Numerical Simulation Study on Through-Anchor Cable Reinforcement Control of Inter-Roadway Coal Pillars in Double-Roadway Layouts

Abstract

This study investigates the traditional coal pillar support methods employed in double-roadway excavation of high-mining-height longwall faces, specifically those with widths ranging from 20 m to 30 m. It highlights that these methods not only result in substantial coal pillar loss and low recovery rates but also create conditions for stress concentration due to inadequate dimensions, thereby increasing the risk of accidents. Based on the engineering context of the Jinjitan Coal Mine’s 113 and 111 working faces, this paper optimizes coal pillar dimensions through theoretical calculations and Flac3D numerical simulations, with the results indicating that the optimal coal pillar width is 12 m. Analysis of a 12 m inter-roadway coal pillar focuses on the bearing characteristics of auxiliary transport roadways and coal transportation roadways. Five different reinforcement schemes are examined, including (no support, conventional anchor reinforcement, presser anchor cable through reinforcement, constant-resistance large-deformation anchor cable through reinforcement, and a combination of presser with negative Poisson’s ratio (NPR) constant-resistance large-deformation anchor cable support). The findings reveal that in the investigation of the reinforcement mechanism for the 12 m wide coal pillar, employing NPR constant-resistance large-deformation anchor cables alongside presser anchor cables effectively mitigates the compression deformation caused by dynamic loading disturbances from the overlying rock layers. This approach not only dissipates energy but also transforms the coal pillar from a biaxial stress state to a triaxial stress state. The reinforcement scheme successfully reduces the peak stress of the coal pillar from 68.5 MPa to 35.3 MPa, significantly enhancing both the peak strength and residual strength of the coal pillar, thereby ensuring the stability of the inter-roadway coal pillar and the safe recovery of the working face.

1. Introduction

Currently, an increasing number of coal mines are adopting narrow coal pillar excavation techniques. This approach places roadways within the low-stress zone and incorporates sectional narrow coal pillars, which not only enhance coal recovery rates but also effectively reduce the risk of rock bursts associated with coal pillars [1,2,3]. Research findings demonstrate that the failure mechanisms of narrow coal pillars can be classified into two primary types: ultimate strength failure and progressive failure. The ultimate strength failure theory proposes a yield pillar design approach; which focuses on optimizing pillar dimensions while implementing reinforcement measures such as grouting and rock bolting. These techniques enhance the pillar’s deformation resistance and overall strength, thereby achieving effective control. On the other hand, the progressive failure theory advocates for a rigid pillar design strategy, emphasizing continuous monitoring and systematic reinforcement to maintain long-term pillar stability. Scholars from the former Soviet Union and Poland have argued that reducing the width of coal pillars contributes to better resource utilization and roadway stability [4,5,6,7]. The first factor is the formation of mining dynamics, which refers to the large-scale movement of overlying strata and the reorganization of rock stresses induced by mining. This is especially significant in the distribution of basal stress in a coal rock mass ahead of the recovery face [8,9]. The second factor is the analysis of coal pillar stress and deformation patterns under the influence of overlying strata during mining. This involves studying the pressure distribution [10,11], constructing the coal pillar bearing structure, and delineating the stress and plastic zones within the inter-roadway coal pillar [12,13,14]. Methods such as avoiding high-stress and plastic zones in the penetrated sections are employed to achieve the goal of reducing coal pillar size. While reducing coal pillar dimensions, the reinforcement technology for narrow coal pillars between roadways plays a critical role in coal mining, particularly in the context of double-roadway excavation in longwall faces with high mining heights. This is especially important as coal mining gradually shifts to deeper levels.

