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Scientific Reports volume 15, Article number: 38382 (2025)
Research on the surrounding rock control technology of along-the-gob roadways in close-distance lower coal seams of the Xiaoyu Mine in Shuozhou City, Shanxi Province, is conducted using theoretical analysis, numerical simulation, field application, and effect monitoring. The results show that due to the residual coal pillars, the surrounding rock of the roadways is in a stress-concentration environment, especially with a significant increase in vertical stress on both sides and shoulders of the roadways, posing a serious risk of shear failure. Small coal pillars in the lower coal seam can effectively reduce the impact of residual coal pillars on the stability of the roadways. In the goaf and solid coal areas, the roadways are in a lower surrounding rock stress environment, and conventional roadway support schemes can be used. In the residual coal pillar area, the roadways are in a stress-concentration environment and require enhanced roadway support. Field monitoring results indicate that during roadheading and recovery, the deformation of both sides and the roof and floor of the along-the-gob roadways is always within a controllable range, and the surrounding rock stability is good.
Coal seam group mining is widespread in China. As the mining depth increases, research on the mutual influence between coal seams is becoming more and more active1,2,3. When mining close-distance coal seams, the mutual influence between seams is particularly significant, especially in downward mining sequences. In such cases, the layout of the working face, roadway support, mine pressure prevention and control, fire prevention and extinguishing, and gas management in the lower coal seam are significantly affected by the overlying goaf and residual coal pillars4,5,6,7,8,9,10.
In the Xiaoyu Mine in Shuozhou City, Shanxi Province (hereinafter referred to as the Xiaoyu Mine), the average distance between the No. 3 and No. 5 coal seams is only 4.76 m. During the mining of the lower coal seam, the manifestation of mine pressure is severe, especially the stability of the surrounding rock of roadways with wide coal pillars is poor, which brings great trouble to the safe mining of the mine. Many scholars have proposed using along-the-goaf roadheading technology in the lower coal seam to control the stability of the roadway surrounding rock and have conducted extensive research on the stress environment of minor coal pillar roadways, coal pillar width, roadway layout, surrounding rock deformation and roadway support11,12,13,14. The above research offers valuable insights into roadway layout and surrounding rock control in close-distance extra-thick coal seams. However, most are case-specific. At the Xiaoyu Mine, along-the-gob roadheading (2202 road) will be first used in the extra-thick coal seam. During roadheading and face recovery, it will encounter various upper-level impact zones like solid coal, goaf, and residual coal. To ensure the safe and stable surrounding rock of the 2202 road during these phases, technologies like theoretical analysis, numerical simulation, and on-site monitoring are adopted to analyze roadway stress and failure patterns. Based on the upper coal seam’s impact zones, corresponding support schemes are made. Also, roadway deformation during roadheading and recovery is monitored to assess the support effectiveness.
The 8202 working face of the Xiaoyu Mine is mining the C5# coal seam, which has an average thickness of 9.8 m and an average burial depth of 254 m. The coal seam has a dip angle of 1°to 6°, averaging 3°, and a Protodyakonov hardness of 2 to 3, classifying it as a medium-hard coal seam. The coal seam structure is complex, with 1 to 4 layers of partings within it, each 0.02 to 0.6 m thick. Overlying the working face is the C3# coal seam, with a distance of 3.5 to 6 m between the two seams. The 8202 working face, the mine’s first small coal pillar working face, has a recoverable strike length of 1,355 m and a dip length of 210 m. It uses a comprehensive mining method with top coal caving, with a mining height of 3.2 m and a mining ratio of 1:2. To the south of the working face is the 8204 gob area, and above it are the 4801 and 4802 gob areas of the C3# coal seam, which are arranged vertically relative to the 8202 working face. A 20 m pillar is left between the two gob areas. Figure 1 illustrates the rock stratum structure and layout of the 8202 working face.
Stratum structure and layout diagram of 8202 working face.
The 8202 working face is arranged perpendicularly to the overlying working face. The lower coal seam roadways are affected by the overlying goaf and residual coal pillars. After the upper coal seam is mined, the original stress in the goaf and its surrounding rock is redistributed. This alters the stress distribution in the lower coal seam. The roof in the goaf gradually collapses, and the floor is compacted, causing the stress around the goaf to nearly return to the original rock stress level. However, the rock layer below the residual coal pillar transmits the coal pillar’s supporting pressure to the lower coal seam, creating a stress concentration zone. When roadways are driven through this area, the sudden release of roof stress can impact the stability of the roadway’s surrounding rock.
