Pattern of Influence of the Mining Direction of the Protective Seam on the Stress of the Surrounding Rock

Abstract

The maximum principal stress of the original rock has obvious directionality, and the pressure relief effect is different when the protective seam is mined along different directions. In this paper, the Fast Lagrangian Analysis of Continua (FLAC3D 6.0) numerical simulation software was used to establish a numerical calculation model according to the actual stratum conditions of the Pingdingshan No. 8 Coal Mine. The distribution and evolutionary characteristics of three-dimensional stress and three-dimensional displacement of the stope are studied under the condition that the mining direction of the protective seam is parallel to or vertical to the maximum principal stress direction of the original rock; the pattern of influence of the mining direction on the pressure relief and outburst prevention effect of the protective seam mining is analyzed. For the protective seam, the maximum principal stress in the coal in front of the protective seam cut–hole is significantly reduced, and the outburst potential is reduced in parallel mining. However, in vertical mining, the maximum principal stress in the coal in front of the protective seam cut–hole increases significantly, and the outburst potential increases. For the protective seam and surrounding rock, parallel mining can more fully reduce the maximum principal stress of the protective seam, reduce the difference in the three-dimensional stress, and effectively reduce the outburst potential of the protective seam. Therefore, parallel mining can not only improve the safety of the protective seam but also improve the pressure relief and outburst prevention effect of the protective seam. This conclusion is verified by the outburst prevention effect of the parallel mining of the remote upper protective seam in the Pingdingshan No. 8 Coal Mine. The research results are helpful for optimizing mine outburst potential prevention and control work from the aspect of mining layout. Through parallel mining, the outburst potential of the mine can be effectively reduced overall.

1. Introduction

Coal and gas outbursts are some of the biggest obstacles to safe mining in deep mines [1]. Ground stress is one of the main factors inducing outburst accidents, and the degree of ground stress of coal seams is comprehensively affected by the burial depth, geological structure, mining disturbance, and other factors [2,3,4]. With the depletion of shallow coal resources, the depth of coal mining continues to increase, the in situ stress of raw rock increases significantly, and the outburst potential becomes more severe [5,6]. Mining the protective seam can reduce the ground stress of the protective seam, increase the permeability of the coal seam, and release coal seam gas, which is one of the most effective outburst prevention technologies at present [7,8,9,10].

Under the influence of crustal movement, the ground stress has obvious directionality; that is, the magnitude of the ground stress in the same place is different in different directions [11,12]. Based on the statistical analysis of the in situ stress data of 286 groups in China, the three-dimensional in situ stress varies with depth; the stress gradients of maximum principal stress σ₁, intermediate principal stress σ₂, and minimum principal stress σ₃ are 3.08, 2.22, and 1.81 MPa/100 m, respectively. The average dip angles of σ₁, σ₂ and σ₃ are 10.7°, 50.3°, and 32.7°, respectively. This indicates that the maximum and minimum principal stresses tend to be in the horizontal direction, while the intermediate principal stresses tend to be in the vertical direction. The gradient of σ₂ with depth is close to that of the stratum geostatic stress, while the gradient of σ₁ is obviously greater than the stress gradient of the stratum geostatic stress, and the gradient of σ₃ is obviously smaller than the stress gradient of the stratum geostatic stress [13,14]. Therefore, σ₂ is mainly affected by the weight of strata, while σ₁ is mainly affected by the tectonic stress field of crustal movement [15].

Mining is always carried out under a specific proto-rock stress field, and the direction of mining and σ₁ may be parallel (“parallel mining”) or vertical (“vertical mining”) to the direction of mining [16,17]. Mining activities destroy the balance state of in situ stress and produce a pressure relief zone and stress concentration zone. According to the Mohr–Coulomb theory, the larger the difference between σ₁ and σ₃, the more likely the coal rock mass is to be destroyed and the more likely it is to induce outburst accidents [18,19]. Therefore, we can fully reduce σ₁ and reduce the difference between σ₁ and σ₃ to fully eliminate the outburst potential [20]. Under the specific in situ stress environment of mines, how does protective seam mining in different directions affect the triaxial stress distribution characteristics of the stope surrounding rock? Can this be used to increase the pressure relief effect and range of the protective seam? These questions still lack in-depth research [21,22].

