Non-Pillar Coal Mining by Driving Roadway During Mining Period in High-Gas Top-Coal-Caving Working Face

Abstract

To solve the problem of the inability to achieve Y-shaped ventilation in the boundary coal mining of high-gas mines and the problem of gas accumulation in the upper corner of a fully mechanized mining face, non-pillar coal mining technology is proposed by a driving roadway during the mining period. A high-gas working face requires Y-shaped ventilation to achieve upper corner gas control, but Y-shaped ventilation conditions are not available at the boundary coal body. In order to handle this challenge, studies have suggested non-pillar coal mining technology, which involves excavating roadways while mining in order to achieve non-pillar coal extraction and use recoverable wide coal pillars. During the simultaneous excavation of a working face and roadway, studies analyzed the distribution characteristics of the complicated stress environment. Following an evaluation of the impact of coal pillar width on the quality of an excavation roadway, this study’s development is in terms of an effective technique for retaining coal pillars as established. During the mining period of a working face, in the goaf of the working face, the research analyzed the distribution properties of the gas flow field, and findings from the study indicate that the width of the recovered coal pillar influences the distribution of gas. Finally, the width of the coal pillar was comprehensively determined, forming non-pillar coal mining technology by a driving roadway during the mining period. The on-site practice has shown that using a wide coal pillar with a width of 70 m to protect the roadway significantly reduces the deformation of the surrounding rock in the mining roadway, the gas concentration at the return airway is lower than the safety production standard, and by decreasing the mining succession time by 15 months, studies achieved improving the working face’s coal extraction rate by 12.6%.

1. Introduction

Non-pillar coal mining technology is frequently used in underground operations by academicians and industry professionals, which can reduce the excavation workload of tunnels, improve the coal extraction rate, improve the stress environment and ventilation lines of tunnels, etc. [1,2]. Researchers and the mining industry started decreasing shallow coal deposits at the beginning of this century; the depth of coal mining and costs have been increasing, producing many safety problems such as coal pillar bursts, rock bursts, and significant rock deformation failures due to the considerable ground stress [3,4]. The studies proposed the ‘cutting cantilever beam’ theory [5,6] and the non-pillar longwall mining by roof cutting (also the ‘N00 mining method’) to address these problems. The new mining method eliminates the requirement to reserve an entry in advance, resulting in no coal pillars remaining after mining [7,8,9].

Scholars have also conducted multidimensional research on applying non-pillar coal mining technology and achieved preliminary results [10,11,12]. Zhang et al. analyzed the three critical technologies of constant-resistance extensive deformation support, directional pre-splitting blasting, and blocking-gangue support systems in non-pillar coal mining [13]. Zhou et al. studied air leakage characteristics concerning a “Y”-type ventilation in gob-side entry retaining with roof cutting, pressure relief, and the law of a resulting gas accumulation [14]. Feng et al. studied the law of airflow movement in a working face and gob under “roof-cutting and pressure-releasing” mining along gob-side entry retaining [15]. Sun et al. explored the distribution law of a stress field under the mining mode of gob-side entry retaining by roof cutting without a pillar (GERRCP) under a goaf [16]. Zhu et al. researched mining-induced ground response development of a non-pillar mining panel with gob-side entry by roof cutting [17]. Ma et al. studied the gob-side entry retaining mechanism by the roof-cutting approach and its three key technologies through a theoretical analysis, numerical simulation, and laboratory and field experiments [18]. Chen et al. established an evaluation index system for roof stability in the roof-cutting non-pillar mining method, including the roof rock integrity and the roof-surrounding rock displacement [19]. Cao et al. determined the support parameters of a roadway and flexible-formwork pre-cast partition wall through a theoretical analysis and numerical simulation [20]. Hao et al. studied pillarless mining by gob-side caving under soft rock roof conditions [21]. By using artificial supports for supporting pillars, certain technologies enable an excavation to be preserved for subsequent applications [22].

Non-pillar coal mining technology involves production processes such as roadway excavation, coal seam mining, and ventilation in mines [23]. However, current research on the application of non-pillar mining technology mainly focuses on retaining tunnels along the goaf without involving pillar-free mining related to the recovery of wide coal pillars. When faced with mining boundary coal bodies, it is impossible to achieve Y-shaped ventilation when the boundary roadway cannot be arranged. Under these conditions, in order to attain pillarless mining, studies proposed substituting Y-shaped ventilation with a W-type method. Based on the actual conditions of the mine, this article proposes a non-pillar coal mining technology that digs roadways during the mining period. By analyzing the spatiotemporal effects of the coupled stress of coal mining and roadway excavation, as well as the distribution characteristics of the gas flow field in a W-shaped fully mechanized caving face, a reasonable width of the protective coal pillar for the roadway is ultimately determined based on the stability of the roadway and gas extraction. The research results will further promote the development of non-pillar mining technology, which is significant for achieving safe, green, and efficient mining in high-gas mines.