In recent years, increasing attention has been focused on how to effectively reduce the size of coal pillars while ensuring their safety and stability. Scholars both domestically and internationally have conducted extensive studies in this field, proposing various reinforcement strategies and optimization solutions. They have investigated the failure mechanisms of reinforced coal pillars and compared the bearing capacities before and after reinforcement [15]. For narrow coal pillars in double-roadway layouts, reinforcement is applied using anchor cables and steel pipe supports. The study employs the UDEC Trigon model and finds that the combined support of anchor bolts and through-anchor cables can effectively control coal pillar deformation. This significantly enhances the coal pillar’s bearing capacity and long-term stability [16]. Based on the actual engineering background of the Jincheng Sieh Mine, an in-depth study was conducted on the deformation characteristics of surrounding rock and support techniques under multiple roadway layouts in the recovery face. A substantial amount of research was carried out on the failure, deformation, and support design of narrow coal pillars between roadways [17]. The support techniques include cross-anchor bolt support, constant-resistance anchor bolt support, and zoned combined support [18,19,20,21,22]. These theories provide technical support for the stability of narrow coal pillars. In terms of support materials, the authors of [23] developed the “Negative Poisson’s Ratio (NPR) anchor cable”, as well as an “NPR anchor cable” designed for large deformations and energy absorption. They proposed the “pre-split roof cutting + NPR anchor cable” support technology, which successfully controls surrounding rock deformation and is suitable for deeply buried fault roadways [24,25,26,27,28]. The study investigates a new type of presser anchor cable, which consists of a presser pipe and a split plug. This system can achieve large-deformation and high-strength presser effects without the need for borehole expansion, with deformation reaching up to 100 mm. It effectively enhances the safety of roadway support. However, the improvement in coal pillar bearing capacity is limited, leading to significant deformation of small coal pillars under the combined effects of base pressure and mining activities. The material selection for single-direction anchor bolts, anchor cables, and bidirectional through-anchor cables plays a crucial role in the coal pillar’s load-bearing capacity, but there are still some limitations.

This study focuses on Panels 113 and 111 in Jinjitan Coal Mine as primary research subjects; these panels were selected based on their exceptional geological characteristics compared to other working faces in the mining area. These panels exhibit several advantageous geological features, including the absence of overlying gas reservoirs, negligible groundwater presence, and nearly horizontal coal seam inclination, making them ideal for comprehensive geological and engineering investigations. The aim is to optimize the coal pillar dimensions through numerical simulations. First, the stability of narrow coal pillars under the double-roadway layout method is analyzed, and the coal pillar dimensions are optimized. Then, five different bidirectional through-anchor cable reinforcement schemes for the inter-roadway coal pillar are compared in terms of damage characteristics and impact patterns. The results confirm that the combined use of presser anchor cables and constant-resistance large-deformation anchor cables provides the best reinforcement solution. One of the best technological solutions is the use of cable anchors, which are characterized by high flexibility. The feasibility and application effectiveness of the proposed approach are further validated, providing a rich practical background and real-world significance for this study.

2. Project Introduction

The Jinjiang Coal Mine is located in Yulin City, Shaanxi Province, China, as shown in Figure 1. The 12-2 upper 113 and 111 working faces currently being mined at the Jinjiang Coal Mine (hereinafter referred to as the “113 and 111 working faces”) are part of the longwall faces in the east wing of the mine’s No. 1 panel area. The working face has an inclined length of 300 m and a strike length of 4847.6 m. It primarily recovers the 2-2 and 2-2 upper coal seams, with a thickness range of 8.3 to 12.2 m and an average thickness of 10.25 m.

