Surrounding Rock Stability and Engineering Practice of the 52607 Working Face Approaching a Fault-Protected Coal Pillar

Surrounding Rock Stability and Engineering Practice of the 52607 Working Face Approaching a Fault-Protected Coal Pillar | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Surrounding Rock Stability and Engineering Practice of the 52607 Working Face Approaching a Fault-Protected Coal Pillar Zenghui Liu, Minjun CHEN, Feiyue Liu This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9489970/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 12 You are reading this latest preprint version Abstract To clarify the instability behavior of surrounding rock and its control effect when a heading face approaches a fault-protected coal pillar, a combined approach involving in-situ stress measurement, theoretical analysis, three-dimensional numerical simulation, and field monitoring was adopted to investigate the displacement response, plastic-zone evolution, and applicability of the existing support system under different fault distances. The results show that the in-situ stress field in the study area is a type-II stress field dominated by horizontal tectonic stress. The coupled effect of fault-induced structural weakening and stress concentration in the protective coal pillar significantly aggravates the deformation and plastic failure of the surrounding rock, and the surrounding rock stability is highly sensitive to the distance between the roadway wall and the fault. Under fault dip angles ranging from 54° to 70°, when the distance between the roadway wall and the fault varies from 5 to 40 m, the displacement and plastic-zone development of the surrounding rock exhibit obvious zonal characteristics. In particular, within 25 m from the fault, the fault influence on plastic-zone expansion and deformation increase is most significant; when the distance exceeds 25 m, the fault disturbance effect weakens markedly. Numerical simulation results further indicate that when the width of the protective coal pillar is less than 20 m, the plastic zone of the coal pillar expands significantly and its stability decreases markedly. Field monitoring results are generally consistent with the numerical simulation results, indicating that the existing bolt-cable support system can effectively control the deformation of surrounding rock in near-fault roadways. The results can provide a basis for stability analysis and support design of roadways in fault-protected coal pillar zones. Physical sciences/Energy science and technology Physical sciences/Engineering Earth and environmental sciences/Natural hazards Earth and environmental sciences/Solid earth sciences Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 1. Introduction With the continuous increase in mining depth and the growing complexity of geological structures, the stability of surrounding rock during roadway excavation has become an increasingly prominent issue. Kang [ 1 ] systematically reviewed the development of support technologies for deep and complex roadways in underground coal mines, and pointed out that high in-situ stress and complex structural conditions are the key factors restricting roadway stability control. Xie et al. [ 2 ] analyzed the instability and support response of surrounding rock in deep coal roadways from the perspective of surrounding-rock control mechanisms, and concluded that the evolution of the bearing structure of the surrounding rock plays a decisive role in roadway stability. Shi et al. [ 3 ] investigated support technologies for deep roadways based on engineering cases, further demonstrating the difficulty of surrounding-rock control under complex stress environments. These studies indicate that under deep high-stress and complex geological conditions, roadway surrounding rock often exhibits large deformation, strong asymmetric failure, and difficult support control. With respect to fault influence, Wang et al. [ 4 ] analyzed the instability mechanism and support technology of roadways in fault fracture zones through an engineering case study, and pointed out that the weakening effect of faults can significantly reduce the bearing capacity of surrounding rock. Zhang et al. [ 5 ] investigated the failure characteristics of surrounding rock near a fault under mining influence by means of physical model tests, revealing the significant effect of faults on surrounding-rock structure and stress transfer paths. Kang et al. [ 6 ] analyzed the stability of deep coal mine roadways crossing fault zones using numerical simulation, and demonstrated that the extent and mechanical parameters of the fault fracture zone play an important controlling role in surrounding-rock instability. Xie et al. [ 7 ] further studied the failure mechanism and hierarchical continuous support technology of roadways in unidirectional fault-affected zones, indicating that the plastic failure of surrounding rock and the support response under fault influence exhibit obvious zonal characteristics. These findings suggest that fault fracture zones are generally characterized by broken rock mass, developed fractures, weakened mechanical properties, and non-uniform stress distribution, which can easily lead to local failure of the surrounding-rock bearing structure and induce asymmetric deformation and local damage. Meanwhile, considerable attention has also been paid to the influence of coal pillars, especially residual coal pillars in close-distance coal seams, on roadway stability. Liu et al. [ 8 ] investigated the instability mechanism and control measures of a roadway under retained coal pillar conditions in close coal seams, and found that stress concentration and plastic failure of the surrounding rock are particularly significant in the strong influence zone of the coal pillar. Wang et al. [ 9 ] analyzed the layout and mechanism of a lower return airway under the influence of a residual coal pillar, and pointed out that the pillar width and the relative position between the roadway and the coal pillar are key factors affecting roadway stability. Wu et al. [ 10 ] revealed the evolution law of the stress field and damage in coal and rock masses in the residual pillar area after top-slice mining of a thick coal seam. Wang et al. [ 11 ] further studied the deformation and failure mechanism of the lower roadway in a close-range residual coal pillar area. Wang et al. [ 12 ] analyzed the stability control of goaf-driven roadways under interchange remaining coal pillar conditions in close-distance coal seams, showing that complex mining-induced stress can significantly intensify the asymmetric deformation of roadway surrounding rock. Xia et al. [ 13 ] investigated the stability of roadways with small coal pillars under repeated mining by numerical simulation, and revealed that mining disturbance promotes the expansion of the plastic zone in both the coal pillar and surrounding rock. These studies indicate that coal pillars can significantly alter the stress distribution, plastic-zone range, and deformation pattern of adjacent roadways, and their influence range and action law have become an important topic in the study of roadway surrounding-rock control. In recent years, with the increasing prominence of roadway engineering problems under complex mining and structural conditions, some scholars have further investigated the deformation and failure behavior of surrounding rock under dynamic pressure, repeated mining, and complex stress fields. Hao et al. [ 14 ] carried out research on surrounding-rock control technology for dynamic-pressure roadways in thick coal seams and pointed out that complex mining-induced loading can significantly increase the difficulty of roadway control. Wang et al. [ 15 ] studied the deformation and stress evolution of surrounding rock in pre-driven longwall recovery rooms at the end of mining, revealing the stage-dependent characteristics of surrounding-rock response under mining influence. Shang et al. [ 16 ] analyzed the instability characteristics and control technology of roadway surrounding rock under repeated mining in close-distance coal seams. Yan et al. [ 17 ] and Xiang et al. [ 18 ] investigated surrounding-rock control in complex conditions from the perspectives of support technology for large-section coal roadways and instability characteristics of bolt support in thick coal seams, respectively. Dong et al. [ 19 ] studied excavation-unloading effects using a similar simulation device for deep roadway excavation. Shi et al. [ 20 ] supplemented the research on surrounding-rock control under complex stress environments from the perspective of support simulation in deep mining. Xie et al. [ 21 ] investigated the deformation mechanism and control technology of surrounding rock in “three-soft” coal roadways under high horizontal stress. Yao et al. [ 22 ] analyzed the instability mechanism and surrounding-rock control technology of roadways subjected to short-distance dynamic loading. These studies provide important references for the stability analysis and support design of roadways under complex conditions. Overall, existing studies have mainly focused on roadways crossing fault fracture zones, roadways affected by residual coal pillars, roadways in close-distance coal seam mining, or roadways under dynamic pressure conditions, whereas relatively few studies have addressed the particular stage in which a heading face gradually approaches a fault-protected coal pillar. In particular, under the coupled action of fault-induced structural weakening and stress concentration in the protective coal pillar, the evolution of surrounding-rock stability with changes in the roadway–fault distance remains unclear. At the same time, under this specific condition, the control effect and engineering applicability of the existing bolt-cable support scheme still require further evaluation. Therefore, taking the 52607 working face of Chengjiagou Coal Mine as the engineering background, this study investigates the deformation and failure behavior of surrounding rock during the process in which the heading face approaches a fault-protected coal pillar. In-situ stress measurement, theoretical analysis, three-dimensional numerical simulation, and field monitoring were combined to systematically analyze the displacement response, plastic-zone development, and deformation characteristics of the surrounding rock under different roadway–fault distances. The main influence range of the fault was further identified, and the control effect and applicability of the existing bolt-cable support system were evaluated. The results provide a reference for surrounding-rock stability analysis and support design in fault-protected coal pillar zones under similar engineering conditions. 2. Project Overview 2.1 Engineering Background Chengjiagou Coal Mine is located in Yangfangkou Town, Ningwu County, Xinzhou City, Shanxi Province, China, and is a medium-sized mine affiliated with Xuangang Coal and Electricity Co., Ltd. Working face 52607 is located in the southern part of the mine field. The ground elevation in the panel area ranges from 1311 to 1478 m, while the floor elevation of No. 5 coal seam ranges from 1080 to 1300 m, corresponding to a burial depth of 178–230 m. The working face has a strike length of approximately 1800 m and a dip width of about 1000 m, with a designed service life of approximately 8 months. In terms of spatial relationship, it is 309 m away from the western boundary of the mine field, 30 m away from the return airway of working face 52606 on the south side, 180 m away from working face 52609 on the east side, and 201 m away from Panel 512 on the north side. Working face 52607 mainly extracts the No. 5 coal seam, which has an average thickness of 13.93 m and relatively stable occurrence conditions. The immediate roof is a 10.3 m thick fine sandstone interbedded with marl and thin coal seams; the main roof is massive and dense mudstone with poorly developed joints; the immediate floor is mudstone interbedded with No. 6 coal seam and is relatively stable; and the lower floor is medium- to coarse-grained sandstone with a thickness of 2.18–8.04 m and an average thickness of about 4.0 m, representing a hard and stable floor. The comprehensive stratigraphic column near the No. 5 coal seam is shown in Fig. 1 . 2.2 Fault Characteristics Working face 52607 is mainly affected by the TF-3 fault. The TF-3 fault is located on the northwestern side of the mine field. It starts from Houhegou and extends eastward approximately along the W–E direction, continuing through Yaozigou. Near the valley area of Chengjiagou Coal Mine, the fault strike turns to the northeast and finally disappears into the Huihe River, with a total length of about 3.8 km. The fault is clearly exposed at the surface and has been confirmed by surface stratum correlation as well as drilling data from boreholes Gou-8, Gou-10, and No. 202. Figure 2 shows the relative position of working face 52607 and the fault.The TF-3 fault is a normal fault dipping to the southeast, with a dip angle ranging from 54° to 70°. The throw is about 35–38 m in the western segment and approximately 75 m in the central segment, showing an overall downthrown southern block. Controlled by this fault, the 52607 return airway is located in the hanging wall of the TF-3 fault. As the roadway advances continuously, its driving direction gradually approaches the fault strike, resulting in an increasingly enhanced weakening effect of the fault structure on the surrounding rock. This constitutes the key geological background for the progressively intensified surrounding-rock stability problems during the excavation of working face 52607. 3. Theoretical Analysis of In-Situ Stress, Roof Deformation, and Plastic Zone in the Fault-Protected Coal Pillar Zone 3.1 In-Situ Stress Measurement and Analysis of Stress Field Characteristics To determine the in-situ stress state of the study area, Chengjiagou Coal Mine adopted an in-situ stress testing method based on the acoustic emission Kaiser effect to back-calculate the three-dimensional principal stresses. First, the original rock samples collected in the field were directionally prepared along six orientations, as shown in Fig. 3 a. According to the azimuth and dip information marked on the top of the rock sample, the sample was restored to its original in-situ orientation. A nearly horizontal plane was selected, and the true north direction, denoted as N, was determined. Taking N as the X-direction, a three-dimensional coordinate system composed of the X, Y, and Z axes was established. In the XOY, XOZ, and YOZ planes, directions making an angle of 45° with the two coordinate axes were then determined, respectively. On this basis, cylindrical specimens were drilled along the six predetermined directions, with a specimen size of 25 mm × 50 mm. In this test, one measuring point was selected, and three core specimens were prepared in each of the six directions, yielding a total of 18 specimens for subsequent acoustic emission Kaiser effect testing and principal stress calculation. The rock cores used in the experiment are shown in Fig. 3 b. The loading process in this experiment was carried out using a rock mechanics testing machine, as shown in Fig. 5 – 6 . The acoustic emission signals were collected using an acoustic emission testing system manufactured by PAC (Physical Acoustics Corporation, USA), as shown in Fig. 3 c. All acoustic emission signals generated during the entire deformation process of the specimen under loading were recorded. After specimen preparation, the 18 specimens obtained from the six directions at the same measuring point were subjected to acoustic emission Kaiser effect tests. One representative result from each direction was selected as the final test result for that direction, and all tests were conducted under uniaxial loading conditions. The calculated in-situ stresses and the orientation of the maximum horizontal principal stress at the measuring point located at the end of the track roadway in Panel 526 are listed in Table 1 . Table 1 Calculated in-situ stress results at the measuring point Measuring point Burial depth/m σ V /MPa σ H /MPa σ h /MPa Orientation of maximum horizontal principal stress 52607 190 4.50 4.63 3.13 E43.2°S The in-situ stress test results at the measuring point at the end of the track roadway in Panel 52607 of Chengjiagou Coal Mine show that the maximum horizontal principal stress is 4.63 MPa, the minimum horizontal principal stress is 3.13 MPa, and the vertical stress is 4.50 MPa. According to the magnitude relationship among the three principal stresses, the in-situ stress field can be classified into three types: Type I,σ H >σ h >σ V ;Type II, σ H >σ V >σ h ;and Type III,σ V >σ H >σ h .Since the measured stress relationship at this point is σ H >σ V >σ h ,the stress field belongs to Type II, indicating that tectonic stress is greater than gravitational stress. 