2. Process Flow of Non-Pillar Coal Mining Technology with Width Pillar

The non-pillar coal mining proposed in this article involves setting up a reasonably wide protective coal pillar to arrange the return airway of the next working face in advance, achieving a “W”-shaped ventilation to replace the “Y + L”-shaped ventilation, and recovering the wide coal pillar. Figure 1 depicts the fundamental procedure.

(1)

01 working face mining stage: Firstly, studies structured the highways on both sides of the 01 working face and the transportation roadway on the 02 working face. Experts have installed two ventilation systems—one for air intake and one for air return—on the 01 working face. The 01 transportation roadway–01 working face–01 air-intake roadway belongs to the “Y” ventilation system, while the 02 working face–02 transportation roadway constitutes the “L” ventilation system. Therefore, the working face is a “Y + L” ventilation system, as shown in Figure 1a.

(2)

Excavating roadway during mining: Researchers have established the ideal coal pillar size by studying the spatiotemporal effects of surrounding rock stress in tunnels and the distribution characteristics of W-shaped gas flow fields. According to studies, research constructed under discussion the return airway on the 02 working face at the same time as mining on the 01 working face, as seen in Figure 1b.

(3)

02 Working face mining stage

The 01 air-intake roadway is retained by leaving a roadway along the goaf and used as an air-intake roadway during the mining period of the 02 working face. In order to support the transportation route for the 02 working face, experts intend to turn the 01 air-return highway into an air-intake roadway. The 02 working face also has two inlets and one return ventilation system, 01 air-intake roadway–02 working face–02 transportation roadway–02 air-return roadway, forming a “W”-shaped ventilation system, as shown in Figure 1c.

In summary, the above process is a non-pillar mining method that retains wide coal pillars and recovers them later. The stability of the road during simultaneous excavation and the gas difficulties that develop during working face mining are two critical concerns that researchers need to address concerning the coal pillar width.

3. Stability of Roadway Under Complex Mining Stress Environment

3.1. Temporal and Spatial Distribution Characteristics of Complex Stress Environment

Using FLAC3D 6.0 software, researchers designed a three-dimensional numerical model that is 500 m × 300 m × 50 m in size, as illustrated in Figure 2. The X direction of the model is the layout direction of the W4301 working face, and the Y direction is the direction of the working face advancement.

Table 1. Physical and Mechanical Parameters of Coal Rock.

Rock	Thickness/m	Bulk Modulus/GPa	Shear Modulus/GPa	Tensile Strength/MPa	Internal Friction Angle/°	Adhesive Force /MPa	Density/Kg·m−3
Overburden	10	5.84	3.75	3.43	36.6	4.62	2500
Middle sandstone	16.5	4.35	2.31	2.73	35.8	4.21	2450
Siltstone	1.0	6.08	3.97	4.27	37.2	4.82	2600
Sandy mudstone	1.72	5.33	3.25	3.74	36.0	4.75	2550
Mudstone	2.2	3.91	1.74	1.50	31.6	2.74	2150
3 # coal	6.08	2.32	0.9	1.20	20.0	2.02	1400
Mudstone	2.46	3.91	1.74	1.50	31.6	2.74	2150
Fine sandstone	3.52	6.08	3.97	4.27	37.2	4.82	2600
Sandy mudstone	4.0	4.24	2.14	2.32	33.2	3.26	2300
Mudstone	2.5	3.91	1.74	1.50	31.6	2.74	2100
Fine sandstone	3.5	5.33	3.25	3.74	36.0	4.75	2550
Undercover rock layer	10	5.84	3.75	3.43	36.6	4.62	2500

shows the mechanical and physical parameters of coal rock. For calculations, the research utilizes the Mohr–Coulomb failure criterion and turns on the significant deformation mode. The boundary conditions are that the bottom boundary restricts vertical displacement, and the peripheral boundary restricts horizontal movement. From the top of the model, the research applies a load that is equally distributed and equal to the weight of the rock layer above it. In order to mitigate the impact of boundary effects, researchers maintain a 50 m wide boundary coal pillar on one side of the 01 working face’s transportation lane. After the initial balance calculation of the model, the 01 working face is excavated from the Y = 50 m position using a staged excavation and cyclic calculation method, with each stage excavating 10 m and corresponding to a numerical calculation of 1000 time steps.

