Current quantitative characterization methods for the mechanical response and damage evolution of coal seams at different burial depths under mining-induced stress remains insufficient. To address this, this study establishes a quantitative characterization model for the evolution of mechanical properties in gas-bearing coal masses at varying burial depths. It innovatively introduces a dual damage quantification technique and develops a coupled damage evolution model that comprehensively considers energy evolution, effective mining-induced stress, permeability, and a damage sensitivity coefficient, followed by extensive analysis. Key findings include: coal damage exhibits heterogeneous evolutionary characteristics under mining-induced stress; based on the theory of irreversible deformation, the proposed damage characterization equation can effectively determine the critical damage threshold of coal; the three-parameter EXP function model is more suitable for characterizing the time-dependent damage process of coal under mining-induced stress; a new characterization method for the coal brittleness evaluation index is proposed, revealing an 800 m burial depth boundary for the coal brittleness index; at the microscopic level, achieving quantitative characterization of the correlation between peak stress and the average reduction in functional groups during mining-induced failure of coal at different burial depths. Finally, the mapping relationship between laboratory experimental parameters and field monitoring indicators for early warning of coal mine dynamic disasters is established.

Quantifying two-phase fluid flow in fractured rocks is essential for resource reutilization in abandoned mines, subsurface energy recovery and underground waste isolation. This study develops a mathematical framework for predicting the permeability of rough fracture networks by integrating fractal geometry with single-phase and two-phase seepage theory. A permeability model for rough fracture networks is first established, and its sensitivity to key geometric parameters is analyzed. A second model is then formulated to relate water-phase saturation to measurable variables, enabling the estimation of two-phase permeability from Reynolds number and aperture. Model predictions show deviations of less than 10% from numerical simulations for both single-phase and two-phase flow, demonstrating the accuracy and robustness of the proposed approach. The results highlight the dominant roles of fracture number, tortuosity and aperture in controlling permeability, as well as the influence of flow regimes on relative permeability. The proposed framework provides a practical and physically based method for analyzing multiphase seepage in fractured rock and offers a foundation for further applications to field-scale fractured systems.

High-voltage electric pulse (HVEP) rock fragmentation has demonstrated substantial potential for sustainable fracturing of hard rocks owing to its energy efficiency. The transient nature and highly disruptive characteristics of its physical fracturing process render experimental investigation of the underlying rock-breaking mechanisms challenging. However, existing numerical studies lack comprehensive models that precisely link electrical breakdown phenomena with mechanical disintegration processes. This study combines COMSOL electrical breakdown simulations with four-dimension lattice spring model (4D-LSM) mechanical analysis to establish a coupled HVEP rock fragmentation model. The core concept of the model construction is to import the temperature field of the plasma channel obtained from the electrical breakdown into the mechanical solver to realize the precise connection between the two stages. The validated numerical model elucidates the full process of HVEP-induced fragmentation under varying electrical parameters. Furthermore, the effects of confining pressure and mineral grain size on fragmentation behavior have been investigated. Finally, parametric simulations across 25 electrical parameter combinations demonstrate the critical role of electrode spacing optimization in achieving energy-efficient rock fragmentation. These findings provide a predictive tool for designing efficient HVEP systems in deep resource extraction and mineral processing engineering.

Thermal spalling in heterogeneous rocks under rapid heating poses critical risks to deep mining and geothermal operations. In this study, we develop a coupled thermal–mechanical–damage (TM-D) model that explicitly incorporates Weibull distributed heterogeneity to a single fracture in rock, and validate it against ceramic quenching and granite acoustic emission experiments. Distance based generalized sensitivity analysis (DGSA) is applied to quantify the influence and interactions of key parameters, revealing the dominant controls on spalling onset, severity, and damage morphology. The results demonstrate that thermal stress dominates crack initiation and propagation, that lateral constraints can significantly delay and suppress spalling, and that material heterogeneity markedly influences peak stress and damage modes within a certain range of thermal expansion coefficient and has multiple effects on thermal spalling. This study provides a theoretical basis for quantitative assessment and parameter optimization of thermal spalling processes in rock masses.