3.2 Roof Displacement Analysis of a Near-Fault Roadway To further reveal the influence of the fault on the stability of surrounding rock in a near-fault roadway, a theoretical analysis of the loading and displacement characteristics of the roadway roof was carried out based on the in-situ stress measurement results. According to the loading characteristics of the roof in a near-fault roadway, the roof can be simplified as a cantilever beam subjected to the load of the overlying strata, and the corresponding mechanical analysis model is shown in Fig. 4 . Assuming that the normal force acting on the fault is Fn,its vertical component can be regarded as an important component in the analysis of roof loading. On this basis, the stress components at different points of the roof and the deflection equation can be derived according to elasticity theory. The influence of the fault on roadway roof deformation can then be analyzed through the deflection equation. Theoretical analysis indicates that, as the distance between the roadway and the fault increases, the effective length of the roof cantilever beam decreases, the beam stiffness is correspondingly enhanced, and the roof deflection gradually decreases. The maximum roof deflection occurs at the free end of the cantilever beam, i.e., at x = 0 and y = 0. The maximum deflection v satisfies a functional relationship with the shortest horizontal distance m between the roadway and the fault plane: $$v(x,0)=\frac{{{a^3}\gamma hb\sin \theta }}{{3\cos \frac{\theta }{2}E\operatorname{Im} }}=\frac{{4{a^3}b\gamma h{{\cos }^3}\theta }}{{{m^4}E{{\sin }^2}\theta \cos \frac{\theta }{2}}}$$ 1 Where: a——roadway step height; b——roadway width; γ——unit weight of the roof rock; h——vertical component of the shortest distance from the left bottom corner of the floor to the fault; E——elastic modulus; m——distance between the roadway wall and the fault, i.e., the width of the protective coal pillar. According to the actual engineering conditions of Chengjiagou Coal Mine, the dip angle of the TF-3 fault was taken as approximately 65°, the unit weight of the roof rock was taken as 13kN/m3, the roadway section size was4.2m×2.8m, and the elastic modulus E of the No. 5 coal seam was taken as 2.85 GPa. The parameter h represents the vertical component of the shortest distance from the left bottom corner of the floor to the nearest point on the fault, and its expression can be further determined from the mechanical relationship of the near-fault roadway. According to the mechanical model shown in Fig. 5 , it can be obtained that: $$\tan \theta =\tan 65^\circ =h/m$$ 2 The shortest horizontal distance between the roadway and the fault plane was taken as m = 25, 20, 15, and 10 m, respectively. Substituting these values into the calculation formula gives the corresponding maximum roof deflections as v 10 = 0.32 m. Similarly, by substituting m = 15, 20, and 25 m into the equation, the results are obtained as v 15 = 0.21 m, v 20 = 0.15m, and v 25 = 0.13m. The calculation results indicate that when the width of the protective coal pillar is 10, 15, 20, and 25 m, the maximum roof deflection is approximately 32, 21, 15, and 13 cm, respectively. Overall, as the shortest horizontal distance between the roadway and the fault increases, the maximum roof deflection decreases significantly, indicating that the controlling effect of the fault on roof deformation gradually weakens with increasing distance. When the width of the protective coal pillar reaches 20 m or more, the reduction in roof deflection becomes noticeably less pronounced, suggesting that the influence of the fault on roof deformation begins to weaken beyond this threshold. These results show that, in the near-fault zone, the roadway roof is strongly disturbed by the fault and exhibits more pronounced bending deformation. As the roadway gradually moves away from the fault, the roof loading condition becomes alleviated, the deflection decreases, and the stability of the surrounding rock correspondingly improves. From the perspective of roof structural response, this analysis demonstrates the sensitivity of roadway surrounding-rock stability to the distance from the fault, and also provides a theoretical basis for the subsequent analysis of plastic-zone development in the near-fault coal pillar. 3.3 Plastic Zone Analysis of the Near-Fault Coal Pillar Based on Limit Equilibrium Theory To investigate the development law of the plastic zone in the surrounding rock on the fault-proximal side of the coal pillar, this study carried out a theoretical analysis of the width of the plastic zone in the near-fault coal pillar based on the existing elastoplastic limit equilibrium theory in rock mechanics, combined with the Mohr–Coulomb strength criterion. Considering the stress characteristics of the roadway surrounding rock under the combined influence of the fault and the coal pillar, the normal force acting on the fault plane was assumed to be Fn. Meanwhile, the shear stress on the fault plane was assumed to be linearly distributed along the fault plane. Accordingly, the expression for calculating the width of the plastic zone on the fault-proximal side of the roadway within the coal pillar can be obtained as follows: $${x_m}= - \frac{{\lambda a}}{{2\tan {\varphi _0}}}\ln (\frac{{\frac{{{C_0}}}{{\tan {\varphi _0}}}+\frac{{{P_x}}}{a}}}{{\frac{{{C_0}}}{{\tan {\varphi _0}}}+{\sigma _v}+\frac{{{\sigma _v}\cos \theta }}{{2\lambda c\cos \frac{\theta }{2}}}}})$$ 3 Where: a——roadway step heigh; λ——lateral pressure coefficient; C 0 ——cohesion of the coal seam; Φ 0 ——internal friction angle of the coal seam; c——distance between the roadway wall and the fault, i.e., the width of the protective coal pillar; P x ——lateral confinement acting on the coal wall; θ ——angle between the fault plane and the vertical direction. Considering that the fault dip angle ranges from 54° to 70°, θ was taken as 20°, 25°, 30°, and 35°; σ v ——vertical stress; The final calculation results are shown in Fig. 6 According to Eq. ( 2 ) and Fig. 6 , the plastic-zone range of the surrounding rock on the fault-proximal side of the roadway is jointly controlled by factors such as the roadway step height, the in-situ stress, the distance between the roadway wall and the protective coal pillar width, and the fault dip angle. When the other parameters remain constant, the plastic-zone range gradually decreases and tends to stabilize with increasing protective coal pillar width. In contrast, as the fault dip angle increases, the plastic-zone range shows an overall slow increasing trend, although the variation is relatively small, indicating that the fault dip angle has a certain influence on plastic-zone development but is not the dominant controlling factor. Combined with the actual engineering conditions of Chengjiagou Coal Mine and the theoretical calculation results, it can be concluded that within 25 m from the fault, the protective coal pillar has a significant effect on plastic-zone development; when the distance exceeds 25 m, this effect weakens markedly and the variation in the plastic zone becomes gradual. 4. Numerical Simulation Analysis of Surrounding Rock Stability in the Fault-Protected Coal Pillar Zone 4.1 Establishment of the Numerical Calculation Model During roadway excavation, excavation-induced disturbance breaks the original equilibrium state of the in-situ stress field, resulting in stress redistribution in the surrounding rock and obvious local stress concentration. Under the complex stress environment near a fault, such stress redistribution is an important factor inducing surrounding-rock deformation and failure. Therefore, it is necessary to systematically analyze the displacement response and plastic-zone evolution of the surrounding rock during roadway excavation by means of numerical simulation. In this study, a three-dimensional numerical model was established using FLAC3D, and the Mohr–Coulomb yield criterion was adopted to determine rock mass failure, without considering the plastic flow effect. During model construction, a three-dimensional geometric model was first established, and an equivalent load was applied to the top of the model to represent the effect of the overlying strata that were not explicitly modeled. After the initial stress equilibrium was reached, step-by-step excavation of the 52607 return airway was carried out, while the installation of the support structure was simulated simultaneously. The calculation results were extracted after the model reached equilibrium again. Figure 7 a shows the established numerical model, and Fig. 7 b shows the relative position of the roadway and the fault. According to the engineering geological conditions of working face 52607, the model dimensions were set to 300 m × 105 m × 750 m. The roadway cross-section was 4.2 m × 2.8 m, the fault zone width was 7 m, and the fault dip angle was 65°. To improve the calculation accuracy in the key study area, the mesh around the roadway was refined to 0.5 m × 0.5 m, while a coarser rectangular mesh was used in the other regions. Both bolts and cables were simulated using built-in cable elements, and the support structure adopted in Chengjiagou Coal Mine is shown in Fig. 7 c. The boundary conditions were set as follows: horizontal displacement was constrained on the lateral boundaries, displacement in all three directions was constrained at the bottom boundary, and an equivalent stress of the overlying strata was applied at the top boundary. To simulate the actual excavation process, the roadway was excavated in increments of 10 m, and the calculation was continued to convergence after each excavation step. Based on the above model and parameter settings, typical working conditions in which the fault-side wall of the return airway was located 10, 20, 30, and 40 m from the fault plane were selected for numerical simulation. The displacement variation law and plastic-zone development characteristics of the surrounding rock under different fault-distance conditions were analyzed, and the displacement responses under different fault dip angles were further examined to reveal the asymmetric deformation mechanism of the surrounding rock in near-fault roadways, thereby providing a reference for the stability analysis of surrounding rock under similar conditions. Table 2 Rock mechanical parameters for numerical simulation. Rock Layer Thickness/m Density/(kg/m 3 ) Cohesion/MPa Internal friction angle /° Tensile strength/MPa Poisson’s ratio Elastic modulus/GPa Compressive strength /MPa Mudstone 10 2690 6.5 40 1.5 0.39 3.2 16.3 Fine sandstone 10.3 2420 18.4 37.31 7.7 0.24 3.1 107.8 No. 5 coal seam 13.93 1350 4.0 50 1.6 0.38 0.76 5.6 Mudstone 1.67 2690 6.5 40 1.5 0.37 3.1 15.3 No. 6 coal seam 1.35 1350 4.2 47 1.7 0.35 0.76 5.8 Mudstone 8 2690 6.5 40 1.5 0.39 3.2 16.1 Medium- to coarse-grained sandstone 4 2400 6.05 44.7 2.5 0.20 4.2 62.4 4.2 Displacement Variation of Surrounding Rock under Different Protective Coal Pillar Widths To analyze the influence of fault distance variation on the deformation characteristics of roadway surrounding rock, typical cases with distances of 10, 20, 30, and 40 m between the fault-side wall of the return airway and the fault plane were selected for FLAC3D numerical simulation. Based on the simulation results for each case, the displacement contours of the surrounding rock were extracted, and the variation laws of roof subsidence, rib convergence, and floor displacement were comparatively analyzed, so as to reveal the evolution characteristics of surrounding-rock deformation under near-fault conditions. Figure 8 presents the displacement contours under different protective coal pillar widths.The numerical simulation results show that, under different working conditions, the displacement of the surrounding rock is mainly concentrated around the roadway profile. Different degrees of deformation occur in the roof, ribs, and floor, among which roof subsidence and rib convergence are more pronounced, and the overall deformation exhibits a certain degree of asymmetry. As the distance between the roadway and the fault increases, the overall displacement level of the surrounding rock gradually decreases, and the range of displacement concentration correspondingly shrinks, indicating that the fault has a significant controlling effect on roadway deformation, which is more pronounced in the near-fault zone. On this basis, the roof subsidence and floor displacement under each simulation case were further extracted, and the displacements of the fault-proximal rib and the coal-seam-side rib were comparatively analyzed, as shown in Fig. 9 . The results indicate that, as the distance between the roadway and the fault increases, the roof subsidence, floor displacement, and rib displacements all show an overall decreasing trend, suggesting that the fault proximity effect significantly intensifies the deformation of roadway surrounding rock. In terms of deformation characteristics in different parts of the roadway, the roof and ribs are more sensitive to changes in fault distance. In particular, the displacement of the fault-proximal rib is generally greater than that of the coal-seam-side rib, indicating that the surrounding rock on the fault side is more strongly disturbed and exhibits more obvious asymmetric deformation. By contrast, although the floor displacement also varies with fault distance, its overall variation amplitude is relatively small. Comprehensive analysis of the simulation results shows that, as the roadway gradually approaches the fault, surrounding-rock deformation becomes significantly aggravated; whereas when the roadway moves away from the fault, the displacement gradually decreases and tends to stabilize. This indicates that the fault distance is an important controlling factor governing the deformation characteristics of surrounding rock in near-fault roadways. 