Coal dust combustion and explosion mechanisms have long posed significant challenges to global mining safety, yet their fundamental molecular-scale dynamics remain unclear, hindering targeted suppression technologies. This study employs a multiscale approach integrating explosion experiments with ReaxFF molecular simulations to reveal the atomistic reaction pathways and kinetic processes governing coal dust deflagration. The results indicate that coal dust combustion is a radical-mediated network of oxygen transfer and carbon oxidation, involving chain reactions, pyrolysis, and recombination. The coal dust explosion follows an "energy accumulation-violent release" pattern. It is initiated by pyrolysis fragments and propagated by three key groups: carbonhydrogen, hydrogen-oxygen, and nitrogen-hydrogen species. The CH3 center dot radical acts as a "chain carrier," propagating the reaction network through rapid formation-decomposition cycle. The hydrogen-oxygen group proliferates radicals via the "H center dot-*HO2 center dot-*HO center dot-*H center dot" cycling, while the nitrogen-hydrogen group accumulates energy through HNO center dot/H2NO center dot cycles. Eventually energy is abruptly released once this threshold is crossed. Experiments further confirm the pivotal roles of key active species: H center dot and O center dot drive chain initiation/propagation; HO center dot promotes energy release through branching reactions; CH2O forms progressively from accumulating intermediates; H2O indicates the dominant energy-release phase. Moreover, increased ignition energy not only accelerates pyrolysis but redirects reactions toward deep oxidation and chain branching. Specifically, it boosts the yields of H center dot, O center dot, and HO center dot radicals and accelerates CH2O consumption, thereby promoting rapid explosion development. This study elucidates the full-chain reaction mechanisms of coal dust combustion and explosion at the molecular level, providing a theoretical foundation for combustion optimization and explosion prevention.

Small molecule organic matter significantly influences methane adsorption and desorption in coal. To understand how these molecules affect methane capacity, this study investigated CO2 injection's microscopic effects on methane recovery. Models incorporated three abundant small molecules at varying compositions and concentrations. Density functional theory (DFT) and molecular dynamics simulations analyzed their impact on methane adsorption. Results show 2,3-2-methylnaphthalene binds methane most strongly, while alkanes exhibit the weakest adsorption. Variations in these molecules' composition and concentration obstruct or block coal pores, reducing methane adsorption capacity. Methane adsorption also decreases with rising temperature and higher concentrations of small organic molecules. Correspondingly, the isosteric heat of methane adsorption declines with temperature and is sensitive to small molecule concentration. Injecting gas (like CO2) into coal rich in small organic molecules effectively enhances methane recovery. However, efficiency declines with increasing alkane concentrations, suggesting that extending injection duration could improve outcomes. These findings provide crucial insights into the microscopic mechanisms of coal methane adsorption, aiding optimization of coalbed methane extraction and mine gas hazard mitigation.

The behavior of methane in nanoporous carbon was investigated at 298 K and 0-20 MPa in the presence of three imidazolium-based ionic liquids (ILs) bearing different alkyl chain lengths: [Emim][BF4], [Bmim][BF4], and [HOmim][BF4]. The ILs suppressed CH4 adsorption, with efficacy decreasing as [Emim][BF4] > [Bmim][BF4] > [HOmim][BF4]. The bilayer methane adsorption structure forms as ILs preferentially occupy high-energy graphene sites, reducing first-layer methane density and displacing molecules to the second layer. CH4 diffusion declined with IL loading due to increased surface roughness and narrowed transport pathways. Molecular insights underpin the application of ILs in CBM recovery and gas control.

