Protective Coal Seam Mining Research Articles

Dynamic mechanical characteristics of coal in front of the mining face under different mining layouts

To study the dynamic mechanical characteristics of coal in the area affected by mining in front of the mining face under different mining methods, an improved split Hopkinson pressure bar (SHPB) was used to apply different static loads to different positions. Then, dynamic mechanical tests were conducted on coal at different positions on the mining face, analyzing the dynamic response under strong dynamic load disturbances, under three different mining layouts. Within the range of static water pressure to the peak support pressure, the dynamic strength of coal gradually increases with increasing distance from the mining face. The dynamic strength is the smallest at the peak support pressure stress, and under strong external disturbances, instability and failure are increasingly likely to occur at the peak stress. Under the same loading rate conditions, the dynamic strength of the peak stress in coal is as follows: Protective coal-seam mining (PCM) > Top-coal caving mining (TCM) > Nonpillar mining (NM).

Impact of Lower Protective Coal Seam Mining on Overlying Strata: Deformation, Pressure Relief, and Permeability Enhancement

Impact of Lower Protective Coal Seam Mining on Overlying Strata: Deformation, Pressure Relief, and Permeability Enhancement

Characterization of energy-driven damage mechanism and gas seepage in coal under mining-induced stress conditions

Gas seepage and progressive failure of coal are common energy-driven mining phenomena. A comprehensive understanding of the energy-driving mechanism behind the catastrophic behavior of mining-induced coal is fundamental to innovating the technology of coal and gas co-mining. Thus, this study simulated three typical mining stress evolution process in protective coal-seam mining (PCM), top-coal caving mining (TCM), and non-pillar mining (NM) to investigate the energy evolution and distribution patterns of coal. The results indicate a strong correlation between energy dissipation and gas seepage. By transitioning from PCM and TCM to NM, the peak elastic strain energy of gas-bearing coal increased by 155.92 %, and the ratio of peak dissipative energy decreased from 51 % to 41 %. Under the PCM stress path, gas seepage decreased the energy storage by 13.52 %, whereas the pre-mining pressure relief and enhanced permeability simulation increased in peak dissipation energy by 49.66 %. Using the cumulative dissipative energy as a damage variable reveals that the degree of coal damage evolution under PCM is higher than other mining methods. Based on the energy-driven damage mechanism, a new coal permeability model was established, and its comparison with classical permeability model demonstrated its excellent fitting effectiveness.

Intensive field measurements for characterizing the permeability and methane release with the treatment process of pressure-relief mining

Characterizing the permeability evolution and methane release is of great significance for the safe mining of the high gas outburst seams, as well as coal and gas simultaneous extraction. It contributes to reduce methane emissions from coal mining for greenhouse effect control. Theoretical analysis, laboratory testing, and numerical simulation are widely used methods to characterize the permeability and methane release with the treatment process of pressure-relief mining. However, these methods cannot fully reflect the complexity of filed practice. In this study, we report the effectiveness of protective coal seam (PCS) mining and the pressure-relief area in the protected coal seam (PDCS) based on detailed and integrated field measurements in a Chinese coal mine. To the best of our knowledge, it is the first time to measure the permeability coefficient and gas pressure evolution in the PDCS during the process of PCS longwall mining. The evolution of the permeability coefficient in the pressure-relief area during PCS mining can be divided into four stages: slowly decreasing, sharply increasing, gradually decreasing, and basically stable. The maximum permeability coefficient is 322 times of the initial value and stabilized at 100 times after the goaf compacted. The gas pressure evolution in the PDCS indicates that the strike pressure relief angle is 52.2° at the active longwall face zone, and 59.3° at the installation roadway side. The inclined pressure relief angles at the lower and upper sides of the longwall face are 75° and 78.9°, respectively. The residual gas content and gas pressure of the PDCS in the pressure-relief area are reduced to less than 6 m3/t and within 0.4 MPa, respectively. The field measurements further prove that pressure-relief mining can prevent coal and gas outbursts in PDCSs. The field observations in this paper can serve as benchmark evidence for theoretical analysis and numerical simulations, and also provide insights into realizing safety mining in similar conditions.

