Working Face Of Mine Research Articles

A Digital Twin-Based Adaptive Height Control for a Shearer

The shearer is an important component of the smart mining workface, and its effective control is a key aspect that guarantees safe and high-efficient production in coal mines. To address the issue of autonomous height adjustment during the shearer’s cutting process, a self-adaptive speed control method driven by digital twin technology is proposed. A digital twin-based control architecture for the shearer is first established, which consists of physical and the corresponding virtual entities, as well as reality–virtual interaction between them. Based on the mathematic model formulated for height adjustment system of the shearer, an adaptive fuzzy sliding mode controller (AFSMC) with the displacement estimation is designed for the virtual entity, with the purpose of guiding the operation of the corresponding physical entity. Simulation experiments on MATLAB compares the control performance among the proposed method and four comparative ones, including PID controller, integral sliding mode controller (ISMC), feedback linearization controller (FLC), and fuzzy sliding mode controller (FSMC). The experimental results confirm the effectiveness of the proposed AFSMC. More specifically, its steady-state error is 0.024, the maximum absolute control input is 8.43, and the settling time is 1.74 s. This also proves that the digital twin-based control method enables the precise adaptive height adjustment of the shearer, providing potential reference for the intelligent development of a smart mining workface.

Quantitative Assessment of Bed-Separation Dynamic Development Caused by Inclined Coal Seam Longwall Mining

Coal mining under the Quaternary thick loose layer affects key strata breakage, Bed-separations development, ground subsidence, and other studies. This paper presents a method for solving the deflection of a large-deflection inclined thin plate under a thick loose-layer cover with additional lateral loads and midplane forces. The methods presented are based on the principle of large-deflection of thin-plate, energy method, and fracture mechanics theory. The 7225 work face in Anhui Province, China, was studied. Combined with the large-deflection inclined thin plate model, the initial breakage distance within the main roof plate was calculated to be 33 m with the initial breakage angle of 61.2°, and the period breakage distance was calculated to be 21 m with the period breakage angle of 55.4°. The distribution range of “Vertical Three Zones” from 7225 working face to the ground, including the height of the caved zone is 38.07 m, the height of the fractured zone is 41.13 m, and the height of the curved zone with the thick loose layer removed is 187.56 m. During the dynamic development of the principal key strata (PKS), the deflection value develops from 0 mm to 2714 mm with 7225 working face mining, and the maximum value of the spatial volume is 56,485 m3, which is verified by Three-dimensional Discrete Element Code (3DEC) numerical simulation. The dynamic development of Bed-separation within the overlying strata, with a maximum development height of 545.2 mm and a maximum volume of 11,228.1 m3 of the Bed-separation cavity. The dynamic development of the Bed-separation height and the cavity under different mining length and width conditions of the working face are also discussed. The large-deflection inclined thin plate model proposed in this paper effectively explores the dynamic deflection and fragmentation law of the overlying strata induced by the inclined working face of Longwall mining and provides a theoretical basis and computational model for quantitatively evaluating the dynamic development of the Bed-separation cavity.

An Automated Approach for Mapping Mining-Induced Fissures Using CNNs and UAS Photogrammetry

Understanding the distribution and development patterns of mining-induced fissures is crucial for environmental protection and geological hazard prevention. To address labor-intensive manual inspection, an automated approach leveraging Convolutional Neural Networks (CNNs) and Unmanned Aerial System Photogrammetry (UASP) is proposed for fissure identification and mapping. Initially, the ResNet-50 network was employed for the binary classification of the cropped UASP orthophoto images. A comparative analysis was conducted to determine the optimal model between DeepLabv3+ and U-Net. Subsequently, the identified fissures were mosaicked and spatially projected onto the original orthophoto image, incorporating precise projection data, thereby furnishing a spatial reference for environmental governance. The results indicate a classification accuracy of 93% for the ResNet-50 model, with the U-Net model demonstrating a superior identification performance. Fissure orientation and distribution patterns are influenced by the mining direction, ground position of the mining workface, and topographic undulations. Enhancing the CNN performance can be achieved by incorporating variables such as slope indices, vegetation density, and mining workface locations. Lastly, a remote unmanned approach is proposed for the automated mapping of mining-induced fissures, integrated with UAS automated charging station technology. This study contributes to the advancement of intelligent, labor-saving, and unmanned management approaches advocated by the mining industry, with potential for broad applications in mining environmental protection efforts.