Previous studies have shown that the concentrated pressure formed by the overlying residual coal pillar significantly increases the vertical stress in the surrounding rock of the return roadway in the lower coal seam15,16,17. Previous studies have shown that the concentrated pressure formed by the overlying residual coal pillar significantly increases the vertical stress in the surrounding rock of the return roadway in the lower coal seam. This stress increase causes varying degrees of damage to different parts of the lower coal seam roadway. By analyzing the stress changes in the surrounding rock at the sides, shoulders, roof and floor of the roadway below the coal pillar, we can determine the approximate failure range of the surrounding rock.
According to the spatial relationship between the residual coal pillar and the lower coal seam roadway, stress analysis elements at different positions of the roadway surrounding rock are selected, as shown in Fig. 2. By analyzing the stress variation process of these elements at different locations, the variation patterns of Mohr’s circles for the surrounding rock at different positions are obtained, as shown in Fig. 3. This further analysis helps to understand the failure characteristics of the surrounding rock at different positions of the roadway.(In the figure, the symbol σij represents the stress types at different positions of the roadway. Specifically, the subscript i denotes stress micro-elements at different positions, where i = 1, 2, 3, 4. Among them, i = 1 stands for the roof, i = 2 for the ribs, i = 3 for the shoulder, and i = 4 for the floor. The subscript j represents different types of stress, where j = 1, 3. Specifically, j = 1 denotes the maximum principal stress, and j = 3 denotes the minimum principal stress.)
Schematic diagram of micro – elements at different positions of the surrounding rock of the roadway under the coal pillar.
Based on the stress variation characteristics of different roadway positions during various mining periods, it is generally considered that the stress variation process of the roadway roof and floor is similar, while that of the two sides and shoulders is similar. Before the upper coal seam is mined, the stress environment at the lower coal seam roadheading location is characterized by the maximum principal stress σ1 and the minimum principal stress σ3. After the upper coal seam is mined, the vertical stress at the lower coal seam roadheading location increases sharply due to the influence of the residual coal pillar’s supporting pressure. That is, the maximum principal stress σ1 increases significantly, while the minimum principal stress σ3 changes little. At this time, the corresponding Mohr’s circle is generally described as circle 2 in Fig. 3. As the lower coal seam roadway is excavated, the stress characteristics at different positions of the surrounding rock change. The vertical unloading of the surrounding rock at the top of the roadway causes σ1 to decrease.
In contrast, the horizontal stress σ3 of the roof rock layer increases due to the stress concentration of the surrounding rock at the shoulder of the roadway. Consequently, the Mohr’s circle changes accordingly, as shown by circle 3 in Fig. 3a. The variation process of Mohr’s circle for the floor rock layer of the roadway is similar to that of the roof, but since the floor rock layer is farther away, the increase in horizontal pressure is relatively more minor, as shown by circle 3 in Fig. 4b. After the roadway is driven, the horizontal stress of the surrounding rock on the two sides of the roadway is released, while the vertical stress increases sharply due to stress concentration. That is, σ1 increases significantly and σ3 decreases. The Mohr’s circle changes to circle 3 in Fig. 3c. When circle 3 is tangent to envelope A, the surrounding rock is in a critical state. When they intersect, shear failure occurs in the surrounding rock. The stress evolution process of the surrounding rock at the two shoulders of the roadway is similar to that of the two sides. However, since this position is closer to the overlying coal pillar, the degree of σ1 increase is greater, and the degree of σ3 decrease is slightly smaller, as shown by circle 3 in Fig. 3d. Envelope A in the figure represents the shear strength envelope of the surrounding rock under its original mechanical state. When circle 3 is tangent to envelope A, it indicates that the surrounding rock is in a critical state; and when the two intersect, it means that shear failure will occur in the surrounding rock. As the degree and scope of damage to the surrounding rock of the roadway increase, the shear strength of the surrounding rock decreases. That is, tanφ decreases, and the slope of the envelope becomes gentler, as shown by envelope B in Fig. 3. This makes the surrounding rock more susceptible to damage, especially on the two sides and shoulders18.
Schematic diagram of Mohr’s circles for surrounding rock at different positions of the roadway under the coal pillar.