The working face is characterized by a monocline structure, with the dip direction toward the northeast and a lower dip toward the southwest. The coal seam strikes approximately north and dips toward the west, with an average dip angle of less than 1°. The elevation range of the working face is from +962.5 m to +986.3 m, with an average elevation of +974.4 m. The surface elevation ranges from +1233.77 m to +1255.61 m, with an average elevation of +1244.73 m. A 20 m wide coal pillar is positioned between the transportation and auxiliary roadways of the working face. In the 113-longwall working face, a double-roadway layout is adopted for the recovery roadways. The double-roadway excavation not only effectively controls the production safety of the mine during the longwall recovery by leaving a coal pillar between the roadways but also addresses ventilation issues during the long-distance excavation process. This study is based primarily on the JB2 geological borehole to carry out the optimization research of the inter-roadway coal pillar. The borehole log is shown in Figure 2. Based on the geological conditions and lithological characteristics obtained from borehole logs, a numerical simulation model was established using FLAC3D v. 6.00 software to accurately represent the geological features of the working face. The model incorporates distinct rock strata, each assigned with corresponding physical parameters based on field data. The gravitational acceleration was set at 9.8 m/s², and the Mohr Coulomb constitutive model was adopted for material characterization. The physical and mechanical parameters of various rock strata in the coal seam, as derived from borehole data, are presented in

Table 1. Physical and mechanical parameters of various rock strata in the coal seam.

Number	Name of Rock	Depth of Burial	Compressive Strength (MPa)	Modulus of Elasticity (GPa)	Poisson’s Ratio	Capacity (kN/m3)	Angle of Internal Friction/°
M9	Medium-grained sandstone	146.25	59.20	25..5	0.24	2.35	37
M8	Siltstone	164.95	39.15	22.0	0.23	2.50	39
M7	Silty mudstone	173.61	33.56	21.0	0.20	2.25	33
M6	Fine-grained sandstone	184.43	43.15	22.0	0.20	2.35	32
M5	Siltstone	192.23	35.09	23.0	0.24	2.35	40
M4	Fine-grained sandstone	203.52	45.34	23.0	0.21	2.25	32
M3	Mudstone	225.01	40.07	21.0	0.23	2.35	33
M2	Fine-grained sandstone	235.12	45.29	22.0	0.20	2.50	34
M1	Siltstone	242.89	42.02	25.0	0.24	2.35	40
Main roof	Silty mudstone	251.93	65.15	21.0	0.20	2.15	39
Coal	2−2 coal	263.00	18.55	19.6	0.24	1.50	37

.

3. Determination of the Width of the Inter-Roadway Coal Pillar

3.1. Numerical Calculation

Based on the production geological conditions of the case working face, a FLAC3D numerical model was established. The model dimensions are 200 m × 50 m × 100 m (length × width × height). Horizontal constraints were applied to the front, rear, and lateral boundaries of the model. The computational grid was divided according to the model’s geometry. Considering the limitations of the total number of model elements and the concentration of the study area, stress boundaries were applied at the top to simulate the overlying load. The roadway depth was simulated as 263 m. The numerical model is shown in Figure 3 and the physical and mechanical parameters of the rock layers in the model are presented in Table 1.

Distribution Law of Lateral Support Pressure During Mining Recovery on Both Sides of the 20 m Inter-Roadway Coal Pillar

The distribution of the inter-roadway coal pillar support pressure for the 113 and 111 working faces, as obtained from numerical calculations, is shown in Figure 4. During mining recovery on both sides, with a coal pillar width of 20 m, the distribution law of lateral support pressure is as follows:

• The 0–2 m and 18–20 m sections are low-stress zones and plastic zones, where the stress values mainly range from 4.5 to 22.5 MPa. A noticeable increase in stress is observed towards the interior of the coal pillar.
• The 2–4 m and 16–18 m sections are stress peak zones and elastic zones, with a peak stress of 34.9 MPa. The overall stress level is relatively high, but due to the three-dimensional stress state, the zone remains in the elastic range without failure.
• The 4–6 m and 14–16 m sections are stress-reduction zones and elastic zones, where the stress levels gradually decrease, and the coal pillar progressively enters a more stable mechanical state. The formation of the stress-relief zone and the elastic zone significantly impacts the overall stability of the coal pillar: the stress-relief zone reduces the risk of localized failure by releasing stress at the edges of the coal pillar, while the elastic zone ensures overall stability by maintaining the high load-bearing capacity of the core region. As the stress level gradually decreases, the coal pillar transitions into a more stable mechanical state, further enhancing its resistance to deformation and failure. These mechanical characteristics directly influence reinforcement strategies: for the stress-relief zone; techniques such as bolting and cable anchoring are required to enhance its residual strength. For the elastic zone, the focus should be on monitoring stress concentration to prevent it from entering a plastic failure stage. Overall, reinforcement strategies should dynamically adjust support methods based on the elastic stress distribution and deformation characteristics of the coal pillar, ensuring its long-term stability and safe mining operations.
• The 6–14 m section is a low-stress zone and elastic zone, with stress values ranging from 15 to 25 MPa. All areas remain in an elastic state, exhibiting good stability.