Efficient exploitation of coalbed methane (CBM) is of paramount importance for energy security and coal mine safety. The adsorption-desorption behavior of CBM represents a critical micro-scale process significantly influencing extraction efficiency. To investigate the regulatory mechanism of ionic liquids on gas adsorption behavior, this study employed quantum chemical calculations, utilizing graphene as a model for coal surface, and selected three imidazolium-based ionic liquids with distinct alkyl side chains ([Bmim][BF4], [Emim][BF4], [HOmim][BF4]). The microscopic effects of methane adsorption on graphene surfaces were systematically investigated. The nature of interactions within the ionic liquid-graphene-methane ternary system was elucidated through electrostatic potential analysis, independent gradient model based on Hirshfeld partition (IGMH) analysis, and atom-in-molecule (AIM) topological analysis. The results indicate that physical adsorption between ionic liquids and graphene primarily occurs via π‒π stacking and van der Waals interactions. The molecular structure of ionic liquids exerts a decisive influence on the regulation of methane adsorption behavior. The butyl chain ionic liquid ([Bmim][BF4]) significantly enhances methane adsorption energy, whereas the ethyl chain ionic liquid ([Emim][BF4]) reduces adsorption energy. The hydroxyethyl ionic liquid ([HOmim][BF4]) slightly promotes methane adsorption due to electrostatic interactions introduced by hydroxyl groups. This study elucidated the molecular-level regulation mechanism of ionic liquid structure on methane adsorption, providing a theoretical foundation for the design of functionalized ionic liquids to modulate the adsorption/desorption process of coalbed methane.

Pre-water injection of coal seams serves a key function in the prevention and control of mine disasters. To enhance cthe efficacy of water injection, this research develops a compounding strategy of surfactants and SiO2 NPs, optimizing a composite nanofluid (CNs) formulation that enhances coal wettability. Employing a vacuum pressurized saturation device at 2 MPa to realistically simulate coal seam water injection, systematically investigating the effects of different CNs on coal wettability, water retention, and surface deposition. The research results indicate that both SiO2 NPs and surfactants can reduce the surface tension of water and exhibit synergistic effects. The wettability of CNs-treated coal pillars followed the order: APG (Alkyl glycosides)>AOS (Sodium alpha-olefin sulfonate)>SDS (sodium dodecyl sulfate)>H2O, while the water retention capacity ranked: SDS>AOS>APG> H2O. This divergence is primarily attributed to differences in the deposited layers formed on the coal surface. Simulation results indicate the dispersion effect of surfactants on SiO2 NPs on the coal surface is SDS>AOS> APG. A stronger dispersion resulted in a more uniform distribution of SiO2 NPs on the coal surface and a denser deposit layer. Conversely, weaker dispersion led to the formation of larger aggregates. The significant gaps between aggregations and between aggregations and coal caused the deposit layer on the coal surface to become sparse. The findings thus provide theoretical support and practical value for coal seam water injection applications, advancing the application of SiO2 NPs in coal seam water injection.

During the coal mining process, the interaction between coal and water significantly affects the methane extraction efficiency. To deeply investigate the microscopic mechanism of how the coal - water interaction influences gas adsorption, this study employed the Monte Carlo, Molecular Dynamics, and Density Functional Theory methods to simulate the pore structure of the Wiser coal matrix under different moisture content. A systematic analysis was carried out on the adsorption isotherms, thermodynamic parameters, radial distribution function, and diffusion coefficients of methane adsorption. Additionally, the adsorption energies of water and methane on the coal-water polymer were calculated accurately. The research results indicate that as the moisture content gradually increases, water molecules preferentially occupy pores larger than 5 & Aring;, reducing the effective adsorption space. By comparing the methane adsorption amounts at different temperatures and moisture contents, it is evident that moisture has a more substantial impact on methane adsorption capacity than temperature. Polar functional groups in coal, mainly oxygen-containing and nitrogen-containing functional groups, are the primary factors influencing water molecule adsorption. The adsorption energy of water molecules on different functional groups follows the order: carboxyl > amino > hydroxyl > carbonyl. When the number of polar functional groups decreases, water molecules will occupy the adsorption sites of methane, thus reducing the amount of methane adsorbed by coal. These research findings provide a theoretical basis for the efficient extraction of coal-bed methane and the prevention and control of gas hazards.

