Coal mine gas is a byproduct of coal and a clean energy source. The accurate prediction of gas concentration is of critical importance to prevent coal mine gas disasters and improve gas utilization efficiency. To fully use monitoring data and accurately predict gas concentration in the working face, the multichannel SpatioTemporal Graph Convolution Network prediction model based on data decomposition and Attention mechanism (Mc-ASTGCN) was proposed. Gas concentration time-series datasets were collected from three monitoring points in the same mining face, and their spatiotemporal distribution patterns were analyzed. The improved multivariate variational mode decomposition method was applied to decompose the data into multimodal components. The multichannel spatiotemporal prediction model was constructed by integrating spatiotemporal convolution modules and attention mechanism. Experimental results demonstrate that the proposed model maintains stable performance in short- and medium-term prediction tasks, with an overall RMSE and R-2 of 0.0130 and 0.9856, respectively. Compared with benchmark models, the prediction error under extreme conditions is reduced by 9-57%, and the prediction interval coverage probability exceeds 0.978 at the 99% confidence level. The results indicate that the Mc-ASTGCN model exhibits practical engineering applicability and provides effective technical support for coal mine gas monitoring and safety early warning.

This study examines the evolving patterns and zoning characteristics of gas migration and storage zones during coal seam mining, taking the 215 fully mechanized longwall face at Huangling No. 2 Coal Mine as the engineering background. By integrating theoretical analysis, physical similarity simulation experiments, and field measurements, the research systematically explores the zonal linkage evolution mechanism of mining-induced depressurization gas migration and storage zones, together with the associated depressurization gas extraction technology. A flow regime determination equation, driven by the fracture expansion coefficient and permeability, is established on the basis of the fluid Reynolds number criterion. According to differences in gas flow states and medium morphology, the mining-induced fracture field is divided into five distinct zones: a high-permeability zone dominated by turbulent transport, a medium-to-high permeability zone with transitional flow as the secondary dominant region, a low-permeability zone featuring linear laminar flow with micro-permeability, an extremely low-permeability zone characterized by linear laminar flow in a locked state, and a zone of abrupt permeability change associated with gas enrichment. The dynamic evolution of depressurization gas migration and storage zones and their regional linkage mechanisms are clarified. On the basis of these findings, a dynamic targeted layout strategy for high-level boreholes is proposed that is consistent with the spatiotemporal evolution of the overburden permeability field. Field engineering practice shows that the optimized high-level borehole layout maintains the overall gas extraction rate at the drilling site stably above 70%, with a peak value of 93.7%, thereby ensuring safe and efficient mining of the working face.

A B S T R A C TThis study systematically investigates the CO2–water interfacial properties, dissolution and mass transfer behaviors, as well as the mineralization and carbon sequestration mechanisms of coal/rock and alkaline solid waste in mined-out area. The results show that the CO2–water interfacial tension (IFT) is synergistically controlled by temperature, pressure, salinity, and cation valence: increasing pressure significantly reduces IFT by enhancing the gas-phase density and decreasing the gas–liquid density difference; higher salinity and divalent cations (Mg2+, Ca2+) strengthen the interfacial ion gradient and elevate IFT. CO2 solubility decreases with increasing temperature and salinity, and is lower in divalent salt solutions. The IFT and solubility prediction models based on the SAFT-LJ–DGT and D-S approaches exhibit small deviations. Using the IFT and contact angle measurements, the capillary sealing safety threshold (carbon sequestration safety threshold) of the caprock is determined to be 4.28–4.29 MPa, providing an upper limit for CO2 injection pressure. Coal-rock and alkaline solid waste display fundamentally different mineralization pathways: the coal/rock system is dominated by slow mineral dissolution, with preferential calcite corrosion, a low Ca2+ leaching rate (10−4 mg·L−1·d−1), and overall undersaturation with local calcium enrichment; solid waste (especially calcium carbide slag) undergoes a rapid hydration–neutralization–precipitation process, with a peak Ca2+ leaching rate as high as 0.26 mg·L−1·min−1 and a carbon sequestration capacity of 648.97 g·kg−1, and the mineralization efficiency is positively correlated with calcium content. The two systems can establish a dual-mode synergistic storage system characterized by “long-term slow mineral trapping + rapid high-capacity chemical fixation”. This study provides constraints on injection pressure, selection of low-cost high-calcium solid waste materials, and process regulation for CO2 storage in mined-out area.