4.3 Evolution of the Plastic Zone under Different Fault-Distance Conditions The development characteristics of the coal pillar plastic zone under different fault-distance conditions show that, as the roadway gradually approaches the fault, the plastic zones on both sides of the coal pillar expand progressively, and the plastic zone on the fault-proximal side develops more significantly,Fig. 10 shows the plastic-zone contours under different protective coal pillar widths.. When the coal pillar width is 40 m and 30 m, respectively, although the coal pillar is already affected by the fault, the overall plastic-zone range remains relatively small. In this case, the maximum development depths of the plastic zone on the coal-seam side are 1.1 m and 1.2 m, respectively, while those on the fault-proximal side are 1.4 m and 1.5 m, respectively. Because a relatively wide elastic core is still preserved inside the coal pillar, the overall deformation of the coal pillar is small, the surrounding rock remains relatively stable, and the coal pillar as a whole is in a stable state. When the coal pillar width decreases to 20 m, the plastic zones on both sides of the coal pillar expand further. The maximum development depth of the plastic zone on the coal-seam side increases to 1.7 m, while that on the fault-proximal side increases to 2.5 m. At this stage, the elastic core inside the coal pillar is obviously reduced, and the bearing capacity of the surrounding rock declines to some extent; however, the coal pillar as a whole can still remain basically stable. When the coal pillar width is further reduced to 10 m, the plastic-zone range of the coal pillar expands significantly. The maximum development range of the plastic zone on the fault-proximal side increases to about 3.0 m, while that on the coal-seam side is about 2.5 m. The plastic zones on both sides of the coal pillar then occupy a relatively large range, and the elastic core is further reduced, indicating that the bearing structure of the coal pillar is significantly weakened, accompanied by a certain degree of deformation and a marked reduction in stability. Comprehensive analysis indicates that, with decreasing coal pillar width, the plastic zones on both sides of the coal pillar continue to expand, and the plastic zone on the fault-proximal side is always larger than that on the coal-seam side, indicating that the weakening effect of the fault on coal pillar stability is clearly asymmetric. When the coal pillar width is relatively large, the interior of the coal pillar still retains strong bearing capacity. However, when the coal pillar width decreases to a certain extent, the plastic zone expands rapidly, the elastic core is significantly reduced, and the stability of the coal pillar correspondingly declines. These numerical simulation results are basically consistent with the previous theoretical analysis, further verifying that the plastic zone of the coal pillar in the near-fault area exhibits obvious asymmetric expansion. 4.4 Displacement Response of Surrounding Rock under Different Fault Dip Angles To investigate the influence of fault dip-angle variation on the deformation characteristics of roadway surrounding rock, FLAC3D numerical simulations were conducted for four typical cases with fault dip angles of 55°, 60°, 65°, and 70°, while keeping the other parameters unchanged and adopting the optimal protective coal pillar width of 20 m. The displacement distributions of the surrounding rock under each case were comparatively analyzed, and the four displacement contour plots under different dip-angle conditions are presented in Fig. 11 . The numerical simulation results indicate that, under different fault dip angles, the displacement of the surrounding rock is still mainly concentrated around the roadway profile, with roof subsidence and rib convergence being relatively pronounced, and the overall deformation exhibiting a certain degree of asymmetry. As the fault dip angle increases from 55° to 70°, the roof displacement decreases from 11.5 cm to 9.0 cm, the displacement of the fault-proximal rib decreases from 10.4 cm to 9.4 cm, and the displacement of the coal-seam-side rib decreases from 7.4 cm to 6.1 cm. Overall, the displacements of all parts of the roadway surrounding rock show a decreasing trend with increasing fault dip angle. From the displacement characteristics of different parts of the roadway, the roof displacement shows the most obvious variation, decreasing from 11.5 cm at 55° to 9.0 cm at 70°, corresponding to a reduction of 21.7%. The displacement of the fault-proximal rib decreases from 10.4 cm to 9.4 cm, corresponding to a reduction of 9.6%, while that of the coal-seam-side rib decreases from 7.4 cm to 6.1 cm, corresponding to a reduction of 17.6%. These results indicate that the roof and the surrounding rock on the fault-proximal side are relatively sensitive to changes in fault dip angle. However, the displacement of the fault-proximal rib remains greater than that of the coal-seam-side rib under all cases, suggesting that the surrounding rock on the fault side is more strongly affected by structural disturbance, and the overall deformation of the roadway still exhibits obvious asymmetric characteristics. Comprehensive analysis shows that variations in fault dip angle have a certain influence on the displacement distribution of surrounding rock in near-fault roadways, but the overall differences under different dip-angle conditions are limited, indicating that fault dip angle is not the dominant factor controlling surrounding-rock deformation. Compared with the simulation results under different fault-distance conditions discussed above, the influence of fault distance on surrounding-rock displacement is more significant. Therefore, in the stability analysis of roadways in fault-protected coal pillar zones, the relative distance between the roadway and the fault should be considered as the primary controlling factor, while the fault dip angle may be treated as a secondary influencing factor. 5. Analysis of Surrounding Rock Control Measures and Evaluation of Engineering Practice Effect 5.1 Support Parameters and Support Form of the Test Section To carry out field verification of the surrounding-rock control effect in the fault-protected coal pillar zone, the section located 50–70 m ahead of measuring point Y12 was selected as the test section. The test section adopted a combined bolt-cable support system. For roof support, Φ20 mm × 2500 mm left-handed rebar bolts without longitudinal ribs were used, together with Z2360 and K2335 resin cartridges for extended anchorage. The bearing plate size was 110 mm × 110 mm × 10 mm, and the bolt spacing was 1000 mm × 1000 mm. The roof cables were Φ17.8 mm × 7300 mm steel strands, anchored with two Z2360 resin cartridges and two K2335 resin cartridges for extended anchorage. The cable plate size was 300 mm × 300 mm × 15 mm, and the cable spacing was 1450 mm × 2000 mm. A W-shaped steel strip with dimensions of 4180 mm × 220 mm × 2.75 mm was installed on the roof, and No. 10 diamond-shaped metal mesh was used for surface support; in roof-fall sections, one additional layer of square mesh and one layer of No. 10 diamond-shaped metal mesh were installed. For rib support, Φ20 mm × 2500 mm left-handed rebar bolts without longitudinal ribs were used. The anchorage method and plate specifications were the same as those of the roof bolts, and the bolt spacing was 1000 mm × 1000 mm. A W-shaped steel strip with dimensions of 400 mm × 220 mm × 2.75 mm was installed on the ribs. When the ribs encountered broken surrounding rock, fault zones, or weak zones, additional W-shaped steel strips were installed for reinforced support. No. 10 diamond-shaped metal mesh was also used for rib support. In roof-fall sections, square mesh and diamond-shaped metal mesh were additionally installed and fixed with tie wires in a “three twists and one fastening” pattern. The material consumption per meter for the support system of the working face is listed in Table 3 . In this way, a support system dominated by bolts and cables, and coordinated with W-shaped steel strips and metal mesh, was formed, providing the support basis for subsequent monitoring of surrounding-rock deformation and field evaluation of the support effect. Table 3 Support material consumption per meter in working face 52607. Material Specification Unit Quantity Remarks Rebar bolt Φ20×2500㎜left-handed rebar set 11 Resin cartridge K2335 cartridge 17 Resin cartridge Z2360 cartridge 17 Steel strand φ17.8×7300㎜ piece 3 Row spacing: 2 m Prestressed bolt plate 110×110×10㎜ piece 11 Prestressed cable plate 300×300×15㎜ piece 3 W-shaped steel strip 4180×220×2.75mm piece 1 5.2. Field Monitoring Scheme and Monitoring Point Layout Combined with the previous theoretical analysis and numerical simulation results, it can be concluded that under fault influence, a reduction in the width of the protective coal pillar will significantly aggravate surrounding-rock deformation and the expansion of the plastic zone. Comprehensive analysis indicates that the width of the protective coal pillar should not be less than 20 m. To further verify the control effect of the existing support conditions on the roadway surrounding rock, field monitoring of surrounding-rock deformation was carried out during roadway reinforcement construction in Chengjiagou Coal Mine. Figure 12 a shows a field photograph of the monitoring layout. The field monitoring adopted the cross-measurement method. One surrounding-rock monitoring station was arranged every 10 m along the roadway strike, and each group contained three monitoring points. The monitoring points were arranged within 2 m of the roof separation indicator. When an additional roof separation indicator was installed in special sections, a surrounding-rock monitoring station was added simultaneously to ensure correspondence between surrounding-rock deformation monitoring and roof separation monitoring. Two measuring stations were arranged in each monitoring group, and the spacing between the two stations did not exceed the support distance of two rows of bolts. The deformation of the surrounding rock was dynamically monitored by measuring the change in horizontal distance between the left and right ribs and the change in vertical distance between the roof and floor. The layout of the monitoring points and the measurement directions are shown in Fig. 12 b. Specifically, rib convergence was characterized by the reduction in horizontal spacing between the monitoring points on the two ribs, i.e., by the change in horizontal distance between points C and D. Roof subsidence was characterized by the reduction in vertical spacing between the roof monitoring point and the floor reference point. For convenience of analysis, all monitoring results were expressed in terms of convergence and subsidence, rather than total displacement. With the above monitoring arrangement, key deformation indices of the roadway surrounding rock, such as roof subsidence and rib convergence during excavation and support, could be continuously monitored, thus providing a field basis for the subsequent analysis of surrounding-rock deformation behavior and the evaluation of the control effect of the existing support scheme. 5.3. Comparative Analysis of Field Monitoring Results and Numerical Simulation Data According to the measured results, the maximum rib convergence at Cross-section 1 was 16.1 cm, including 9.3 cm on the fault-proximal side and 6.8 cm on the coal-seam side, while the maximum roof subsidence was 8.2 cm. At Cross-section 2, the maximum rib convergence was 14.7 cm, including 8.7 cm on the fault-proximal side and 6.0 cm on the coal-seam side, and the maximum roof subsidence was 9.0 cm. At Cross-section 3, the maximum rib convergence was 15.8 cm, including 8.9 cm on the fault-proximal side and 6.9 cm on the coal-seam side, while the maximum roof subsidence was 9.5 cm. Comprehensive analysis indicates that the overall surrounding-rock deformation at all monitored cross-sections was relatively small, and the roadway as a whole remained in a stable state. Meanwhile, the displacement on the fault-proximal side was consistently greater than that on the coal-seam side, indicating that the fault exerted a certain asymmetric influence on roadway surrounding-rock deformation, which is basically consistent with the previous theoretical analysis and numerical simulation results. Cross-section 1 was taken as an example to illustrate the variations of the roof, floor, and two ribs, as shown in Fig. 13 .\ Table 4 was prepared based on a comparison between the field monitoring results and the numerical simulation results. Cross-Section Max Convergence of Ribs (cm) Max. fault-proximal side (cm) Max. coal-seam side(cm) Roof subsidence (cm) Cross-section 1 16.1 9.3 6.8 8.2 Cross-section 2 14.7 8.7 6.0 9.0 Cross-section 3 15.8 8.9 6.9 9.5 Numerical simulation (Scheme d) 13.5 7.5 6 7.1 Table 4 . Statistical comparison of field monitoring results and numerical simulation results. A comparison between the field monitoring results and the numerical simulation results can be used to verify the rationality of the established model. As shown in Table 4 , the maximum roof subsidence at the three monitored cross-sections was 8.2 cm, 9.0 cm, and 9.5 cm, respectively, while the maximum rib convergence was 16.1 cm, 14.7 cm, and 15.8 cm, respectively, indicating that the overall deformation of the surrounding rock in the test section was relatively small. In comparison, the numerical simulation results for Scheme d show that the maximum roof subsidence was 7.1 cm, and the maximum displacements on the fault-proximal side and the coal-seam side were 7.5 cm and 6.0 cm, respectively, corresponding to a maximum rib convergence of 13.5 cm. Overall, the numerical simulation results are generally consistent with the field monitoring results in both magnitude and variation trend, both indicating that the roof subsidence and rib convergence remained relatively small and that the deformation on the fault-proximal side was greater than that on the coal-seam side. This suggests that the established numerical model can reasonably reflect the actual deformation characteristics of the surrounding rock in the near-fault roadway. It should be noted that some differences still exist between the numerical simulation results and the field monitoring data. On the one hand, field monitoring was strongly affected by the construction process and site conditions, and the monitoring data therefore exhibit obvious stage-dependent characteristics. In addition, only three typical cross-sections were selected for analysis in this study, which imposes certain limitations on the representativeness of the monitoring results. On the other hand, the numerical simulation results reflect the overall response of the roadway after excavation and support installation under idealized conditions when a new equilibrium state is reached, whereas the actual field deformation is also affected by multiple factors, such as the contact condition between the support structure and the surrounding rock, the arrangement of monitoring points, reading conditions, and construction disturbance. Furthermore, necessary simplifications were made in the numerical modeling with respect to rock-mass homogeneity, constitutive relations, boundary conditions, and the construction process, which may also lead to some deviation between the simulated results and the field measurements. Nevertheless, the field monitoring results and the numerical simulation results are consistent in terms of the overall trend, both showing that, under the existing bolt-cable support conditions, the overall deformation of the roadway surrounding rock remains relatively small and the support system has a good controlling effect on the surrounding rock in the fault-protected coal pillar zone. This result indicates that the numerical model established in the previous sections has good applicability, and also verifies the effectiveness of the existing support scheme under the present engineering conditions. 