Experimental Study on Gas Seepage Characteristics of Axially Unloaded Coal under Different Confining Pressures and Gas Pressures

Protective coal seam mining can not only effectively prevent coal and gas outbursts in mines, but also provide stress unloading space for the protected coal seam. The coal body in the protected coal seam might undergo deformation, internal damage and structural damage, which changes its gas seepage characteristics. This study aims to explore the variations of permeability of the coal body in the protected coal seam under axial unloading. With the coal body from the outburst coal seam in the Huaibei mining area as the research object, experiments were conducted to explore the gas seepage characteristics of axially unloaded coal body under different confining pressures and gas pressures, using the TAWD-2000 coal-rock mechanics-seepage experimental system. According to the results, with respect to the gas seepage, the variations of permeabilities of axially unloaded coal samples are closely related to their deformation and damage. As the confining pressure and gas pressure rise, the difference between the permeability at the final failure point and the initial permeability rises at a decreasing rate. The experiments fully demonstrate that the protective coal seam is technically important for the unloaded gas drainage and the coal and gas outburst prevention of the protected coal seam. Under different confining pressures and gas pressures, the permeability of axially unloaded coal varies to different extents and at different rates. The mining scheme for the protective coal seam should be designed in accordance with its confining pressure and gas pressure. This study is of guiding significance for the prevention and control of coal and gas outbursts in coal seam groups.

Study on pressure relief effect of upper protective coal seam mining based on distributed optical fiber sensing monitoring

On site real-time monitoring of protective layer mining is an important method to deeply study its pressure relief mechanism. It is proposed that the distributed optical fiber sensing technology (BOTDA) based on Brillouin optical time domain analysis is used to conduct mining industry tests on the deformation law and pressure relief effect of the underlying coal and rock mass during the mining of the upper protective layer. Taking the 21,104 comprehensive mechanized working face of Hulusu Coal Mine as an example, the strain transmission relationship between the coal and rock mass and the force-bearing optical fiber sensor is analyzed, and the design scheme, implantation scheme and installation process of the optical fiber sensor monitoring system are introduced. Implemented the accuracy analysis of the optical fiber sensing monitoring system and the spatial positioning of the sensors. According to the mining progress of the working face, the optical fiber sensing monitoring system regularly collects data, and by analyzing the strain distribution characteristics of the sensing optical cable and its dynamic change process, the deformation law of the underlying coal and rock mass in the mining of the upper protective layer is obtained. The monitoring results show that the underlying coal and rock mass undergoes a dynamic process of compressive strain increase, tensile strain increase and tensile strain recovery during the mining of the upper protective layer, and the scale of increase and decrease of strain of coal and rock mass at different depths are different; The intensity of coal rock deformation and pressure relief effect are characterized by the fluctuation amplitude of optical fiber strain increment. The pressure relief process can be divided into three stages: the pressure relief start stage is 40.8 m, the pressure relief active stage is 68.3 m, and the pressure relief decline stage; Finally, the strike pressure relief angle of the upper protective layer mining is 58.7°, the inclined pressure relief angle is 63.6°, the pressure relief lag distance is 14.2 m, and the maximum vertical distance of pressure relief is 28.4 m. The research shows that the application of BOTDA distributed optical fiber sensing technology in monitoring the pressure relief effect of protective layer mining can provide a reliable basis for coal mine safety mining.

Numerical Simulation of the Volumetric Strain Distribution of a Protected Coal Seam

To investigate the deformation characteristics of protected coal seams, the numerical simulation of the mining of an upper protective coal seam was carried out in the present study. Based on the basic definition of strain, a method for the extraction of the strain data of the protected coal seam was proposed, and the strain distribution characteristics were obtained. It was found that the x -direction strain is mainly distributed near the coal pillars on both sides and inside the goaf, the y -direction strain is mainly distributed at the working face, the initial mining line, and inside the goaf, and the z -direction strain is mainly distributed at the working face, the initial mining line, the coal pillars on both sides, and inside the goaf. The distribution characteristics and the value of volumetric strain were found to be basically consistent with the z -direction strain. As the working face advances, the protected coal seam undergoes compression and damage expansion in turn. The turning point between compression and damage expansion is approximately 15 m in front of the working face. The variation law of gas drainage in the boreholes of the protected coal seam is closely related to the distribution characteristics of volumetric strain. The results of this research are of great significance for the comprehensive investigation of the effects of pressure relief and the permeability enhancement of protective coal seam mining.

