To rationally determine the borehole radius and borehole spacing for gas drainage using along-seam boreholes, a fluid-solid coupling framework incorporating coal deformation, fracture seepage, and matrix diffusion was adopted. A one-way coupled numerical simulation method based on FLAC3D and COMSOL was employed to systematically reveal the evolution of the plastic zone, stress field, permeability field, and gas pressure field in the coal surrounding boreholes under different borehole-radius conditions. Results show that, according to the spacing criterion 2r <= L <= R, the reasonable spacing range is 2-8 m, and L = 5 m was selected as the unified borehole spacing. Under this condition, the plastic-zone area increased with borehole radius, while stress redistribution and permeability enhancement both showed nonlinear characteristics. Among the tested schemes, the 150 mm borehole radius produced more uniform plastic-zone expansion, more effective stress relief, and greater permeability enhancement. Gas pressure decreased nonlinearly with drainage time, and the low-pressure zone progressively expanded outward from the borehole vicinity; the 150 mm scheme showed the fastest pressure attenuation. Field tests further confirmed that the combination of a 150 mm borehole radius and 5 m spacing increased the pure gas drainage rate by 35.4% relative to the conventional scheme.

This study aims to address the challenge of precisely determining the optimal spacing for gas extraction boreholes following hydraulic fracturing. Laboratory experiments and theoretical modeling were conducted to analyze the gas adsorption/desorption characteristics of coal with preexisting fractures, investigating the influence of reduced matrix scale on gas desorption behavior. This provides more accurate parameters for modeling the post-fracturing gas desorption-diffusion-seepage processes. Ultimately, a fluid-solid coupling model was developed, incorporating the impact of coal damage on gas flow. Field trials of hydraulic fracturing in coal seams were carried out, and the model's validity was verified through analysis of the gas extraction results. Numerical simulations indicate that, compared to pre-fracturing conditions, the effective extraction rate of boreholes increased by over 50%. Hydraulic fracturing significantly enhanced coal seam permeability and improved gas extraction efficiency. This research provides a basis for the optimized design of gas extraction boreholes in coal mines.

Underground water-sealed caverns are critical infrastructures for China’s strategic oil reserves. Seepage control is highly stringent, and existing sealing techniques often fail to meet the requirements for managing water in water-rich fractured rock masses, thus failing to ensure the airtightness of the cavern. In this study, an underground water-sealed cavern project was used as a case study, with geological drilling, geological sketching, and advanced water exploration methods applied to assess the surrounding rock conditions and identify water-rich sections. Based on these assessments, a comprehensive grouting strategy based on the principle of “prioritizing pre-grouting, supplemented by post-excavation grouting, with multi-batch grouting” was proposed, and the grouting effect was evaluated using ground penetrating radar (GPR) and water pressure testing methods. Meanwhile, the theories of grouting in rock fractures were integrated with the practical techniques used in this project to analyze the mechanisms of slurry diffusion and blockage in the multi-batch grouting process. The research results indicated that advanced pre-grouting successfully filled most of the seepage channels within 20 m ahead of the excavation face, resulting in a significant decline in the permeability of the surrounding rock. The water inflow was reduced by 62.67 L per minute (L/min) after pre-grouting, which achieved a reduction rate of up to 94

Investigating the mechanics-permeability similarities between natural-like and natural gas-bearing coal–rock specimens provides a theoretical basis for using natural-like specimens as substitutes for natural ones in laboratory simulations of the incubation of coal–rock gas composite dynamic disasters. Based on the similarity between coal and rock in uniaxial compressive strength ratio, natural-like coal–rock specimens were prepared; their mechanics-permeability responses were analyzed through uniaxial and triaxial tests. Both specimen types underwent brittle failure under uniaxial compression, with compressive strength falling between those of coal and rock components but closer to that of coal. Under loading axial stress (LAS), bearing capacity was directly proportional to confining stress (σ3) for both specimen types—at instability failure, both axial and radial strains increased with σ3, whereas the axial-to-radial strain ratio decreased; under unloading confining stress (UCS), both specimen types showed reductions in compressive strength and axial strain at peak strength, along with an increase in radial strain, reflecting pronounced dilatancy. Overall, the natural coal–rock specimen (NRCS) and natural-like coal–rock specimen (NLRCS) exhibited similar mechanics-permeability patterns under both uniaxial and triaxial tests, suggesting that natural-like specimens can serve as substitutes for natural ones in laboratory simulations.