Numerical simulation is widely used in coal mines. It can simulate the evolution process of rock mass throughout the whole cycle, and many experts have used it to explore the original ground stress and the redistribution after disturbance [23,24,25]. In this paper, the Fast Lagrangian Analysis of Continua (FLAC3D) numerical simulation and engineering practice verification method are used to study the pattern of influence of the mining direction of the protective seam on the triaxial stress field of the surrounding rock; the differences in the triaxial stress and displacement distribution and the evolutionary pattern of the protective seam under parallel mining and vertical mining are described. The conclusions of this paper are conducive to optimizing mining deployment, fully improving the pressure relief effect of protective seam mining, and achieving the purpose of preventing outbursts [26,27].

2. Methods of Numerical Simulation Research

2.1. Model Establishment

Based on the Mohr–Coulomb failure criterion, the numerical calculation model is established by using FLAC3D software and combining it with the rock column diagram of the No. 204 section in the E_9–10 coal seam of the Pingdingshan No. 8 Mine (Figure 1). The relevant rock mass mechanical parameters of the model are listed in

Table 1. Mechanical parameters of rock mass.

Soil Seam	Density (kg/m3)	Elastic Modulus (GPa)	Poisson ( )	Friction Angle (°)	Cohesion (MPa)
mudstone	2483	5.50	0.3	30	4.5
#1 sandstone	2550	7.50	0.27	31	4.9
#2 sandstone	2550	7.60	0.27	34	5.5
#3 sandstone	2550	7.75	0.27	35	5.0
D5–6 coal	1300	2.50	0.32	20	2.3
#4 sandstone	2550	7.50	0.27	35	5.0
E8 coal	1350	2.60	0.31	22	2.4
E9–10 coal	1350	2.60	0.31	22	2.3
#5 sandstone	2550	7.50	0.27	35	5.0
#6 sandstone	2550	7.50	0.27	35	5.0

. The D_5–6 coal seam is a near-horizontal coal seam. It is assumed that the coal seam dip angle is 0° in the calculation, and the coal seam floor is taken as the 0-point elevation of the model. The top elevation of the model is 679 m, and the bottom elevation is −350 m. The total width of the model along the X-direction is 1000 m, and the total length along the Y-direction is 1400 m. The protective seam section located in the D_5–6 coal seam is 600 m long along the Y-direction. The width of the cut–hole along the X-direction is 120 m. The center point of the model is located in the center of the protective seam section, and the section is mined from −300 m to 300 m along the Y-direction, with a cumulative mining length of 600 m. In the numerical model, the rock surrounding the section of the protective seam is large enough to significantly reduce the boundary effect.

A roll branch boundary is applied to the bottom and four sides of the model. Nodes can slide on the boundary surface but cannot leave the boundary surface. The top of the model simulates the earth’s surface, balancing itself under the action of geostatic stress. The model uses the radial grid, excavated every 2 m.

The E_9–10 coal seam is located 88 m below the D_5–6 coal seam. The distribution pattern of the triaxial stress of the surrounding rock after mining the D_5–6 coal seam is studied, and the distribution pattern of residual triaxial stress in the E_9–10 coal seam is analyzed emphatically.

2.2. Setting of the Initial Stress Field

The in situ stress of the D_5–6 coal seam measured at the test site is shown in

Table 2. The original stress of the experimental stress field.

Principal Stress	Values (MPa)	Azimuth (°)	Dip (°)
σ1	32.2	99.8	3.5
σ2	17.7	\	6.4
σ3	12.1	\	82

. σ₁ is 32.2 MPa, the dip angle is 3.5°, and the dip is basically along the horizontal direction.

The direction of the protective seam section can be parallel, vertical, or at an angle to σ1. In this paper, the stress of the surrounding rock and the movement pattern of the rock stratum under vertical mining and parallel mining are studied.

Table 3. Study plane.

Study Plane	σX (MPa)	σY (MPa)	σZ (MPa)
Parallel mining	12.1	32.2	17.7
Vertical mining	32.2	12.1	17.7

shows the value of the initial ground stress in the D_5–6 coal seam. The model is assigned initial values along the direction of the longitudinal stress according to Formula (1).

$${\sigma }_{hi}={\sigma }_{oi}-\frac{{\sigma }_{oi}}{h_0}h$$

(1)

where h is the horizontal elevation, in m; σ_hi is the ground stress along the direction of i at the horizontal elevation of h; σ₀ is the ground stress along the direction of i at the horizontal elevation of h, in MPa; and h₀ is the burial depth where the horizontal elevation is 0 m, which is 679 m in this calculation.