Permeability Enhancement and Gas Drainage Effect in Deep High Gassy Coal Seams via Long-Distance Pressure Relief Mining: A Case Study

Coal 3 in group A is employed as a protective layer to release long-distance coal 4 in group B in Paner colliery (approximately 80 m vertical interval) as the mining depth extends downward, which is the first engineering test in the Huainan coal mining area. To evaluate the validity of the scheme, the permeability distribution, and evolution law, gas pressure distribution characteristics, swelling deformation, pressure relief range, and gas drainage volume of the protected coal seam are analyzed using a FLAC3D numerical simulation and field measurements. Therefore, different stress-permeability models are adopted for caved, fractured, and continuous deformation zones, and a double-yield model is applied in the goaf based on compaction theory to improve the accuracy of the numerical simulation. The results indicate that the extraction of coal 3 has a positive effect on permeability enhancement and pressure relief gas drainage. However, the dip angle of coal measurements causes asymmetric strata movement, which leads to the pressure relief and permeability enhancement area shifting to the downhill side, where the permeability enhancement effect of the downhill side is better than that of the uphill side. The permeability enhancement zone is an inverted trapezoid, but the effective pressure relief range is a positive trapezoid. The permeability of the protected coal seam in the pressure relief zone is significantly higher than that in the compressive failure zone. The permeability in the pressure relief zone will decrease again due to the recompaction of the coal seam with an advancement of the longwall face. Thus, pressure relief gas drainage is suggested during long-distance protective coal seam mining to eliminate gas hazards.

Stress Distribution and Gas Concentration Evolution during Protective Coal Seam Mining

Coal and gas burst is one of the significant and catastrophic hazards in underground longwall operations. To date, the protective coal seam mining has been recognized as the most effective mining method for minimizing or even avoiding the effect of the coal and gas burst. In this paper, numerical modelling and field test were carried out for the longwall operation in Qidong Coal Mine in order to investigate the induced stress and coal seam gas drainage performance in the protected coal seam after the complete extraction of the protective coal seam. It was found that four stress zones can be classified in the protected coal seam being the original stress zone, stress concentration zone, stress relief zone, and recompaction zone. In addition, the monitoring data of gas concentration and volume change in the field agree well with the numerical modelling results.

Elimination of Coal and Gas Outburst Dynamic Disasters in Dengfeng Coalfield through Gas Extraction Based on Extremely Thin Protective Coal Seam Mining

No. 21 coal seam is a full‐thickness structured soft coal in Dengfeng coalfield. The coal seam gas‐bearing capacity is high, and the permeability is poor, thus resulting in serious coal and gas outburst dynamic disasters. According to the gas geological conditions of Baoyushan Mine, No. 17 coal seam without outburst danger, which is 0.5 m thick and 23.4 m under No. 21 coal seam, was mined in advance as the lower protective seam. At the same time, a gas extraction roadway was constructed in No. 21 coal seam floor. Cross‐layer boreholes were constructed to extract the pressure relief gas of No. 21 coal seam for comprehensive treatment of mine gas. The mobile deformation of the overburden coal and rock mass after mining No. 17 coal seam, the fracture development characteristics of No. 21 coal seam, the pressure relief gas migration of the coal seam, the gas extraction, and the outburst danger elimination were studied. The research findings showed the following: (1) after mining No. 17 coal seam, the overburden hard and extremely thick limestone roof sagged slowly, albeit leading to no craving zone. (2) The permeability of No. 21 coal seam was increased by about 394 times, from 0.0012 mD to 0.4732 mD. (3) After the extraction of pressure relief gas through the gas extraction roadway on the floor through the cross‐layer borehole, the gas pressure of No. 21 coal seam decreased from 1.17 MPa to 0.12 MPa, while the gas content decreased from 9.74 m3/t to 3.1 m3/t, which suggested that the coal and gas outburst dynamic danger of No. 21 coal seam was totally eliminated and the goal of safe and efficient mining in the mine was realized.

Gas Flow Characteristics and Optimization of Gas Drainage Borehole Layout in Protective Coal Seam Mining: A Case Study from the Shaqu Coal Mine, Shanxi Province, China