To address the deficiencies in the stress-strain curve observed in numerical simulations of particle flow, a single-bearing loading damage test was conducted on prefabricated borehole coal samples. The deformation and damage characteristics of the samples containing boreholes under uniaxial loading were investigated using a three-dimensional optical scattering system and particle flow numerical simulation software. The results indicate the following: (1) The damage process of coal is accompanied by localized spalling. The compressive strength of the samples decreases with increasing borehole diameter, and the macroscopic failure is primarily characterized by vertically penetrating tensile cracks. (2) Numerical simulations reveal that no distinct cracks appear before the peak stress. Microfractures initially occur around the borehole at peak stress, exhibiting pronounced stress concentration and deflection. After the stress drops to 80% of the peak value (sigma(f)), cracks propagate rapidly, leading to a surge in tensile damage that evolves into macroscopic fractures, with intensified stress deflection. (3) Taking into account the variation in porosity prior to loading, a segmented damage constitutive model incorporating the compaction effect was developed based on the Weibull distribution function and the Drucker-Prager strength criterion. Model validation demonstrated consistency with the mechanical behavior observed in experimental results, and the model shape parameter k was found to correlate with the sample's peak strength.

Improving fracture structures is crucial for enhancing coalbed methane (CBM) production in low-permeability coal seams. To investigate energy evolution during the thawing of frozen coal, a self-developed acoustic emission (AE) monitoring system was employed. The results show that the AE energy exhibits two distinct phases: growth and quiescence. Peak energy increases linearly with water saturation, reaching approximately 1.74 times that of dry coal at 100% water saturation. Both the cumulative energy and AE events increase linearly with water saturation. AE count time series exhibits chaotic fractal behavior. Energy release efficiency during thawing increases exponentially with water saturation, reaching 34.00% at 100% water saturation, about 1.96 times that of dry coal (17.37%). Fractures are dominated by shear fractures, whereas tensile fractures, though less abundant, act as primary flow channels, and shear fractures enhance connectivity; together, they improve permeability and promote efficient CBM drainage.

To investigate the aggregation mechanism of coal dust in water spray influenced by acoustic wave perturbation, based on the theory of acoustic agglomeration, a self-developed acoustic excitation platform was used to excite the wetted coal dust through the independently constructed simulation platform for dust reduction by water spray under acoustic wave perturbation and scanning electron microscope experiments to study the influence of different acoustic wave parameters on the diffusion and distribution law of coal dust particles, analyze the influence of liquid droplets on the agglomeration effect of coal dust particles under the acoustic wave disturbance, and reveal the mechanism of water spraying to increase the efficiency of dust reduction under the acoustic wave disturbance. The results showed that when acoustic wave and water spray synergistic dust reduction, with the increase of sound pressure level (SPL), the dust concentration was decreasing in an exponential function trend; with the increase of acoustic frequency, the dust concentration was decreasing and then increasing in a parabolic trend, and the dust reduction effect was optimal when f=1,300 Hz and SPL=120 dB. Compared with the dust reduction effect of water spray alone, the average dust reduction efficiency of total dust and respiratory dust increased by 10.05% and 28.95%, respectively, and the dust reduction efficiency of respiratory dust was more prominent. The microscopic morphology of coal dust showed that the volume of coal dust agglomerates increased with the enhancement of SPL, and the best agglomeration effect was achieved at 1,300 Hz acoustic frequency. Acoustic waves promote the diffusion and distribution of coal dust and effectively enhance the collision frequency between droplets and coal dust. Meanwhile, the pressure wave generated when the acoustic wave propagated will deform the droplets, increased their surface area and surface energy, which can adsorb more small particles, promote the wetting and agglomeration of coal dust, and improved the efficiency of dust reduction.

