Roof cavity is a typical form of longwall face instability arising from complex geological, geotechnical, and roof-shield interactions, posing risks to operational safety and productivity. This study develops a mechanism-informed data-driven approach for cavity forecasting by integrating numerical modelling with machine learning (ML). Discontinuum modelling combined with a Taguchi L9 sensitivity analysis identifies cover depth as the most influential factor, followed by mining height and roof strata competency. The modelling results also indicate an initial increase in shield leg pressure followed by pronounced unloading as the cavity develops, supporting the use of shield pressure drop as an indicator of cavity occurrence. Based on this mechanistic interpretation, an AutoEncoder-Long Short-Term Memory (AE-LSTM) architecture is developed to capture spatiotemporal patterns in shield monitoring data. The ML-based model exhibits temporal prediction accuracies of 89.3% to 94.7% and three-zone spatial localisation accuracies of 81.7% to 88.9% under within-panel validation, enabling one-cut-ahead forecasting and regional identification of cavity-prone areas along the face. Cross-site validation using independent datasets from another mine yields accuracies of 83.9% to 89.0% and F1-scores of 79.0% to 86.6%, demonstrating the transferability of the forecasting approach. The probability outputs are further interpreted as low, moderate, and high cavity risk levels to offer graded risk information beyond binary cavity or non-cavity classification. An online tool is developed to integrate data input, model execution, forecast visualisation, and risk interpretation, providing a practical basis for early warning and targeted roof management in longwall mining.
The in-situ non-uniform stress environment and time-dependent deformation characteristics of coal mass surrounding gas drainage boreholes exert a pronounced influence on the permeability evolution during gas drainage in deep high-gas coal mines. Elucidating the influence mechanisms of non-uniform stress conditions on the time-dependent deformation of coal mass and gas transport behavior is of great significance for achieving safe and efficient gas drainage. This study incorporates non-uniform stress boundary conditions and a fractional order Maxwell viscoelastic model to derive a non-uniform visco-elastoplastic stress-strain solution for coal mass surrounding boreholes. Based on the assumption of equivalent fracture evolution in damaged coal, a permeability model is established by considering non-uniform visco-elastoplastic deformation and non-uniform adsorption swelling deformation. Furthermore, a new coupled model for gas flow under non-uniform pressure-relief conditions is developed using Darcy's law. The model is implemented in COMSOL Multiphysics for numerical analysis, enabling a quantitative investigation of the spatio-temporal evolution of stress-strain characteristics and permeability of coal mass surrounding boreholes. The results demonstrate that the proposed model accurately captures the zonal pressure-relief zones and the inhomogeneous evolution of gas permeability around boreholes. It reveals the underlying mechanisms by which time-dependent deformation induced by non-uniform loading influences gas drainage performance. By comparing different field gas drainage data with model predictions, the validity of the proposed model in characterizing gas migration under the influence of non-uniform time-dependent deformation is verified. In addition, a systematic investigation is conducted on the effects of key parameters controlling non-uniform time-dependent deformation, plastic yielding, and shear dilation on pressure-relief and permeability increase in coal mass.
Rockburst in high-stress rock masses is triggered by rapid conversion of stored elastic energy into kinetic energy, resulting in violent fragment ejection. Assessing rockburst proneness requires capturing both the amount of energy accumulated before peak stress and the rate of energy release after peak. In this study, nine rock types with distinct mechanical properties undergo uniaxial compression testing, during which fragment ejection is recorded. The far-near field ejection weight ratio and the average ejection kinetic energy are quantified as indicators of failure intensity. Laboratory rockburst proneness is categorized by combining failure patterns and rock fragment ejection characteristics. Building on these observations, a novel index, i.e., the energy release rate (VER), is introduced to characterize post-peak energy release in both magnitude and rate. Rocks with higher rockburst proneness exhibit larger VER, reflecting rapid energy release and extensive fragment dispersion, whereas lower-rockburst proneness rocks show smaller VER. A rockburst proneness criterion based on VER is proposed and validated against laboratory observations, providing a potential method for quantitative evaluation of rockburst susceptibility in different rock types.