To improve mine safety and production efficiency, it is essential to thoroughly understand the intrinsic mechanisms by which the mine environment affects methane (CH4) explosions. This study explores the processes of chain initiation and the critical elementary reactions in CH4 oxidation under varying temperatures and environmental conditions (O2/CO/CO2/H2O) through reactive molecular dynamics simulations. The findings suggest that in CO/CO2 atmospheres, CO plays a dominant role in initiating the chain reaction for CH4 explosions. Additionally, as the concentration of CO decreases, the time required to initiate the CH4 reaction increases. CO2 engages in the reaction CO2 + H -> CO + OH (R1) at high temperatures, thereby increasing the concentration of highly reactive OH radicals. In CO/H2O atmospheres, CO remains a dominant factor in the CH4 explosion chain initiation, while H2O enhances the reaction by increasing OH radical content. In CO2/H2O atmospheres, the chemical equilibrium effects of CO2 and H2O, along with the third-body effect of H2O, collectively inhibit the CH4 reaction rate at low temperatures and high CO2 concentrations. However, at higher temperatures, the reactivities of CO2 and H2O are enhanced, generating OH radicals, which accelerates the CH4 reaction. Furthermore, H2O competes with CO2 for H radicals, inhibiting reaction R1.

CO2-Enhanced Coalbed Methane Recovery (CO2-ECBM) is an integrated technology that couples coalbed methane exploitation with CO2 geological sequestration. It achieves effective displacement of coalbed CH4 via CO2 injection. Based on molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations, this study investigated the microscopic mechanism of CO2 displacing CH4 in coal nanopores. The influences of injection pressure, temperature, water content and pore size on CH4 adsorption and CO2 displacement efficiency were systematically analyzed. The results show that the isosteric adsorption heat of CO2 increases first and then decreases with partial pressure ratio, while that of CH4 declines continuously. Rising temperature and water content both weaken the coal's adsorption capacity for CH4. Water molecules form hydration films on coal surfaces and further inhibit CH4 adsorption and diffusion. High temperature enhances gas diffusivity but cannot reverse CO2's advantage in competitive adsorption. High temperature, low injection pressure and high water content are unfavorable for CH4 displacement, whereas enlarging pore size can significantly improve CO2 displacement efficiency. This study provides a theoretical basis for parameter optimization and engineering application of CO2-ECBM.

To investigate the intrinsic chemical reactions in the process of clean and efficient coal utilization, a thorough understanding of coal's molecular structure is essential. In this work, integrated experimental and theoretical approaches were applied to characterize the molecular configuration of Dayan lignite from Inner Mongolia, China. Reactive force field (ReaxFF) simulations were further conducted to explore the pyrolysis mechanism of Dayan lignite. Results indicate that the dominant framework consists mainly of aromatic clusters. The ratio of aromatic bridge carbon to aromatic peripheral carbon (XBP) is 0.05, indicating that the structure mainly consists of benzene and naphthalene rings. Oxygen exists primarily in functional groups including ether (C-O), carbonyl (C=O), and carboxyl (-COO) groups. Nitrogen occurs in forms such as pyrrole, pyridine, and quaternary nitrogen functionalities. Among aliphatic constituents, methylene groups are predominant. Accordingly, an average macromolecular model with the molecular formula C174H143O41N4 was established. Validation of the proposed structural model was achieved by aligning 13C NMR spectra with corresponding experimental measurements. Moreover, agreement between thermogravimetric analysis profiles and ReaxFF-derived curves confirms the reliability of the model in predicting pyrolysis predicting pyrolysis behavior and thermal stability characteristics. Ultimately, based on the developed molecular representation, mechanistic insights into the pyrolysis behavior of Dayan lignite over the temperature range of 1200-3000 K was examined. It was observed that primary decomposition prevails at relatively low temperatures, whereas secondary cracking of tar becomes pronounced above 2200 K, resulting in elevated char yields. Additionally, underlying mechanisms driving secondary reactions of tars have also been elucidated.