3.2. Simulation of Coal Pillars with Different Dimensions

Based on the lateral support pressure distribution law during mining recovery on both sides of the 20 m coal pillar, an elastic core zone ranging from 6 m to 14 m appears within the coal pillar. It is necessary to appropriately reduce the coal pillar size and shrink the range of the elastic core zone. This change has little impact on the peak stress, and the coal pillar can still maintain stability. Therefore, a stability analysis of roadways with different inter-roadway coal pillar widths between the 111 and 113 working faces should be conducted to propose a more reasonable coal pillar dimension.

Figure 5 shows the distribution pattern of the lateral plastic zone in the coal pillar during mining. In the process of mining the 111 working face, the plastic zone near the gob area on both sides of the coal pillar significantly expands, and the extent of the plastic zone decreases as the coal pillar size increases. At the top and bottom of the coal pillar in both the 113 and 111 working faces, the plastic zone gradually forms a through-going feature. As the coal pillar size increases, the elastic zone expands. When the coal pillar width is ≤10 m, the coal pillar exhibits a tendency for the plastic zone to penetrate; when the width exceeds 12 m, the elastic core extends beyond 4.8 m, and the stability of the coal pillar is effectively maintained. Reducing the coal pillar width to 20 m does not negatively affect stability, but increasing the width helps to enhance the pillar’s bearing capacity on the roof, thus reducing the overall plastic zone volume. However, when tensile plastic zones appear, there is a risk of side-wall bulging. Taking into account the distribution of the plastic zone during mining and the coal recovery rate, the optimal coal pillar width is set at 12 m, and a bidirectional through-anchor support scheme is selected to ensure stability.

4. Negative Poisson’s Ratio (NPR) Anchor Cables and Pressurizer Pressure Characteristics

To effectively control inter-seam coal pillars under complex geological conditions, support materials must offer high constant resistance and extensibility to enable both significant deformation and high compensatory force. Traditional anchor systems, with limited elongation and mechanical strength, fail to accommodate large deformations in surrounding rock and the nonlinear failure characteristics of overburden movement. This challenge has been extensively studied by researchers in the field.

He Manchao [20] developed a new type of constant-resistance large-deformation anchor/strand with a negative Poisson’s ratio (NPR) structure, introducing the concept of NPR support and its mechanical behavior in the field of rock mechanics. The NPR anchor strand, which exhibits negative Poisson’s ratio effects, consists primarily of a constant-resistance body, steel strands, a tray, and nuts. The steel strands are conventional materials with a positive Poisson’s ratio, while the constant-resistance body is made from NPR materials. As shown in Figure 6.

At the same time, scholar Wu Yuyi [28] developed a new type of anchor cable pressure-relief device consisting of a pressure-relief pipe, locking device, steel strands, and tray. The pressure-relief device undergoes a complex mechanical transformation process during the pressure-relief process. Installed between the tray and locking device, it does not require hole expansion, achieving effects similar to large-deformation and constant-resistance devices while being relatively cost-effective to manufacture. As shown in Figure 7.