Reliable analytical models can serve as robust tools for assessing injection-induced seismicity. Existing analytical models are largely restricted to isotropic reservoirs and therefore do not capture the poroelastic anisotropy typical of layered sedimentary formations. Here, we derive a closed-form analytical solution for injection-induced poroelastic fields in a transversely isotropic reservoir intersected by a displaced fault, based on Eshelby's inclusion theory and orthotropic Green's functions. The solution recovers existing isotropic solutions as limiting cases and agrees well with finite-element simulations. Parametric and lithology-based analyses show that within the investigated parameter ranges and representative lithologies, elastic anisotropy has a comparatively limited influence on the predicted reactivation response, whereas the directional Biot's coefficients exert a stronger control on fault reactivation potential and pre-slip length. Their influence is also geometry dependent, with the vertical Biot's coefficient being more important for gently dipping faults and the horizontal Biot's coefficient being more important for steeply dipping faults. Comparative analysis of the five representative lithologies further shows that the clay-rich cases examined here exhibit higher fault-reactivation potential, owing to the combined effects of strong poroelastic effect and relatively low frictional resistance. These results collectively indicate that neglecting poroelastic anisotropy may lead to underestimation of the predicted fault-reactivation potential, particularly for mechanically weak, clay-rich parameter sets under the conditions considered here. This analytical solution provides a rapid and physically transparent tool for first-order assessment of fault reactivation in injection-related subsurface operations.
To clarify the deterioration mechanism of limestones in the hydro-fluctuation belt of the Three Gorges Reservoir, uniaxial compression tests were conducted on fissured limestone under coupled prestress and wet–dry cycling. X-ray diffraction (XRD), scanning electron microscopy (SEM), acoustic emission (AE), and digital image correlation (DIC) were employed to investigate the deterioration mechanism of the rock mass in terms of microstructure, mechanical response, energy evolution, and deformation and failure characteristics. The results showed that wet–dry cycling dominated microscale damage in the rock mass, whereas prestress intensified the deterioration induced by wet–dry cycling. Their synergistic coupling further led to damage of the rock skeleton and degradation of strength. As the fissure angle increased, the peak stress and elastic energy of the specimens increased by 32.94%–38.67% and 32.91%–44.56%, respectively. After coupled deterioration, the maximum reduction rates of these two parameters reached 26.81%–30.14% and 36.19%–47.17%, respectively. Based on the evolution characteristics of AE and surface strain, the deformation process of the rock specimens was divided into five and three stages, respectively. The duration of each stage was jointly controlled by the fissure angle and the coupled effect. The failure mode of the rock specimens was primarily controlled by the fissure angle and evolved from shear failure at 0° to splitting failure at 90°. Meanwhile, the coupled effect significantly reshaped the internal stress transfer path and thereby altered the local deformation characteristics. Furthermore, the chaotic initial stress σcis, determined from the nonlinear evolution characteristics of energy, was found to be approximately 0.808–0.875σp. Combined analysis of AE response and surface strain evolution verified that σcis can serve as an equivalent indicator of the crack damage stress (σcd) and can be regarded as a precursor point for identifying rock failure.
Asperity wear governs the degradation of joint morphology and the evolution of shear strength during rock joint shearing. However, its progressive development is difficult to observe and quantify due to the limited observability of conventional joint shear tests. This study develops transparent rock-like joints and a modified shear box to enable in situ observation and reconstruction of wear evolution. A three-dimensional topography inversion method is further applied to quantify morphology degradation. Results show that asperity wear evolves through three stages: initial development, rapid expansion, and stabilization. The critical displacement of wear initiation decreases linearly with increasing normal stress, while the coalescence displacement shows a non-monotonic trend, decreasing first and then increasing. Wear is mainly concentrated at relative elevations of approximately 4.48-6.23 mm and extends up to 7.65 mm under a normal stress of 4.0 MPa, while remaining primarily confined to an apparent dip angle range of ±10°. The wear area follows an approximately Gaussian distribution with respect to apparent dip angle. The wear area ratio decreases linearly with the θmax*/(C+1), which indicates that wear area can be used as a quantitative indicator of roughness degradation. This study provides experimental evidence for understanding morphology degradation and enables process-resolved characterization of joint surface evolution.