To mitigate coal dust pollution during mining and achieve cost-effective dust suppression through wetting, this study investigates the inherent wetting characteristics of APG (alkyl polyglycoside-0810), water-based SiO2, APG-modified SiO2 (APG-SiO2), and their effects on the wettability of bituminous coal. ST (surface tension) and CA (contact angle) measurements indicate that all three wetting agents reduce the CA on the coal surface, enhance the penetration rate of H2O, and improve the wetting of coal. Moreover, APG and SiO2 exhibit a positive synergistic effect in lowering both the ST of water and the CA on coal. At the microscopic level, several strong hydrogen bonds form at the wetting agent/H2O interface, reflecting a strong attraction of the wetting agents toward H2O. The adsorption of wetting agents on the coal surface improves the adsorption thickness between H2O and coal, intensifies the movement of H2O toward the coal surface, and enhances the non-bonded interaction energy between H2O and coal, thereby improving the hydrophilicity of coal. Among the wetting agents, APG-SiO2 exhibits the most pronounced effect. Furthermore, the APG- SiO2 system demonstrates relatively high adsorption heat in narrow pores under low gas pressure, which hinders gas desorption from coal and is beneficial for mine gas control. The insights offer a theoretical support for research on enhancing coal wettability through surfactant-nanoparticle synergy and for its practical application in coal seam water injection.

The synergistic control of coal seam stability and efficient gas extraction is critical for deep coal mining and geological carbon sequestration (CO2-ECBM). However, traditional predictive models often rely on rigidframework assumptions, failing to capture the complex adsorption-desorption hysteresis and matrix swelling phenomena observed experimentally. To bridge this fundamental gap, this study employed a coupled Grand Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) approach within a flexible Wiser coal matrix to systematically investigate the multi-scale structural evolution and thermodynamic mechanisms of CH4 and CO2 during a complete adsorption-desorption cycle. Results demonstrate that under equivalent conditions, the absolute adsorption capacity of CO2 is 1.3-1.87 times that of CH4. Notably, CO2 exhibits a significantly broader hysteresis loop driven by a pronounced low-pressure retention effect. Dynamic structural characterizations reveal that the persistence of substantial residual porosity, residual specific surface area, and permanent volumetric strain at the termination of desorption provides multi-dimensional evidence of delayed topological recovery rather than permanent plastic damage. Conversely, high-temperature CH4 desorption induces an anomalous matrix compaction. Thermodynamically, this macroscopic hysteresis originates from the dynamic path-dependency of gas-solid interaction energy. The delayed structural recovery forces retained molecules into highly constricted geometries with overlapped potential fields, thermodynamically locking them into abnormally deep potential wells during decompression. These molecular-level insights suggest that the potent interaction energy and energetic hysteresis of CO2 facilitate efficient methane displacement and stable long-term entrapment, providing a robust mechanistic framework for optimizing CO2-ECBM strategies in deep, high-geothermal geological environments.

In deep coal seam gas extraction, the coupled effects of cyclic mining-induced stress, repeated blasting disturbances and cumulative plastic damage to coal bodies significantly impact borehole stability and extraction efficiency. To investigate the coupling mechanism of coal damage-permeation under cyclic dynamic disturbance, this study establishes a cyclic loading plastic damage model based on equivalent plastic strain and the model was validated through digital image correlation (DIC) experiments. Combining coal fluid–solid coupling theory with numerical simulation, this study systematically investigates the impacts of cyclic loading intensity, frequency, and path on coal damage evolution and gas extraction efficiency. Results demonstrate: (1) Under constant horizontal stress, an increase in vertical stress leads to the progressive concentration of damage zones around the borehole along the horizontal direction. This is accompanied by horizontal contraction of the borehole. (2) With the peak load increasing from the elastic range to the yield threshold, the coal surrounding the borehole undergoes a transition from elastic deformation to an annular plastic zone. When the peak load significantly exceeds the yield strength, a composite “annular -X-shaped” fracture network develops in the coal. (3) Damage intensifies with cycle numbers, showing linear growth in damage factor within four cycles. Gas pressure decreases with cycles but at diminishing rates. (4) A key finding is that, under equivalent total energy input, the cyclic loading path exerts a decisive influence. Under equivalent energy input, cyclic loading paths significantly influence damage evolution and gas extraction efficiency. The decreasing path results in the most severe damage and the lowest gas pressure. In contrast, the increasing path leads to the widest damage distribution but relatively mild localized damage. The constant path generates the least damage overall. These findings provide theoretical support for maintaining borehole stability and optimizing extraction parameters under cyclic dynamic disturbance.