Coal and gas outburst disaster seriously restricts the safe development of deep coal resources. This study aimed to elucidate the evolution characteristics of dynamic behavior and two-phase flow migration mechanism throughout the various stages of outburst. The dynamic characteristics of fluids at different outburst stages were analyzed in terms of impact force and static pressure primarily based on physical simulation tests of outbursts. Based on gas dynamics, a complex wave system distribution model of the turning structure was constructed, and a numerical simulation revealed the migration mechanism of outburst fluids within the turning structure. The results show that the shock in the stage1 shows an evolutionary trend of multi-peak oscillations. Coal–gas two-phase flow in the stage2 mainly has strong disaster-causing characteristics at the front end and middle of the straight roadway, and the impact force has a sudden and intermittent steep increase-drop phenomenon. Impact force decline process has a recovery phenomenon, the larger the solid–gas ratio, the faster the impact force attenuation. Coal powder can promote the attenuation of static pressure, and the larger the solid–gas ratio, the greater the attenuation. The fluid in the high-velocity jet region is fast and unevenly distributed, and the static pressure is negatively distributed, with expansion-compression phenomenon. In the turning roadway, there is a steep increase in velocity, and the distribution is strong–weak, which is consistent with the phenomenon of steep increase in impact force in the test. The research results are of crucial guiding significance for accurately assessing the impact range of outburst accidents, optimizing the design of disaster prevention facilities, and formulating emergency rescue plans for accidents.

In the process of deep coal seam mining, the dynamic damage and failure of coal under impact load disturbance are key factors triggering major dynamic disasters. To explore the dynamic tensile properties of coal samples under impact loads, the Split Hopkinson Pressure Bar (SHPB) test system was adopted to perform dynamic splitting tensile tests on coal samples under varying impact velocities, while a high-speed camera was utilized to record the crack initiation and propagation processes of the samples. The dynamic tensile mechanical properties of coal samples under varying impact velocities were systematically investigated, and the failure processes and modes of coal samples in the dynamic Brazilian splitting tests were analyzed in detail. Based on the combined element model theory and statistical damage theory, a dynamic damage constitutive model for coal was established, and its rationality was verified by means of experimental data. The test results indicated that the peak tensile strength of coal samples exhibited a positive proportional relationship with impact velocity, whereas the peak strain showed an inverse proportional relationship with impact velocity. This phenomenon implied that as the impact velocity increases, the deformation response time of coal samples is significantly shortened, and macroscopic fracture occurs with only minimal deformation. In the dynamic splitting tests, a central main crack initiated in the central region of coal samples, followed by the continuous propagation, coalescence, and eventual penetration of microcracks, ultimately resulting in the complete fracture of the samples. Notably, stress concentration occurred near the pressure bar end faces, accompanied by the formation of crushing zones. As impact velocity rose, the energy absorbed by coal samples similarly increased, and incident, reflected, transmitted, and dissipated energies all exhibited an upward trend. Among these, incident energy showed the steepest growth slope; transmitted energy had the smallest variation range and the gentlest growth slope; and the growth slopes of dissipated and reflected energies of coal samples were approximately equal. The energy dissipation density of coal samples increased linearly with increasing impact velocity. This demonstrates that as impact velocity increases, high energy input induces rapid energy transfer and accumulation in the coal matrix, with local regions sustaining higher energy densities, thereby enhancing the fracture degree of coal samples. Based on the Zhu-Wang-Tang model and statistical damage theory, damage characteristics of specific elastic components were incorporated into plastic elements. The Zhu-Wang-Tang constitutive model was then modified, and accordingly, a viscoelastic-elastoplastic dynamic damage constitutive model was established for coal subjected to Brazilian splitting under impact loads. This model effectively characterized the elastic and plastic stages of coal under impact loads and accurately reflected the dynamic stress-strain relationships of coal under different impact velocities, thus verifying the reliability of the constitutive model.