The complex stress environment in which roadway excavation occurs includes temporal and spatial effects [24,25]. A time effect refers to one or several stages that will be experienced during the process of roadway excavation, including the solid coal excavation stage (the stage of stress influence on the surrounding rock of the roadway), the advanced mining influence stage, the stage of roadway excavation through the working face, and the stage of mining influence on this working face, along the time gradient. A spatial effect refers to the specific range of each stage in space corresponding to the temporal effect. Figure 3 shows the schematic diagram of the complex stress environment experienced by roadway excavation.

The study reveals significant differences in the stress environment of the surrounding rock while attempting to place the 02 air-return roadway in various locations. As the width of the coal pillar increases, the roadway will no longer be affected by the stress of the surrounding rock of the 01 intake airway. The range of the solid coal roadway excavation gradually increases, and the range of the advanced mining influence stage gradually decreases. Roadway 4 has almost no advanced mining influence stage, directly transitioning from the solid coal roadway excavation stage to the working face excavation stage. The complexity of the surrounding rock’s stress conditions and the difficulty in maintaining the stability of the surrounding rock increase with the breadth of the protecting coal pillar. From Figure 3, as a result, studies can determine the distribution of supporting pressure in the rock surrounding the 01 working face; the range of the advanced mining influence zone is 50 m in front of the working face, and the range of the lateral supporting pressure influence zone is within 40 m inside the coal wall.

To further quantify the specific range of the stress-affected area by mining the stress-affected area and positioning measurement lines on one side of the solid coal, researchers can determine accuracy. Based on the distribution of bearing pressure obtained from the survey line, using a stress measurement that is 5% more than the initial rock stress, experts can identify the boundary between the advanced mining influence zone and the excavation stress influence zone, which can determine the actual range of the excavation stress influence zone and the advanced mining influence zone at different positions. Figure 4 below depicts the curve of the influence range of bearing pressure on the working face and its roadway.

As shown in Figure 4, the range of the stress influence zone of the roadway and the lateral pressure influence zone are constant. The range of the stress influence zone of the 01 air-intake roadway is between 10.8 and 12.5 m, and the fluctuation is mainly due to the boundary effect of the model and the weak mining influence of the 01 working face. After averaging treatment, the range of the excavation stress influence zone is 11.7 m. The maximum influence range of lateral support pressure is 40 m inside the coal wall, and its range continuously changes with the expected distance to the W4301 working face, roughly showing a linear relationship. Finally, at an average distance of 0 from the working face, it is connected to the boundary of the lateral support pressure influence zone. The segmented equations for the range of support pressure influence zones in various regions of the 01 working face can be obtained by researchers through the fitting, specifically

$$y=\left\{\begin{array}{c}11.74,(x>50)\\ 35.12-0.47x(0\le x<50)\\ 40,(x\le 0)\end{array}\right.$$

(1)

where x is the average distance between the 02 air-return roadway and the 01 working face, m; y is the distance from the range of support pressure influence to the 01 air-inlet roadway, m.

According to Equation (1), when excavating the 02 air-return roadway in complicated stress situations, experts can determine the spatiotemporal impacts of stress distribution and deformation failure in the surrounding rock.

(1)

If the width of the coal pillar is 10 m, when x > 50 m, the 02 air-return roadway will be affected by the stress of the 01 air-inlet roadway. When x = 50 m, the roadway will enter the stage of advanced mining influence. When x < 0 m, it will enter the lateral support pressure influence stage.

(2)

If the width of the coal pillar is 25 m, according to Equation (1), when x > 21.5 m, the 02 air-return roadway is in the stage of solid coal excavation. When 0 < x < 21.5 m, the roadway is in the stage of advanced mining influence.

(3)

If the width of the coal pillar is 50 m, there is no intersection point throughout the segmented equation, indicating that the excavation process of the 02 air-return roadway is not affected by the stress of the 01 working face and surrounding rock of the roadway; that is, the roadway excavation process is always in the stage of solid coal excavation.

