Search Results (109)

This study focuses on how rocks respond mechanically and how to keep them stable when soft rock roadways are under deep tectonic stress. It does this through a combination of theoretical analysis, numerical simulations, and field applications. We created a mechanical model of roof strata to calculate how much they would bend under both horizontal tectonic stress and their weight. This modeling helped us determine the critical yield limits. A systematic study of the angle θ between the direction of tectonic stress and the axis of the roadway showed that the concentration of horizontal stress on the roof gets stronger as θ increases, while the vertical stress on the sidewalls slowly gets weaker. The main sign of surrounding rock failure is shear damage that is most severe at the roof, floor, and shoulder angles. The maximum plastic zone depth occurs at θ = 90°. Studies that looked at both gob-side and along-roadway stages found that the two types of failure were very different, characterized by severe roof damage during roadway advancement and pronounced coal pillar instability in gob-side conditions. Based on these results, targeted support strategies were successfully used in field engineering to control deformations and provide both theoretical foundations and practical solutions for stabilizing deep soft rock roadways under tectonic stress. Full article

Pillarless mining technology is of great significance for improving coal recovery rates, but the intense mining-induced stress disturbances on gob-side entries often lead to surrounding rock instability. In this study, we focused on the ground control challenges in the headgate of Panel 81308 at Huayang Mine No. 2. Comprehensive monitoring of roof–floor convergence, rib deformation, and support resistance revealed the gob-side entry retaining deformation mechanisms with roof-cutting pressure relief; the results show that this retaining deformation exhibits the following three phases of characteristics: the rapid, decelerated, and stable stages. The average roof–floor convergence (607 mm) was significantly greater than the average rib deformation (170 mm), with floor heave accounting for 72.6% of total convergence. The coal pillar side showed dominant deformation in rib movements. The mining influence zones can be divided, based on their distances behind the working face, into strong disturbance zones (0–88 m), weak disturbance zones (88–142 m), and stabilized zones (>178 m). The cable bolt support system demonstrated advanced response characteristics. Compared with conventional gob-side entry retaining, the roof-cutting pressure relief technique altered stress transmission paths, significantly reduced roof load transfer efficiency, and effectively controlled roadway convergence, providing technical guidance for safe production in both this panel and mines with similar geological conditions. Full article

To resolve the critical issues of severe deformation, structural failure, and maintenance difficulties in the advanced reuse zone of gob-side-entry retaining roadways under pillarless mining conditions in ultra-long fully mechanized top-coal caving isolated mining faces, this study proposes a surrounding rock control technology incorporating pressure relief through roof cutting. Taking the 3203 ultra-long isolated mining face at Nanyang Coal Industry as the engineering case, an integrated methodology combining laboratory experiments, theoretical analysis, numerical simulations, and industrial-scale field trials was implemented. The deformation and failure mechanism of flexible formwork walls in gob-side-entry retaining and the fundamental principles of pressure relief via roof cutting were systematically examined. The vertical stress variations in the advanced reuse zone of the retained roadway before and after roof cutting were investigated, with specific focus on the strata pressure behavior of roadways and face-end hydraulic supports on both the wide coal-pillar side and the pillarless side following roof cutting. The key findings are as follows: ① Blast-induced roof cutting reduces the cantilever beam length adjacent to the flexible formwork wall, thereby decreasing the load per unit area on the flexible concrete wall. This reduction consequently alleviates lateral abutment stress and loading in the floor heave-affected zone, achieving effective control of roadway surrounding rock stability. ② Compared with non-roof cutting, the plastic zone damage area of surrounding rock in the gob-side entry retained by flexible formwork concrete wall is significantly reduced after roof cutting, and the vertical stress on the flexible formwork wall is also significantly decreased. ③ Distinct differences exist in the distribution patterns and magnitudes of working resistance for face-end hydraulic supports between the wide coal-pillar side and the pillarless gob-side-entry retaining side after roof cutting. As the interval resistance increases, the average working resistance of hydraulic supports on the wide pillar side demonstrates uniform distribution, whereas the pillarless side exhibits a declining frequency trend in average working resistance, with an average reduction of 30% compared to non-cutting conditions. ④ After roof cutting, the surrounding rock deformation control effectiveness of the track gateway on the gob-side-entry retaining side is comparable to that of the haulage gateway on the 50 m wide coal-pillar side, ensuring safe mining of the working face. Full article