In coal seams subjected to the compound hazards of high gas content and strong rockburst tendency, the coordinated layout of gas extraction boreholes (GEB) and pressure relief boreholes (PRB) is an important means of achieving gas pre-drainage and coal seam pressure relief. The spacing between double-prevention boreholes (DPBs) directly affects the deformation release capacity of the PRB and the stability of the GEB. To reveal the mechanisms of crack propagation around DPBs and the coordinated borehole deformation under different borehole spacings, this study established double-circular-borehole coal-like specimens considering the grouting and sealing of the GEB, and conducted DIC-based progressive failure observation tests under small (25 mm), medium (37.5 mm), and large (50 mm) borehole spacings. By integrating stress–strain curves, composite strain fields, crack opening and shear displacement, crack fractal dimension, borehole expansion–contraction amount, and the Euclidean distance of Fourier descriptors, the crack propagation, borehole deformation, and coordinated evolution characteristics of DPBs were quantitatively analyzed. The main conclusions are as follows: (1) The specimens with the three borehole spacings all exhibited distinct staged mechanical characteristics. The specimen with medium borehole spacing showed the highest peak strength, reaching 6.21 MPa, and the most gradual post-peak unloading process. (2) In the specimen with small borehole spacing, shear connection of the inter-borehole rock bridge occurred earlier, and cracks tended to propagate toward the sealed section of the GEB, forming potential gas leakage channels. In the specimen with large borehole spacing, the interaction between the two boreholes weakened, and cracks mainly exhibited independent propagation. After the peak, shear displacement around the GEB intensified and induced instability of the rock bridge. (3) The analyses of crack fractal dimension and borehole deformation further indicated that, under small borehole spacing, the crack complexity of the two boreholes tended to converge in the later stage, showing a strongly coupled failure characteristic (C ≈ 1.73/1.43, S ≈ 0.75/0.79). Under large borehole spacing, the crack and deformation evolution trends of the two boreholes were similar, indicating insufficient dominance of the PRB. Under medium borehole spacing, crack propagation was mainly concentrated around the PRB, while the fractal dimension and expansion–contraction amount of the GEB remained at relatively low levels (C ≈ 1.10, S ≈ 0.915). (4) Fourier descriptor analysis showed that, under the 37.5 mm borehole spacing, the Euclidean distance of the PRB remained consistently greater than that of the GEB, and the borehole deformation differentiation coefficient reached its maximum value (ζ = 159.65). This indicates that contour deformation and failure were concentrated mainly around the PRB, while the GEB maintained relatively stable contour morphology. Overall, within the investigated laboratory range, the intermediate-spacing condition exhibited a more favorable response than the small- and large-spacing conditions, providing a better balance between PRB-dominated deformation and GEB stability.

During coal seam mining,pore gas pressure and in-situ stress exhibit dynamic coupling characteristics in-volving multi-cycle synchronous loading and unloading.Coal deformation and gas migration are jointly driven by these two factors,triggering coal-rock gas dynamic disasters in mines.To further reveal the mechanical-seepage response char-acteristics of coal and their dominant controlling mechanisms under multi-cycle coupling of in-situ stress and gas pressure,triaxial seepage tests are conducted under three cyclic loading-unloading paths:stress-only(OS)cycling with fixed pore pressure,pore pressure-only(OPP)cycling with fixed stress,and stress-pore pressure coupled(SPPC)cycling.A damage constitutive model for coal under SPPC conditions is developed based on statistical damage theory.The results indicate that stress and pore pressure both promote axial compression and radial expansion of coal,while exerting an opposite com-petitive relationship on volumetric strain.This leads to their differentiated effects on seepage channels:stress facilitates volumetric compression,thereby inhibiting gas seepage,whereas pore pressure induces volumetric expansion,thus enhan-cing gas seepage.With an increasing number of cycles,axial strain of coal under all three cyclic paths exhibits a fluctuat-ing increase,whereas radial strain shows a fluctuating decrease.Under the coupled effect of stress and seepage fields,coal subjected to SPPC cycling demonstrates a more sensitive deformation response and greater susceptibility to damage accu-mulation.By the end of the tests,its cumulative residual strain is the largest(axial 0.203× 10-2 and radial-0.059× 10-2)Additionally,permeability of coal under all three cyclic paths at the end of loading exhibits exponential decay with an in-creasing number of cycles,indicating that accumulated cyclic damage hinders the recovery of pore-fractures apertures to their initial state,resulting in diminished seepage capacity.Permeability of coal under OS and SPPC cycling at the end of unloading gradually decreases with more cycles,whereas the opposite is observed under OPP cycling.High-velocity gas repeatedly scours loose coal particles or clay minerals adhering to fracture surfaces,facilitating the expansion of fracture channels.Contribution rate analyses reveal that coal strain evolution is dominantly controlled by stress,with average con-tribution rates of 97.5％,64.9％,and 79.7％to axial,radial,and volumetric strains,respectively.Permeability evolution is absolutely dominated by pore pressure,with a contribution rate exceeding 97.6％.Finally,based on the characteristic that coal element strength follows a Weibull distribution,and considering the strength degradation effect of pore pressure on coal,a coupled damage variable is proposed,and a damage constitutive model based on the D-P(Drucker-Prager)cri-terion under SPPC conditions is developed.This model effectively describes the deformation response characteristics of coal under SPPC during loading-unloading stages.The results provide theoretical support for further elucidating the mech-anical mechanism of coal-rock gas dynamic disasters in mines.