In igneous-intruded coal seams, coal undergoes significant metamorphism, which critically alters its pore structure and oxygen consumption dynamics, thereby elevating its spontaneous combustion tendency. This study investigates the specific surface area, pore volume, structure complexity/connectivity, heterogeneity/local features of pore size distribution, and oxygen consumption dynamics of igneous metamorphic coal through N₂/CO₂ isothermal adsorption tests and low-temperature oxidation experiments, and elucidates the influence mechanisms of pore structure evolution on oxygen consumption dynamics during low-temperature oxidation. With increasing metamorphic degree, igneous metamorphic coal exhibits a more pronounced reduction in specific surface area during oxidation, while the increase in structure complexity due to coal-oxygen reactions is suppressed. Thermally metamorphic coal demonstrates accelerated oxygen consumption, with oxidation amplifying the difference in reaction rates compared to raw coal. Key mechanisms include oxidation-induced reduction in mesopore complexity and micropore volume, decreased dominance of small-pore-volume apertures, and increased heterogeneity, collectively leading to a lower half-oxygen-consuming temperature and steeper oxygen consumption curves. Simultaneously, increased pore volume/complexity and reduced uniformity/connectivity act synergistically to enhance oxygen consumption capacity, highlighting the coupling between pore structure evolution and oxidation behavior in igneous metamorphic coal. This study provides theoretical insights into the pore-oxygen coupling mechanisms governing coal spontaneous combustion in igneous intrusion areas.

A critical scientific gap exists in quantifying the intrinsic mechanisms of shale mechanical property degradation induced by the combined effects of perforation (impact) and acidization—two core techniques for shale reservoir permeability enhancement. To address this gap, this study proposed an innovative coupled experimental framework integrating dynamic-static cyclic loading (to simulate perforation impact) and acid erosion. Static uniaxial compression tests were performed on treated damaged shale samples, with microstructural characterization via X-ray diffraction (XRD) and scanning electron microscopy (SEM). Key findings include: (1) The damage factor (characterized by longitudinal wave velocity) showed a significant positive correlation with acid concentration; (2) Combined damage (impact + acidization) caused far more severe mechanical deterioration than single damage modes—for instance, samples under combined damage with 20% hydrochloric acid exhibited a strength reduction to 158.97 MPa, with sharp decreases in peak strength and elastic modulus; (3) Damage reduced total energy and elastic strain energy of samples while increasing dissipated energy proportion, leading to more developed internal fractures and severe failure in combined damage samples; (4) Acidization promoted sample fragmentation into smaller debris, resulting in significantly higher fractal dimensions of acidized shale than other damage types under the same acid concentration; (5) XRD and SEM analyses confirmed that high-concentration acid erosion reduced shale carbonate content, and the synergy of mechanical pre-damage and chemical dissolution in combined damage accelerated acid-rock reactions, significantly increasing micro-interfacial pores and degrading shale structural integrity. This study’s innovation lies in establishing a coupled experimental framework that reproduces the actual ‘‘perforation-acidization” sequence, quantitatively revealing the synergistic degradation mechanism of shale mechanical properties under combined damage—providing a novel theoretical basis for optimizing shale reservoir stimulation parameters.

Microseismic (MS) monitoring is an effective technique to detect mining-induced rock fractures. However, recognizing grouting-induced signals is challenging due to complex geological conditions in deep rock plates. Therefore, a hybrid model (WM-ResNet50) integrating data enhancement, a deep convolutional neural network (CNN), and convolutional block attention modules (CBAM) was proposed. Firstly, an MS system was established at the Xieqiao coal mine in Anhui Province, China. MS waveforms and injection parameters were acquired during grouting. Secondly, signals were categorized based on time–frequency characteristics to build a dataset, which was divided into training, validation, and test sets at a ratio of 4:1:1. Subsequently, the performance of WM-ResNet50 was evaluated based on indices such as individual precision, total accuracy, recall, and loss function. The results indicated that WM-ResNet50 achieved an average recognition accuracy of 94.38%, surpassing that of a simple CNN (90.04%), ResNet18 (91.72%), and ResNet50 (92.48%). Finally, WM-ResNet50 was applied to monitor the whole process at laboratory tests and field cases. Both results affirmed the feasibility and effectiveness of MS inversion in predicting actual slurry diffusion ranges within deep rock layers. By comparison, it was revealed that the MS sources classified by WM-ResNet50 matched grouting records well. A solution to address insufficient diffusion under long-borehole grouting has been proposed. WM-ResNet50′s accuracy was validated through in-situ coring and XRD analysis for cement-based hydration products. This study provides a beneficial reference for similar rock signal processing and in-field grouting practices.