The previous section has focused on the influence of residual coal pillar loads on the stress distribution and failure modes of roadway surrounding rock, revealing the instability characteristics of surrounding rock under local concentrated loads. However, the influence of goaf on roadway surrounding rock differs significantly from that of residual coal pillar. Therefore, this section focuses on the stress distribution and failure mechanism of roadway surrounding rock under the action of goafs, providing targeted theoretical support for subsequent support schemes.
Previous research has shown that after a working face is mined, a depressurization zone forms in the goaf, reducing the vertical stress on its floor. As the gob’s rubble collapses and gradually compacts over time, the floor stress in the goaf slowly returns to near the original rock stress level15,19,20. Under the influence of the overlying goaf, the stress variations at different positions of the roadway surrounding rock are distinct. Stress analysis elements at various positions of the surrounding rock, as shown in Fig. 4, are selected for analysis. The variations of Mohr’s circles for these positions are obtained, as depicted in Fig. 5, to analyze further the failure characteristics of the surrounding rock at different positions of the roadway under the goaf.
Before the upper coal seam is mined, the lower coal seam roadway is in a state of maximum principal stress (σ1) and minimum principal stress (σ3). As the upper coal seam is mined and the goaf floor’s vertical stress is released, the maximum principal stress in the goaf floor shifts to the horizontal direction, and the minimum principal stress to the vertical direction. This causes a sharp drop in vertical stress and a relative increase in horizontal stress at the lower coal seam roadway location. The Mohr’s circle changes from circle 1 to circle 2, as shown in Fig. 5. During the excavation of the lower coal seam roadway, different positions of the surrounding rock experience distinct stress changes. After excavation, the vertical stress of the roadway roof surrounding rock is further released, and the horizontal stress (maximum principal stress σ1) increases. The Mohr’s circle for this position changes from circle 2 to circle 3 (Fig. 5a). The stress variation of the roadway floor surrounding rock is similar to that of the roof but with more minor stress changes due to its greater distance from the upper coal seam (Fig. 5b). After excavation, the horizontal stress of the roadway sides’ surrounding rock is released, reducing the maximum principal stress.
Meanwhile, vertical stress concentration slightly increases the minimum principal stress, changing the Mohr’s circle to a smaller circle 3 (Fig. 5c). The stress variation at the roadway shoulders is similar to that of the sides but with a larger increase in horizontal stress due to their closer proximity to the upper coal seam. Thus, Mohr’s circle 2 at the shoulders has a relatively larger radius. After excavation, the maximum principal stress is sharply released, and the minimum principal stress slightly increases. In summary, the supporting pressure on the roadway surrounding rock under the upper goaf is relatively small, making the surrounding rock relatively stable. After excavation, the roof’s horizontal stress increases, and vertical stress decreases, making it prone to shear failure.
Schematic diagram of micro-elements at different positions of the surrounding rock of the roadway under the goaf.
Schematic diagram of Mohr’s circles for surrounding rock at different positions of the roadway under the goaf.
In order to further explore the impact of the upper coal seam’s residual coal pillar on the stress environment of roadways excavated along the goaf and its influence on the width of the coal pillar in the lower coal seam working face section, the numerical simulation software is used. The study simulates the stress changes in the 2202 roadway as it crosses the coal pillar and identifies the main areas influenced by the upper coal seam’s residual coal pillar and the position of the coal pillar. All numerical simulations in this study were performed using the Fast Lagrangian Analysis of Continua in 2 Dimensions (FLAC2D), Version 5.0, developed by Itasca Consulting Group, Inc. Further details about the software can be found at: https://www.itascacg.com/Software/FLAC2D.
To achieve the research objectives, two cross-sectional profiles, I-I and II-II, were selected (as indicated in Fig. 2). The I-I profile was modelled to analyze the stress variations in the 2202 roadway as it traverses the coal pillar. The II-II profile was modelled to investigate the impact range of the upper coal seam’s residual coal pillar and its influence on the roadway excavation position.