Injection of liquid nitrogen (LN2) into low-permeability coal beds can improve the extraction efficiency of coalbed methane (CBM). To address the research gap in understanding coal fracturing using LN2 under in-situ reservoir stress conditions, we conducted a series of cyclic LN2 injection experiments on coal specimens under true triaxial stress loading, utilizing an independently developed true triaxial fracturing system. The temperature evolution and acoustic emission (AE) signals within the coal mass throughout the entire injection process were simultaneously monitored by integrating ultra-low temperature sensors with a sophisticated AE monitoring system. The results showed that the low-temperature propagation radius of the coal was enlarged by 3 times after 9 times of LN2 injection. The cumulative energy of AE increased 9.98 times. The number of AE events increased significantly with the number of cyclic injections. The proportion of tensile cracks in the coal exhibited a linear increase with the number of cycles, while the proportion of shear cracks demonstrated a linear decrease with the number of cycles. The AE characteristic dimension rmax increased rapidly with the increase of the number of cycles and approached the maximum value after the 7th injection. The findings of this study address a critical gap in the research pertaining to coal fracturing through cyclic LN2 injection under in-situ stress conditions.

In order to explore the multifractal characteristics of the pore structure of coal under multistage pulse ultrasonic excitation and its impact on the desorption kinetic laws of gas,the ultrasonic excitation test system for gas-containing coal was employed to conduct the gas desorption test of water-saturated coal under multi-level pulse ultrasonic excitation.Coupled with low-pressure CO2 adsorption,low-temperature N2 adsorption,and high-pressure mercury intrusion tests,based on the multifractal theory,the multifractal characteristics of micropores(<2 nm),mesopores(2-50 nm),and macropores(>50 nm)of coal under multi-level pulse ultrasonic stimulation and their influ-ence on the kinetics of gas desorption were studied.The results indicate that compared with the continuous ultrasonic excitation of coal,the pore volume and specific surface area of each pore diameter segment of coal under multi-level pulse ultrasonic excitation have all in-creased.The pore distribution of coal under multi-level pulse ultrasonic excitation exhibits multifractal characteristics.The multifractal sin-gularity spectrum width ∆α of micropores ranges from 0.422 3 to 0.481 4,that of mesopores ranges from 0.485 7 to 0.574 2,and that of macropores ranges from 2.099 8 to 2.100 8.The multifractal difference Dmin-Dmax of micropores and mesopores in coal under ultrasonic ex-citation undergoes a significant change and shows a decreasing trend with the increase in the number of multi-level pulse ultrasonic waves,while the change in the multifractal difference Dmin-Dmax of macropores under ultrasonic excitation is not obvious.Compared with the Langmuir model and the pseudo-first-order kinetic model,the pseudo-second-order kinetic model can more accurately describe the kinet-ics of gas desorption from coal under ultrasonic excitation.With the increase in ultrasonic power and the number of multistage pulses,the multifractal spectrum parameter ∆α of micropores and mesopores of coal presents a downward trend,while the generalized fractal dimen-sion D,the limit gas desorption amount Q∞,the equilibrium constant b,and the desorption rate constants k1 and k2 all increase.Under the excitation of multilevel pulse ultrasonic waves,the uniformity of coal pores is improved,which leads to the increase of the ultimate de-sorption amount of gas Q∞ and the desorption rate constant k2 by 105.660%and 125.641%respectively compared with the excitation of non-pulse ultrasonic waves(200 W).Multi-level pulse ultrasonic waves activate the synergistic multi-scale transformation of coal pores and significantly enhance the geometric morphology,connectivity,and uniformity of micropores and mesopores of coal,influencing the strong adsorption sites of gas within micropores and mesopores,thereby promoting the desorption of gas in coal.Subsequently,issues such as the construction of a multi-scale gas desorption and diffusion model of coal under the action of ultrasonic waves can be further explored.