The fault fracture zone has the characteristics of low strength and poor water resistance. These factors often lead to stress concentration and significant deformation during roadway excavation. In order to improve the anti-deformation ability and strength of the surrounding rock and reduce the support pressure, taking the roadway passing through the F2 fault in the Wugou coal mine as an example, the evolution characteristics of the surrounding rock of the roadway passing through the fault were studied using FLAC3D numerical simulation software, and the stress evolution law and failure characteristics of the surrounding rock in three stages of the roadway driving through the fault fracture zone were analyzed. The slurry diffusion characteristics under different grouting hole layouts were studied using COMSOL software, and the effectiveness of ground directional grouting (combined directional drilling technology with ground grouting technology) reinforcement technology was explored via similar simulation experiments. After the pre-grouting reinforcement of the surrounding rock by the ground directional hole in the field, the fault fracture zone was successfully excavated. The key technical system of the shield roadway passing through the fault based on the directional drilling and ground grouting technology was summarized and put forward. The three-hole drilling and the circumferential four-hole drilling layouts were used to realize the grouting in the fault fracture zone. Engineering practice shows that ground directional grouting has significant advantages and improves the mechanical properties of the broken weak surrounding rock. The deformation of the roadway roof is 128 mm, and the deformation of the two sides is controlled within 100 mm. This method greatly improves the stability of the roadway and has been verified by the field results. Full article

The non-uniform deformation and failure phenomena encountered in steeply inclined coal seams during roof-cutting and gob-side entry retaining operations demand urgent resolution. Taking the haulage roadway of the 3131 working face in Longmenxia South Coal Mine as the research background, the theoretical analysis method is adopted to explore the mechanical state of the main roof in inclined coal seams and the design of roadside support resistance. According to the structural evolution characteristics of the main roof, it is divided into four periods. Based on the elastic theory, corresponding mechanical models are established, and the mechanical expressions of the main roof stress and deflection are derived. The distribution characteristics of the main roof’s mechanical state in each zone and the influence law of the coal seam dip angle on the main roof’s mechanical state are studied. This study reveals a critical transition from symmetric to asymmetric mechanical behavior in the main roof structure due to the coal seam dip angle and roof structure evolution. The results show that, in the absence of roadside support, during the roadway retaining period, the upper surface of the main roof is in tension, and the lower surface is under compression. The stress value increases slowly from the high-sidewall side to the middle, while it increases sharply from the middle to the short-sidewall side. Under the inclined coal seam, as the dip angle of the coal and rock strata increases, the component load perpendicular to the roof direction decreases, and the roof deflection also decreases accordingly. On this basis, the design formula for the roadside support resistance of gob-side entry retaining with roof cutting in inclined coal seams is presented, and the roadside support resistance of the No. 3131 haulage roadway is designed. Building upon this foundation, a design formula for roadside support resistance in steeply inclined coal seams with roof-cutting and gob-side entry retaining has been developed. This formula was applied to the No. 3131 haulage roadway support design. Field engineering tests demonstrated that the maximum roof-to-floor deformation at the high sidewall decreased from 600 mm (unsupported condition) to 165 mm during the entry retaining period. During the advanced influence phase of secondary mining operations, the maximum deformation at the high sidewall was maintained at approximately 193 mm. Full article

This study investigates the surrounding rock failure caused by the fracture line of the main roof above the gob-side roadway during fully mechanized top-coal caving mining in a 19 m thick coal seam. As mining progresses, stress concentration occurs in the roadway roof. Furthermore, the fracture line of the main roof above the roadway poses a significant threat to the structural stability of the gob-side roadway, leading to the localized failure of the roof structure, which consequently affects the safe and efficient production of the mine. This study investigates the shear failure mechanism of the roadway top coal and analyzes the failure characteristics and stress evolution law of the surrounding rock when the main roof fracture line (MRFL) is located above the roadway through three integrated approaches: theoretical analysis, numerical simulation, and physical similarity modeling. To effectively mitigate damage to the top coal, it is proposed to implement a five-hole tray coupled with high-strength prestressed anchor cables for reinforcing the surrounding rock, while compact wooden piles in combination with single pillars are employed to strengthen the roadway support control measures. It is verified by field tests that these control methods significantly improve the stability of coal above the entry and greatly mitigate the likelihood of surrounding rock failure. Full article