Analysis of Lateral Roof Structure and Stability Control Technology in Island Working Face Mining Roadways

Analysis of Lateral Roof Structure and Stability Control Technology in Island Working Face Mining Roadways

Characteristics of waterproof failure and optimal width of narrow coal pillars under the coupled effects of mining, excavation and seepage

The failure of waterproof coal pillars under the coupled effects of mining, excavation and water seepage is a significant factor contributing to sudden water inflow accidents in underground roadways. Investigating the instability characteristics and optimal width of waterproof coal pillars holds vital significance for water control and resource protection in mines. This study focus on the rational width of waterproof coal pillar at Dongzhuang Coal Mine in Shanxi Province. Using FLAC3D, a fluid–structure interaction numerical model of waterproof coal pillar was established, revealing the coupling characteristics of stress fields, plastic zones, and seepage zones within coal pillars under the influence of mining, excavation and water infiltration weakening. Furthermore, the stability characteristics of waterproof coal pillars with different widths were compared. The results are as follows: (1) Under the combined action of overlying strata pressure and water pressure from the gob, the coal mass on the water-inflow side of coal pillar is the first to fail. Additionally, with the infiltration of water, the elastic modulus, cohesion, and friction angle of the coal mass in the seepage zone decrease. (2) The lifecycle of waterproof coal pillar can be divided into three stages: working face mining, water infiltration from the gob, and roadway excavation. Based on this, the connectivity between plastic zones and seepage zones serves as the critical condition for the stability of waterproof coal pillar was proposed. (3) When the width of waterproof coal pillar is 3 m and 5 m, plastic zones become connected, forming a water-conducting channel. When the width of waterproof coal pillar is 7 m, 9 m, and 11 m, seepage zones and plastic zones are not connected, and the coal pillar exhibits load-bearing and water-barrier properties.

Numerical study on the dynamic pressure control for self-forming roadways using CHRCT in thin coal seams with thick and hard roofs

Close-hole roof-cutting technology (CHRCT, also called “dense drilling”) has been widely applied in coal mines due to its economic and safety benefits. Inappropriate cutting parameters and support schemes can lead to dynamic pressure disturbances in self-forming roadways with thick and hard roofs. Moreover, fully characterizing the procedure and process of self-forming roadways using CHRCT in the field is difficult, resulting in unconvincing results. Therefore, this study aims to fill the gaps in theoretical knowledge and methodology. First, the dynamic pressure characteristics of the self-forming roadway using CHRCT were investigated, and the dynamic pressure types of the roadway were classified. There are three main types: roof cut off along the coal wall side of, severe deformation, and overhanging roof of a roadway after the second working face mining. The effects of different hole parameters (inclination angle, depth and spacing) on the roof cutting to form a roadway were also investigated. The optimal hole inclination, depth and spacing of 15°, 8 m, and 200 mm were determined through a series of experiments. Then, three support schemes embedded in the roadway were compared in terms of stress evolution, bolt and cable axial forces, roof displacement, and structure. Finally, this study proposes a dynamic pressure mitigation strategy through the optimization of parameters for close-hole roof-cutting and support schemes, monitoring and controlling ground pressure in roadways, and taking auxiliary measures for pressure relief. The results show that this strategy can effectively eliminate the dynamic pressure of the roadway and meet the stability requirements of the full mining cycle. This paper presents a methodology for analysing CHRCT via numerical simulation. Moreover, this approach is of great theoretical and practical importance for dynamic pressure control for self-forming roadways using CHRCT in thin coal seams with thick and hard roofs.

Research on process parameter optimization of irregular coal face.

Based on the engineering background of 1353 working face in Daizhuang Coalmine, the paper identifies three primary issues with the working face mining process: conventional pressure relief means are limited, risk of impact and the length of working face changes, It also proposes comprehensive control measures to improve the blasting roof cutting scheme, optimize mining speed and the location of the stopping line. The three improvement measures mentioned above are simulated numerically, and the effects of the drilling and blasting plan, mining speed, and stopping line location on stress distribution are determined. The results show that by implementing the three improvement measures, the stress variation interval can be efficiently controlled and the working face's production safety can be increased. Finally, it is determined that the 1353 working face of Daizhuang Coalmine adopts the pressure relief method of drilling on one side and cutting the roof 20m deep on the other side, and the mining speed of the working face is 3m/day and the length of the stopping line is 85m. Based on the on-site monitoring results, the implementation of comprehensive treatment measures can effectively improve the surrounding rock state of 1353 working face, which has certain guiding significance for the mining of irregular working face.