6. Discussion The deformation characteristics observed in this study reflect the combined influence of tectonic stress concentration and structural weakening caused by the TF-3 fault. Near the fault-protected coal pillar, the surrounding rock is more prone to asymmetric deformation because the fault changes the stress transfer path and weakens the bearing capacity of the rock mass on the fault-proximal side. This indicates that roadway stability control in such areas should not only focus on support strength, but also consider the spatial relationship between the roadway, fault plane, and protective coal pillar during roadway layout and excavation design. Although the numerical simulation and field monitoring results show similar deformation trends, the findings should be interpreted within the specific engineering context of the 52607 working face. The numerical model simplifies rock-mass heterogeneity, boundary conditions, and excavation-support processes, while the field monitoring was limited in spatial coverage and monitoring duration. Therefore, the proposed understanding of near-fault roadway stability should be further verified under different burial depths, fault properties, stress states, and mining layouts before broader application. 7. Conclusions This study took the 52607 return airway of Chengjiagou Coal Mine as the engineering background and employed in-situ stress measurement, theoretical analysis, numerical simulation, and field monitoring to investigate the surrounding-rock stability and support performance as the heading face approached a fault-protected coal pillar. The main conclusions are as follows: (1) The in-situ stress field in the study area is characterized by relatively strong horizontal tectonic stress. At the measuring point at the end of the track roadway in Panel 526, the maximum horizontal principal stress, vertical stress, and minimum horizontal principal stress were 4.63 MPa, 4.50 MPa, and 3.13 MPa, respectively, showing a stress relationship of σH > σV > σh, which corresponds to a Type-II stress field. This stress condition suggests that horizontal tectonic stress may play an important role in roadway deformation in the study area. (2) Under the geological and mining conditions considered in this study, the relative distance between the roadway and the fault is one of the key factors influencing surrounding-rock deformation and plastic-zone development. Theoretical analysis and numerical simulation results indicate that, as the roadway approaches the fault, roof deflection, rib convergence, and the plastic zone of the coal pillar tend to increase, with more pronounced deformation on the fault-proximal side. When the protective coal pillar width is reduced to less than 20 m, the plastic zone expands more obviously and the pillar stability decreases. Therefore, for the 52607 working face, a protective coal pillar width of not less than 20 m is suggested. (3) The field monitoring results are generally consistent with the numerical simulation results in terms of deformation magnitude and trend, supporting the applicability of the established numerical model to this case. The maximum rib convergence values at the three typical cross-sections were 16.1 cm, 14.7 cm, and 15.8 cm, while the maximum roof subsidence values were 8.2 cm, 9.0 cm, and 9.5 cm, respectively. Under the monitored conditions, the overall roadway deformation remained within a controllable range, and the existing bolt-cable support system showed a satisfactory control effect. However, deformation on the fault-proximal side was greater than that on the coal-seam side, indicating that the fault had an asymmetric influence on roadway deformation. Declarations Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Funding Coal-Major Project (2025ZD1700904) Author Contribution LIU Zenghui: investigation, data curation,validation,writing—original draft. CHEN Minjun: investigation, validation, writing—review and editing.LIU Feiyue:experiment data curation,validation Data Availability The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author. The raw data supporting the conclusions of this article will be made available by the corresponding author on request. References KANG, H. 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Failure Characteristics and Stability Control of Bolt Support in Thick-Coal-Seam Roadway of Three Typical Coal Mines in China. Shock and Vibration 2021, 5589085. (2021). https://doi.org/10.1155/2021/5589085 DONG, C. L. et al. Similar simulation device for unloading effect of deep roadway excavation and its application. J. Mt. Sci. 15 , 1115–1128. https://doi.org/10.1007/s11629-017-4784-2 (2018). SHI, J. & FENG, J. Simulate on Support Technology of Deep Mining. Geotechnical and Geological Engineering 2021, 39, 4663–4668. https://doi.org/10.1007/s10706-021-01746-7 XIE, X. et al. Deformation Mechanism and Control Technology of Surrounding Rock of Three-Soft Coal Roadways under High Horizontal Stress. Energies 16 , 728. https://doi.org/10.3390/en16020728 (2023). YAO, W., LIU, G., PANG, J. & HUANG, X. Instability Mechanism and Surrounding Rock Control Technology of Roadway Subjected to Mining Dynamic Loading with Short Distance: A Case Study of the Gubei Coal Mine in China. Geotech. Geol. Eng. 41 , 1407–1427. https://doi.org/10.1007/s10706-022-02343-y (2023). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 06 May, 2026 Reviews received at journal 06 May, 2026 Reviewers agreed at journal 05 May, 2026 Reviews received at journal 02 May, 2026 Reviewers agreed at journal 30 Apr, 2026 Reviewers agreed at journal 30 Apr, 2026 Reviewers agreed at journal 30 Apr, 2026 Reviewers invited by journal 30 Apr, 2026 Editor assigned by journal 30 Apr, 2026 Editor invited by journal 29 Apr, 2026 Submission checks completed at journal 24 Apr, 2026 First submitted to journal 24 Apr, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9489970","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":635287186,"identity":"30e025b8-b162-46dc-ab3a-e4514733c06c","order_by":0,"name":"Zenghui Liu","email":"","orcid":"","institution":"Anhui University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Zenghui","middleName":"","lastName":"Liu","suffix":""},{"id":635287187,"identity":"e321b934-17cc-40c2-a7c2-7eef3776651c","order_by":1,"name":"Minjun 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4","display":"","copyAsset":false,"role":"figure","size":18498,"visible":true,"origin":"","legend":"\u003cp\u003eMechanical model of the roof in a near-fault roadway.\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9489970/v1/ac77c552476656a58a530825.jpg"},{"id":108799562,"identity":"98e8817b-f26b-4bb2-a68f-b699a5272c56","added_by":"auto","created_at":"2026-05-08 13:59:11","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":11409,"visible":true,"origin":"","legend":"\u003cp\u003eMechanical relationship of the near-fault roadway.\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9489970/v1/04699c766369793fac43b488.jpg"},{"id":108799514,"identity":"24c29844-0ee0-4d7a-8680-1bdde0c489e1","added_by":"auto","created_at":"2026-05-08 13:59:00","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":112787,"visible":true,"origin":"","legend":"\u003cp\u003ePlastic-zone range of the surrounding rock on the fault-proximal side under different fault dip angles and protective coal pillar widths.\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9489970/v1/36718fdcf69d6d774da2e5c4.jpg"},{"id":108799605,"identity":"a7b9b747-0416-487a-a6e2-3f3c1d7080db","added_by":"auto","created_at":"2026-05-08 13:59:37","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":191991,"visible":true,"origin":"","legend":"\u003cp\u003eNumerical simulation model.\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9489970/v1/2856de6fabd435c12e435393.jpg"},{"id":108799563,"identity":"8b546e6b-e52e-4e72-8eff-ce8f09e01c1f","added_by":"auto","created_at":"2026-05-08 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13:59:47","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":119272,"visible":true,"origin":"","legend":"\u003cp\u003ePlastic-zone contours under different protective coal pillar widths.\u003c/p\u003e","description":"","filename":"10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9489970/v1/21e0335dac81b42b3041b4b0.jpg"},{"id":108799616,"identity":"c5a86eb5-b4fa-4031-a89d-e060be94e126","added_by":"auto","created_at":"2026-05-08 13:59:41","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":165827,"visible":true,"origin":"","legend":"\u003cp\u003eDisplacement contours under different fault dip angles.\u003c/p\u003e","description":"","filename":"11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9489970/v1/d9d14e68d6d44d90e71cb76d.jpg"},{"id":108799579,"identity":"0c887a50-715c-42c0-acec-d63224bec5b1","added_by":"auto","created_at":"2026-05-08 13:59:21","extension":"jpg","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":69021,"visible":true,"origin":"","legend":"\u003cp\u003eField monitoring arrangement.\u003c/p\u003e","description":"","filename":"12.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9489970/v1/1ae093192ddedcee412758ff.jpg"},{"id":108799519,"identity":"b4589042-62e0-4882-be29-109d5057366c","added_by":"auto","created_at":"2026-05-08 13:59:01","extension":"jpg","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":47504,"visible":true,"origin":"","legend":"\u003cp\u003eMeasured 24-h displacement variation at Cross-section 1.\u003c/p\u003e","description":"","filename":"13.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9489970/v1/00d3372241111c14e2319752.jpg"},{"id":108799733,"identity":"de764010-1ceb-4d3b-afc4-ec44a3037de4","added_by":"auto","created_at":"2026-05-08 14:00:11","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1737714,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9489970/v1/9fecf7d4-a95e-42e8-8d64-796e88fb37db.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Surrounding Rock Stability and Engineering Practice of the 52607 Working Face Approaching a Fault-Protected Coal Pillar","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eWith the continuous increase in mining depth and the growing complexity of geological structures, the stability of surrounding rock during roadway excavation has become an increasingly prominent issue. Kang [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e] systematically reviewed the development of support technologies for deep and complex roadways in underground coal mines, and pointed out that high in-situ stress and complex structural conditions are the key factors restricting roadway stability control. Xie et al. [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e] analyzed the instability and support response of surrounding rock in deep coal roadways from the perspective of surrounding-rock control mechanisms, and concluded that the evolution of the bearing structure of the surrounding rock plays a decisive role in roadway stability. Shi et al. [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e] investigated support technologies for deep roadways based on engineering cases, further demonstrating the difficulty of surrounding-rock control under complex stress environments. These studies indicate that under deep high-stress and complex geological conditions, roadway surrounding rock often exhibits large deformation, strong asymmetric failure, and difficult support control.\u003c/p\u003e \u003cp\u003eWith respect to fault influence, Wang et al. [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e] analyzed the instability mechanism and support technology of roadways in fault fracture zones through an engineering case study, and pointed out that the weakening effect of faults can significantly reduce the bearing capacity of surrounding rock. Zhang et al. [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] investigated the failure characteristics of surrounding rock near a fault under mining influence by means of physical model tests, revealing the significant effect of faults on surrounding-rock structure and stress transfer paths. Kang et al. [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e] analyzed the stability of deep coal mine roadways crossing fault zones using numerical simulation, and demonstrated that the extent and mechanical parameters of the fault fracture zone play an important controlling role in surrounding-rock instability. Xie et al. [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] further studied the failure mechanism and hierarchical continuous support technology of roadways in unidirectional fault-affected zones, indicating that the plastic failure of surrounding rock and the support response under fault influence exhibit obvious zonal characteristics. These findings suggest that fault fracture zones are generally characterized by broken rock mass, developed fractures, weakened mechanical properties, and non-uniform stress distribution, which can easily lead to local failure of the surrounding-rock bearing structure and induce asymmetric deformation and local damage.\u003c/p\u003e \u003cp\u003eMeanwhile, considerable attention has also been paid to the influence of coal pillars, especially residual coal pillars in close-distance coal seams, on roadway stability. Liu et al. [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] investigated the instability mechanism and control measures of a roadway under retained coal pillar conditions in close coal seams, and found that stress concentration and plastic failure of the surrounding rock are particularly significant in the strong influence zone of the coal pillar. Wang et al. [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] analyzed the layout and mechanism of a lower return airway under the influence of a residual coal pillar, and pointed out that the pillar width and the relative position between the roadway and the coal pillar are key factors affecting roadway stability. Wu et al. [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] revealed the evolution law of the stress field and damage in coal and rock masses in the residual pillar area after top-slice mining of a thick coal seam. Wang et al. [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] further studied the deformation and failure mechanism of the lower roadway in a close-range residual coal pillar area. Wang et al. [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] analyzed the stability control of goaf-driven roadways under interchange remaining coal pillar conditions in close-distance coal seams, showing that complex mining-induced stress can significantly intensify the asymmetric deformation of roadway surrounding rock. Xia et al. [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] investigated the stability of roadways with small coal pillars under repeated mining by numerical simulation, and revealed that mining disturbance promotes the expansion of the plastic zone in both the coal pillar and surrounding rock. These studies indicate that coal pillars can significantly alter the stress distribution, plastic-zone range, and deformation pattern of adjacent roadways, and their influence range and action law have become an important topic in the study of roadway surrounding-rock control.