A numerical model was established based on the lithology of the roof and floor strata of the 8202 working face at Xiaoyu Mine. The Mohr-Coulomb model is used in the model to simulate the coal and rock layers, with a total of 30 layers set. The reference mechanical parameters of the model are shown in Table 1. The simulation is 400 m long and 150 m high. After rounding the thickness of the simulated rock layers, the thickness of the 5# coal seam is 10 m, the thickness of the 3# coal seam is 14 m, and the distance between the two coal seams is 5 m. A vertical stress of 5 MPa was applied at the top of the model to simulate the overlying rock strata’s weight, as shown in Fig. 6. The bottom of the model was fixed vertically, and the sides were fixed horizontally. Interfaces were introduced into the model to simulate the collapse of the goaf. During the simulation of the II-II profile, a vertical stress of 20 MPa was applied at the location of the No. 3 coal seam to mimic the increased stress near the coal pillar. In the simulation process, the I-I profile model monitored the vertical stress of the 2202 roadway to capture the stress impacts as it crossed the upper coal pillar. The II-II profile model monitored the stress and displacement of the roadway surrounding rock to evaluate the roadway’s stress state and deformation under different coal pillar widths, as shown in Fig. 8.
Numerical mode.
Schematic diagram of boundary conditions
In the I-I section model, excavation was simulated for the upper coal seam’s 4801 and 4802 working faces. After the 4801 goaf and 4802 goaf goaves stabilized, vertical stress distribution cloud charts were extracted, and stress monitoring was conducted at the lower coal seam’s tunnelling location. The simulation results are shown in Fig. 8.
Vertical stress distribution contour after upper coal seam mining.
The simulation shows that the coal pillar between the two goaves of the upper coal seam has undergone plastic deformation but still has some load-bearing capacity. This allows stress to be transmitted downward, creating a saddle-shaped high-stress area at the lower coal seam’s tunnelling position (see Fig. 8). The stress monitoring curve also shows that the stress at the lower coal seam’s tunnelling position varies significantly between the goaf and residual coal pillar areas. Under the goaf, the floor rock layer is depressurized, and the vertical stress decreases within the upper goaf range. Within the residual coal pillar and solid coal edges, the stress remains high. In the coal pillar area, the surrounding rock stress rises sharply to a peak from the edge to the centre, with the peak stress increasing by nearly 20 MPa compared to the original rock stress. Within the solid coal range, the surrounding rock stress first rises sharply to a peak. It then gradually decreases to the original rock stress level from the edge to the interior.
As the 8202 working face is the mine’s first small coal pillar working face, to analyze the stress environment of the roadway surrounding rock under different coal pillar widths, the study simulated coal pillars of 7.8 m and 30 m (traditional width). Since the residual coal pillar of the upper coal seam affects the lower coal seam roadway more than the goaf, the simulation focused on the stress distribution below the residual coal pillar. Using the model in Fig. 8(b), after mining the 8204 working face and stabilizing the goaf, the lateral stress distribution was monitored. The peak lateral supporting pressure was found about 24 m from the goaf, with a stress reduction zone of around 13 m. Thus, a 7.8 m coal pillar places the roadway in the stress reduction zone, while a 30 m coal pillar positions it in the stress increase zone, raising the risk of roadway failure. Subsequently, small and wide coal pillar roadways were driven, and the vertical stress distribution in the surrounding rock was mapped, as shown in Fig. 9. The maximum stress values at different locations in the surrounding rock are listed in Table 2.
Vertical stress distribution contour of roadway surrounding rock.
As observed from Fig. 9, the small-coal-pillar roadway is situated within the stress-reduction zone on the goaf side. In contrast, the wide-coal-pillar roadway lies in the stress-concentration zone, with rib stresses significantly exceeding roof stresses. Table 1 demonstrates that compared to the wide-coal-pillar roadway, stresses at different locations of the surrounding rock in the small-coal-pillar roadway – whether every day or shear stresses – remain at lower levels. Thus, implementing small coal pillars maintains roadways within lower-stress environments, correspondingly reducing surrounding rock deformation and facilitating roadway surrounding rock control.
Based on the location of the 2202 roadway relative to the upper coal seam’s goaf, the influence of the upper coal seam during excavation can be categorized into three zones: solid coal zone, goaf zone, and residual coal pillar zone. From the stress distribution theory and numerical simulation results, the roadway is least affected by the upper coal seam in the goaf zone, moderately affected in the solid coal zone, and most affected in the residual coal pillar zone, particularly within 20 m of the coal pillar. To ensure rational and stable roadway support, conventional support is used in areas of low influence, while enhanced support is applied in areas of significant stress impact.