Deformation mechanism and control technology of gob-side roadway with continuous mining and continuous backfilling: a case study

Gob-side roadways are excavations created during the mining process, serving to alleviate mining-induced stress. Previous studies have predominantly focused on the caving method, neglecting the examination of failure mechanisms in gob-side roadway associated with continuous mining and continuous backfilling (CMCB). In this study, focusing on Sima Coal Mine, we employed numerical simulation method to thoroughly investigate the full-cycle stress evolution patterns of the gob-side roadway. The numerical simulation results reveal that during the upper working face mining period, severe stress concentration phenomena occur within the coal pillars, with peak stresses reaching 36.0 MPa. Throughout the mining period of next working face, as the CMCB process progressed, the coal inside the working face was gradually replaced by the filling body, forming various coal pillars with decreasing widths. The alternant load between the coal pillar and filling body led to the gradual increase of the internal stress of the coal pillar, with the peak stress reaching 45.0 MPa. To mitigate stress concentration in the surrounding rock of the roadways, this study proposes a control methodology that incorporates "directional control of hydraulic fracturing slots" in conjunction with "reinforcement support of coal pillars" and "temporary support of single hydraulic props" as core components. Industrial experiments were conducted to validate the efficacy of the proposed control techniques. Field monitoring results demonstrate significant improvements in the stress environment, effectively mitigating deformation of roadway.

Application of an Automated Top Coal Caving Control System: The Case of Wangjialing Coal Mine

China has made notable advancements in the intelligent construction of coal mines. However, for longwall top coal caving (LTCC) mining faces, a key obstacle impeding the intelligent transition of the coal-cutting process is automated control. This paper focuses on the aforementioned issue and comprehensively considers the pre-, intra-, and post-coal-caving stages. In this work, diverse detection and monitoring technologies are integrated at various stages through a computer platform, facilitating the construction of an automated coal caving control system with self-perception, self-learning, self-decision-making, and self-execution capabilities. Key technologies include ground-penetrating radar-based top coal thickness detection, inertial navigation-based shearer positioning, tail beam vibration-based identification of coal and gangue, and magnetostrictive sensor-based monitoring of the tail beam and insert plate attitude. In this study, the 12309 working face of the Wangjialing Coal Mine was experimentally validated, and the efficacy of the aforementioned key technologies was assessed. The results demonstrated that the control requirements for automated coal caving are satisfied by the maximum errors. Automatic regulation of coal caving was realized through the implementation of this system, thereby facilitating initiation and cessation and yielding promising experimental outcomes. Overall, this system offers practical insights for intelligent construction in current LTCC mining faces and the sustainable development of coal resources.

Plastic Damage Characteristics of Roadways under the Influence of Overlying Working Face Mining

Plastic Damage Characteristics of Roadways under the Influence of Overlying Working Face Mining

Research on Active-passive Joint Support Technology for the Roadway of Thick Coal Seam Mining

The lower trench of 2301 working face of Anyang Main Coking Coal Mine has the problems of large deformation of surrounding rock and high difficulty of maintenance in the process of digging. According to the deformation characteristics of the surrounding rock, a "U-type steel + anchor cable" joint support technology is proposed to control the deformation. In this paper, the main parameters of joint support are studied through numerical simulation, and the effect of perimeter rock control is verified through on-site monitoring. The results show that: within a reasonable range of preload force, the larger the preload force of the anchor cable, the better the effect of controlling the deformation of the surrounding rock; when the bracket row spacing is 600-800mm, the stability of the surrounding rock of the roadway can be ensured; during the roadway excavation, the maximum deformation of the surrounding rock is 40mm, which realizes the control of the stability of the surrounding rock in the roadway of the top coal of the soft and thick coal seam.

Research on Deformation Monitoring of Roadway Surrounding Rock Based on Mobile 3D Laser Scanning Technology