\u003c/p\u003e \u003cp\u003eIn recent years, with the increasing prominence of roadway engineering problems under complex mining and structural conditions, some scholars have further investigated the deformation and failure behavior of surrounding rock under dynamic pressure, repeated mining, and complex stress fields. Hao et al. [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e] carried out research on surrounding-rock control technology for dynamic-pressure roadways in thick coal seams and pointed out that complex mining-induced loading can significantly increase the difficulty of roadway control. Wang et al. [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] studied the deformation and stress evolution of surrounding rock in pre-driven longwall recovery rooms at the end of mining, revealing the stage-dependent characteristics of surrounding-rock response under mining influence. Shang et al. [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] analyzed the instability characteristics and control technology of roadway surrounding rock under repeated mining in close-distance coal seams. Yan et al. [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] and Xiang et al. [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] investigated surrounding-rock control in complex conditions from the perspectives of support technology for large-section coal roadways and instability characteristics of bolt support in thick coal seams, respectively. Dong et al. [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e] studied excavation-unloading effects using a similar simulation device for deep roadway excavation. Shi et al. [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e] supplemented the research on surrounding-rock control under complex stress environments from the perspective of support simulation in deep mining. Xie et al. [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] investigated the deformation mechanism and control technology of surrounding rock in \u0026ldquo;three-soft\u0026rdquo; coal roadways under high horizontal stress. Yao et al. [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] analyzed the instability mechanism and surrounding-rock control technology of roadways subjected to short-distance dynamic loading. These studies provide important references for the stability analysis and support design of roadways under complex conditions.\u003c/p\u003e \u003cp\u003eOverall, existing studies have mainly focused on roadways crossing fault fracture zones, roadways affected by residual coal pillars, roadways in close-distance coal seam mining, or roadways under dynamic pressure conditions, whereas relatively few studies have addressed the particular stage in which a heading face gradually approaches a fault-protected coal pillar. In particular, under the coupled action of fault-induced structural weakening and stress concentration in the protective coal pillar, the evolution of surrounding-rock stability with changes in the roadway\u0026ndash;fault distance remains unclear. At the same time, under this specific condition, the control effect and engineering applicability of the existing bolt-cable support scheme still require further evaluation.\u003c/p\u003e \u003cp\u003eTherefore, taking the 52607 working face of Chengjiagou Coal Mine as the engineering background, this study investigates the deformation and failure behavior of surrounding rock during the process in which the heading face approaches a fault-protected coal pillar. In-situ stress measurement, theoretical analysis, three-dimensional numerical simulation, and field monitoring were combined to systematically analyze the displacement response, plastic-zone development, and deformation characteristics of the surrounding rock under different roadway\u0026ndash;fault distances. The main influence range of the fault was further identified, and the control effect and applicability of the existing bolt-cable support system were evaluated. The results provide a reference for surrounding-rock stability analysis and support design in fault-protected coal pillar zones under similar engineering conditions.\u003c/p\u003e"},{"header":"2. Project Overview","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Engineering Background\u003c/h2\u003e \u003cp\u003eChengjiagou Coal Mine is located in Yangfangkou Town, Ningwu County, Xinzhou City, Shanxi Province, China, and is a medium-sized mine affiliated with Xuangang Coal and Electricity Co., Ltd. Working face 52607 is located in the southern part of the mine field. The ground elevation in the panel area ranges from 1311 to 1478 m, while the floor elevation of No. 5 coal seam ranges from 1080 to 1300 m, corresponding to a burial depth of 178–230 m. The working face has a strike length of approximately 1800 m and a dip width of about 1000 m, with a designed service life of approximately 8 months. In terms of spatial relationship, it is 309 m away from the western boundary of the mine field, 30 m away from the return airway of working face 52606 on the south side, 180 m away from working face 52609 on the east side, and 201 m away from Panel 512 on the north side.\u003c/p\u003e \u003cp\u003eWorking face 52607 mainly extracts the No. 5 coal seam, which has an average thickness of 13.93 m and relatively stable occurrence conditions. The immediate roof is a 10.3 m thick fine sandstone interbedded with marl and thin coal seams; the main roof is massive and dense mudstone with poorly developed joints; the immediate floor is mudstone interbedded with No. 6 coal seam and is relatively stable; and the lower floor is medium- to coarse-grained sandstone with a thickness of 2.18–8.04 m and an average thickness of about 4.0 m, representing a hard and stable floor. The comprehensive stratigraphic column near the No. 5 coal seam is shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Fault Characteristics\u003c/h2\u003e \u003cp\u003eWorking face 52607 is mainly affected by the TF-3 fault. The TF-3 fault is located on the northwestern side of the mine field. It starts from Houhegou and extends eastward approximately along the W–E direction, continuing through Yaozigou. Near the valley area of Chengjiagou Coal Mine, the fault strike turns to the northeast and finally disappears into the Huihe River, with a total length of about 3.8 km. The fault is clearly exposed at the surface and has been confirmed by surface stratum correlation as well as drilling data from boreholes Gou-8, Gou-10, and No. 202.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e shows the relative position of working face 52607 and the fault.The TF-3 fault is a normal fault dipping to the southeast, with a dip angle ranging from 54° to 70°. The throw is about 35–38 m in the western segment and approximately 75 m in the central segment, showing an overall downthrown southern block. Controlled by this fault, the 52607 return airway is located in the hanging wall of the TF-3 fault. As the roadway advances continuously, its driving direction gradually approaches the fault strike, resulting in an increasingly enhanced weakening effect of the fault structure on the surrounding rock. This constitutes the key geological background for the progressively intensified surrounding-rock stability problems during the excavation of working face 52607.\u003c/p\u003e "},{"header":"3. Theoretical Analysis of In-Situ Stress, Roof Deformation, and Plastic Zone in the Fault-Protected Coal Pillar Zone","content":"\u003ch2\u003e3.1 In-Situ Stress Measurement and Analysis of Stress Field Characteristics\u003c/h2\u003e\u003cp\u003eTo determine the in-situ stress state of the study area, Chengjiagou Coal Mine adopted an in-situ stress testing method based on the acoustic emission Kaiser effect to back-calculate the three-dimensional principal stresses. First, the original rock samples collected in the field were directionally prepared along six orientations, as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea. According to the azimuth and dip information marked on the top of the rock sample, the sample was restored to its original in-situ orientation. A nearly horizontal plane was selected, and the true north direction, denoted as N, was determined. Taking N as the X-direction, a three-dimensional coordinate system composed of the X, Y, and Z axes was established. In the XOY, XOZ, and YOZ planes, directions making an angle of 45° with the two coordinate axes were then determined, respectively.\u003c/p\u003e\u003cp\u003eOn this basis, cylindrical specimens were drilled along the six predetermined directions, with a specimen size of 25 mm × 50 mm. In this test, one measuring point was selected, and three core specimens were prepared in each of the six directions, yielding a total of 18 specimens for subsequent acoustic emission Kaiser effect testing and principal stress calculation. The rock cores used in the experiment are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb.\u003c/p\u003e\u003cp\u003eThe loading process in this experiment was carried out using a rock mechanics testing machine, as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e–\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e. The acoustic emission signals were collected using an acoustic emission testing system manufactured by PAC (Physical Acoustics Corporation, USA), as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ec. All acoustic emission signals generated during the entire deformation process of the specimen under loading were recorded.\u003c/p\u003e\u003cp\u003eAfter specimen preparation, the 18 specimens obtained from the six directions at the same measuring point were subjected to acoustic emission Kaiser effect tests. One representative result from each direction was selected as the final test result for that direction, and all tests were conducted under uniaxial loading conditions.\u003c/p\u003e\u003cp\u003eThe calculated in-situ stresses and the orientation of the maximum horizontal principal stress at the measuring point located at the end of the track roadway in Panel 526 are listed in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\u003cdiv class=\"gridtable\"\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003ctable id=\"Tab1\" border=\"1\"\u003e \u003ccaption\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCalculated in-situ stress results at the measuring point\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003c/colgroup\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\"\u003e \u003cp\u003eMeasuring point\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eBurial depth/m\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eσ\u003csub\u003e\u003cem\u003eV\u003c/em\u003e\u003c/sub\u003e/MPa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eσ\u003csub\u003e\u003cem\u003eH\u003c/em\u003e\u003c/sub\u003e/MPa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eσ\u003csub\u003e\u003cem\u003eh\u003c/em\u003e\u003c/sub\u003e/MPa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eOrientation of maximum horizontal principal stress\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e52607\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e190\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e4.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e4.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e3.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003eE43.2°S\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/table\u003e\u003c/div\u003e\u003cp\u003eThe in-situ stress test results at the measuring point at the end of the track roadway in Panel 52607 of Chengjiagou Coal Mine show that the maximum horizontal principal stress is 4.63 MPa, the minimum horizontal principal stress is 3.13 MPa, and the vertical stress is 4.50 MPa.\u003c/p\u003e\u003cp\u003eAccording to the magnitude relationship among the three principal stresses, the in-situ stress field can be classified into three types: Type I,σ\u003csub\u003e\u003cem\u003eH\u003c/em\u003e\u003c/sub\u003e\u0026gt;σ\u003csub\u003e\u003cem\u003eh\u003c/em\u003e\u003c/sub\u003e\u0026gt;σ\u003csub\u003e\u003cem\u003eV\u003c/em\u003e\u003c/sub\u003e;Type II, σ\u003csub\u003e\u003cem\u003eH\u003c/em\u003e\u003c/sub\u003e\u0026gt;σ\u003csub\u003e\u003cem\u003eV\u003c/em\u003e\u003c/sub\u003e\u0026gt;σ\u003csub\u003e\u003cem\u003eh\u003c/em\u003e\u003c/sub\u003e;and Type III,σ\u003csub\u003e\u003cem\u003eV\u003c/em\u003e\u003c/sub\u003e\u0026gt;σ\u003csub\u003e\u003cem\u003eH\u003c/em\u003e\u003c/sub\u003e\u0026gt;σ\u003csub\u003e\u003cem\u003eh\u003c/em\u003e\u003c/sub\u003e.Since the measured stress relationship at this point is σ\u003csub\u003e\u003cem\u003eH\u003c/em\u003e\u003c/sub\u003e\u0026gt;σ\u003csub\u003e\u003cem\u003eV\u003c/em\u003e\u003c/sub\u003e\u0026gt;σ\u003csub\u003e\u003cem\u003eh\u003c/em\u003e\u003c/sub\u003e,the stress field belongs to Type II, indicating that tectonic stress is greater than gravitational stress.\u003c/p\u003e\u003ch2\u003e3.2 Roof Displacement Analysis of a Near-Fault Roadway\u003c/h2\u003e\u003cp\u003eTo further reveal the influence of the fault on the stability of surrounding rock in a near-fault roadway, a theoretical analysis of the loading and displacement characteristics of the roadway roof was carried out based on the in-situ stress measurement results. According to the loading characteristics of the roof in a near-fault roadway, the roof can be simplified as a cantilever beam subjected to the load of the overlying strata, and the corresponding mechanical analysis model is shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e\u003cp\u003eAssuming that the normal force acting on the fault is Fn,its vertical component can be regarded as an important component in the analysis of roof loading. On this basis, the stress components at different points of the roof and the deflection equation can be derived according to elasticity theory. The influence of the fault on roadway roof deformation can then be analyzed through the deflection equation. Theoretical analysis indicates that, as the distance between the roadway and the fault increases, the effective length of the roof cantilever beam decreases, the beam stiffness is correspondingly enhanced, and the roof deflection gradually decreases. The maximum roof deflection occurs at the free end of the cantilever beam, i.e., at x = 0 and y = 0. The maximum deflection v satisfies a functional relationship with the shortest horizontal distance m between the roadway and the fault plane:\u003c/p\u003e\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$v(x,0)=\\frac{{{a^3}\\gamma hb\\sin \\theta }}{{3\\cos \\frac{\\theta }{2}E\\operatorname{Im} }}=\\frac{{4{a^3}b\\gamma h{{\\cos }^3}\\theta }}{{{m^4}E{{\\sin }^2}\\theta \\cos \\frac{\\theta }{2}}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003cp\u003eWhere:\u003c/p\u003e\u003cp\u003ea——roadway step height;\u003c/p\u003e\u003cp\u003eb——roadway width;\u003c/p\u003e\u003cp\u003eγ——unit weight of the roof rock;\u003c/p\u003e\u003cp\u003eh——vertical component of the shortest distance from the left bottom corner of the floor to the fault;\u003c/p\u003e\u003cp\u003eE——elastic modulus;\u003c/p\u003e\u003cp\u003em——distance between the roadway wall and the fault, i.e., the width of the protective coal pillar.