In deep shale gas reservoirs, shale shear failure under coupled high-temperature and high-stress conditions governs both hydraulic fracture formation and fracture-wall stability. However, the temperature-dependent evolution of Mohr–Coulomb strength parameters, energy redistribution, heterogeneous damage, and shear instability precursors remains underexplored. In this study, direct shear tests coupled with real-time acoustic emission (AE) monitoring were performed on shale specimens after thermal treatment at 25–600°C. The results indicate that the peak and residual shear strengths and shear stiffness increase with temperature. Total input energy increases with both temperature and normal stress, while the relative elastic-energy contribution peaks at 200–400°C, indicating enhanced energy-storage capacity. Analysis of the AE frequency spectrum further suggests that the coexistence of a strengthened matrix and a dense network of thermally induced microcracks promotes large-scale fracture development. Moreover, distinct precursory signals are observed near the shear instability threshold. The b-value sharply decreases, while information entropy rapidly increases, providing reliable laboratory-scale indicators of shear-slip failure in high-temperature shale. Accordingly, a thermal hardening–damage framework is established. Within this framework, thermal hardening and thermal damage are interpreted as competing processes throughout high-temperature treatment. The proposed thermal-barrier effect increases the effective thermal resistance, limits excessive thermal-crack interconnection, and preserves the load-bearing framework, contributing to thermal hardening. In contrast, thermally induced ductilization accommodates local deformation, relieves stress concentrations, and promotes progressive frictional sliding, reflecting the evolution of thermal damage. The interaction between these competing processes governs the nonlinear evolution of shear strength and failure behavior. These findings provide theoretical guidance for the stability assessment and early warning of shear-slip failure in deep shale reservoirs under complex thermal conditions.
Laminated fine-grained porous media commonly consist of micrometer-scale, multimineral laminae, including felsic-mineral, clay-mineral, carbonate-mineral, and mixed-mineral laminae. Because these laminae and associated lamina-parallel fractures occur at small scales and involve complex mineral mixing, conventional laboratory and imaging workflows often struggle to quantify how lamina architecture and lamina fractures influence bulk physical properties. Digital rock analysis provides an effective pathway to address these limitations, yet robust reconstruction of 3D, large-scale, and multimineral laminated digital rocks from 2D images remains challenging. In this study, we propose a hybrid workflow (2D-3DGAN-MPS) that integrates a 2D-to-3D Generative Adversarial Network (2D-3DGAN) with Multiple-Point Statistics (MPS) to reconstruct large-scale 3D multimineral laminated digital rocks from 2D imagery. The 2D-3DGAN is used to generate 3D digital models for individual lamina types, and MPS is then applied to upscale the model size. Two or more lamina types with prescribed thicknesses are subsequently fused to form laminated digital rocks with and without lamina fractures. Using these reconstructions, we systematically evaluate the impacts of lamina combination style and lamina fractures on porosity, permeability, and brittleness. For systems containing two lamina types, the felsic-mineral plus clay-mineral configuration yields the highest porosity, permeability, and elastic moduli, and these properties improve with increasing felsic-lamina thickness. Across the reconstructed samples, porosity and permeability follow a power-law relationship, whereas the brittleness index varies linearly with brittle-mineral content. Particularly, the fitted relationships differ substantially between fractured and unfractured laminations. Lamina fractures reduce the energy threshold for fracture propagation, resulting in higher apparent brittleness. The proposed workflow enables efficient predictive models for permeability and brittleness in laminated fine-grained reservoirs, with practical implications for identifying sweet spots and improving digital-rock-based property evaluation.
Bedding rock slopes are prone to large-scale landslides subject to earthquakes, and their stability evaluation and prevention are key research focuses in the field of geological hazards. Taking a soft-hard interbedded bedding rock slope as the prototype, this study proposes a novel anchor with energy-dissipating and self-centering (ED&SC) functions. Large-scale shaking table tests are conducted to study dynamic responses of the bedding rock slope reinforced by two types of pile-anchor composite structures (PACS). It is found that the dynamic responses of the bedding rock slope exhibit obvious spatial differences affected by lithologic distribution, seismic intensity, waveform characteristics and excitation mode. The acceleration amplification factor (AAF) increases stepwise along multiple slope directions and evolves following a “decrease-increase- decrease” pattern within 0.050 g - 0.600 g. The AAF under the excitation of Wenchuan wave and bidirectional wave is obviously larger than those under Ludian wave and unidirectional wave. The slope exhibits progressive failure characteristics, sequentially undergoing a compaction stage of the lower soft rock layer, a tensile crack development stage of the middle hard rock layer, and a formation stage of through-going shear sliding zones along upper lithologic interfaces. Compared with conventional anchors, the ED&SC anchor improves the seismic performance of PACS by reducing the anchor axial force and rock lateral pressure. Graded energy dissipation of ED&SC anchor facilitates load redistribution, and enhances the cooperative bearing capacity and overall seismic resistance of the system. The findings provide technical support for the seismic design of bedding rock slopes in high-seismic-intensity regions.