To investigate the impact of loading rate on the failure characteristics and crack evolution mechanisms of containing hole sandstone, uniaxial compression tests on containing hole sandstone at different loading rates were conducted. Acoustic emission and digital image correlation technologies were combined to analyze the mechanical failure characteristics and crack evolution patterns of containing hole sandstone under varying loading rates from macro and micro perspectives. The results reveal the following:(1) Strength and Failure Modes: Drilling reduces the strength of sandstone. Unperforated sandstone exhibits splitting failure, while containing hole sandstone experiences mixed tensile-shear failure with a significant reduction in brittleness. At low loading rates, pore defects substantially deteriorate the samples, and the strength of containing hole sandstone increases and then decreases with loading rate increase, with 0.2 MPa/s identified as the peak turning point.(2) Acoustic Emission and Crack Evolution: The progressive damage process of sandstone containing holes under varying loading rates can be characterized by acoustic emission features, which show significant nonlinear variations. Changes in acoustic emission ring counts reflect internal crack propagation. The RA-AF scatter plot indicates a higher proportion of tensile region compared to shear region, with tensile cracks initially increasing and then decreasing with loading rate, suggesting that loading rate within a certain range promotes tensile crack propagation, and its effect stabilizes and deteriorates beyond a certain range.(3)Crack Evolution Mechanism: The transverse strain around the pore quantified the crack evolution mechanism. The overall trend of transverse strain at various points around the pore is consistent across loading rates, starting from compression stage, increasing to a peak at crack propagation stage, and then decreasing slightly during the crack through stage. The distribution of tensile stress fields reveals the main trend of crack initiation.(4) Correlation with DIC (Digital Image Correlation) Parameters: The peak transverse strain evolution correlates with the trend of tensile cracks in RA-AF, with peak tensile strain at 0.4 MPa/s decreasing by 15.6 % compared to 0.2 MPa/s, indicating that the mechanisms of internal crack propagation and surface macroscopic strain evolution are generally consistent.

The study of mechanical properties and quantitative characterization of fissured rock masses under mining unloading conditions is crucial for ensuring the safety of underground engineering excavations. Research on the strength characteristics and damage features of rock bodies with different inclination angles of cracks under true-triaxial unloading conditions, and analyse the influence of the path on the fissure extension rules. Simultaneously, based on the YOLO (You Only Look Once) object detection model, an automatic crack detection method with a deep learning model of computer vision is proposed. The study indicates that rock masses with a single fissure exhibit lower peak strength and failure strain under unloading conditions. The stress-strain curves and strength properties of the constant axial pressure single-sided unloaded specimens at the same inclination have similarities, and the response of the incremental axial pressure single- sided unloading to the external load is relatively slow. Under the same stress path, the peak strength of the specimens tends to increase with the greater fissure dip angle, and the peak strength and strain show greater sensitivity to changes in the stress path. The crack types of the specimens after unloading damage were classified into two types of tensile cracks, three types of shear cracks, two types of far-field cracks, and surface spalling, and their damage characteristics were analyzed. The accuracy, recall, and mean average precision of the proposed quantitative characterization detection model for fissures exceed 80%, and it can effectively improve the intelligent recognition of the fissure rock rupture process with good robustness by training the fissure rock rupture images under unloading conditions. This study has important guiding significance for rock damage monitoring in deep engineering.