3. Numerical Simulation Results and Discussion

3.1. Distribution Characteristics of the Maximum Principal Stress in the Protective Seam

The redistribution of surrounding rock stress caused by the mining of the protective seam is shown in Figure 2. The distribution characteristics of the maximum principal stress in the protective seam under parallel mining and vertical mining schemes are shown in Figure 2. The comparison shows that the inner stress of the goaf is significantly reduced under the two schemes, but there is a great difference in the ground stress in the square-shaped coal seam before the cut–hole.

In parallel mining, the maximum principal stress in the square-shaped coal seam decreases before the cut–hole of the protective seam. However, the maximum principal stress increases in vertical mining. This is mainly because the stress in the Y-direction is the maximum in parallel mining, which promotes the movement of coal in front of the mining goaf and redistributes the ground stress. The stress in the Y-direction in front of the mining is significantly reduced, and the difference in three-dimensional stress is also reduced simultaneously, which is conducive to reducing the outburst potential. When the protective seam is mined along the Y-direction, the X-direction stress in front of the cut–hole surface compresses the coal and prevents the coal from moving along the Y-direction, forming a small pressure-relief zone. The further increase in the X-direction stress in the stress concentration zone increases the maximum principal stress gradient and three-dimensional stress difference in front of the cut–hole and thus increases the outburst potential. Therefore, parallel mining can significantly reduce the risk of self-mining of protective seams.

3.2. Three-Dimensional Stress Distribution Pattern in the Upper and Lower Square Roof and Bottom Plate of the Protective Seam

After the end of mining in the protective seam section, the distribution characteristics of the three-dimensional ground stress at different positions within 300 m and −200 m above and below the center of the protective seam section are shown in Figure 3. The left side is the three-dimensional stress, the right side is the three-dimensional stress concentration coefficient (residual stress/original stress), and the vertical coordinate represents the vertical distance from the protective seam floor.

After parallel mining and vertical mining of the protective seam, the pressure relief range based on the residual three-dimensional stress distribution characteristics under the two schemes is shown in

Table 4. Pressure relief range of the protective seam under the parallel and vertical schemes (m).

Pressure Relief Range	σX		σY		σZ
	Parallel	Vertical	Parallel	Vertical	Parallel	Vertical
Upper bound	70	80	148	80	210	82
Lower bound	−55	−75	−130	−75	−140	−75

.

As shown in Table 4, the pressure relief range of stress in the X-direction in vertical mining is greater than that in parallel mining, and the pressure relief range of stress in the X-direction is −75–80 m. In parallel mining, the unloading range of stress in the Y- and Z-directions is greater than that of vertical mining, and the unloading range of the Y-direction stress reaches −130–148 m, greatly increasing the unloading range.

A comparative analysis of the longitudinal three-dimensional stress distribution of the protective seam after parallel mining and vertical mining in Figure 3 shows that the pressure relief uniformity and pressure relief amplitude of parallel mining are significantly better than those of vertical mining. Therefore, parallel mining can fully reduce the maximum principal stress of the surrounding rock and increase the relief effect and range of protective seam mining.

3.3. Three-Dimensional Displacement Distribution Pattern in the Upper and Lower Square Roof and Bottom Plate of the Protective Seam

Figure 4 shows the distribution pattern of three-dimensional displacement in the rock mass at different distances above and below the center of the section after the mining of the protective seam in parallel and vertical mining schemes. In Figure 4, the vertical coordinate represents the vertical distance from the center of the protective seam, and the horizontal coordinate represents the displacement.

Compared with Figure 4, regardless of parallel or vertical mining, the X displacement changes are small, which can be ignored compared with the Y and Z displacement changes. The Y displacement is mainly negative, which indicates that the surrounding rock above and below moves toward the depth of the goaf after the mining of the protective seam section, but the Y displacement in parallel mining is larger than that in vertical mining. The Y displacement of coal is larger in the range of −100 to 100 m in parallel mining, while the displacement of the rock mass is larger only in the range of −75 to 75 m in vertical mining. The larger the Z displacement of the surrounding rock is, the greater the difference is: in parallel mining, the upper rock mass moves downwards, while the lower rock mass moves upwards. However, during vertical mining, the rock mass at −75 m below moves downwards, while the coal mass at 75 m above moves upwards. Such rock mass movement inevitably forces the rock masses to squeeze together, resulting in greater stress concentration, which is not conducive to increasing the pressure relief range. The conclusions of this part are mutually verified with those of the stress distribution in Section 3.2.