This study based on extensive field experience in tunnel blasting, proposes a novel poly-energy blasting method. Taking the Jinpingyan Tunnel of the Chengdu-Lanzhou project as a case study, the study conducts numerical simulations of conventional blasting and the novel poly-energy blasting method under the same engineering conditions for Class III, IV, and V rock masses. By conducting a detailed analysis and comparison of the blast-induced ground vibration, loosening circle range, borehole, charge quantity, and plastic zone between the two blasting methods, and combining the actual blasting excavation effects on site, it was found that the novel poly-energy blasting method results in a more reasonable distribution of ground vibrations, causing less disturbance to surrounding buildings and structures during construction. The novel poly-energy blasting method requires fewer boreholes and less explosive consumption, thereby improving the utilization rate of explosives. Specifically, compared with conventional smooth blasting, the proposed method reduces the number of peripheral holes by ≈50

The permeability of composite coal-rock specimens is crucial for engineering applications, such as coal seam gas extraction, CO2/H2 geological storage, and the prevention of gas-induced coal-rock disasters. This study investigated the permeability behavior of coal, rock, and composite coal-rock specimens. Single-component permeability evolution tests were conducted under true triaxial stress conditions to examine the effects of stress on the permeability of each specimen. Moreover, permeability variations among the specimens were compared under the same stress path. Differences in gas adsorption between coal and rock and their stress interactions were incorporated using the elastic-stage permeability evolution model of coal and rock. A mathematical model for the permeability of composite coal-rock specimens under true triaxial stress was developed. The permeability evolution model was further extended to describe the entire instability process of composite coal-rock along the true triaxial path. The results reveal that the model accurately captures the permeability characteristics of composite coal-rock under true triaxial stress.

Accurate gas concentration prediction is vital for preventing mining accidents. Traditional methods exhibit limited accuracy and computational inefficiency in handling complex time-series data. This paper proposes a CEEMDAN–SCSSA–CNN–BiLSTM hybrid model to enhance prediction performance. The framework integrates a trigonometric-enhanced Cauchy mutation sparrow search algorithm (SCSSA) to optimize hyperparameters, improving global convergence and nonlinear optimization capabilities. A convolutional neural network (CNN) extracts spatial features from decomposed signals, while a bidirectional long short-term memory (BiLSTM) captures bidirectional temporal dependencies, enhancing sensitivity to concentration variations. The complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) preprocesses raw data through multi-scale decomposition and noise reduction, followed by feature reconstruction. Comparative experiments showed that the proposed model achieved root mean squared errors (RMSEs) of 0.0026 and 0.0053 on the training and test sets, respectively; mean absolute errors (MAEs) of 0.0020 and 0.0043; mean absolute percentage errors (MAPEs) of 2.7

Coal remains an essential energy resource supporting global industry and economic development, and the continuous depletion of shallow coal reserves has driven mining activities toward greater depths [...]

This study investigates the Jinggong No.1 Mine, Jinggong No.3 Mine, and Xiali Yuan Mine in the Pingshuo mining area. Through field sampling and hydrochemical-seepage coupled tests, we reveal the seepage-solute coupled dynamic behaviors of groundwater systems across different mines. By analyzing fluid pressure gradients, ion concentration fields, and permeability coefficients from multiple aquifers (surface water, goaf water, sandstone fissure water, and Ordovician limestone water), combined with Piper trilinear diagrams and solute transport models, we decipher the controlling mechanisms of groundwater seepage pathways on hydrochemical evolution. Key findings include: The high total dissolved solids (TDS) (>4000 mg/L) and SO42- dominance (>84%) in the goaf water of Jinggong No.1 Mine stem from evaporation-concentration effects in low-velocity seepage zones (permeability coefficient K = 1.2 × 10−6 m/s, significantly lower than other mines); hydrochemical differentiation in sandstone aquifers is governed by heterogeneous seepage fields (hydraulic gradient of 0.15 in Jinggong No.1 Mine induces mixing, while stable seepage in Jinggong No.3 and Xiali Yuan Mines maintains K = 5 × 10−5 m/s); the temporal increase in TDS of Ordovician limestone water (annual growth rate 18%) reflects accelerated vertical seepage along fault zones (Darcian velocity rising from 0.3 to 0.8 m/d), driving the migration of Ca-Mg-SO4-type hydrochemical fronts. This study establishes quantitative response relationships between hydrochemical indices and seepage parameters, providing theoretical support for groundwater hydrodynamic field regulation and water-inrush channel identification in mining areas.