With increasing demands for coal resources, coal has been gradually mined in deep coal seams. Due to high gas content, pressure and in situ stress, deep coal seams show great risks of coal and gas outburst. Protective coal seam mining, as a safe and effective method for gas control, has been widely used in major coal-producing countries in the world. However, at present, the relevant problems, such as gas seepage characteristics and optimization of gas drainage borehole layout in protective coal seam mining have been rarely studied. Firstly, by combining with formulas for measuring and testing permeability of coal and rock mass in different stress regimes and failure modes in the laboratory, this study investigated stress–seepage coupling laws by using built-in language Fish of numerical simulation software FLAC3D. In addition, this research analyzed distribution characteristics of permeability in a protected coal seam in the process of protective coal seam mining. Secondly, the protected coal seam was divided into a zone with initial permeability, a zone with decreasing permeability, and permeability increasing zones 1 and 2 according to the changes of permeability. In these zones, permeability rises the most in the permeability increasing zone 2. Moreover, by taking Shaqu Coal Mine, Shanxi Province, China as an example, layout of gas drainage boreholes in the protected coal seam was optimized based on the above permeability-based zoning. Finally, numerical simulation and field application showed that gas drainage volume and concentration rise significantly after optimizing borehole layout. Therefore, when gas is drained through boreholes crossing coal seams during the protective coal seam mining in other coal mines, optimization of borehole layout in Shaqu Coal Mine has certain reference values.

Key technologies and engineering practices for soft-rock protective seam mining

Severe gas disasters in deep mining areas are increasing, and traditional protective coal seam mining is facing significant challenges. This paper proposes an innovative technology using soft rock as the protective seam in the absence of an appropriate coal seam. Based on the geological engineering conditions of the new horizontal first mining area of Luling Coal Mine in Huaibei, China, the impacts of different mining parameters of the soft-rock protective seam on the pressure-relief effect of the protected coal seam were analyzed through numerical simulation. The unit stress of the protected coal seam, which was less than half of the primary rock stress, was used as the mining stress pressure-relief index. The optimized interlayer space was found to be 59 m for the first soft-rock working face, with a 2 m mining thickness and 105 m face length. The physicochemical characteristics of the orebody were analyzed, and a device selection framework for the soft-rock protective seam was developed. Optimal equipment for the working face was selected, including the fully-mechanized hydraulic support and coal cutter. A production technology that combined fully-mechanized and blasting-assisted soft-rock mining was developed. Engineering practices demonstrated that normal circulation operation can be achieved on the working face of the soft-rock protective seam, with an average advancement rate of 1.64 m/d. The maximum residual gas pressure and content, which were measured at the cut hole position of the protected coal seams (Nos. 8 and 9), decreased to 0.35 MPa and 4.87 m3/t, respectively. The results suggested that soft-rock protective seam mining can produce a significant gas-control effect.

A protective seam mining method by cutting roof with chainsaw arm machine

Abstract Multiple-layered coal seams widely exist in main coal mining areas of China. When these coal seams are exploited, the pillar mining method is always employed. This leads to many coal pillars left in the upper coal seams as a protective barrier. As a result, these residual pillars will not only cause the loss of coal resources but also could trigger environmental issues and a serious of mine disasters. A theoretical model was built to analyse the effect of the residual pillars. From the theoretical model, it was found that four stress concentration areas were formed by the upper residual coal pillars. To address the issues of the residual coal pillars, Datong Coal Mine Group has developed an innovative technology of the roof cutting with a chainsaw. A new protective coal seam mining method using chainsaw roof-cutting technology is introduced. A numerical model is constructed to analyse the mining pressure distribution law in working face within the lower layer coal seam. From the numerical simulation, the new protective layer mining method could reduce about 15.2% of the advancing stress, which contributes a lot to controlling the mining pressure within the lower layer. The field measurement showed that the hydraulic support utilised at the site was at lower pressure levels, which proves the new protective seam mining method can significantly reduce the working face pressure.

Acoustic Emission Characteristics of Coal Samples under Different Stress Paths Corresponding to Different Mining Layouts