5. Reinforcement and Numerical Analysis of the 12 m Coal Pillar Section

5.1. Design Parameters for Double-Roadway Coal Pillar Support

Through the optimization study of the inter-roadway coal pillar dimensions at the 113 and 111 longwall faces of the Jinjitan Coal Mine, the dimensions of the inter-roadway coal pillar under a double-roadway layout were determined. The optimized size of the coal pillar, under the reinforcement measures involving bidirectional through-anchor cables, is 12 m, as illustrated in Figure 8. The reinforcement scheme using a combination of pressure-relief anchor cables and constant-resistance large-deformation anchor cables (NPR) involves the cross-layout of pressure-relief anchor cables and NPR constant-resistance large-deformation anchor cables with a spacing of 2.5 m. The cross-sectional and plan views of this reinforcement scheme are shown in Figure 9 and Figure 10.

5.2. Numerical Analysis of Cross-Through Reinforcement Using Pressure-Relief Anchor Cables and NPR Anchor Cables

The 12 m wide inter-roadway coal pillar is selected as the subject for numerical simulation. The changes in the internal bearing stress and plastic zone distribution within the coal pillar during both single-sided and double-sided mining processes under the reinforcement scheme combining NPR constant-resistance large-deformation anchor cables and pressure-relief anchor cables are analyzed. The stress distribution within the coal pillar is a crucial indicator for evaluating its stability and potential failure. The combination of NPR constant-resistance large-deformation anchor cables and pressure-relief anchor cables is determined to be the optimal reinforcement scheme. As shown in Figure 11.

5.2.1. Stress Distribution

The reinforcement scheme using a combination of NPR constant-resistance large-deformation anchor cables and pressure-relief anchor cables, with a cross-through layout, results in a peak stress of 35.3 MPa. The coal pillar transitions from a biaxial stress state (vertical direction and along the mining face’s horizontal direction) to a more favorable triaxial stress state, as shown in Figure 12. This significantly enhances the coal pillar’s stability while optimizing its performance.

5.2.2. Distribution of the Plastic Zone in the Surrounding Rock

The distribution of the plastic zone in the surrounding rock indicates a change in the stress state of the coal pillar. The most unfavorable shear and tensile-controlled plastic zone near the free face transforms into a shear plastic zone under the triaxial stress state. The shear plastic zone is 2.5~2.8 m on each side of the left and right sides, which contributes to the overall stability of the coal pillar, as shown in Figure 13.

5.2.3. Distribution of the Plastic Zone in the Surrounding Rock, as Shown in Figure 14

(1)

Location of maximum deformation: The maximum horizontal deformation of the 12 m coal pillar occurs in the lower section of the roadway.

(2)

Maximum horizontal deformation: The unilateral deformation reaches 33.7 cm. Due to the reinforcing effect of the cross-through anchor cables and the constraints of the triaxial stress state, the horizontal deformation of the coal pillar is significantly reduced, enhancing its stability against horizontal deformation.

(3)

Anchor cable extension in the cross-through scheme: At the maximum deformation of the coal pillar, the pressure-relief anchor exceeds its pressure-relief capacity, preventing the NPR anchor cables from fully extending. This effectively restricts the pillar’s deformation, maintaining its stability.

Figure 14. Cross-through reinforcement using pressure-relief anchor cables and NPR anchor cables.

Figure 14. Cross-through reinforcement using pressure-relief anchor cables and NPR anchor cables.

6. Discussion

The conventional support methods for narrow coal pillars between roadways include no support, reinforcement with conventional bolts, pressure-relief anchor cables, and cross-through anchor cables, all of which suffer from inadequate pressure support on the coal pillar. The combined use of negative Poisson’s ratio (NPR) constant-resistance large-deformation anchor cables and pressure-relief anchor cables offers the advantage of maintaining stable pressure-bearing conditions for the coal pillar throughout the mining process. This study conducts a comparative analysis of five different support methods: no support, conventional bolt reinforcement, pressure-relief anchor cables, NPR constant-resistance large-deformation anchor cables, and the combined use of NPR and pressure-relief anchor cables.

6.1. Comparison and Analysis of Stress Distribution in the 12 m Coal Pillar

The comparison of reinforcement schemes, including conventional bolt reinforcement, pressure-relief anchor cable, constant-resistance large-deformation anchor cable cross-passing reinforcement, and the alternating combination of pressure-relief and constant-resistance large-deformation anchor cables, is shown in Figure 15.