\u003c/p\u003e\u003cp\u003eAccording to the actual engineering conditions of Chengjiagou Coal Mine, the dip angle of the TF-3 fault was taken as approximately 65°, the unit weight of the roof rock was taken as 13kN/m3, the roadway section size was4.2m×2.8m, and the elastic modulus E of the No. 5 coal seam was taken as 2.85 GPa. The parameter h represents the vertical component of the shortest distance from the left bottom corner of the floor to the nearest point on the fault, and its expression can be further determined from the mechanical relationship of the near-fault roadway. According to the mechanical model shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e, it can be obtained that:\u003c/p\u003e\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\tan \\theta =\\tan 65^\\circ =h/m$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003cp\u003eThe shortest horizontal distance between the roadway and the fault plane was taken as m = 25, 20, 15, and 10 m, respectively. Substituting these values into the calculation formula gives the corresponding maximum roof deflections as v\u003csub\u003e10\u003c/sub\u003e= 0.32 m. Similarly, by substituting m = 15, 20, and 25 m into the equation, the results are obtained as v\u003csub\u003e15\u003c/sub\u003e= 0.21 m, v\u003csub\u003e20\u003c/sub\u003e= 0.15m, and v\u003csub\u003e25\u003c/sub\u003e = 0.13m.\u003c/p\u003e\u003cp\u003eThe calculation results indicate that when the width of the protective coal pillar is 10, 15, 20, and 25 m, the maximum roof deflection is approximately 32, 21, 15, and 13 cm, respectively. Overall, as the shortest horizontal distance between the roadway and the fault increases, the maximum roof deflection decreases significantly, indicating that the controlling effect of the fault on roof deformation gradually weakens with increasing distance. When the width of the protective coal pillar reaches 20 m or more, the reduction in roof deflection becomes noticeably less pronounced, suggesting that the influence of the fault on roof deformation begins to weaken beyond this threshold.\u003c/p\u003e\u003cp\u003eThese results show that, in the near-fault zone, the roadway roof is strongly disturbed by the fault and exhibits more pronounced bending deformation. As the roadway gradually moves away from the fault, the roof loading condition becomes alleviated, the deflection decreases, and the stability of the surrounding rock correspondingly improves. From the perspective of roof structural response, this analysis demonstrates the sensitivity of roadway surrounding-rock stability to the distance from the fault, and also provides a theoretical basis for the subsequent analysis of plastic-zone development in the near-fault coal pillar.\u003c/p\u003e\u003ch2\u003e3.3 Plastic Zone Analysis of the Near-Fault Coal Pillar Based on Limit Equilibrium Theory\u003c/h2\u003e\u003cp\u003eTo investigate the development law of the plastic zone in the surrounding rock on the fault-proximal side of the coal pillar, this study carried out a theoretical analysis of the width of the plastic zone in the near-fault coal pillar based on the existing elastoplastic limit equilibrium theory in rock mechanics, combined with the Mohr–Coulomb strength criterion.\u003c/p\u003e\u003cp\u003eConsidering the stress characteristics of the roadway surrounding rock under the combined influence of the fault and the coal pillar, the normal force acting on the fault plane was assumed to be Fn. Meanwhile, the shear stress on the fault plane was assumed to be linearly distributed along the fault plane. Accordingly, the expression for calculating the width of the plastic zone on the fault-proximal side of the roadway within the coal pillar can be obtained as follows:\u003c/p\u003e\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$${x_m}= - \\frac{{\\lambda a}}{{2\\tan {\\varphi _0}}}\\ln (\\frac{{\\frac{{{C_0}}}{{\\tan {\\varphi _0}}}+\\frac{{{P_x}}}{a}}}{{\\frac{{{C_0}}}{{\\tan {\\varphi _0}}}+{\\sigma _v}+\\frac{{{\\sigma _v}\\cos \\theta }}{{2\\lambda c\\cos \\frac{\\theta }{2}}}}})$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003cp\u003eWhere:\u003c/p\u003e\u003cp\u003ea——roadway step heigh;\u003c/p\u003e\u003cp\u003eλ——lateral pressure coefficient;\u003c/p\u003e\u003cp\u003eC\u003csub\u003e0\u003c/sub\u003e——cohesion of the coal seam;\u003c/p\u003e\u003cp\u003eΦ\u003csub\u003e0\u003c/sub\u003e——internal friction angle of the coal seam;\u003c/p\u003e\u003cp\u003ec——distance between the roadway wall and the fault, i.e., the width of the protective coal pillar;\u003c/p\u003e\u003cp\u003eP\u003csub\u003ex\u003c/sub\u003e——lateral confinement acting on the coal wall;\u003c/p\u003e\u003cp\u003eθ ——angle between the fault plane and the vertical direction. Considering that the fault dip angle ranges from 54° to 70°, θ was taken as 20°, 25°, 30°, and 35°;\u003c/p\u003e\u003cp\u003eσ\u003csub\u003ev\u003c/sub\u003e ——vertical stress;\u003c/p\u003e\u003cp\u003eThe final calculation results are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e\u003c/p\u003e\u003cp\u003eAccording to Eq.\u0026nbsp;(\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e) and Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e, the plastic-zone range of the surrounding rock on the fault-proximal side of the roadway is jointly controlled by factors such as the roadway step height, the in-situ stress, the distance between the roadway wall and the protective coal pillar width, and the fault dip angle. When the other parameters remain constant, the plastic-zone range gradually decreases and tends to stabilize with increasing protective coal pillar width. In contrast, as the fault dip angle increases, the plastic-zone range shows an overall slow increasing trend, although the variation is relatively small, indicating that the fault dip angle has a certain influence on plastic-zone development but is not the dominant controlling factor. Combined with the actual engineering conditions of Chengjiagou Coal Mine and the theoretical calculation results, it can be concluded that within 25 m from the fault, the protective coal pillar has a significant effect on plastic-zone development; when the distance exceeds 25 m, this effect weakens markedly and the variation in the plastic zone becomes gradual.\u003c/p\u003e"},{"header":"4. Numerical Simulation Analysis of Surrounding Rock Stability in the Fault-Protected Coal Pillar Zone","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Establishment of the Numerical Calculation Model\u003c/h2\u003e \u003cp\u003eDuring roadway excavation, excavation-induced disturbance breaks the original equilibrium state of the in-situ stress field, resulting in stress redistribution in the surrounding rock and obvious local stress concentration. Under the complex stress environment near a fault, such stress redistribution is an important factor inducing surrounding-rock deformation and failure. Therefore, it is necessary to systematically analyze the displacement response and plastic-zone evolution of the surrounding rock during roadway excavation by means of numerical simulation.\u003c/p\u003e \u003cp\u003eIn this study, a three-dimensional numerical model was established using FLAC3D, and the Mohr\u0026ndash;Coulomb yield criterion was adopted to determine rock mass failure, without considering the plastic flow effect. During model construction, a three-dimensional geometric model was first established, and an equivalent load was applied to the top of the model to represent the effect of the overlying strata that were not explicitly modeled. After the initial stress equilibrium was reached, step-by-step excavation of the 52607 return airway was carried out, while the installation of the support structure was simulated simultaneously. The calculation results were extracted after the model reached equilibrium again. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea shows the established numerical model, and Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb shows the relative position of the roadway and the fault.\u003c/p\u003e \u003cp\u003eAccording to the engineering geological conditions of working face 52607, the model dimensions were set to 300 m \u0026times; 105 m \u0026times; 750 m. The roadway cross-section was 4.2 m \u0026times; 2.8 m, the fault zone width was 7 m, and the fault dip angle was 65\u0026deg;. To improve the calculation accuracy in the key study area, the mesh around the roadway was refined to 0.5 m \u0026times; 0.5 m, while a coarser rectangular mesh was used in the other regions. Both bolts and cables were simulated using built-in cable elements, and the support structure adopted in Chengjiagou Coal Mine is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ec. The boundary conditions were set as follows: horizontal displacement was constrained on the lateral boundaries, displacement in all three directions was constrained at the bottom boundary, and an equivalent stress of the overlying strata was applied at the top boundary. To simulate the actual excavation process, the roadway was excavated in increments of 10 m, and the calculation was continued to convergence after each excavation step.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBased on the above model and parameter settings, typical working conditions in which the fault-side wall of the return airway was located 10, 20, 30, and 40 m from the fault plane were selected for numerical simulation. The displacement variation law and plastic-zone development characteristics of the surrounding rock under different fault-distance conditions were analyzed, and the displacement responses under different fault dip angles were further examined to reveal the asymmetric deformation mechanism of the surrounding rock in near-fault roadways, thereby providing a reference for the stability analysis of surrounding rock under similar conditions.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eRock mechanical parameters for numerical simulation.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRock Layer\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eThickness/m\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eDensity/(kg/m\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCohesion/MPa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eInternal friction angle /\u0026deg;\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTensile strength/MPa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003ePoisson\u0026rsquo;s ratio\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eElastic modulus/GPa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eCompressive strength /MPa\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMudstone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2690\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e6.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e3.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e16.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFine sandstone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2420\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e18.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e37.31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e7.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e3.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e107.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNo. 5 coal seam\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e13.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1350\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e5.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMudstone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2690\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e6.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.37\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e3.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e15.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNo. 6 coal seam\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1350\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e5.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMudstone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2690\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e6.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e3.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e16.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMedium- to coarse-grained sandstone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2400\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e6.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e44.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e4.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e62.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Displacement Variation of Surrounding Rock under Different Protective Coal Pillar Widths\u003c/h2\u003e \u003cp\u003eTo analyze the influence of fault distance variation on the deformation characteristics of roadway surrounding rock, typical cases with distances of 10, 20, 30, and 40 m between the fault-side wall of the return airway and the fault plane were selected for FLAC3D numerical simulation. Based on the simulation results for each case, the displacement contours of the surrounding rock were extracted, and the variation laws of roof subsidence, rib convergence, and floor displacement were comparatively analyzed, so as to reveal the evolution characteristics of surrounding-rock deformation under near-fault conditions.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e presents the displacement contours under different protective coal pillar widths.The numerical simulation results show that, under different working conditions, the displacement of the surrounding rock is mainly concentrated around the roadway profile. Different degrees of deformation occur in the roof, ribs, and floor, among which roof subsidence and rib convergence are more pronounced, and the overall deformation exhibits a certain degree of asymmetry. As the distance between the roadway and the fault increases, the overall displacement level of the surrounding rock gradually decreases, and the range of displacement concentration correspondingly shrinks, indicating that the fault has a significant controlling effect on roadway deformation, which is more pronounced in the near-fault zone.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eOn this basis, the roof subsidence and floor displacement under each simulation case were further extracted, and the displacements of the fault-proximal rib and the coal-seam-side rib were comparatively analyzed, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. The results indicate that, as the distance between the roadway and the fault increases, the roof subsidence, floor displacement, and rib displacements all show an overall decreasing trend, suggesting that the fault proximity effect significantly intensifies the deformation of roadway surrounding rock.\u003c/p\u003e \u003cp\u003eIn terms of deformation characteristics in different parts of the roadway, the roof and ribs are more sensitive to changes in fault distance. In particular, the displacement of the fault-proximal rib is generally greater than that of the coal-seam-side rib, indicating that the surrounding rock on the fault side is more strongly disturbed and exhibits more obvious asymmetric deformation. By contrast, although the floor displacement also varies with fault distance, its overall variation amplitude is relatively small. Comprehensive analysis of the simulation results shows that, as the roadway gradually approaches the fault, surrounding-rock deformation becomes significantly aggravated; whereas when the roadway moves away from the fault, the displacement gradually decreases and tends to stabilize. This indicates that the fault distance is an important controlling factor governing the deformation characteristics of surrounding rock in near-fault roadways.