3.2. Reasonable Size of Coal Pillars Based on Rock Stability

Currently, there are two main types of roadway protection methods for mining, roadway excavation along the goaf and retaining coal pillars for roadway protection, as shown in Figure 5. For traditional roadway excavation along the next goaf, according to studies, it is recommended to start excavation only after the overlying rock strata on the adjacent working face have stabilized [26]. Given that the researchers appropriately determine the narrow coal pillar’s breadth, the lateral fundamental roof fracture structure protects the roadway, and in order to attain adequate support, researchers can use appropriate anchor rod support technology and place the roadway in the stress reduction zone [27]. However, when facing the mining face, the roadway undergoes a complete dynamic pressure caused by the adjacent mining process, including lateral fundamental top fracture, rotation, contact with gangue, and re-stabilization. This process will inevitably significantly impact the stability of the surrounding rock along the goaf roadway, causing significant deformation and complex maintenance. Therefore, wide coal pillars can effectively solve this problem. In order to preserve the tunnel smoothly, experts use flexible formwork support at the edge of the roadway. A support structure is formed by arranging flexible formwork bags around the roadway and pumping concrete into them.

As shown in Figure 6, when the width of the coal pillar is large enough, the stability of the coal pillar will be maintained by forming an elastic zone in the centre, in the middle of the coal pillar, to ensure its stability [28]. During the excavation of the 02 air-return roadway, one side is a goaf, and the other is solid coal, but it is subject to secondary mining stress during the mining period of this working face. The width of the coal pillar should be conducive to controlling the stability of the surrounding rock in the roadway. Therefore, in order to avoid the severe deformation of the surrounding rock, a roof collapse, floor bulging, and other disasters, the width of the protective coal pillar should not be too small [29]. The theoretical calculation formula for setting a reasonable width is

$$B=x_1+x_2+x_3$$

(2)

where x₁ is the width of the plastic zone generated by the mining of the 01 working face, m; x₂ is the width of the plastic zone generated by the mining of the 02 working face, m; and x₃ is the width of the middle elastic zone, which is not less than twice the height of the coal pillar.

By implementing the limit equilibrium theory of rock masses, researchers can determine the diameter of the plastic zone as follows [30]:

$$x_1={\displaystyle \frac{M}{2\xi f}}\mathrm{l}\mathrm{n}{\displaystyle \frac{K\gamma H+C\mathrm{c}\mathrm{o}\mathrm{t}\phi }{\xi (Q_1+C\mathrm{c}\mathrm{o}\mathrm{t}\phi )}}$$

(3)

where K is the stress concentration factor; Q₁ is the resistance to coal support; C is the cohesive force of coal; φ is the internal friction angle of the coal body; F is the friction coefficient of the contact surface between the coal seam and the roof and floor; ξ is the triaxial stress coefficient; γ is the bulk density of the overlying rock layer, N; and H is the height of the overlying rock layer.

On one side of the coal pillar, researchers calculate that the plastic zone is 6.5 m wide, and considering the mining influence coefficient of 1.5, studies determined that the width of the coal pillar should not be less than 31.7 m.

Numerical simulation methods are further adopted to study the influence of coal pillar width. The simulation model adopts the model described in Section 3.1, and Figure 7 shows the excavation form. According to studies, the coal pillar’s width was varied to 10 m, 20 m, 30 m, 40 m, 50 m, 60 m, and 70 m. During the excavation of the roadway in the working face, Figure 8 shows the distribution of internal support pressure of the protective coal pillar in different simulation schemes.

Figure 8 shows that the extreme values of the support pressure inside the protective coal pillar are consistent in different simulation schemes. Affected by the lateral advance support pressure of the 01 working face, the range of the ultimate equilibrium zone on the side of the 01 air-intake roadway increases; that is, the development range of the plastic zone increases. As the width of the coal pillar increases, the range of the impact area of the peak support pressure in the heading section gradually decreases, and the peak support pressure on both sides of the coal pillar gradually decreases. When the width of the coal pillar exceeds 30 m, the peak change is insignificant. The peak support pressure on both sides of the coal pillar has not yet overlapped, indicating that the roadway coal pillar’s overall stability is still stable.

Figure 9 depicts the bearing pressure in the coal pillar while mining the 02 working face. With the mining of the 02 working face, the peak support pressure inside the protective coal pillar in each simulation scheme continues to increase. When the width of the protective coal pillar is less than 20 m, the peak support pressure on both sides will overlap, and the coal pillar will undergo plastic failure as a whole. That is, when the width of the protective coal pillar is greater than or equal to 30 m, a stable elastic core zone will appear inside. There is no original rock stress zone inside the protective coal pillars of all schemes.