Given the degree of influence from the upper coal seam on the 2202 roadway, two support schemes are adopted: conventional and enhanced. Conventional support is implemented in sections along the excavation direction from 94 to 231 m, 255–363 m, 403–455 m, 479–784 m, and 809–1528 m. Enhanced support is required in sections from 0 to 94 m, 231–255 m, 363–403 m, 455–479 m, 784–809 m, and 1528–1550 m. The support parameters are determined based on the theories of high-strength anchor bolt support for roadway surrounding rock strengthening, anchorage balance, and cable suspension reinforcement. Following the principles of anchor bolt and cable coupled support and dynamic system design and considering the mechanical properties of the surrounding rock in the 2202 belt conveyor roadway, the support density, length, and other parameters for anchor bolts and cables are finalized (Table 3).
The roof anchor bolts are arranged in a grid of 900 mm × 850 mm. The outermost anchor bolts are 200 mm from the sides, with the outer two at a 75° angle and the rest at 90°. They are paired with 150 × 150 × 10 mm arch-shaped prestressed steel trays, W-shaped steel strips, and 70 × 70 mm metal mesh for protection. Between the two rows of anchor bolts, three and four anchor cables are staggered. The three anchor cables are spaced at 1,800 mm × 1,375 mm and perpendicular to the roof. Of the four anchor cables, the middle two are perpendicular to the roof with a spacing of 1,800 mm × 1,800 mm, and the other two are placed at the roadway corners, all using 300 × 300 × 14 mm arch-shaped prestressed steel trays.
The side wall anchor bolts are arranged in a grid of 900 mm × 900 mm. The upper anchor bolts are 300 mm from the roof at an upward angle of 20°, while the lower ones are 300 mm from the floor at a downward angle of 20°. The middle anchor bolts are perpendicular to the roadway sides. All anchor bolts use 150 × 150 × 10 mm arch-shaped prestressed steel trays. In every second row, the second anchor bolt is replaced with an anchor cable. The support layout for the roof and sides is shown in Fig. 10.
Schematic diagram of conventional support scheme for 2202 conventional support area.
The roof uses two rows of anchor bolts and one row of anchor cables arranged alternately, as shown in Fig. 11(c). The anchor bolts and cables are spaced at 900 × 850 mm. The two outermost anchor bolts are 200 mm from the sides at a 75° angle, while the others are vertical (90°). They are paired with 150 × 150 × 10 mm arch-shaped prestressed steel trays, W – W-shaped steel strips, and 50 × 50 mm metal mesh for protection. The anchor cables are vertical, with 300 × 300 × 14 mm arch-shaped prestressed steel trays, and have JW-shaped steel strips and metal mesh for protection. Angle anchor cables are arranged at the roadway shoulders at a 45° angle, spaced 1,800 mm apart, and are paired with 600 mm – short I – beams and 300 × 300 × 14 mm arch-shaped prestressed steel trays. A combined anchor cable unit is added between the two rows of anchor bolts in the middle at a spacing of 2,700 × 2,400 mm. Each unit consists of three anchor cables forming an isosceles triangle with a combined anchor cable tray.
The sides of the roadway use a combined anchor bolt and anchor cable support system. One row of anchor cables is installed 300 mm from the roof, at a 10° upward angle, with a spacing of 900 mm and a 300 × 300 × 10 mm high-strength arched tray. One row of anchor bolts is installed 300 mm from the floor, at a 20° downward angle, with a spacing of 900 mm and a 150 × 150 × 10 mm high-strength arched tray. In between, two rows of anchor bolts and cables are alternately arranged in a 900 mm × 900 mm grid, perpendicular to the roadway side, with W-shaped steel strips and 70 × 70 mm metal mesh for protection, as shown in Fig. 11b.
Schematic diagram of reinforced support scheme for 2202 reinforced support area.
During roadway excavation, continuous monitoring of the deformation rate of the roadway surrounding rock is carried out to achieve real-time evaluation and analysis of the stability of the roadway. The measuring points are arranged in the goaf influence zone, solid coal area, and residual coal pillar influence zone. The roadway deformation data within 40 days after the excavation of the roadway are recorded, as shown in Fig. 12.
Statistical chart of deformation parameters of roadway surrounding rock during excavation.
Analysis of the deformation patterns of roadways in different zones shows that the convergence of the two sides is slightly greater than that of the roof and floor. In the residual coal pillar zone, the maximum convergence of the two sides and the floor is 73 mm and 62 mm, respectively. In the goaf influence zone, these values are minimal at 58 mm and 52 mm. Deformation-rate monitoring reveals that the roadway deforms quickly initially, then gradually stabilizes within about 10–15 days. Overall, during excavation, the small – coal-pillar roadway exhibits small deformation and good stability.