It is crucial to study the damage and failure characteristics of gas-bearing coal-rock combination (GBCRC) structures under cyclic loading for the prevention and management of coal-rock gas composite dynamic disasters. In order to analyze the progressive damage and permeability evolution behavior of GBCRC specimens subjected to triaxial cyclic loading-unloading (TCLU). Acoustic emission (AE)-seepage-damage TCLU tests were performed on GBCRC specimens with various confining pressures and gas pressures using the rock triaxial test system. The findings reveal that improving the confining pressure limits the initiation and propagation of cracks, increasing the progressive damage characteristic stress value of the specimen. Simultaneously, its energy storage limit is improved. The elevated gas pressure hinders the closure of the specimen's internal crack, while simultaneously accelerating the propagation rate of crack, also, the energy storage limit drops as gas pressure increases. The absolute recovery rate of permeability in combination specimens initially declines and thereafter rises progressively. The stress sensitivity of permeability reduces progressively with a rise in the number of stress cycles. The production and spread of cracks are intimately linked to the generation of AE signals, and the evolution of permeability will be impacted by the propagation of cracks. At the same time, as one of the driving forces of crack propagation, energy dissipation behavior also indirectly affects the change of AE signal and permeability. The progressive damage and failure behaviors of GBCRC specimens under TCLU can be fully reflected by the evolution behavior of the AE signal, energy dissipation, and permeability.

The comprehension of the collapse law of overlying strata and the corresponding evolution of overburden fractures is the foundation for solving mine disasters related to rock mass dynamics and fluid flow in shallow multi-seam mining, and the correlation study is inadequate. In this work, a three-dimensional (3D) model of shallow multi-seam is developed based on discrete element method to simulate the whole process of overlapping mining. The overburden caving, fracture propagation and strata subsidence are investigated from a spatial perspective, and the evolution and distribution of highly fractured areas are assessed. Based on the stability and transformation characteristics of the collapsed overburden structure influenced by geological features and the disturbance of secondary mining, the propagation mechanism of overburden fractures is determined. Additionally, a calculation criteria of overburden collapse and fractures development height in shallow multi-seam mining with separation height as a single judgment factor is proposed. The spatial distribution models of overburden fractures in full mining stage of upper and lower coal seams are established singly, and regions are divided based on the degree of fracturing. Finally, the spatial models of overburden fractures is verified and supplemented by field investigations of morphology and distribution features of surface cracks.

The initiation and propagation of strain localization can lead to degradation of intergranular cementation, local strength loss of materials, and accelerated deformation instability, which can induce underground engineering disasters. Describing the strain localization process from the perspective of phase transition theory is reasonable. When solving the theoretical model, two analytical methods, the perturbation method and the phase plane method, are used for analysis. Both calculation results can effectively describe the strain localization process in rock masses. This study compares and analyzes the two solution methods, describing the strain localization process in rocks separately to determine which method is more reasonable for describing the evolution of strain localization. The research finds that the phase plane analysis method can describe the strain localization evolution phenomenon in materials, offering both rationality and simplicity. Through a multi-objective optimization algorithm (NSGA-II), the optimal numerical solution for the phase plane is matched, demonstrating speed and intelligence compared to traditional approximate analytical methods.

To address the complex gas flow and significant gas disaster threats in the goaf of deep thick coal seam mining, this study investigates the gas flow patterns and optimizes the spatial parameters for roof directional borehole in the goaf. By combining particle flow code and COMSOL numerical simulations, the study analyzes the stress-permeability evolution in the goaf and the gas migration patterns. The results reveal a strong correlation between the permeability of the goaf and the stress distribution, showing distinct zonal characteristics. The permeability decreases slowly in the coal wall-supported separation zone, drops rapidly in the transition zone, and stabilizes in the compaction zone. Without gas extraction, the gas concentration in the goaf can exceed 40% at 100 m from the working face and surpass 70% in the deepest parts. Additionally, gas accumulation at the upper corner can exceed 0.6%. The optimal spatial parameters for roof directional boreholes were determined as a 25 m from the return airway, a vertical height of 25–35 m, a horizontal spacing of 6 m, and an extraction pressure of 20 kPa. Field implementation confirmed that these parameters significantly improve gas extraction effect and reduce gas concentrations in the upper corner of the return airway, providing a reliable reference for gas control in similar mining conditions.

