stress at the roadway ribs decreases by 26.5%-43.3%, and the influence range of the second invariant of the deviatoric stress tensor (J₂) shrinks. The attenuation of stress gradient leads to a decrease in the evolution rate of plastic damage with increasing coal pillar width, while the position of the fracture line has a weak regulatory effect on the stress-plastic response of the coal pillar. The results of theoretical analysis and 3D DEM simulations have effectively guided on-site engineering practice.

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.