The weakening of coal strength caused by crude oil intrusion serves as a primary trigger for frequent disasters in coal-oil symbiotic mines. Understanding the degradation characteristics and underlying mechanisms of crude oil intrusion into coal is crucial for safe mining operations. This study examined the uniaxial strength of coal following varying periods of crude oil saturation. Comparative analyses were performed on the evolution of compressive strength, elastic modulus, strain, and damage coefficient. By employing acoustic emission monitoring, we investigated crack propagation patterns and failure mode transitions, thereby elucidating the degradation mechanism of crude oil-intruded coal. The results demonstrated that with increasing crude oil intrusion duration, strength and elastic modulus progressively decreased whereas strain and damage coefficient exhibit gradual increased. Concurrently, the compaction stage (OA), yield stage (BC), and postpeak failure stage (CD) became prolonged, whereas the elastic stage (AB) shortened. Notably distinct postfailure stress drop patterns were observed: original coal exhibited a direct stress drop; coal samples intruded for 7 and 14 days displayed single-step stress drops; and those exposed for 30 and 60 days manifested multistep stress drop characteristics. The cumulative AE count exhibited an exponential functional relationship with crude oil intrusion duration. Compared with original coal samples, those subjected to crude oil intrusion for 7, 14, 30, and 60 days demonstrated reductions in cumulative AE counts of 43.25%, 52.46%, 73.83%, and 77.91%, respectively. As the coal intrusion duration increases, the failure mode of the coal become increasingly complex, with crack types transitioning from shear-dominated to tensile-dominated. The ratios of tensile cracks for invasion durations of 0, 7, 14, 30, and 60 days were 12.87%, 69.63%, 77.03%, 80.74%, and 84.36%, respectively. Macroscopically, this evolution was characterized by a transition from shear failure to tensile-shear composite failure. As the coal intrusion duration increases, the fractal dimension of the fragmented coal gradually decreases, the mass fraction of larger-sized fragments progressively declines, and the mass proportions of fragments in other size ranges generally increase. These findings provide valuable insights for the stability assessment in coal-oil symbiotic mining systems.

N2-enhanced coalbed methane (N2-ECBM) offers a promising method for improving gas production, yet the influence of water saturation, which is ubiquitous in coal seams, remains poorly understood. To address this issue, this study developed a thermal-hydraulic-mechanical (THM) coupled model to numerically simulate N2-ECBM in water-bearing coal over a water saturation range from 0 to 80%. The model integrated binary gas transport, gas-water two-phase flow, coal deformation, heat transfer, and capillary pressure effects. Validation against experimental data shown strong consistency with Pearson correlation coefficients exceeding 0.97 for gas concentrations. The results demonstrated that water saturation significantly impeded N2-ECBM efficiency. Higher water saturation delayed N2 breakthrough and reduced CH4 production. After 600 min of N2 injection, cumulative CH4 recovery dropped from 61.89% in dry coal to 42.91% at 80% saturation. Permeability enhancement by N2 injection was also suppressed under wet conditions, and the permeability ratio (k/k 0) at the injection side fell from 1.099 in dry coal to 1.037 at 80% saturation. Permeability declined nearly linearly from the injection to the outflow side, a gradient that weakened with increasing saturation. Adsorption-induced strain evolution was retarded by water saturation, the time to reach a peak strain of 9.52 & times; 10-3 increased from 6 min in dry coal to 23 min at 80% water saturation. Consequently, residual strain after 600 min was 46% higher in 80%-saturated coal (6.30 & times; 10-3) than in dry coal (4.32 & times; 10-3), reflecting inhibited desorption and prolonged matrix swelling. The final gas concentration remained higher at 80% saturation (343.12 mol/m3) than in dry coal (293.99 mol/m3), confirming reduced displacement efficiency. In summary, water saturation exerted a strongly negative impact on N2-ECBM by obstructing flow pathways, amplifying capillary resistance, and coating the coal matrix, thereby hindering N2 diffusion, retarding CH4 desorption, suppressing matrix shrinkage, and limiting permeability enhancement. These findings provided critical insights for sustainable resource recovery from challenging wet coal seams.