To monitor the deformation during the retreat mining of the 8202 working faces, surface-displacement monitoring points were set up in the goaf, solid-coal area, and residual-coal-pillar zone. Deformation data of the roadway surrounding rock was recorded from before the roadway was affected by mining until the monitoring points were reached, as shown in Fig. 13.
Statistical chart of roadway deformation during retreat mining.
The monitoring results indicate that in the upper coal pillar zone, influenced by concentrated stress and advanced support pressure, the roadway deformation is the most significant. Here, the maximum convergence of the two sides reaches 805 mm, and the roof/floor convergence reaches 604 mm. In contrast, within the goaf zone, due to the depressurization effect, the deformation is minimal, with the maximum side convergence at 105 mm and roof/floor convergence at 121 mm. As the working face approaches the monitoring points, the deformation rate accelerates within 80 m of the working face and peaks within 30 m. Overall, the deformation is relatively small in the goaf and solid coal zones. However, it is larger in the residual coal pillar zone. Nevertheless, enhanced support measures have effectively controlled the stability of the roadway in this area.
Based on the spatial relationship between the working faces of the 3# coal seam and 5# coal seam in Xiaoyu Coal Mine, a theoretical analysis was conducted on the stress variation characteristics of the surrounding rock of the lower coal seam roadway under the influence of the overlying goaf and residual coal pillars. The analysis results show that: affected by the transfer of concentrated stress from residual coal pillars, the maximum principal stress of the surrounding rock of the lower coal seam roadway increases significantly, especially at the side and shoulder positions of the roadway. Calculations based on the Mohr-Coulomb strength criterion indicate that the surrounding rock in this area exhibits shear effects and faces a high risk of severe shear failure, requiring focused attention on support design; in contrast, the goaf plays a pressure-relief role, placing the surrounding rock of the lower coal seam roadway in a low-stress environment. This can significantly reduce the deformation risk of the roadway after excavation and provide favorable conditions for roadway stability.
According to the numerical simulation results, the floor rock stratum under the upper coal seam goaf undergoes pressure relief, and the vertical stress shows a decreasing trend within the range of the upper goaf; the vertical stress remains at a high level within the range of residual coal pillars and the edge of the solid coal. Among these areas, the vertical stress at the center of the coal pillar area rises to a peak value, which is nearly 20 MPa higher than the original rock stress. Meanwhile, it is verified that adopting a small coal pillar roadway layout in the lower coal seam can locate the roadway in a stress-reduced zone, effectively minimizing the impact of residual coal pillars on roadway stability.
Based on the occurrence characteristics of the overlying rock strata of the coal seam, the excavation area of the lower coal seam roadway is divided into three zones: the goaf zone, the solid coal zone, and the residual coal pillar zone. In the goaf zone and solid coal zone, the roadway is in a low surrounding rock stress environment, allowing the use of a conventional roadway support scheme; however, in the residual coal pillar zone, the roadway is in a stress-concentrated environment, necessitating enhanced support for the surrounding rock of the roadway. Through monitoring the deformation characteristics of the roadway during both roadway excavation and working face mining, it was found that the deformation of the roadway sides, roof, and floor remained within a controllable range at all times.
All data generated or analysed during this study are included in this published article [and its supplementary information files].
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This study is supported by the National Natural Science Foundation of China (No. 52174073); Henan Polytechnic University Natural Science Foundation Doctoral Fund Project B2023-26.
School of Architecture and Art Design, Henan Polytechnic Universityg, Jiaozuo, 454000, China
Sichao Li
School of Safety Science and Engineering, Henan Polytechnic University, Jiaozuo, 454000, China
Zuguang Wang
PubMed Google Scholar
PubMed Google Scholar
S. L. wrote the main manuscript text and Z. W. prepared figures and tables. S. L. and Z. W.jointly acquired the data, with S. L. being responsible for data organization and analysis.All authors reviewed the manuscript.
Correspondence to Sichao Li.
The authors declare no competing interests.
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Li, S., Wang, Z. Research on surrounding rock control technology for gob-side entry in close-distance lower coal seam. Sci Rep 15, 38382 (2025). https://doi.org/10.1038/s41598-025-22181-1
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