To establish a permeability prediction model applicable to deep coal seam gas drainage engineering and accurately describe the fracture structure characteristics of fractured coal rock bodies and assess the impact of different fracture parameters on gas permeability characteristics, three-dimensional (3D) reconstruction and quantitative characterization of the fracture surfaces were performed. Permeability tests and numerical simulations were conducted on fractured coal-rock bodies with varying fracture dip angles and connectivity under different confining pressures. The numerical simulation results further revealed the gas flow patterns and distribution characteristics within coal rock masses containing different fracture dip angles and connectivities under varying confining pressures. These simulations validated and supplemented the experimental findings. The results indicate the permeability of the coal-rock body decreases with an increase in fracture dip angle. A localized diffusion zone forms within the coal-rock matrix near the fracture channel, and the size of this zone decreases as the fracture dip angle increases. In the gas exchange areas between fractures of different connectivity, there are phenomena of intersecting and biased flow. Near these gas exchange areas, there is also an increase in local permeability velocity within the coal-rock matrix. During the confining pressure loading stage, the permeability of specimens containing coal-rock bodies with different fracture dip angles and connectivity decreases with increasing confining pressure. During the confining pressure unloading stage, the permeability of the specimens increases but remains lower than the permeability measured at the same confining pressure during the loading stage. Fracture dip angle and connectivity are the primary factors influencing the permeability capacity of coal-rock bodies, particularly at low confining pressure levels. Fracture roughness significantly affects permeability. The rougher the fracture, the greater the dispersion of gas permeability velocity distribution within the fracture. Fracture roughness exerts a “retarding” effect on gas flow, and this effect becomes more pronounced with increasing fracture roughness. This research revealed the regulatory mechanism of fracture evolution on gas migration under engineering disturbances.

Moisture in coal seams significantly affects coalbed methane (CBM) exploitation by hindering CH4 diffusion and extraction; however, the micro-mechanisms remain unclear. This study employs various experimental and computational approaches to examine the effect of moisture on CBM exploitation. Adsorption experiments were conducted to analyze the influence of moisture on methane (CH4) adsorption. The adsorption behaviors of H2O, CO2, and CH4 on coal segments were calculated, and the effects of moisture on CH4 adsorption, isosteric adsorption heat, density distribution, and diffusion coefficients were studied. The optimal CO2 injection pressure for displacing CH4 under varying moisture contents was thoroughly investigated. Results indicate that CH4 and CO2 adsorption decrease as moisture content increases. Water clusters form on the coal matrix surface at 5 % moisture content and significantly clog nanopores at 10 %, thereby impeding diffusion. Additionally, a 10 MPa injection pressure is sufficient to achieve high displacement efficiency at low moisture contents. However, as moisture content increases, the injection pressure should be progressively elevated. This work provides microscopic insights into the influence of moisture on CH4 adsorption, and diffusion and outlines optimal gas injection pressures under different moisture conditions. This research offers valuable guidance for engineering practices in CBM exploitation.

The investigation of fracture seepage characteristics in coal-rock mass is critical for the safe and efficient development of coalbed methane resources, as well as for ensuring the safety of engineering designs. This research examines the influence of fracture structure characteristics and stress environments on gas flow properties in filled fracture coal-rock mass. Samples with varying fractal dimensions and fracture apertures were fabricated using the W-M fractal function and 3D printing technology. Gas seepage tests were performed on these samples under varying confining and osmotic pressures, utilizing the HADP-II geomechanical fluid–solid coupling test system. The results demonstrate that both the fractal dimension of fractures and fracture aperture significantly influence the permeability of coal-rock mass. Specifically, permeability increases with larger fracture apertures, while decreasing as the fractal dimension increases. Moreover, the non-linear flow intensity coefficient of gas in fractures increases exponentially with the fractal dimension. A permeability coefficient, quantifying the relative seepage capacity of filled fracture coal-rock mass, is introduced. A two-parameter model is proposed to correlate the permeability coefficient with fractal dimension and fracture aperture. When the fracture aperture exceeds 1.6 mm, it exerts a greater influence on permeability than the fractal dimension. As the fracture aperture increases, it becomes the dominant factor governing the permeability of the filled-fracture coal-rock mass. The effect of confining pressure on permeability is classified into three stages: rapid decline, gradual decline, and steady stabilization. Furthermore, permeability exhibits a quadratic relationship with osmotic pressure, showing a breakthrough pressure point between stages. When osmotic pressure surpasses this point, permeability increases significantly.