From the comparative stress analysis chart, it is evident that under the unsupported scenario, the coal pillar experiences consistently high stress throughout. In the standard anchor-reinforcement scheme, low-stress zones appear on both sides of the coal pillar’s exposed surfaces, with primary stress levels around 3–6 MPa at depths of 1–2 m, which then rapidly increase to peak stress (Figure 16). The use of pressure-release anchors and high-resistance large-deformation (NPR) anchors significantly improves the stress conditions on both sides of the pillar, transitioning the exposed surfaces from zero to confined stress, effectively stabilizing the coal pillar’s sides. In the pressure-release anchor cross-through scheme, primary stress reaches 14.5–18.0 MPa at a 1–2 m depth, while the high-resistance large-deformation anchor cross-through scheme shows stress levels of 17.5–24.5 MPa. The cross-through anchors significantly alter the stress distribution in the pillar, with the high-resistance large-deformation anchor showing superior performance compared to the pressure-release anchor. However, the alternating cross-through use of pressure-release and high-resistance large-deformation anchors achieves the best control over peak stress.

6.2. Comparison and Analysis of the Distribution of Plastic Zones in Surrounding Rock

The distribution of the surrounding rock plastic zone indicates that the stress state of the coal pillar changes under the five calculation schemes, leading to corresponding adjustments in the plastic zone. As shown in Figure 17, there is no significant change in the fracture location and depth of the rock beam. After reinforcement with the cross-through anchor scheme, the plastic zone of the 12 m coal pillar is significantly improved. Notably, the depth of the plastic zone near the coal pillar’s side surface and the open face is reduced by approximately 0.5 m. Furthermore, the most unfavorable shear and tensile-controlled plastic zone near the open face transforms into a shear plastic zone under the triaxial stress state, which contributes to the overall stability of the coal pillar.

6.3. Comparison of Strata Deformation

As shown in Figure 18, the deformation cloud map of the surrounding rock indicates significant changes in the horizontal deformation of the strata under various reinforcement schemes, including no support, conventional bolt reinforcement, cross-anchor reinforcement with pressure-relieving cables, and cross-anchor reinforcement with constant-resistance large-deformation cables. These changes are primarily manifested as follows:

(1)

Maximum deformation location: In the no-support scheme, the deformation of the coal pillar is very large, making it difficult to maintain stability. In the conventional anchor rod reinforcement scheme, the maximum horizontal deformation of the 12 m coal pillar occurs near the top of the roadway and 1.5 m downward. In the schemes using pressure-relief anchor cables and bidirectional large-deformation constant-resistance anchor cables, the maximum horizontal deformation occurs in the middle and lower parts of the coal pillar.

(2)

Maximum horizontal deformation: The maximum horizontal deformations (on one side) for the five schemes are 89.2 cm, 52.3 cm, 46.1 cm, and 38.5 cm, respectively. The bidirectional anchor cable reinforcement significantly reduces the horizontal deformation of the coal pillar under a three-dimensional stress state, thus improving its stability.

(3)

Anchor cable extension in bidirectional scheme: As shown in Figure 19, in the pressure-relief anchor cable scheme, the maximum horizontal deformation of the coal pillar is 46.1 cm, which does not exceed the pressure-relief limit of the anchor cable. In the bidirectional constant-resistance large-deformation anchor cable scheme, the maximum horizontal deformation reaches 38.5 cm, exceeding the extension limit of the constant-resistance anchor cable. Therefore, both pressure-relief and constant-resistance large-deformation anchor cables can be used together for reinforcement in the design.

Based on the above discussion, the negative Poisson’s ratio (NPR) constant-resistance large-deformation anchor cable and the yielding anchor cable are alternately used as the optimal reinforcement method for the 12 m coal pillar.