Research on the mining-induced mechanical behavior and microcrack evolution of deep-mined coal has become increasingly important with the sharp increase in mining depth. For rock units in front of the working face, the microcrack evolution characteristics, structural characteristics, and stress state correspond well to mining layouts and depths under deep mining. The acoustic emission (AE) characteristics of typical coal under deep mining were obtained by conducting laboratory experiments to simulate mining-induced behavior and utilizing AE techniques to capture the variation in AE temporal and spatial parameters in real time, which provide an important basis for studying the rupture mechanisms and mechanical behavior of deep-mined coal. The findings were as follows: (1) AE activity under deep mining was characterized by three stages, corresponding to crack initiation, crack stable propagation, and crack unstable propagation. As the three stages proceeded, the AE counting rate and AE energy rate presented stronger clustering characteristics, and the cumulative AE counting and cumulative AE energy exhibited a sharp increase by an order of magnitude. (2) The crack initiation and the main stages of crack propagation were determined by characteristic points of variation curves in the AE parameters over time. In the main crack propagation stage, the number of cumulative AE events and the cumulative AE counts were similar among the three mining conditions, while coal samples under coal pillar mining released the largest amount of AE energy. The amount of accumulated AE energy released by coal samples increased by one order of magnitude according to the sequence of protective coal-seam mining, top-coal caving mining, and nonpillar mining. (3) Fractal technology was applied to quantitatively analyze the AE spatial evolution process, showing that the fractal dimension of the AE location decreased as the peak stress increased, corresponding to protective seam mining, caving-coal mining, and nonpillar mining. The above results showed that the deformation and fracture characteristics of coal under deep mining followed a general law, but were affected by different mining conditions. The crack initiation and main rupture activity of coal occurred earlier under the conditions of protective seam mining, top-coal caving mining, and nonpillar mining, successively. Moreover, nonpillar mining induced the strongest and highest degree of unstable rupture of the coal body in front of the working face.

Size and spatial fractal distributions of coal fracture networks under different mining-induced stress conditions

Coal permeability is a key issue in CO2 injection and enhanced coalbed methane (CBM) recovery, and it is determined by the fracture network, which is strongly influenced by mining-induced stress evolutions. For a comprehensive understanding of the size and spatial distribution characteristics of coal fracture networks under different mining-induced stress conditions, a series of laboratory experiments, computed tomography (CT) scans and image analyses focusing on 3D coal fracture systems have been conducted considering the stress conditions induced by three typical mining layouts, i.e., top-coal caving mining (TCM), non-pillar mining (NM) and protective coal-seam mining (PCM). The size and spatial distributions of mining-induced coal microfractures and the anisotropic tortuosity characteristics of coal fracture networks have been quantitatively determined based on fractal theory. The results show that the size distributions of microfracture geometries, the fractal dimensions of fracture size distribution and the tortuosity of the mining-induced coal fracture networks vary according to the mining-induced stress conditions, resulting in differences in the seepage capacity of coal masses. The coal samples subjected to PCM conditions have the highest percentage of large microfractures, and those exposed to NM conditions have the lowest percentage. The fractal dimensions (Da and Dd) of the microfracture size distributions of the typical coal specimens decrease in the order of PCM, NM and TCM conditions, and the Da and Dd of coal specimens without pre-mining unloading-expansion simulation (PUES) are much lower than those of specimens with PUES. The tortuosity fractal dimensions (δ) of the mining-induced fracture network are spatially anisotropic. The ranges of δ for the coal masses exposed to PCM, NM and TCM conditions are 1.0–1.2, 1.2–1.3 and 1.25–1.4, respectively. Using fractal theory and the measured fracture network data, the anisotropic spatial distribution of coal permeability can be theoretically estimated.

Permeability distribution characteristics of underlying coal seam disturbed by mining activity

ABSTRACTThe permeability distribution law for protected coal seam is the core problem linked to protective coal seam mining. Based on the geological conditions of the Zhongxing coal mine, a numerical protective coal seam mining model was constructed in order to investigate the spatial evolution of stress and the damage characteristics of protected coal seams. During the mining of protective coal seam, the coal body of the protected coal seam undergoes loading followed by three-directional stress unloading. The permeability evolution law of the protected coal seam was derived by combining the relationship between the permeability and axial strain of the coal sample from mechanical-seepage experiments and the swelling and relaxation value of the protected coal seam from numerical simulations. We divided the permeability of the protected coal seam into the original permeability zone, the permeability decreasing zone, the permeability increasing zone, the permeability stable zone, and the permeability re-decreasing zone. The gas drainage data of the protected coal seam during the mining of the protective coal seam were measured in situ. The change laws of the gas drainage volume and gas concentration were essentially consistent with the permeability distribution of the protected coal seam.