Simultaneously detecting the deformation displacement at different positions is shown in Figure 10. The load directly acts on the roof and side support during the coal seam excavation. Compared to other displacement curves, the overall deformation of the 02 air-return roadway floor is relatively small, indicating that the roof and two sides are critical areas for roadway maintenance. As the width of the protective coal pillar increases, the displacement gradually decreases, which is more favourable for controlling the stability of the surrounding rock in the mining roadway. When the width of the coal pillar is 10 m, the displacement of the surrounding rock is much higher than in other schemes. As the width of the coal pillar increases, the displacement gradually decreases, and the magnitude of the decrease gradually decreases. When the width of the protective coal pillar exceeds 40 m, the displacement of the surrounding rock no longer changes significantly. Therefore, the best control impact on the surrounding rock of the mining roadway is achieved, according to research, when the protective coal pillar’s width is greater than 40 m.

4. Gas Control Method for Non-Pillar Coal Mining in High-Gas Top-Coal-Caving Face

4.1. Gas Concentration Law of W-Shaped Ventilation Fully Mechanized Top-Coal-Caving Face

Experts studied the migration rule of the gas flow field in the working face using FLUENT 18.2 software. Based on the design of mining parameters and gas control mode for the 02 working face, Gambit 2.4 software was used to establish models with coal pillar widths of 10 m, 30 m, 50 m, 70 m, and 90 m, as shown in Figure 11. Research analyzed how the distribution of the gas flow field in the 02 working face is affected by the width of the coal pillar.

The 02 working face layout length is 320 m, and the height of the working face is 3.5 m. The net width and height of the return airway section are 5.2 m and 3.7 m, respectively. The net width and height of the transportation airway are 5.2 m and 3.7 m, respectively. The net width and height of the intake duct are 5.8 m and 3.8 m, respectively. The gas content is 6.0007 m³/t, the residual gas content is 3.0039 m³/t, and the maximum coal gas emission per cycle is 1.0 m³/min.

The numerical simulation boundary conditions and calculation parameters were set in FLUENT software, with the selection of boundary conditions referring to

Table 2. Boundary conditions.

Boundary Name	Boundary Type	Boundary Type
Air-intake roadway	Velocity inlet	0.76 m/s
Transportation roadway	Velocity inlet	2.17 m/s
Air-return roadway	Outflow	0.9
High-pumping roadway	Outflow	0.1
Internal interface of model	Interior	-
Other external walls of model	Wall	-

and the selection of discrete phase parameters referring to

Table 3. Continuous phase parameters.

Model	Definition
Solver	Pressure-Based
Viscous Model	k-Epsilon
Energy	On
Material	Methane Air

.

The caving zone formed during coal seam mining is the primary medium of the flow field in the goaf [31]. As the falling rock blocks and gangue are compacted, the compression of the height of the falling zone approximately follows a negative exponential function relationship [32]. Therefore, the distribution law of porosity and permeability of the porous medium in the goaf of the W-shaped fully mechanized face also approximately follows a negative exponential function relationship. Figure 12 shows the distribution characteristics of permeability in the goaf of a W shape. Along the direction of the movement, as it moves away from the working face, the porosity gradually decreases [33]. In the direction of inclination, the porosity at the inlet and outlet air ducts is higher, while the porosity at the solid coal is lower.

In the W4302 goaf, researchers can obtain the distribution characteristics of the gas flow field by establishing a three-dimensional CFD model, as shown in Figure 13. The distribution characteristics of gas concentration behind the goaf are similar to those of U-shaped ventilation. Under the gas control mode of a W-shaped ventilation system combined with a high-extraction roadway, gas accumulates in the deep part of the goaf and enters an enrichment zone as the working face advances. Due to the leakage of fresh air from the air-intake roadway and transportation roadway towards the goaf, gas is blown towards the deeper part of the goaf [34]. The air-return roadway contains gas air that leaks from the goaf, resulting in a higher gas content near the return airway in the middle of the goaf than on both sides of the goaf. Due to the gas being pumped into the high extraction roadway below the goaf, a gas reduction area appears behind the working face, which can promote safe mining of the working face [35].