Aiming at the problems of low data acquisition efficiency, unintuitive data form, low relative accuracy, and inability to continuously monitor the whole cross-section in traditional roadway rock deformation monitoring methods, a roadway rock deformation monitoring method based on mobile 3D laser scanning technology is proposed. Firstly, the mobile 3D laser scanning technology is used to obtain the real 3D point cloud data of the roadway surrounding rock; secondly, the multi-scale dimensional features are used to classify the 3D point cloud data, filter the invalid point cloud data, and form the accurate point cloud data of the roadway surrounding rock surface; then the 3D laser scanning is carried out on a regular basis for the deformation-prone areas of the roadway, and the Iterative Closest Point Algorithm (ICP algorithm) is used to align the overlapping part of the point cloud to achieve the point cloud splicing and point cloud stitching of the two scans. The point cloud splicing and point cloud overlapping of the two scans are achieved; finally, the multi-scale model-to-model point cloud comparison algorithm (M3C2 algorithm) is used to compare the point cloud data of the two periods of the roadway, and the appropriate parameters are selected to indicate the displacement change of the surface of the roadway rock with the size of the color value, so as to realize the monitoring of the deformation of the roadway rock in the three-dimensional full cross-section of the roadway. The method is applied to the deformation monitoring of the surrounding rock in the return roadway of 21407 working face in a coal mine, and the results show that: the mobile laser scanning technology can be used to obtain the complete point cloud data of the roadway, and the deformation area of the surrounding rock is successfully identified after the classification of the scanned point clouds in different time periods, the alignment of the point clouds, and the comparison of the point clouds, and the deformation condition of the surrounding rock of the roadway is visually reflected in the three-dimensional full-section deformation condition of the surrounding rock of the roadway. This method is suitable for monitoring the overall de-formation of the surrounding rock of the roadway under complex environmental conditions, and the de-formation of the surrounding rock is identified by different color areas.

Evolution of mining-induced water inrush disaster from a hidden fault in coal seam floor based on a coupled stress–seepage–damage model

Water inrush originating from hidden faults in the coal seam floor is challenging to prevent due to their concealed nature. This paper develops a coupled stress–seepage–damage model for simulating rock fracture, implemented using the finite element method. The model is validated against compression-seepage tests on rock samples, capturing realistic dynamics of shear and tensile damage as well as permeability. The model is applied to the 27305 working face of a coal mine in Shandong Province, China, revealing the evolution of water inrush caused by a hidden fault. The results indicate that as the working face progresses, both the floor damage and the internal damage within the hidden fault escalate gradually. When mining reaches 80 m, the hidden fault has been activated internally, and the depth of floor damage reaches 13 m, which still has a certain distance from the hidden fault. At 100 m, the depth of the floor damage has stabilized, while the stress concentration at the hidden fault's tip increases, and it begins to expand if conditions for tensile damage are met. By the time mining reaches 110 m, the hidden fault has expanded 9.2 m in length and connected with the floor damage zone, forming a water inrush channel that links the aquifer to the working face, presenting a significant water inrush risk. This work provides an intuitive approach to understanding the evolution of water inrush from a hidden fault, aiding in the prevention of water inrush disasters in practical engineering applications.

Research on Pressure Relief and Anti-impact Technology for Segmental Hydraulic Fracturing in Directional Long Borehole in Roof

After large-scale underground mining operations in coal mines, the stress of the overlying strata above the goaf is transferred to the surrounding support areas, creating support pressures. These pressures can easily trigger dynamic disasters such as gas outbursts and roof collapses, seriously threatening mine safety and production. To ensure the safety of underground mining operations, directional long borehole segment hydraulic fracturing technology was used in the roof strata of the 2305 comprehensive caving working face of Cuijiagou Coal Mine in Shaanxi Province to conduct experimental research on the technology of directional long borehole segment fracturing for pressure relief and anti-impact. The hydraulic fracturing of the roof’s directional long borehole reduced the stress peak coefficient of the coal body in front of the working face (K≈2.9), blocked the propagation of mining stress and high stress in the goaf to the mining roadway, reduced the deformation of the mining roadway, and reduced the average working resistance of the working face support by 22% compared to the working face without any measures. The effective reduction of the length of the hanging roof, the improvement of the support resistance, and timely roof collapse during the working face mining period helped ensure the initial pressure did not form a strong impact. The initial pressure interval of the thick hard roof calculated theoretically was shortened by 53%, and the periodic pressure interval during normal mining was reduced by 27% compared with the 2303 working face under the same geological conditions. The experimental results show that the coverage of the directional long hole on the roof is extensive, with the utilization rate of segmented hydraulic fracturing wells reaching up to 80%. This technology effectively diminishes the strength of the roof above the coal seam on a large scale, thereby reducing the periodic pressure interval and intensity. As a result, it prevents the impact caused by the hanging roof during the mining period of the working face, ensuring a safe working environment for underground workers and facilitating the safe and efficient progress of mining operations.