Coal surface modification using surfactants has emerged as an effective strategy for regulating the adsorption-desorption and diffusion behaviors of coalbed methane (CBM), yet the underlying molecular mechanisms remain insufficiently understood. In this study, a lignite molecular model (Wender model, C42H40O10) was employed to investigate the effects of four representative surfactants on methane adsorption capacity, interaction energies, and diffusion kinetics in a coal slit model using Grand Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) simulations. The results show that water and surfactants competitively occupy high-energy adsorption sites on the coal surface, significantly reducing methane adsorption capacity and weakening CH4-coal interactions. Surfactants further reconstruct the interfacial electrostatic field, stabilize water films, and introduce steric barriers that reduce available pore volume. These effects collectively promote methane desorption while inhibiting diffusion, with the overall influence following the order: CTAB > CAB-35 > CDEA > SDS. CTAB forms the densest adsorption layer and most strongly suppresses methane mobility, whereas SDS shows the weakest effect due to electrostatic repulsion from the coal surface. This study provides a unified molecular-level explanation for the coexistence of enhanced desorption and suppressed diffusion, offering theoretical guidance for surfactant selection in CBM extraction from low-rank coal seams.

The issue of heat hazard caused by high-temperature surrounding rock in deep mines is becoming increasingly prominent, while the potential for geothermal energy exploitation form surrounding rock is considerable. Therefore, the synergetic technology of mine geothermal mining and heat hazard prevention has garnered significant attention. Previous studies have primarily focused on the coupled effects of open-loop systems and formation cooling, with limited exploration of the mechanisms underlying the cooling effects of geothermal extraction from closed-loop systems on roadway airflow. This research utilizes COMSOL software to establish a coupled heat transfer and seepage model for the synergistic implementation of heat extraction and cooling through buried tubes within the surrounding rock. The heat transfer behavior of surrounding rock, the cooling effect on airflow, and the geothermal extraction performance during long-term heat transfer processes are studied. The results indicate that when groundwater seeps horizontally and perpendicularly to the axial direction of the roadway, and a single buried tube is located in the upstream seepage zone of the roadway, the cold domain range on the downstream side of the fluid cooling influence zone in the buried tube is significantly expanded, which is more likely to overlap with the cold domain range on the upstream side of the airflow cooling influence zone in the roadway and form a cold accumulation, resulting in the best cooling effect of the airflow. As the distance between the buried tube and roadway increases, the cooling effect of the airflow decreases, and the fluid temperature at the outlet of the buried tube and thermal power increase, but the improvement in both becomes negligible once the distance reaches a certain value. Lowering the fluid temperature at the inlet of the buried tube has a significant effect on improving the cooling effect of the airflow and thermal power, but it can cause a decrease in the fluid temperature at the outlet of the buried tube. Reducing the fluid mass flow rate of the buried tube can significantly increase the fluid temperature at the outlet of the buried tube, while increasing the fluid mass flow rate of the buried tube can enhance the cooling effect of the airflow and thermal power, but the impact on both is no longer significant after the fluid mass flow rate of the buried tube increases to a certain value.

A thorough understanding of the dynamic interaction and synergistic evolution mechanisms of stress, seepage, temperature, and chemical fields under mining disturbances is of great significance for ensuring the safe and efficient extraction of coal resources, which serve as the "ballast" of the national economy. This paper reviews the current research status of multi-field coupling evolution mechanisms, experimental techniques, and numerical simulation methods in mining activities, and proposes suggestions for future research priorities. First, the multi-field coupling mechanisms, including hydro-mechanical, thermo-hydro-mechanical, and thermo-hydro-mechanical-chemical, are systematically analyzed, and nonlinear cross-scale constitutive models based on statistical damage and fractal theories are summarized. Second, the experimental technology system is detailed, ranging from true triaxial multi-field synergistic loading and real-time meso-scale damage observations to engineering-scale solid-gas/solid-liquid similarity simulations. Finally, the numerical solution strategies for multi-field coupling and the pros and cons of mainstream simulation platforms in handling discontinuous large-deformation problems are compared and evaluated. Through a systematic review of existing research, it is pointed out that damage evolution mechanisms under complex stress paths, cross-scale cascade effects, and multi-field interaction mechanisms in deep high-temperature environments still require further clarification. Furthermore, identifying the set of key coupling factors in deep strata, breaking through in-situ precise detection technologies, and deepening the integration of artificial intelligence with multi-field coupling physical models are expected to provide more efficient and intelligent solutions for the smart mining of deep coal resources and intelligent disaster early warning.