Water jet technology shows significant potential for marine mineral resource extraction. However, its rock-breaking effectiveness over long distances is limited by high resistance encountered in submerged environments. This paper proposes a Laval nozzle-based annular air-shielded nozzle allowing to overcome this limitation. Submerged sandstone erosion experiments are conducted at different air injection pressures and standoff distances. Erosion pit morphology, area, depth, volume, and specific energy consumption are used to evaluate the rock-breaking effectiveness. Flow visualization experiments are also conducted and the flow-field evolution is evaluated using the cavity length and the modified Froude number. The rock-breaking mechanism is then revealed by combining erosion and flow-field results, and the long-distance rock-breaking performances of the Laval and conventional jets are compared. The obtained results show that, when the standoff distance increases, the rock-breaking performance decreases, whereas it is increased through air injection at medium-to-long standoff distances (40d-60d, 160-240 mm). The optimal condition is achieved at 0.6 MPa and 50d. When the air injection pressure increases from 0.2 MPa to 0.6 MPa, the average axial cavity length is increased by 130.4%, and the modified Froude number increases from 7.02 to 84.42. In addition, various rock-breaking mechanisms were identified at different standoff distances, including hydraulic impact and stress waves, hydraulic–cavitation interaction, and weak erosion at 20d, 40d, and 60d, respectively. At 0.6 MPa and 60d, the rock-breaking volume of the Laval jet is 2.75 times that of the conventional jet. This study provides a theoretical basis for the efficient exploitation of marine mineral resources.
Rock-concrete (R-C) composites are susceptible to thermal damage and mechanical degradation in high-temperature environments. Clarifying their thermal damage evolution and post-heating fracture mechanisms holds theoretical and engineering value for ensuring the service safety of rock foundation structures. To address this issue, a mesoscale thermomechanical combined finite-discrete element method (FDEM) framework was developed for cracked straight-through Brazilian disc (CSTBD) specimens containing rock, concrete, and their interface. The model incorporates a grain-based rock and cement-aggregate-interface transition zone mesostructure, and its reliability was validated using experimental mechanical data. A parametric study, including the interface loading angle, interface strength, concrete strength, and pre-crack length, was conducted to quantitatively analyze the regulatory effects of temperature on damage evolution from the mesoscopic to the macroscopic scale. The results identify a critical temperature of approximately 400 °C, beyond which thermal damage accelerates significantly. In the rock phase, intergranular cracks predominated, while transgranular cracks were prevalent in feldspar. Due to aggregate interfacial stress constraints, concrete cracks exhibited a characteristic circumferential pattern. The R-C interface served as a bidirectional pathway for damage transfer. Elevated temperatures reduce peak load and weaken the influence of loading angle on fracture behavior, while increasing interface strength promotes a transition from interface-controlled to matrix-controlled failure. Fracture toughness across all modes deteriorated most severely between 300 °C and 500 °C. Specifically, the KIc/KIIc exhibited a temperature-independent linear correlation under the same mixed-mode ratio. This study provides an improved numerical approach for assessing the fracture resistance and stability of R-C structures under thermomechanical coupling.
Water-rock interaction (WRI) is prevalent in major engineering projects such as mining, tunneling, and slope engineering. It readily induces damage and weakening in coal-rock masses, potentially leading to instability and failure under subsequent engineering disturbances. However, existing constitutive models often focus on specific WRI conditions, lacking a unified characterization capability. To address this, a piecewise unified constitutive model incorporating initial damage was developed based on mesoscopic statistical damage theory. The Gumbel distribution was introduced to describe the nonlinear closure behavior of microcracks during the initial compaction stage. Combined with the Weibull distribution, the model framework was constructed. Parameter sensitivity analysis clarified the physical meanings of key parameters: the initial damage extent s, the brittleness-ductility coefficient k, and the critical failure strain p. A systematic methodology for determining these parameters was proposed. The model's reliability was verified via uniaxial compression tests on sandstone with different water saturations, showing that the model achieves a coefficient of determination (R2) exceeding 0.984 and a root mean square error (RMSE) remaining below 1.421. Furthermore, the model was successfully extended to two representative WRI conditions: long-term water immersion and wetting-drying cycles. Validation across different lithologies (e.g., coal, argillaceous siltstone) and under both uniaxial and triaxial quasi-static loading conditions demonstrated that the model maintains an average R2 above 0.975 and an average RMSE below 1.130, performing significantly better than existing models. Moreover, by fitting and extrapolating the parameters, the model successfully predicted the mechanical response of coal-rock under extreme conditions, such as 100-year water immersion and 50 wetting-drying cycles. This research provides a reliable theoretical tool for stability assessment and hazard prevention in coal-rock engineering within complex WRI conditions.