Study on Failure Behaviors of Roofs with Varying Thicknesses in Longwall Coal Mining Working Face

Study on Failure Behaviors of Roofs with Varying Thicknesses in Longwall Coal Mining Working Face

Mitigating Coal Spontaneous Combustion Risk within Goaf of Gob-Side Entry Retaining by Roof Cutting: Investigation of Air Leakage Characteristics and Effective Plugging Techniques

Relative to conventional coal pillar retention mining technology (the 121 mining method), gob-side entry retaining by cutting roof (the 110 mining method), a non-pillar mining technique, efficiently addresses issues like poor coal resource recovery and significant rock burst damage. Nonetheless, the open-type goaf created by 110 mining techniques suffers from complex and significant air leaks, increasing the likelihood of coal spontaneous combustion (CSC) within the gob area. To address the CSC problem caused by complex air leakage within the goaf of gob-side entry retaining by roof cutting, this study takes the 17202 working face of Dongrong Second Coal Mine as the object of study. Field tests and simulation calculations are conducted to research the features of air leakage and the distribution of the oxidation zone within the goaf. Subsequently, plugging technology with varying plugging lengths is proposed and implemented. The tests and simulations reveal that the airflow migration within the goaf follows an L-shaped pattern, while air leakage primarily originates from gaps found in the gob-side entry retaining wall. The amount of air leaking into the gob-side entry retaining section is 171.59 m3/min, which represents 7.3% of the overall airflow. The maximum oxidation zone within the goaf ranges from 58.7 m to 151.8 m. After the air leakage is blocked, the airflow migration route within the goaf is transformed into a U-shaped distribution, and the maximum oxidation zone range changes from 42.8 m to 80.7 m. Engineering practice demonstrates that after air leakage plugging, the total air leakage volume within the gob-side entry retaining section significantly reduces to 20.59 m3/min, representing only 0.78% of the total airflow volume. This research provides reference on how to prevent the occurrence of CSC in similar mine goafs.

Distribution of H2S in the 10103 excavation working face of the Baozigou coal mine

Based on the production conditions of the 10103 excavation working face of the Baozigou coal mine, this paper analyzes the potential sources of H2S and the expected emission concentrations of H2S in the working face. Considering the previous engineering practice for controlling H2S disasters in coal mine working faces, numerical simulations were conducted to investigate air flow and H2S migration and diffusion in the tunnel in the excavation working face. The migration and distribution of H2S in the coal seam mining face were studied, and the effects of outlet wind speed, duct location, and duct diameter on the H2S concentration distribution were explored. The higher the outlet wind speed, the more conducive to the emission of H2S gas, but too high a wind speed will be detrimental to the concentrated extraction and purification absorption of H2S; the closer the outlet position of the air duct is to the end of the working surface, the lower the H2S concentration in the vortex area at the corner; the air duct If the diameter is too small, the harmful gases released from hard-to-break coal cannot be entrained and taken away. When the diameter of the air duct is too large, the entrainment volume during the jet process will be expanded. To verify the field distribution of H2S concentration at the bottom, middle, and top of the boring machine, a CD4-type portable H2S instrument was used to analyze the distribution of H2S near the excavation working face.

Seepage evolution characteristics and water inrush mechanism in collapse column under mining influence

To obtain the seepage evolution rule and water inrush mechanism of the collapse column, a multi-field coupled mechanical model for water inrush disasters caused by the collapse column is established in this paper, on the basis of the specific engineering conditions of the 1908 working face in the Qianjin coal mine. The mechanical model is composed of internal column elements within the collapse column and surrounding rock masses. The research focuses on the seepage evolution rule in the roof collapse column under different mining conditions and investigates the permeation instability mechanism of collapse column based on the transition of flow state. The research results indicate that the seepage pathway evolves continuously, ultimately forming a channel for water inrush, as the working face advances towards the collapse column. Besides, the water inflow increases rapidly when the working face advances 100 m, then gradually stabilizes, indicating that the seepage channel entry of the collapse column is in a stable stage. Meanwhile, mass loss in the collapse column gradually moves upward. the collapse column remains stable as a whole in the initial stage of water flow, with a small permeability, exhibiting linear flow. As time steps increases, particle loss in collapse column gradually extends to the upper part, forming a stable seepage channel. The flow velocity shows fluctuations with a slow declining trend over time.

Simulation and On-Site Detection of the Failure Characteristics of Overlying Strata under the Mining Disturbance of Coal Seams with Thin Bedrock and Thick Alluvium.