With the development in coalbed methane (CBM) extraction technology, fracturing fluid technology has become a critical method for enhancing recovery efficiency. The effects of various fracturing fluids (H2O, acetic acid (HAc), [Bmim][BF4], and HAc + [Bmim][BF4]) on CBM recovery efficiency were investigated through MD simulations. Distinct regulatory effects on gas adsorption and desorption were observed for different fracturing fluids. In the Wiser + H2O system, H2O molecules formed compact clusters, occupying adsorption sites and promoting methane desorption. Interestingly, the addition of HAc resulted in looser fracturing fluid clusters in the Wiser + HAc system, enhancing coal surface coverage, desorption efficiency, and fluid flowability. Following the addition of [Bmim][BF4], the synergistic effect of HAc and [Bmim][BF4] led to even looser clusters, achieving the highest desorption efficiency. Moreover, the synergistic system demonstrated the highest displacement efficiency at moderate and low pressures. Quantum chemistry calculations further elucidated the interaction mechanisms between fracturing fluids and coal molecules, revealing that [Bmim][BF4] molecules enhanced the regulatory effect of fracturing fluids. Specifically, the contact area between clusters and coal surfaces was increased, promoting gas desorption, and the interaction between fluids and coal molecules was weakened, facilitating fluid backflow. The results provide a theoretical foundation for optimizing CBM recovery.

Studying the failure mechanism of roof sandstone under the influence of drilling unloading and mining disturbance is crucial for preventing roof disasters and achieving safe and efficient mining in coal mines. Therefore, this research conducted unloading tests on sandstone with different borehole bottom location under varying radial stress gradients. First, the deformation and acoustic emission (AE) characteristics of sandstone during unloading were analyzed for different borehole bottom location. Next, the plastic and energy characteristics of the sandstone were examined and explained based on statistical damage theory. Finally, the damage mechanisms of sandstone under drilling pressure relief and support in the goaf with different borehole bottom location were discussed. The results indicate that different radial stress gradients have a detrimental effect on the mechanical properties of sandstone, and the depth of the hole exhibits a nonlinear degradation effect on these properties. By employing a damage constitutive model, energy evolution and acoustic emission characteristics validated the nonlinear degradation related to the borehole bottom location and effectively reflected the internal crack propagation in the rock. Appropriate borehole bottom location and support measures can effectively prevent roof fracturing while maintaining economic efficiency. This study aims to effectively mitigate damage to the roof under the influence of drilling unloading and mining disturbance, ensuring safe and efficient mining operations.

The synergistic mechanism between crack network evolution and energy release in deep coal mine roof sandstone is a critical factor triggering rock burst disasters. This study combined acoustic emission (AE) monitoring with digital image correlation (DIC) technology to conduct uniaxial compression tests on double-flawed sandstone, systematically analyzing how rock bridge dip angle regulates crack propagation paths and damage evolution. A mechanical criterion for mixed-mode crack propagation was developed based on stress intensity factor theory, optimizing traditional crack classification standards. Results show that as rock bridge dip angle increases, crack penetration length shortens, energy dissipation channels decrease, and AE energy accumulation intensifies. Under low rock bridge angles, tensile stress drives crack initiation with predominantly mixed I/II propagation modes, whereas at high angles, cracks initiate via shear slip, dominated by mixed III modes. The regulatory mechanism of rock bridge dip angle on crack network configuration and energy release paths is revealed, providing a theoretical basis for achieving directional energy release in roof rock through active optimization of rock bridge angles.