3.4. Comparison of the Pressure Relief Effects of the Protective Seam

After the mining of the protective seam, Figure 5 shows the distribution characteristics of the maximum principal stress of the protective seam, and the maximum principal stress is located 88 m below the protective seam.

A comparison of the results of parallel mining and vertical mining in Figure 5 shows that the distribution characteristics of the maximum residual principal stress in the protective seam are completely different. In parallel mining, the maximum residual principal stress of the protective seam decreases from approximately 38 MPa in the original state to approximately 28.8 MPa. In vertical mining, the maximum residual principal stress increases from approximately 38 MPa to approximately 44.7 MPa. Therefore, parallel mining can reduce the outburst potential of the protective seam, while vertical mining increases the outburst potential of the protective seam.

3.5. Stress Evolutionary Law of the Protective Seam

In the process of mining the protective seam, the stress of the surrounding rock changes dynamically. Figure 6 shows the three-dimensional stress evolutionary law in the protective seam immediately below the center of the protective seam section under the parallel and vertical mining schemes. The measurement point is 88 m away from the vertical distance of the protective seam. The horizontal coordinate in Figure 6 indicates the position of the cut–hole during the mining of the protective seam section: when the cut–hole is located at −300 m, the measuring point is at 300 m above the cut–hole; when the cut–hole is located at 0 m, the cut–hole is directly above the measuring point. When the incision is at 300 m, the measuring point is 300 m behind the incision.

By comparing the two mining schemes in Figure 6, it is found that the trend of the variation in the three-dimensional stress is basically the same regardless of parallel or vertical mining. As shown in Figure 6a, when parallel mining occurs, the stress in the Y-direction reaches its maximum value. Protective seam mining results in a decrease in the Y-direction stress in the protective seam, and the decrease is the largest for the three-dimensional stress. However, as shown in Figure 6b, when vertical mining occurs, the stress in the X-direction reaches the maximum, and protective seam mining results in a significant increase in the X-direction stress of the protective seam. Therefore, when the interval between seams reaches 88 m, parallel mining can reduce the outburst potential of the protective seam, while vertical mining cannot.

3.6. Displacement Evolutionary Law of the Protective Seam

In the mining process of the protective seam section, the displacement of the surrounding rock changes dynamically. Figure 7 shows the three-dimensional motion law of the measuring point in the protective seam directly below the center of the protective seam. Regardless of parallel or vertical mining, when the protective seam is mined along the Y-direction, the X displacement of the measuring point is basically zero, and the Y and Z displacements change greatly. The evolutionary curve of the Y displacement and Z displacement shows that the measuring point does not move monotonously along a certain direction but rather reciprocates. A positive value of the Z-direction displacement indicates the upward movement of the measuring point, and a negative value indicates the downward movement. A positive Y-displacement value means that the direction of movement of the measuring point is the same as the mining direction, while a negative value means the opposite.

To clarify the law of motion of measuring points under two mining schemes, motion trajectories of measuring points under two vertical and parallel mining schemes are drawn, as shown in Figure 8. Because the X displacement of the measuring point is small, the motion trajectory of the measuring point on the YZ plane is mainly drawn.

As shown in Figure 7 and Figure 8, the motion trajectory of the measuring point can be divided into two stages: the first stage is the mining of the protective seam from −300 m to 0 m; the second stage is the mining of the protective seam from 0 m to 300 m. In parallel mining, the measuring point moves in the negative Y-direction while moving upwards in the first stage, and the maximum value of the Y displacement reaches −75 cm. In the second stage, the measuring point continues to move upwards while moving in the positive Y-direction, and the final Y displacement is −14 cm. In vertical mining, while the measuring point moves downwards in the first stage, it has a small amplitude of motion in the Y-direction. In the second stage, the measuring point rebounds upwards at a small amplitude and migrates in the positive Y-direction at a small amplitude.

The amplitude of motion of the measuring point along the negative Y-direction and positive Z-direction in parallel mining is much larger than that in vertical mining. In vertical mining, the measurement points move less along the Y-direction, and the measurement points mainly move downwards, indicating that the disturbance of parallel mining on the protective seam is more intense.