Investigating the damage and permeability characteristics of gas-bearing coal-rock composites is essential for understanding the mechanisms driving dynamic disasters in coal and rock gas composites. This study focuses on the uniaxial compressive strength of natural coal-rock specimens, from which similar natural composites with transition interfaces were created using the pouring-core sampling method. We conducted mechanical-seepage experiments on gas-bearing coal-rock composites under various confining stresses, gas pressures, and stress paths. The results show a positive correlation between the specimens' compressive strength and confining stress; as confining stress increases, both total input energy and elastic strain energy of the specimens increase, while dissipated energy decreases. When specimens reach instability, they require more energy to maintain this state. At peak strength, the stored elastic strain energy in the specimens gradually increases. Furthermore, higher gas pressure reduces the specimens' bearing capacity. At peak strength, specimen strain decreases, resulting in diminished deformation capacity. Among different testing paths, specimens exhibit the highest strength under the loading axial stress path, while the lowest strength occurs under the compound loading axial and unloading confining path, exhibiting significant deformation and expansion. In contrast, under the unloading confining stress path, specimen strain is minimal, and the overall energy required for specimen instability-including elastic strain energy and dissipated energy-remains relatively low.

Coal structures are commonly found in coal rock formations. Understanding the evolutionary laws of mechanics, deformation, and permeability of gas-bearing coal rock during the failure process at different bedding angles is crucial for studying the prevention and control techniques of coal and rock gas dynamic disaster mitigation. In this study, a mechanical seepage test of gas-bearing coal under various bedding angles was conducted using the fluid–solid coupling triaxial servo test system. The results indicate the following corrections: ① Both axial peak strain (ε1) and radial peak strain (ε3) initially increase and then decrease, reaching their maximum values at 45°, indicating that the specimen eventually slips along the bedding plane and fails. ② As the bedding angle increases, the peak stress of the coal body shows a “V”-shaped distribution, with the peak strength of the gas-bearing coal sample being the lowest at 60°. ③ The minimum permeability of the coal sample increases with the rise in the bedding angle. The bedding direction of the coal samples at 90° and 75° aligns with the axial direction, leading to more seepage channels. ④ At a bedding angle of 60°, the minimum dissipated energy (Ud) is required for sample failure, indicating that the sample is highly prone to failure.

In order to address the issue of inadequate negative pressure distribution in the gas extraction pipeline network and to enhance the efficiency of gas extraction, a study was conducted on the mechanisms of mutual influence between various branches within the gas extraction pipeline network. Using graph theory principles, a gas extraction network graph was built, and the gas extraction pipeline network was solved through the assignment adjustment iterative method. The study summarizes the sensitivity analysis of various control parameters, regulation patterns of branch valves and extraction pump control parameters at different network positions, and the impact of time parameters on the network’s operational conditions. Based on the solution results, an intelligent gas extraction control strategy was proposed. The results indicate that, under safety and efficiency constraints, gas concentration increased by approximately 11%, and gas purity increased by 0.3 m3/min, resulting in a 4.7% improvement after the implementation of intelligent control. The overall performance of the pipeline network was significantly enhanced. These research findings are of great significance for achieving efficient gas extraction.

To solve the problem of difficulty in accurately calculating the height of roof crack development in shallow mining under the threat of composite water body, a study was conducted using Gaotouyao coal mine in Dongsheng coalfield as an example. Firstly, taking the mining and geological conditions of coal seams 2-3 and 3-1 in Gaotouyao coal mine as the research background, physical similarity simulation and three-dimensional discrete element code (3DEC) numerical calculation were used to study the development height of shallow buried closed coal seam roof cracks under composite water bodies. Then, in response to the complexity of the evolution law of shallow buried closed strata roof cracks in composite water bodies, the estimation formula for the height of roof crack development was revised. Finally, by combining similar material physical simulation experiments and numerical simulation calculations, the accuracy and applicability of the revised formula were verified through on-site monitoring of the development height of roof cracks in the 2-3 and 3-1 coal seams of Gaotouyao coal mine. The research results indicate that: Under the influence of mining the No. 3-1 coal seam, roof fractures expanded and connected, and previously compacted fractures in the roof of the No. 2-3 coal seam re-developed due to repeated mining, resulting in an increase in fracture width. The evolution law of shallow buried closed strata roof cracks in composite water bodies was revealed. And field measurements showed that the roof fracture development height after mining the No. 2-3 coal seam at Gaotouyao coal mine was 47.0 m, and after repeated mining of the No. 3-1 coal seam, the roof fracture development height was 88.5 m. These results are close to the calculations obtained using the revised formula, validating the accuracy of the revised formula for estimating roof fracture development height in shallow, closely spaced coal seams under composite water bodies. The research results have certain theoretical guidance significance for the safe and efficient mining of shallow and close range coal seams.