6.4. Field Monitoring

The field application involved reinforcing a 12 m narrow coal pillar using a cross-penetration system that integrates negative Poisson’s ratio (NPR) constant-resistance large-deformation anchor cables with yield-absorbing anchor cables. During the advancement of Panel 111, when the working face reached 30 m, a comprehensive monitoring program was implemented. This included the use of a borehole inspection system to examine fracture development within a 6 m deep borehole drilled into the coal pillar side of the return airway. The results of the borehole inspection, which are presented in Figure 20, provide critical insights into the fracture network characteristics and spatial distribution patterns within the reinforced coal pillar structure, offering valuable data for assessing the effectiveness of the reinforcement system.

The borehole inspection results revealed well-preserved borehole walls within the elastic zone of the coal pillar, demonstrating that mining-induced stresses and abutment pressure had not caused significant disturbance in this region. These findings provide compelling evidence for the technical reliability and practical applicability of the cross-penetration reinforcement system, which combines negative Poisson’s ratio (NPR) constant-resistance large-deformation anchor cables with yield-absorbing anchor cables for 12 m narrow coal pillar stabilization. The system’s effectiveness in maintaining the structural integrity of the coal pillar under complex stress conditions not only validates the theoretical foundation of this innovative approach but also establishes its practical value for engineering applications in similar mining environments, particularly in addressing stability challenges associated with narrow coal pillars.

7. Conclusions

This study introduces a significant advancement in narrow coal pillar reinforcement by implementing a novel approach in FLAC3D modeling. Unlike conventional through-type reinforcement methods previously reported [29,30,31], our methodology integrates two innovative technologies: the negative Poisson’s ratio (NPR) constant-resistance large-deformation anchor cable system for energy absorption and the yield-absorbing anchor cable technology. This integrated approach enables active control of theoretical and technical parameters, effectively preventing and mitigating potential disasters. The implementation of this system has demonstrated remarkable improvements, not only significantly enhancing coal recovery rates but also effectively addressing the longstanding challenge of narrow coal pillar stability. The successful application of this methodology provides valuable insights and serves as a reference for similar mining operations worldwide.

(1)

The feasibility of optimizing the coal pillar from 20 m to 12 m was exploited to enhance the pressure-relief performance of the through-going reinforcement zone coal pillar. After reinforcement, the two free surfaces of the reinforced coal body were compressed under a certain preload, which enhanced the bearing capacity of the coal body in the reinforcement area and significantly improved the mechanical properties of the reinforced coal body, thereby considerably enhancing the peak strength and residual strength of the narrow coal pillar between the roadways.

(2)

By employing Flac3D numerical simulation software, the situation of the coal pillar in the section under five distinct states was simulated. The characteristics of vertical stress, plastic zone distribution, and ground deformation were compared and analyzed through numerical simulation. It was ascertained that the 12 m coal pillar could be stably maintained for a prolonged period by adopting negative Poisson’s ratio (NPR) constant-resistance large-deformation anchor rods and pressure-relief anchor rods interlaced and drilled through.

(3)

The interlacing and intersection of the negative Poisson’s ratio (NPR) constant-resistance large-deformation anchor rope and the pressure-relief anchor rope through the coal pillar gave rise to a reduction in the peak stress value of the coal pillar from 68.5 MPa to 35.3 MPa. This conspicuously enhanced the peak strength and residual strength of the coal pillar, furnishing guidance for the optimization of the dynamic pressure coal pillar in Jinjitan Coal Mine.

(4)

The innovative cross-penetration reinforcement system utilizing negative Poisson’s ratio (NPR) constant-resistance large-deformation anchor cables combined with yield-absorbing anchor cables demonstrates significant advantages: it effectively constrains the instability deformation of narrow coal pillars and enhances their overall load-bearing capacity, particularly showing remarkable performance in high-stress environments. However, this advanced technique presents certain implementation challenges, primarily the requirement for simultaneous reinforcement installation during roadway excavation, which necessitates precise coordination between excavation and support operations.