3.7. Comprehensive Analysis of Stress and Displacement

In the process of protective seam mining, rock strata movement, and stress evolution complement each other: the stress gradient promotes rock mass movement, which also provides pressure relief space and promotes the redistribution of in situ stress [28,29]. During the process of protective seam mining, the stress in the interior of the goaf decreases significantly, while the coal rock mass in front of the cut–hole is in a state of stress concentration or original stress, thus forming a stress gradient. The stress gradient pushes the rock strata to move along the longitudinal and mining directions and reduces the stress in the surrounding rock. Generally, the greater the range of rock movement, the greater the relief effect is.

The above research shows that when the protective seam is mined along the Y-direction, the rock seam mainly moves along the Z-direction and Y-direction, while the movement along the X-direction is small. The Z-direction movement of the top and bottom strata is mainly affected by the Z-direction stress gradient. When the Z-direction stress pushes the strata to move along the Z-direction, the Z-direction stress inevitably decreases. Similarly, the Y-direction stress decreases as it pushes the rock along the Y-direction. Due to the significant directionality of the ground stress, the maximum principal stress decreases the most when the maximum stress is along the Y-direction, that is when the maximum stress is in parallel mining, which is conducive to reducing the difference in the three-dimensional stress and reducing the outburst potential of the coal seam to the greatest extent.

4. Field Test

4.1. Overview of Experimental Sites

Pingdingshan mining area, where Pingdingshan No. 8 Coal Mine is located, includes the Pingdingshan urban area, Xiangxian County, Jiaxian County, and Baofeng County. It is located in central and southern Henan Province, with a mining area of about 650 km². Railways and highways crisscross the mining area, and the traffic is very convenient. Pingdingshan No. 8 Coal Mine was identified as a coal and gas outburst mine in 1989 and has had 40 outburst occurrences in its history. There are great differences in the gas parameters of different coal seams in the minefield. The gas pressure and content of the D coal are the smallest, and the J coal seam is the largest. The gas pressure and content increase with the increase of the buried depth. The maximum gas content is 13.07 m³/t in the J₁₅ coal seam in the J₅ mining area. The maximum gas pressure is 1.4 MPa, measured in both E coal seams and J coal seams.

Section #204 of the Pingdingshan No. 8 Coal Mine is located inside the E_9–10 coal seam, 88 m apart from the D_5–6 coal seam above it. The above numerical model is established based on the formation conditions. The primary rock stress of No. 8 Mine of Pingdingshan Tian’an Coal Industry Co., Ltd. (Intrinsic safety type for mining Strain gauge, made in Beijing, China). is shown in Table 2. The maximum principal stress dip angle is only 3.5°, and the azimuth angle is 99.8°. The layout of each section near section #204 is shown in Figure 9: the depths of the D_5–6 coal seam and E_9–10 coal seam are −550 m and −640 m, respectively, and the thicknesses are 2.2 m and 3 m, respectively. The D_5–6 coal seam has no outburst risk, while the E_9–10 coal seam has an outburst risk. Section #204 is located in the E_9–10 coal seam and is mined along the azimuth direction of 103°. Before section #204 was mined, sections #101, #103, #105, and #107 within the D_5–6 coal seam were pre-mined at an azimuth of 98°.

According to “The Rules for the Prevention and Control of Coal and Gas Outburst”, the ultimate protective spacing between the protective seam and the protective seam for mining is 60 m [30,31]. As the spacing between the D_5–6 coal seam and the E_9–10 coal seam reaches 88 m, it is generally believed that mining the D_5–6 coal seam cannot eliminate the outburst risk of the E_9–10 coal seam. However, the above research shows that parallel mining of the protective seam can obviously increase the pressure relief effect, and the mining direction of the section in the D_5–6 coal seam of the Ba Mine happens to be parallel to the direction of the maximum principal stress, which should increase the protective effect of the protective seam.

As shown in Figure 9, section #204 is partly below the goaf and partly below the original coal because it is longer. This paper focuses on investigating the distribution pattern of outburst potential in the driving process of the #204 air inlet roadway and verifies the correctness of the conclusion of this study by comparing the difference in the outburst potential in the inner and outer parts of the D_5–6 coal seam goaf. If the outburst potential under the goaf is obviously less than that outside the goaf, it can suggest the correctness of this conclusion to a certain extent.