When mining deep coal seams with thin bedrock and thick alluvium, the collapse and fracture of thin bedrock layers may cause geological disasters, such as water inrush and sand inrush of the mining face. Comprehensively obtaining the response data of coal mining and reasonably analyzing the failure characteristics of overlying strata are helpful in guiding safe production. In this study, the caving zone heights of overlying strata are obtained by field detection during layered mining. Then, the caving zone heights during the once-full-height mining are evaluated by theoretical analysis. Further, the force and failure characteristics of coal-rock structures under different mining conditions are compared by the simulation detection and analysis. Finally, the results of on-site observation, theoretical analysis, and simulation detection are compared and discussed, and an optimized mining technology is proposed to ensure safe mining. The research shows the caving zone heights of on-site and simulation detections are, respectively, 14.65 m and 13.5 m during bottom-layer mining, which is larger than the caving zone heights of the top-layer coal mining. During once-full-height mining, the maximum caving zone height of simulation detection is 21 m, which is in between two standard results. For the mechanical responses of an aquiclude clay layer under thick loose alluvium, the maximum disturbance displacement of clay aquiclude is 5.8 m during layered mining, which is slightly larger than the disturbance displacement of once full-height mining; however, the maximum stress of the clay layer is 25 MPa during once-full-height mining, which is larger than the maximum stress of clay layer during layered mining. For the clay aquiclude failure, the clay layer during layered mining is in the deflection deformation area, and there is no obvious fracture structure to inrush the water and sand of thick loose alluvium; however, the clay layer during once-full-height mining is prone to produce obvious fracture structure. Therefore, the layered mining technology can effectively reduce and prevent the water/sand inrush disaster of mining working face.

Analyzing the Optimization of Unloading Gas Extraction Drilling Arrangement Based on Stress Distribution in the Protected Layer

In the process of protected seam mining, the reduction in stress and the enhancement of the gas mobility that affects the protected seam are crucial manifestations of the protection effect. Taking the working face of E8-32010 and the upper D5-6 coal seam of the Six Mines of Ping Coal Company Limited as the study object, the research method combining theoretical analysis, numerical simulation, and a field test was adopted. In combination with the actual production, we adopted the stress distribution law pertaining to the coal body of the protected seam under the condition of 2.2 m mining height. When the length of the tendency of the working face mining is under the condition of 2.2 m mining height and when the working face mining inclination lengths are 120 m, 160 m, 200 m, 220 m, 240 m, and 280 m, the stress distribution law that regulates the coal body of the protected seam is analyzed, and, based on the stress distribution law, the unpressurized extraction drilling holes are designed, and the effect of the coal body stress at the final hole position of the unpressurized extraction drilling holes on the efficiency of unpressurized extraction is determined through on−site extracting data. The research results indicate the following: (1) as the tendency length of the working face increases, the degree and range of pressure unloading that affects the protected layer are increasing, the stress increase in the deep D5-6 seam is larger than that of the shallow D5-6 seam, and the tendency direction can be divided into the stress elevation area, pressure unloading area, and stress elevation area from the shallow zone to the deep zone. Moreover, the minimum stresses in the pressure unloading area are 7.80 MPa, 6.42 MPa, 5.59 MPa, 5.59 MPa, 5.42 MPa, 5.30 MPa, and 5.21 MPa, and the minimum stress is less than 60% of the original stress; (2) the vertical stresses at the final locations of the No. 1, No. 2, and No. 3 drill holes after the protective layer is mined are 16.42 MPa, 10.74 MPa, and 6.72 MPa, respectively, and the pure amount of gas extracted from the unpressurized extracting drill holes has increased immensely; the higher the rate of unloading, the greater the increase, and, the more the unpressurized extracting drill holes are extracted, the greater the increase. The higher the unloading rate, the greater the increase: 19.77–21.31 times, 41.62–41.68 times, and 68.68–74.66 times the pure amount of gas extracted from the corresponding pre−pumping holes; (3) the No. 3 depressurized extraction borehole is 261.02–281.04 times, 191.77–205.55 times, and 138.43–148.18 times higher than the No. 1, No. 2, and No. 3 pre−pressurized extraction boreholes, respectively, and 6.09–7.14 times and 2.28–2.49 times higher than the No. 1 and No. 2 depressurized extraction boreholes, respectively. The research results can not only provide a theoretical basis for verifying the protection effect of the protected layer but also a scientific rationale for the layout of the unpressurized extraction drill holes.