Predicting rock failure under excavation-induced non-uniform stress remains challenging due to the inability of conventional homogeneous specimens to replicate field-scale stress gradients. A novel trapezoidal sandstone specimen with adjustable top-surface inclinations (S75/S85) is proposed, uniquely simulating asymmetric stress gradients to mimic excavation unloading. Geometric asymmetry combined with multi-scale characterization (CT, SEM, PFC) decouples stress gradient effects from material heterogeneity. The key findings include the following points. (1) Inclination angles > 15° reduce peak strength by 24.2%, transitioning failure from brittle (transgranular cracks > 60) to mixed brittle-ductile modes (2) Stress gradients govern fracture pathways: transgranular cracks dominate high-stress zones, while intergranular cracks propagate along weak cementation interfaces. (3) PFC simulations reveal a 147% stress disparity between specimen sides and validate shear localization angles θ = 52° ± 3°), aligning with field data. This experimental–numerical framework resolves limitations of traditional methods, providing mechanistic insights into non-uniform load-driven failure. The methodology enables targeted support strategies for deep asymmetric roadways, including shear band mitigation and plastic zone reinforcement. By bridging lab-scale tests and engineering stress states, the study advances safety and sustainability in deep roadway excavation. Full article

The extensive adoption of large mining height technology and the progressive deepening of mining operations have presented formidable challenges to the safety of roadway support. The selection of roadway support configurations and their operational parameters is critically important in underground mining operations. Taking the open cut of Hongliu Coal Mine as the engineering background, this study conducts similar model experiments and field monitoring to evaluate the large-section open-cut support system. We aim to address unreasonable parameters and the low efficiency of this system in fully mechanized mining faces with large mining heights. The results demonstrate that deformation and failure initially occur at the cut corners. According to field observation data, the convergence of the system’s two sides across the three measuring stations is markedly greater than the roof subsidence on average (104.9 mm vs. 46.0 mm). This indicates the collapse of surrounding rocks on both sides. The peak abutment pressure of the cutting hole occurs approximately 16 cm from the coal wall (scaled to 3.2 m on site). Full article

This study aims to comprehensively analyze the stability of rock mass around the gob side driving roadway in a significant inclined mining face. By considering the geological parameters and engineering conditions of specific cases, we carefully explored many factors affecting the stability of the surrounding rock mass, such as the mechanical properties of rocks, formation inclination, and the existence of goaf. Based on this, we construct a numerical model for analyzing the stability of the rock mass around the gob side driving roadway. Subsequently, we made a detailed investigation of the stress distribution and the characteristics of the plastic zone. In addition, through the analysis of the destruction mode and stress distribution characteristics of the rock mass, we establish the appropriate width of the coal pillar and thus provide a scientific basis for the formulation of support countermeasures; finally, the support countermeasures proposed in this study have achieved remarkable results in practical application and verify the feasibility and practicability of the research method. This support scheme ensures the stability of the gob side entry over its service life. It is hoped that this scheme can be promoted in similar projects to help maintain mine safety. Full article

In coal mine roadways excavated along the goaf with water accumulation, the roadway is subjected to the combined effects of water infiltration and multiple stresses from excavation activities, leading to significant deformation and challenges in determining the appropriate coal pillar width. This study, based on the Jianxin Coal Mine 4301 tailgate, utilizes the advanced three-dimensional numerical calculation software FLAC^3D 6.0 to develop a comprehensive seepage flow model. By analyzing the distribution of key roadway surrounding rock properties, such as deviatoric stress, plastic zone, and dissipated energy, the influence of coal pillar width on roadway deformation and failure characteristics is systematically investigated. The findings provide novel insights into the roadway stability control under complex geological conditions. Specifically, the results reveal that: (1) When the coal pillar width is less than 9 m, stress concentration zones are observed, fully connected by plastic zones and dissipated energy. For widths exceeding 9 m, the influence of the goaf diminishes, leading to a stress reduction zone within the coal pillar and a shift in dissipated energy density distribution from a penetrating shape to an independent double-core shape. The plastic zones on both the goaf and roadway sides become independent, indicating a transition from an unstable to a stable coal pillar state. (2) Using the Analytic Hierarchy Process (AHP), a zoning control system for the roadway surrounding rock is established, dividing the roadway into three regions: normal support, reinforced support, and special support. Industrial experiments corroborate the simulation results, and on-site monitoring demonstrates that the control measures significantly improve roadway stability. This study presents an innovative approach to the design and control of coal pillars in water-affected mine roadways, offering valuable contributions to both the scientific understanding and practical application of mining engineering in similar geological settings. Full article