Nitrogen injection displacement technology can effectively enhance the desorption and diffusion of coalbed methane, and promote coalbed methane extraction and safe coal mining. To further investigate the kinetic characteristics of CH4 displacement by N-2 injection under different pressures, displacement experiments were conducted at N-2 injection pressures of 0.4 similar to 0.9 MPa using a self-developed dynamic monitoring system. Results show that the "displacement curve" effectively describes the entire process of CH4 adsorption and N-2 injection displacement. Higher N-2 injection pressure accelerates the segmented injection-production ratio (R) growth and hastens the decline of segmented displacement efficiency (eta). At 0.4 MPa, R ranges from 1.44 to 25.37, and eta ranges from 48.33% to 2.73%, the smallest ranges observed. At 0.9 MPa, R ranges from 5.33 to 232.67, and eta ranges from 61.36% to 1.47%, the largest ranges. The maximum outlet CH4 flow rate is 5.64 similar to 9.50 mL/min, exhibiting a linear positive correlation with N-2 injection pressure. The Yoon-Nelson model can simply describe the process of CH4 displacement by N-2 injection. The mass transfer rates of both CH4 and N-2 are positively correlated with N-2 injection pressure, with mass transfer rate constants of -0.012 to -0.019 min(-1) for CH4 and 0.017 to 0.023 min(-1) for N-2. A kinetic model for CH4 displacement by N-2 injection was derived and validated based on the Yoon-Nelson model, showing high stability and accuracy with goodness of fit > 0.98995 for both CH4 and N-2. These findings help to further elucidate the dynamic process and mechanism of CH4 displacement by N-2 injection, providing a theoretical basis for field applications of N-2 injection for coalbed methane recovery.

In cold-region open-pit mine slopes, damage accumulation and mechanical deterioration induced by in situ stress and seasonal freeze–thaw alternation can easily trigger sudden instability. To investigate the effects of temperature difference under coupled constant loading and freeze–thaw action on the mechanical response and failure precursors of rock, based on the self-developed TCDR-I temperature–stress coupled testing system, uniaxial compression tests and real-time acoustic emission monitoring were conducted on water-saturated sandstone under a constant load of 1.4 MPa and multiple freeze–thaw temperature gradients. The mechanical behavior of freeze–thawed water-saturated sandstone and the acoustic emission characteristics during failure were analyzed. Combined with critical slowing down theory, the failure precursor characteristics of water-saturated sandstone under freeze–thaw action were investigated, and the internal mechanism of damage accumulation and defect evolution under the coupled effects of constant load and freeze–thaw temperature difference was revealed. The results show that, with increasing freeze–thaw temperature difference, the number of cracks and crack ratio in the loaded water-saturated sandstone gradually increased, whereas the compressive strength, elastic modulus, and total strain energy gradually decreased. After freeze–thaw treatment at −40 to 20 °C, the compressive strength, elastic modulus, and total strain energy decreased by 19.24%, 13.72%, and 44.77%, respectively, compared with those of the unfrozen–thawed specimens. During specimen failure, the dominant crack type gradually shifted from shear cracking to tensile cracking. The acoustic emission b-value and precursor points identified from multiparameter variance can both be used as criteria for predicting specimen failure. The warning lead time increased with increasing freeze–thaw temperature difference. After freeze–thaw treatment at −40 to 20 °C, the predicted failure times based on these two indicators preceded the actual failure time by 11.05 s and 16.19 s, respectively. The findings provide a theoretical basis for the early warning of sudden disasters in rock masses in cold-region engineering.

Mined-out areas offer substantial potential for CO₂ storage, yet efficient carbon fixation under realistic in-situ conditions remains challenging. This study systematically investigates the synergistic CO₂ mineralization potential of three alkaline solid wastes—coal fly ash (CFA), steel slag (SS), and carbide slag (CS)—under moderate temperature (25–45°C) and pressure (0.5–2.5 MPa) conditions relevant to mined-out environments. Results show that carbonation efficiency is primarily governed by calcium accessibility. CS, rich in soluble Ca (OH)₂, achieves the highest sequestration capacity (up to 694.5 g·kg⁻¹), significantly outperforming SS and CFA. A temperature–pressure coordination mechanism is identified: pressure enhances CO₂ dissolution, increasing efficiency by up to 28.5%, while temperature accelerates initial Ca²⁺ release but promotes passivating calcite coatings. Kinetic analysis supports a surface coverage model that limits long-term reactivity. Based on material costs and sequestration capacity, a strategic waste screening framework is proposed: CFA for large-scale backfilling and CS for targeted, high-concentration CO₂ sources. This work provides a mechanistic and practical basis for integrating solid waste management with secure carbon sequestration.