To address the issue of an unknown transportation mechanism and the difficulty of determining parameters in coal bed gas extraction processes, a coupled flow-solid model was created using the dual medium assumption for pore-fracture. This model considers the influence of the multi-mechanism coal bed gas flow as well as the creep effect. Coal seam gas extraction was simulated using the COMSOL numerical simulation program, which was based on the theoretical model mentioned above. The software calculated the appropriate hole spacing and pre-drainage time by analyzing the dynamic distribution law of pressure of gas over time. According to the study's findings, a single borehole's effective extraction radius follows a power function of time (r1=0.318⋅t0.621 R2=0.987). At 180 d, the effective extraction radius is 2.26 m. In multi-hole extraction, the borehole spacing needs to satisfy 3r≤L≤r+0.17R, and the optimal spacing is 6.8–9.2 m. The best spacing is 6.8–9.2 m; after 220 d of pre-drainage, the maximum gas pressure around the borehole decreased to 0.70 MPa, which is below the safety threshold of 0.74 MPa. The results reveal the dynamic coupling mechanism between seepage and stress fields and optimize the method of determining the spacing of boreholes and pre-drainage period. Through the field engineering application verification, the optimized hole spacing and pre drainage period can reduce the number of boreholes in the working face by 25%, shorten the gas pre-drainage time by 20 days, stabilize the residual gas pressure below the safety threshold, and significantly reduce the mine gas disaster risk.

The overall failure of gas-bearing coal–rock composite is the main cause of composite dynamic disasters. Investigating the mechanical-seepage characteristics of coal–rock specimens is the key to understanding the mechanism and minimizing composite dynamic disasters. In this paper, true triaxial mechanical experiments are designed and conducted under different maximum principal stress-loading rates. The mechanical properties, strength characteristics, and energy responses of samples under different loading rates are studied. A damage constitutive model of coal–rock specimens under different true triaxial loading rates is established; the solving methods for micro strength parameters m and F0 are described. The results show that as maximum principal stress-loading rate increases, the bearing capacity of the sample increases, the deformation parameters gradually increase, the degree of energy change increases, and the deformation failure becomes more severe. The model of gas-bearing coal–rock specimens under different true triaxial loading rates is in agreement with the test curves. Our model can provide useful references for predicting the stability of underground gas-bearing coal–rock.

The soft rock roadway in deep extra-thick coal seam is prone to large deformation disaster. In order to solve this problem effectively, taking the W3101 coalface of Xiao’kang coal mine as the engineering background, the failure mechanisms and the corresponding control technology were investigated by the methods of laboratory test, numerical simulation and field measurement. First, a series of tests were carried out on the basic mechanical properties of rock mass, in-situ stress and loose zone, and it was found that the failure mechanisms of soft rock roadway in deep extra-thick coal seam are poor lithology of surrounding rock, high in-situ stress, large loose circle and unreasonable original support. Then, based on the supporting mechanisms of grouting cable and concrete-filled steel tube (CFST) of bottom angle, a new collaborative reinforcement support (CRS) technology combining the two was proposed. Next, the numerical simulation shows that the CRS technology has good applicability in controlling large deformation of soft rock roadway in deep extra-thick coal seam. Finally, to exhibit the engineering application effect of the proposed CRS scheme, it was also applied in Xiao’kang coal mine. Comparing to the controlling effect of original support scheme, it can be seen that the average deformation of soft rock roadway reduces by 73.2 % under the proposed CRS scheme, and the steel arch frame of bottom angle is slightly deformed. Meanwhile, it is found that the grouts diffusion radius is nearly 1.21 m, and the deepest diffusion depth is 4.25 m, which also indicates again that the feasibility of the proposed CRS scheme in controlling large deformation of soft rock roadway in deep extra-thick coal seam.