Efficient hard-rock fragmentation remains a critical challenge in mechanized mining. This study designed an adjustable-spacing mold and conducted double cutting pick indentation tests on granite. Mechanical responses and fragmentation characteristics under varying horizontal stresses, pick spacings, and groove depths were systematically analyzed. Unidirectional stress concentration altered the rock fragmentation modes, exhibiting a dual effect on the fragmentation process. The maximum indentation force (F_max), indentation hardness index (IHI), indentation modulus (IM), and indentation energy (W) initially increased and then decreased with rising horizontal stress. Appropriate spacing promoted radial crack coalescence, whereas too small a spacing (20 mm) caused repetitive re-fragmentation of rock chips, and too large a spacing (50 mm) resulted in unbroken ridges. Pre-cut grooves weakened the rock, reducing F_max and specific energy (SE), thus improving fragmentation efficiency, although the improvement slowed beyond a 10-mm groove depth. Based on the results and rock-mass conditioning assisted fragmentation mechanism, a ‘‘stress-structure dual control” assisted fragmentation mechanism was proposed, and a ‘‘pre-drilling unloading − alternate stopping” mining scheme was exploratorily designed. This approach creates favorable conditions for rock fragmentation by reducing stress levels and rock mass integrity in target zones, providing theoretical support and an engineering paradigm for mechanized mining of deep resources.

Temperature is one of the main causes of spontaneous coal combustion. To improve the flame retardant performance, CaCl₂, ammonium polyphosphate (APP), and calcium phosphate (CaHP) were compounded to control the temperature response of different stages of coal spontaneous combustion through physical and chemical synergy. Simultaneous thermal analysis, thermogravimetric-Fourier infrared spectroscopy (TG-FTIR), in-situ FTIR and electron paramagnetic resonance (EPR) were used to study the multi-temperature stage synergistic inhibition of coal spontaneous combustion. The results show that the proposed method is effective. By obtaining the characteristics of the spontaneous combustion reaction stage of coal in advance, the method of configuring an appropriate composite inhibitor can effectively realize the intelligent control of the temperature response of coal spontaneous combustion. The ignition point of long-flame coal increased by 37.15 °C. The inhibition rate of the gas phase products was more than 20%, and the inhibition rate of the functional groups was more than 30%. It has a good quenching effect on free radicals and can effectively inhibit the oxidation activity of active free radicals such as H, HO, and O. The results provide experimental and theoretical support for the study of temperature-responsive composite flame retardants for coal with different metamorphic degrees.

Natural gas hydrate in Class I reservoirs holds significant commercial potential, as demonstrated by production trials in the South China Sea. However, experimental studies have focused largely on Class III systems, with Class I/II reservoirs remaining underrepresented due to the difficulties in simulating the geothermal gradient and interlayer interactions. This study investigates depressurization performance across all three classes using a novel 360° rotatable reactor with segmented temperature control, enabling precise simulation of reservoir conditions. Results reveal: (i) Class I shows two-stage gas production, with 50% from early free gas enabling rapid depressurization, followed by dissociated gas dominance. They achieve 38.4%–78.3% higher cumulative production and superior gas-to-water ratios due to efficient energy use. (ii) The free gas layer in Class I accelerates pressure and heat transfer. Class II’s water layer provides sensible heat but causes water blocking, impairing heat flow. Class III exhibits rapid initial dissociation but a quick decline without fluid support. (iii) Low temperature, low hydrate saturation, and high production pressure collectively reduce efficiency by increasing flow resistance, limiting gas supply, and reducing dissociation drive. Over-depressurization risks hydrate reformation and ice blockage. This work bridges experimental gaps for Class I/II reservoirs, offering key insights for optimizing recovery.

Cemented rockfill (CRF) combines structural support with sustainable reuse of coal-derived solid waste. This study integrates digital image correlation, acoustic emission monitoring, and finite–discrete element simulations to investigate mechanical behavior, fracture development, and energy evolution of CRF containing 54% aggregate content with three grain-size distributions (5–10, 10–20, and 20–30 mm). Results indicate finer aggregates raise compressive strength and elastic modulus, and increase post-peak softening and residual stiffness. Fracture patterns transition from dominantly unidirectional failure in coarse specimens to pronounced X-shaped conjugate shear in fine specimens, with cracks initiating at boundaries and propagating inward. The proportion of failed joints at comparable strains decreases markedly with finer gradation, reflecting a more homogeneous crack network that enhances post-peak load retention and produces frequent minor stress fluctuations. Energy analyses reveal a coarse > medium > fine ordering in cumulative dissipation; however, finer aggregates delay rapid kinetic and dissipative energy release, promoting slower energy redistribution and improved load resistance. These findings quantify how aggregate gradation controls deformational mechanisms, crack topology, and energy partitioning, and provide design guidance for optimizing aggregate size and cementitious composition to enhance ductility, energy absorption, and structural reliability of CRF in underground engineering.