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e4.3 Evolution of the Plastic Zone under Different Fault-Distance Conditions\u003c/h2\u003e \u003cp\u003eThe development characteristics of the coal pillar plastic zone under different fault-distance conditions show that, as the roadway gradually approaches the fault, the plastic zones on both sides of the coal pillar expand progressively, and the plastic zone on the fault-proximal side develops more significantly,Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e shows the plastic-zone contours under different protective coal pillar widths..\u003c/p\u003e \u003cp\u003eWhen the coal pillar width is 40 m and 30 m, respectively, although the coal pillar is already affected by the fault, the overall plastic-zone range remains relatively small. In this case, the maximum development depths of the plastic zone on the coal-seam side are 1.1 m and 1.2 m, respectively, while those on the fault-proximal side are 1.4 m and 1.5 m, respectively. Because a relatively wide elastic core is still preserved inside the coal pillar, the overall deformation of the coal pillar is small, the surrounding rock remains relatively stable, and the coal pillar as a whole is in a stable state.\u003c/p\u003e \u003cp\u003eWhen the coal pillar width decreases to 20 m, the plastic zones on both sides of the coal pillar expand further. The maximum development depth of the plastic zone on the coal-seam side increases to 1.7 m, while that on the fault-proximal side increases to 2.5 m. At this stage, the elastic core inside the coal pillar is obviously reduced, and the bearing capacity of the surrounding rock declines to some extent; however, the coal pillar as a whole can still remain basically stable.\u003c/p\u003e \u003cp\u003eWhen the coal pillar width is further reduced to 10 m, the plastic-zone range of the coal pillar expands significantly. The maximum development range of the plastic zone on the fault-proximal side increases to about 3.0 m, while that on the coal-seam side is about 2.5 m. The plastic zones on both sides of the coal pillar then occupy a relatively large range, and the elastic core is further reduced, indicating that the bearing structure of the coal pillar is significantly weakened, accompanied by a certain degree of deformation and a marked reduction in stability.\u003c/p\u003e \u003cp\u003eComprehensive analysis indicates that, with decreasing coal pillar width, the plastic zones on both sides of the coal pillar continue to expand, and the plastic zone on the fault-proximal side is always larger than that on the coal-seam side, indicating that the weakening effect of the fault on coal pillar stability is clearly asymmetric. When the coal pillar width is relatively large, the interior of the coal pillar still retains strong bearing capacity. However, when the coal pillar width decreases to a certain extent, the plastic zone expands rapidly, the elastic core is significantly reduced, and the stability of the coal pillar correspondingly declines. These numerical simulation results are basically consistent with the previous theoretical analysis, further verifying that the plastic zone of the coal pillar in the near-fault area exhibits obvious asymmetric expansion.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e4.4 Displacement Response of Surrounding Rock under Different Fault Dip Angles\u003c/h2\u003e \u003cp\u003eTo investigate the influence of fault dip-angle variation on the deformation characteristics of roadway surrounding rock, FLAC3D numerical simulations were conducted for four typical cases with fault dip angles of 55\u0026deg;, 60\u0026deg;, 65\u0026deg;, and 70\u0026deg;, while keeping the other parameters unchanged and adopting the optimal protective coal pillar width of 20 m. The displacement distributions of the surrounding rock under each case were comparatively analyzed, and the four displacement contour plots under different dip-angle conditions are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eThe numerical simulation results indicate that, under different fault dip angles, the displacement of the surrounding rock is still mainly concentrated around the roadway profile, with roof subsidence and rib convergence being relatively pronounced, and the overall deformation exhibiting a certain degree of asymmetry. As the fault dip angle increases from 55\u0026deg; to 70\u0026deg;, the roof displacement decreases from 11.5 cm to 9.0 cm, the displacement of the fault-proximal rib decreases from 10.4 cm to 9.4 cm, and the displacement of the coal-seam-side rib decreases from 7.4 cm to 6.1 cm. Overall, the displacements of all parts of the roadway surrounding rock show a decreasing trend with increasing fault dip angle.\u003c/p\u003e \u003cp\u003eFrom the displacement characteristics of different parts of the roadway, the roof displacement shows the most obvious variation, decreasing from 11.5 cm at 55\u0026deg; to 9.0 cm at 70\u0026deg;, corresponding to a reduction of 21.7%. The displacement of the fault-proximal rib decreases from 10.4 cm to 9.4 cm, corresponding to a reduction of 9.6%, while that of the coal-seam-side rib decreases from 7.4 cm to 6.1 cm, corresponding to a reduction of 17.6%. These results indicate that the roof and the surrounding rock on the fault-proximal side are relatively sensitive to changes in fault dip angle. However, the displacement of the fault-proximal rib remains greater than that of the coal-seam-side rib under all cases, suggesting that the surrounding rock on the fault side is more strongly affected by structural disturbance, and the overall deformation of the roadway still exhibits obvious asymmetric characteristics.\u003c/p\u003e \u003cp\u003eComprehensive analysis shows that variations in fault dip angle have a certain influence on the displacement distribution of surrounding rock in near-fault roadways, but the overall differences under different dip-angle conditions are limited, indicating that fault dip angle is not the dominant factor controlling surrounding-rock deformation. Compared with the simulation results under different fault-distance conditions discussed above, the influence of fault distance on surrounding-rock displacement is more significant. Therefore, in the stability analysis of roadways in fault-protected coal pillar zones, the relative distance between the roadway and the fault should be considered as the primary controlling factor, while the fault dip angle may be treated as a secondary influencing factor.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"5. Analysis of Surrounding Rock Control Measures and Evaluation of Engineering Practice Effect","content":"\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e5.1 Support Parameters and Support Form of the Test Section\u003c/h2\u003e \u003cp\u003eTo carry out field verification of the surrounding-rock control effect in the fault-protected coal pillar zone, the section located 50\u0026ndash;70 m ahead of measuring point Y12 was selected as the test section.\u003c/p\u003e \u003cp\u003eThe test section adopted a combined bolt-cable support system. For roof support, Φ20 mm \u0026times; 2500 mm left-handed rebar bolts without longitudinal ribs were used, together with Z2360 and K2335 resin cartridges for extended anchorage. The bearing plate size was 110 mm \u0026times; 110 mm \u0026times; 10 mm, and the bolt spacing was 1000 mm \u0026times; 1000 mm. The roof cables were Φ17.8 mm \u0026times; 7300 mm steel strands, anchored with two Z2360 resin cartridges and two K2335 resin cartridges for extended anchorage. The cable plate size was 300 mm \u0026times; 300 mm \u0026times; 15 mm, and the cable spacing was 1450 mm \u0026times; 2000 mm. A W-shaped steel strip with dimensions of 4180 mm \u0026times; 220 mm \u0026times; 2.75 mm was installed on the roof, and No. 10 diamond-shaped metal mesh was used for surface support; in roof-fall sections, one additional layer of square mesh and one layer of No. 10 diamond-shaped metal mesh were installed.\u003c/p\u003e \u003cp\u003eFor rib support, Φ20 mm \u0026times; 2500 mm left-handed rebar bolts without longitudinal ribs were used. The anchorage method and plate specifications were the same as those of the roof bolts, and the bolt spacing was 1000 mm \u0026times; 1000 mm. A W-shaped steel strip with dimensions of 400 mm \u0026times; 220 mm \u0026times; 2.75 mm was installed on the ribs. When the ribs encountered broken surrounding rock, fault zones, or weak zones, additional W-shaped steel strips were installed for reinforced support. No. 10 diamond-shaped metal mesh was also used for rib support. In roof-fall sections, square mesh and diamond-shaped metal mesh were additionally installed and fixed with tie wires in a \u0026ldquo;three twists and one fastening\u0026rdquo; pattern. The material consumption per meter for the support system of the working face is listed in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eIn this way, a support system dominated by bolts and cables, and coordinated with W-shaped steel strips and metal mesh, was formed, providing the support basis for subsequent monitoring of surrounding-rock deformation and field evaluation of the support effect.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSupport material consumption per meter in working face 52607.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaterial\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSpecification\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eUnit\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eQuantity\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRemarks\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRebar bolt\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eΦ20\u0026times;2500㎜left-handed rebar\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eset\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eResin cartridge\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eK2335\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ecartridge\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eResin cartridge\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eZ2360\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ecartridge\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSteel strand\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eφ17.8\u0026times;7300㎜\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003epiece\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRow spacing: 2 m\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePrestressed bolt plate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e110\u0026times;110\u0026times;10㎜\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003epiece\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePrestressed cable plate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e300\u0026times;300\u0026times;15㎜\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003epiece\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW-shaped steel strip\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4180\u0026times;220\u0026times;2.75mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003epiece\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e5.2. Field Monitoring Scheme and Monitoring Point Layout\u003c/h2\u003e \u003cp\u003eCombined with the previous theoretical analysis and numerical simulation results, it can be concluded that under fault influence, a reduction in the width of the protective coal pillar will significantly aggravate surrounding-rock deformation and the expansion of the plastic zone. Comprehensive analysis indicates that the width of the protective coal pillar should not be less than 20 m. To further verify the control effect of the existing support conditions on the roadway surrounding rock, field monitoring of surrounding-rock deformation was carried out during roadway reinforcement construction in Chengjiagou Coal Mine.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003ea shows a field photograph of the monitoring layout. The field monitoring adopted the cross-measurement method. One surrounding-rock monitoring station was arranged every 10 m along the roadway strike, and each group contained three monitoring points. The monitoring points were arranged within 2 m of the roof separation indicator. When an additional roof separation indicator was installed in special sections, a surrounding-rock monitoring station was added simultaneously to ensure correspondence between surrounding-rock deformation monitoring and roof separation monitoring. Two measuring stations were arranged in each monitoring group, and the spacing between the two stations did not exceed the support distance of two rows of bolts. The deformation of the surrounding rock was dynamically monitored by measuring the change in horizontal distance between the left and right ribs and the change in vertical distance between the roof and floor. The layout of the monitoring points and the measurement directions are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003eb.\u003c/p\u003e \u003cp\u003eSpecifically, rib convergence was characterized by the reduction in horizontal spacing between the monitoring points on the two ribs, i.e., by the change in horizontal distance between points C and D. Roof subsidence was characterized by the reduction in vertical spacing between the roof monitoring point and the floor reference point. For convenience of analysis, all monitoring results were expressed in terms of convergence and subsidence, rather than total displacement.\u003c/p\u003e \u003cp\u003eWith the above monitoring arrangement, key deformation indices of the roadway surrounding rock, such as roof subsidence and rib convergence during excavation and support, could be continuously monitored, thus providing a field basis for the subsequent analysis of surrounding-rock deformation behavior and the evaluation of the control effect of the existing support scheme.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e5.3. Comparative Analysis of Field Monitoring Results and Numerical Simulation Data\u003c/h2\u003e \u003cp\u003eAccording to the measured results, the maximum rib convergence at Cross-section 1 was 16.1 cm, including 9.3 cm on the fault-proximal side and 6.8 cm on the coal-seam side, while the maximum roof subsidence was 8.2 cm. At Cross-section 2, the maximum rib convergence was 14.7 cm, including 8.7 cm on the fault-proximal side and 6.0 cm on the coal-seam side, and the maximum roof subsidence was 9.0 cm. At Cross-section 3, the maximum rib convergence was 15.8 cm, including 8.9 cm on the fault-proximal side and 6.9 cm on the coal-seam side, while the maximum roof subsidence was 9.5 cm. Comprehensive analysis indicates that the overall surrounding-rock deformation at all monitored cross-sections was relatively small, and the roadway as a whole remained in a stable state. Meanwhile, the displacement on the fault-proximal side was consistently greater than that on the coal-seam side, indicating that the fault exerted a certain asymmetric influence on roadway surrounding-rock deformation, which is basically consistent with the previous theoretical analysis and numerical simulation results. Cross-section 1 was taken as an example to illustrate the variations of the roof, floor, and two ribs, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e.