A Gas Seepage Modeling Study for Mitigating Gas Accumulation Risk in Upper Protective Coal Seam Mining Process

Protective coal seam mining (PCSM) is one of the most significant mitigation measures of regional outburst in the process of deep coal seam mining, which has high outburst risk in China. During the PCSM process, the phenomenon of methane concentration exceeding the limit usually occurs in the working face. It is vital to understand factors affecting gas emission from the protective seam working face (PSWF) and to obtain an equation for determining the quantity of gas emission. A gas seepage model (GSM) was developed to simulate the gas emission during the process of upper PCSM. In this study, an equation was formulated to determine the quantity of gas desorbed from the protected seam into PSWF. These equations have been developed by using Fick’s second law of diffusion and Darcy’s flow law. The relationship between permeability and stress was described in an elastic-plastic state, and the mechanics of surrounding rock were investigated. It can be concluded from GSM that the initial gas pressure of protected seam, the characteristics of interlayer rocks, and the ventilation pressure of PSWF were the main factors that influenced the desorption of gas emission from the protected seam into PSWF. The developed GSM was tested for calculating gas emission quantity from the PCSM process by utilizing the actual geological condition data of a coal mine, which is located in Hancheng, China. The results have shown great agreement with obtained field measurements, which is done by combining the fitting curve of ventilation air methane quantity for PSWF with an interlayer spacing. A loss coefficient (δ) of 1.012 × 10−3 was obtained in this study.

Rational Boreholes Arrangement of Gas Extraction from Unloaded Coal Seam

In order to enhance gas extraction from unloaded coal seam by drilling borehole in the floor roadway, the mechanism of stress relief improving permeability by protective coal seam mining was analyzed. Based on the multiphysics field theory, the hydraulic-mechanical coupling model of gas extraction in the unloading coal seam was established, and the gas extraction process by drilling borehole in the floor roadway in the overburden of Panyi Coal Mine 1551 (1) panel was simulated. The influence of different drilling arrangements on the gas extraction effect was analyzed. The results show that the permeability of protected coal seams is characterized by zoning and can be divided into the permeability-enhanced zone, the permeability-reduced zone, and the original permeability zone according to the stress state of coal seam. Under the condition of uniform borehole distribution, the gas pressure decreased slowly in the permeability-reduced zone and is still greater than 0.74 MPa after 180 days of extraction, and there is a large extraction blind area in the protected panel. Under the condition of nonuniform borehole distribution arrangement according to the characteristics of permeability zoning, the effective extraction area can almost cover the protected panel, and the blind extraction area is reduced by 91.22% when compared to uniform borehole distribution. These can provide a reference for unloading gas extraction under similar conditions.

Deformation, Permeability and Acoustic Emission Characteristics of Coal Masses under Mining-Induced Stress Paths

The geomechanical and seepage evolution characteristics of coal masses during mining are the key factors that affect the drainage of coalbed methane and the safety of coal mining. Nevertheless, the influence of mining paths on coal seam permeability is rarely investigated given the complexity of mining-induced stress experiments. To study the effect of mining-induced stress on coal mining, the mechanical properties, acoustic emission characteristics and energy evolution of coal masses were experimentally evaluated through mining-induced stress experiments. Experimental results indicated that at peak intensity, the deviatoric stress and axial strain of coal samples under the stress path of protective coal-seam mining are lower than those of coal samples under the non-pillar stress path. The unloading ratio of confining pressure is large under a stress path of non-pillar mining, and the elastic energy, the absorbed energy, and the dissipated energy of coal mass are low during destruction. The effect of high confining pressure on AE events is pronounced under the non-pillar mining path. The overall b value under high confining pressure is smaller than that under low confining pressure, and AE events generally have high energy. The fracture structure of coal mass is complex, and the fractal size of coal is large under high unloading rates of confining pressure, which induce the increase of permeability after coal destruction.

Numerical simulation of spatial distributions of mining-induced stress and fracture fields for three coal mining layouts

In this study, the spatial distributions of stress and fracture fields for three typical underground coal mining layouts, i.e. non-pillar mining (NM), top-coal caving mining (TCM) and protective coal-seam mining (PCM), are modeled using discrete element software UDEC. The numerical results show that different mining layouts can lead to different mining-induced stress fields, resulting in diverse fracture fields. For the PCM, the mining influenced area in front of the mining faces is the largest, and the stress concentration factor in front of the mining faces is the lowest. The spatial shapes of the mining-induced fracture fields under NM, TCM and PCM differ, and they are characterized by trapezoidal, triangular and tower shapes, respectively. The fractal dimensions of mining-induced fractures of the three mining layouts decrease in the order of PCM, TCM and NM. It is also shown that the PCM can result in a better gas control effect in coal mines with high outburst potential. The numerical results are expected to provide a basis for understanding of mining-induced gas seepage fields and provide a reference for high-efficiency coal mining.