4.2. Pressure Relief Effect of the Remote Protective Seam

In the driving process of the #204 inlet roadway, the cutting amount, S value, and initial gas release velocity q of the borehole were continuously tested, as shown in Figure 10.

The prediction index of the outburst risk within the protective range of the D_5–6 coal seam is significantly lower than that outside the protective range; in particular, the q value outside the protective range appears to frequently overlimit, while the prediction index value within the protective range is relatively gentle.

The driving speed of the #204 inlet roadway is mainly subject to the level of outburst potential. When the prediction index exceeds the limit, driving must be stopped, and anti-outburst drilling must be constructed, which inevitably slows down the driving speed. The tunneling speed of the #204 inlet roadway during tunneling is shown in Figure 11. The tunneling speed of the roadway located below the goaf is faster, with the maximum monthly average tunneling speed reaching 6.5 m/day; however, the tunneling speed of the roadway outside the goaf decreases significantly, with an average tunneling speed of less than 3 m/day.

Since the spacing between the D_5–6 and E_9–10 coal seams reaches 88 m, it is generally believed that mining the D_5–6 coal seam cannot effectively reduce the outburst potential of the E_9–10 coal seam. However, the sections in the D_5–6 coal seam and E_9–10 coal seam are mined along the direction parallel to the maximum principal stress, which fully reduces the maximum horizontal stress and outburst potential of the protective seam.

Although the protective seam is parallel-mined in the field experiment and the vertical mining of the protective seam is not studied, it can still be suggested to a certain extent that parallel mining can significantly increase the range of pressure relief of protective seam mining compared with the range of pressure relief of the unexploited protective seam.

4.3. Field Application

A gas outburst accident is one of the most serious disasters in the coal mine, and a lot of manpower and material resources are put into prevention and control every year. This paper mainly studies the influence law of the mining direction of the protective layer on the anti-outburst effect and finds that parallel mining can not only improve the mining safety of the protective layer itself but also improve the anti-outburst effect of the protected layer. This conclusion is verified by the anti-outburst effect of the long-distance parallel mining of the upper protective layer in Pingmei No. 8 Mine. This method, by controlling the stoping direction of the working face, not only enhances the safety but also increases the economic benefit of the coal mine and has important practical value for promoting the sustainable development of the mine.

5. Discussion

Although the model simulates the geometric parameters of the protective seam and the mechanical parameters of the rock mass in Section #204 of Pingdingshan No. 8 Coal Mine, it is still an idealized model with some defects. There is no further simulation of the actual field geometry information, including the formation form. The selected rock mass mechanical parameters have isotropic properties, and the actual rock mass should be a more complex heterogeneous body; its rock mass mechanical parameters are also difficult to be numerically simulated. In the simulation, the relevant parameters are empirically reduced. On the other hand, the paper only considers the pressure relief effect of a single working face after mining in the protective layer. However, in actual situations, the stress environment of the mining face is very complicated due to the influence of mining of multiple mining faces. More complex production conditions can be considered in the next step to further improve the content of the paper.

6. Main Conclusions

(1) Combined with the actual stratum situation of the Pingdingshan No. 8 Coal Mine, a numerical calculation model is established by using FLAC3D software, and the distribution and evolutionary law of the three-dimensional stress and displacement of the stope under the circumstance that the mining direction of the protective seam is parallel to the maximum principal stress of the primary rock and vertical mining is studied.

(2) Parallel mining can fully reduce the maximum principal stress at the cut–hole in front of the protective seam, while vertical mining can lead to the concentration of the maximum principal stress ahead of the mining face. Therefore, parallel mining can more fully improve the safety of the protective seam.

(3) Compared with vertical mining, parallel mining can fully reduce the maximum principal stress of the protective seam, which is conducive to eliminating the outburst potential of the protective seam. Vertical mining may even produce stress concentration within the protective seam when the interval is far enough apart, which is not conducive to outburst relief.

(4) The effect of pressure relief and outburst reduction of the upper protective seam at a distance of 88 m between the seams of the Pingdingshan No. 8 Coal Mine is studied. When the protective seam is mined along the direction of the maximum principal stress, the outburst potential of the protective seam is significantly reduced, which indicates that parallel mining along the maximum principal stress can improve the pressure relief effect.