\\\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ewas prepared based on a comparison between the field monitoring results and the numerical simulation results.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCross-Section\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMax Convergence of Ribs (cm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMax. fault-proximal side (cm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMax. coal-seam side(cm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRoof subsidence (cm)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCross-section 1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e16.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e9.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e8.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCross-section 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e14.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e8.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e9.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCross-section 3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e15.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e8.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e9.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNumerical simulation (Scheme d)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e13.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e7.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e7.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. Statistical comparison of field monitoring results and numerical simulation results.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003eA comparison between the field monitoring results and the numerical simulation results can be used to verify the rationality of the established model. As shown in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, the maximum roof subsidence at the three monitored cross-sections was 8.2 cm, 9.0 cm, and 9.5 cm, respectively, while the maximum rib convergence was 16.1 cm, 14.7 cm, and 15.8 cm, respectively, indicating that the overall deformation of the surrounding rock in the test section was relatively small. In comparison, the numerical simulation results for Scheme d show that the maximum roof subsidence was 7.1 cm, and the maximum displacements on the fault-proximal side and the coal-seam side were 7.5 cm and 6.0 cm, respectively, corresponding to a maximum rib convergence of 13.5 cm. Overall, the numerical simulation results are generally consistent with the field monitoring results in both magnitude and variation trend, both indicating that the roof subsidence and rib convergence remained relatively small and that the deformation on the fault-proximal side was greater than that on the coal-seam side. This suggests that the established numerical model can reasonably reflect the actual deformation characteristics of the surrounding rock in the near-fault roadway.\u003c/p\u003e \u003cp\u003eIt should be noted that some differences still exist between the numerical simulation results and the field monitoring data. On the one hand, field monitoring was strongly affected by the construction process and site conditions, and the monitoring data therefore exhibit obvious stage-dependent characteristics. In addition, only three typical cross-sections were selected for analysis in this study, which imposes certain limitations on the representativeness of the monitoring results. On the other hand, the numerical simulation results reflect the overall response of the roadway after excavation and support installation under idealized conditions when a new equilibrium state is reached, whereas the actual field deformation is also affected by multiple factors, such as the contact condition between the support structure and the surrounding rock, the arrangement of monitoring points, reading conditions, and construction disturbance. Furthermore, necessary simplifications were made in the numerical modeling with respect to rock-mass homogeneity, constitutive relations, boundary conditions, and the construction process, which may also lead to some deviation between the simulated results and the field measurements.\u003c/p\u003e \u003cp\u003eNevertheless, the field monitoring results and the numerical simulation results are consistent in terms of the overall trend, both showing that, under the existing bolt-cable support conditions, the overall deformation of the roadway surrounding rock remains relatively small and the support system has a good controlling effect on the surrounding rock in the fault-protected coal pillar zone. This result indicates that the numerical model established in the previous sections has good applicability, and also verifies the effectiveness of the existing support scheme under the present engineering conditions.\u003c/p\u003e \u003c/div\u003e"},{"header":"6. Discussion","content":"\u003cp\u003eThe deformation characteristics observed in this study reflect the combined influence of tectonic stress concentration and structural weakening caused by the TF-3 fault. Near the fault-protected coal pillar, the surrounding rock is more prone to asymmetric deformation because the fault changes the stress transfer path and weakens the bearing capacity of the rock mass on the fault-proximal side. This indicates that roadway stability control in such areas should not only focus on support strength, but also consider the spatial relationship between the roadway, fault plane, and protective coal pillar during roadway layout and excavation design.\u003c/p\u003e \u003cp\u003eAlthough the numerical simulation and field monitoring results show similar deformation trends, the findings should be interpreted within the specific engineering context of the 52607 working face. The numerical model simplifies rock-mass heterogeneity, boundary conditions, and excavation-support processes, while the field monitoring was limited in spatial coverage and monitoring duration. Therefore, the proposed understanding of near-fault roadway stability should be further verified under different burial depths, fault properties, stress states, and mining layouts before broader application.\u003c/p\u003e"},{"header":"7. Conclusions","content":"\u003cp\u003eThis study took the 52607 return airway of Chengjiagou Coal Mine as the engineering background and employed in-situ stress measurement, theoretical analysis, numerical simulation, and field monitoring to investigate the surrounding-rock stability and support performance as the heading face approached a fault-protected coal pillar. The main conclusions are as follows:\u003c/p\u003e \u003cp\u003e(1) The in-situ stress field in the study area is characterized by relatively strong horizontal tectonic stress. At the measuring point at the end of the track roadway in Panel 526, the maximum horizontal principal stress, vertical stress, and minimum horizontal principal stress were 4.63 MPa, 4.50 MPa, and 3.13 MPa, respectively, showing a stress relationship of σH\u0026thinsp;\u0026gt;\u0026thinsp;σV\u0026thinsp;\u0026gt;\u0026thinsp;σh, which corresponds to a Type-II stress field. This stress condition suggests that horizontal tectonic stress may play an important role in roadway deformation in the study area.\u003c/p\u003e \u003cp\u003e(2) Under the geological and mining conditions considered in this study, the relative distance between the roadway and the fault is one of the key factors influencing surrounding-rock deformation and plastic-zone development. Theoretical analysis and numerical simulation results indicate that, as the roadway approaches the fault, roof deflection, rib convergence, and the plastic zone of the coal pillar tend to increase, with more pronounced deformation on the fault-proximal side. When the protective coal pillar width is reduced to less than 20 m, the plastic zone expands more obviously and the pillar stability decreases. Therefore, for the 52607 working face, a protective coal pillar width of not less than 20 m is suggested.\u003c/p\u003e \u003cp\u003e(3) The field monitoring results are generally consistent with the numerical simulation results in terms of deformation magnitude and trend, supporting the applicability of the established numerical model to this case. The maximum rib convergence values at the three typical cross-sections were 16.1 cm, 14.7 cm, and 15.8 cm, while the maximum roof subsidence values were 8.2 cm, 9.0 cm, and 9.5 cm, respectively. Under the monitored conditions, the overall roadway deformation remained within a controllable range, and the existing bolt-cable support system showed a satisfactory control effect. However, deformation on the fault-proximal side was greater than that on the coal-seam side, indicating that the fault had an asymmetric influence on roadway deformation.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eDeclaration of competing interest\u003c/h2\u003e \u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eCoal-Major Project (2025ZD1700904)\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eLIU Zenghui: investigation, data curation,validation,writing\u0026mdash;original draft. CHEN Minjun: investigation, validation, writing\u0026mdash;review and editing.LIU Feiyue:experiment data curation,validation\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author. The raw data supporting the conclusions of this article will be made available by the corresponding author on request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eKANG, H. Support technologies for deep and complex roadways in underground coal mines: a review. \u003cem\u003eInt. J. Coal Sci. 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Instability Mechanism and Surrounding Rock Control Technology of Roadway Subjected to Mining Dynamic Loading with Short Distance: A Case Study of the Gubei Coal Mine in China. \u003cem\u003eGeotech. Geol. Eng.\u003c/em\u003e \u003cb\u003e41\u003c/b\u003e, 1407\u0026ndash;1427. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s10706-022-02343-y\u003c/span\u003e\u003cspan address=\"10.1007/s10706-022-02343-y\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2023).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-9489970/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9489970/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eTo clarify the instability behavior of surrounding rock and its control effect when a heading face approaches a fault-protected coal pillar, a combined approach involving in-situ stress measurement, theoretical analysis, three-dimensional numerical simulation, and field monitoring was adopted to investigate the displacement response, plastic-zone evolution, and applicability of the existing support system under different fault distances. The results show that the in-situ stress field in the study area is a type-II stress field dominated by horizontal tectonic stress. The coupled effect of fault-induced structural weakening and stress concentration in the protective coal pillar significantly aggravates the deformation and plastic failure of the surrounding rock, and the surrounding rock stability is highly sensitive to the distance between the roadway wall and the fault. Under fault dip angles ranging from 54\u0026deg; to 70\u0026deg;, when the distance between the roadway wall and the fault varies from 5 to 40 m, the displacement and plastic-zone development of the surrounding rock exhibit obvious zonal characteristics. In particular, within 25 m from the fault, the fault influence on plastic-zone expansion and deformation increase is most significant; when the distance exceeds 25 m, the fault disturbance effect weakens markedly. Numerical simulation results further indicate that when the width of the protective coal pillar is less than 20 m, the plastic zone of the coal pillar expands significantly and its stability decreases markedly. Field monitoring results are generally consistent with the numerical simulation results, indicating that the existing bolt-cable support system can effectively control the deformation of surrounding rock in near-fault roadways. The results can provide a basis for stability analysis and support design of roadways in fault-protected coal pillar zones.\u003c/p\u003e","manuscriptTitle":"Surrounding Rock Stability and Engineering Practice of the 52607 Working Face Approaching a Fault-Protected Coal Pillar","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-08 13:56:57","doi":"10.21203/rs.3.rs-9489970/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-05-06T07:34:37+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-06T05:46:22+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"64675725757068365454786585012208304040","date":"2026-05-06T00:46:35+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-03T03:02:42+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"55378883779872860800332217659939209716","date":"2026-04-30T16:08:39+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"21468376176581349633625221382911866792","date":"2026-04-30T13:16:03+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"328509392369196413465030082352454400138","date":"2026-04-30T08:39:16+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-30T08:23:44+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-30T08:03:25+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-04-29T04:09:38+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-04-24T11:12:21+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2026-04-24T09:53:49+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"f06bdd7c-b8ad-4c1f-98ef-e1972bf46bc1","owner":[],"postedDate":"May 8th, 2026","published":true,"recentEditorialEvents":[{"type":"decision","content":"Revision requested","date":"2026-05-06T07:34:37+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-06T05:46:22+00:00","index":38,"fulltext":""},{"type":"reviewerAgreed","content":"64675725757068365454786585012208304040","date":"2026-05-06T00:46:35+00:00","index":37,"fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-03T03:02:42+00:00","index":36,"fulltext":""},{"type":"reviewerAgreed","content":"55378883779872860800332217659939209716","date":"2026-04-30T16:08:39+00:00","index":35,"fulltext":""},{"type":"reviewerAgreed","content":"21468376176581349633625221382911866792","date":"2026-04-30T13:16:03+00:00","index":34,"fulltext":""},{"type":"reviewerAgreed","content":"328509392369196413465030082352454400138","date":"2026-04-30T08:39:16+00:00","index":33,"fulltext":""},{"type":"reviewersInvited","content":"5","date":"2026-04-30T08:23:44+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-30T08:03:25+00:00","index":"","fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":67610452,"name":"Physical sciences/Energy science and technology"},{"id":67610453,"name":"Physical sciences/Engineering"},{"id":67610454,"name":"Earth and environmental sciences/Natural hazards"},{"id":67610455,"name":"Earth and environmental sciences/Solid earth sciences"}],"tags":[],"updatedAt":"2026-05-18T05:39:05+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-08 13:56:57","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9489970","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9489970","identity":"rs-9489970","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}