4.2. Reasonable Coal Pillar Size Based on Gas Control

FLUENT software was used to simulate the distribution characteristics of the gas flow field in the W4302 working face with coal pillar widths of 10 m, 30 m, 50 m, 70 m, and 90 m. Figure 14 shows the sliced cloud maps of the gas flow field. In the high-extraction lane and the return-air roadway, experts found a correlation between coal pillar width and gas concentration by taking the average concentration through measuring lines at the return-air roadway and high-extraction roadway, as shown in Figure 14.

Figure 15 shows the variation curve of gas concentration with coal pillar width. As the width of the coal pillar decreases, the gas content in the return airway gradually decreases. When the width of the coal pillar is 70 m, the gas concentration at the return airway is 0.75%, which can meet the operational requirements. When the width of the coal pillar is greater than 70 m, the rate of decrease in gas concentration at the return airway slows down. As the width of the coal pillar increases from 70 m to 90 m, the gas concentration decreases by 0.03%. The gas concentration extracted from the high-level suction roadway is between 50% and 51% and is not significantly affected by the width of the coal pillar. Through a theoretical analysis and numerical simulation, based on the stability control of the roadway-surrounding rock and the migration law of the gas flow field, the width of the protective coal pillar should exceed 70 m to meet the requirements of gas control and roadway stability control.

5. On-Site Application Effect Analysis

Figure 16 shows the 02 roadway’s cross-section, which is held up by cables and anchor rods. To track the deformation of the surrounding rock, experts placed eight measuring stations symmetrically on the top and bottom plates and on the left and right sides of the 02 air-return lanes. Figure 17 shows the location of the measuring points.

The “cross” point method is used to observe the deformation of the surrounding rock of the roadway, as shown in Figure 18. A hole with a diameter of 30 mm and a depth of 380 mm is set in the middle of the top and bottom plates vertically and horizontally. A 400 mm long wooden pile with a diameter of 30 mm is driven into the hole, and a measuring nail is installed at the end of the wooden pile. The two monitoring sections are spaced 0.6–1.0 m apart along the axial direction of the roadway. During measurement, tension measuring ropes are installed at points C and D, and steel tape measures are tightened between points A and B to measure A.O. and O.B. values.

Similarly, steel tape measures are tightened between points C and D to measure C.O. and O.D. values. The measurement accuracy requirement is 1 mm, and an estimated 0.5 mm is obtained. A leather tape measures the distance from the monitoring section to the excavation working face.

By monitoring the displacement of different points daily, Figure 19 shows the overall deformation of the roadway. Within the first ten days of excavation, the mining roadways showed the deformation rate of the two sides as the highest, reaching 2.25 mm/d. After 10 days, the deformation rate showed a decreasing trend of fluctuation. However, the overall movement of the two sides continued to increase until 60 days after excavation, when the movement of the two sides tended to stabilize and the deformation rate approached 0. The cumulative movement of the two sides was approximately 90 mm. On-site observations showed that the integrity of the surrounding rock in the mining roadway was high, and there were no apparent cracks or fissures on the surface of the surrounding rock.

6. Conclusions

This article proposes an innovative non-pillar coal mining method that recovers coal pillars in a later stage. The width of the coal pillar is the key to achieving this process. Based on the stability of the surrounding rock and gas movement, experts calculated the coal pillar’s breadth, which led to the following key findings.

(1)

The proposed non-pillar coal mining technology by a driving roadway during the mining period, which reserves wide coal pillars, arranges W-shaped fully mechanized caving faces in sequence to replace Y-shaped ventilated fully mechanized caving faces, and reserves wide coal pillars for mining. The extraction rate of the working face has increased by 12.6%, and the mining replacement time has been shortened by 15 months.

(2)

The paper analyzes the complex stress environment of mining, determines the segmented equations for the boundaries of different mining influence ranges, and reveals the spatiotemporal effects of the stress environment of an excavation roadway during mining. The influence range of lateral support pressure is within 40 m from the coal wall on the side of the roadway.

(3)

To determine the reasonable width of the coal pillar, the stability of the protective coal pillar and the deformation of the surrounding rock of the roadway were studied. In addition to analyzing the effects of changes in the protective coal pillar’s width on the working face gas flow field’s movement law, the reasonable width of the protective coal pillar was finally determined to be 70 m.

(4)

The determined coal pillar width was successfully applied in the on-site implementation project, verifying the correctness of relevant theories. The cumulative movement of the two sides was approximately 90 mm, which meets the on-site usage requirements.