Based on the engineering problem of large deformation and support failure in the roadway of Ronghua No. 1 Mine, on-site in situ stress testing was carried out to understand the distribution characteristics of the in situ stress around the roadway. Then, a stability analysis of the roadway was conducted on the key factors causing support failure. Combining the on-site situation and the results of the stability analysis, the principle of surrounding rock stability control in a high horizontal stress roadway was proposed. Based on this principle, an optimized scheme was designed. The optimized scheme and the original scheme were comparatively analyzed through numerical simulation to verify the applicability of the optimized scheme. Finally, the optimized scheme was applied on-site, and the roadway was monitored. The results were as follows: (1) from the results of the in situ stress test conducted in Ronghua No. 1 mine, the horizontal tectonic stress field is dominant. (2) Based on the characteristics of in situ stress distribution, the angle between the direction of the maximum horizontal principal stress and the roadway orientation, along with varying lateral pressure coefficients, is directly proportional to the stress and deformation of the surrounding rock. (3) Through numerical simulation analysis, an optimized support scheme was proposed based on the original design. The roof subsidence was reduced by 37.3%, the floor heave was reduced by 49.5%, and the side convergence was reduced by 34.7%. The surrounding rock stability of the roadway was significantly improved. (4) The optimized support scheme was applied in the 6A# Left Second roadway at Ronghua No. 1 Mine. Through on-site monitoring of the perimeter rock deformation, significant reductions in deformation and increased stability were observed. The research content provides a theoretical basis and practical experience for the stabilization of high horizontal stress roadways. Full article

Currently, research on the stability of roadway-side supports in gob-side entry techniques primarily focuses on vertical stress, neglecting the lateral effects induced via roof collapse and waste rock compaction in the mined-out area. This paper systematically investigates the effect of roof rotation and the compression of waste gangue on the lateral load-bearing behavior of the roadway-side support system, combining theoretical analysis with FLAC3D numerical simulations. The results indicate that the lateral load-bearing capacity of the support system is positively correlated with both mining height and the width of the roadway-side support. When the mining height or the support width is small, the lateral load-bearing capacity of the support system is weaker, making it more prone to sliding failure. Furthermore, lateral load control technology for the roadway-side support system is proposed, which includes “roof cutting + increasing width”. When the stress transfer path of the roof is blocked, as the support system width increases from 1 m to 2 m, the lateral load-bearing capacity of the roadway-side support significantly increases and then stabilizes. This results in different extents of expansion in the elastic region within the support system, providing valuable insights for the design of roadway-side supports. Full article

Due to the poor stability of the roof and floor of the roadway in the 3-1 coal seam of Chahasu Coal Mine, traditional gob-side entry retaining (GER) methods fail to meet the production safety requirements. To address this, a GER technology using paste backfill was proposed. This study reveals the stability mechanism of the surrounding rock in GER with paste backfill through theoretical analysis, numerical simulation, and industrial experiments. First, theoretical analysis was conducted to determine the overburden movement characteristics under varying backfill ratios. Uniaxial compressive tests on the paste material demonstrated that its bearing capacity reaches a relatively stable state after 14–28 days of curing. Second, numerical simulations were performed to study the deformation patterns of the surrounding rock and mine pressure characteristics under backfill ratios of 65%, 75%, 85%, and 95%. The Strain-Softening model was used to calibrate the backfill material parameters. The results showed that as the backfill ratio increased, the support provided by the backfill material improved, leading to enhanced bearing capacity of the overlying strata, reduced mine pressure intensity, significantly decreased deformation of the roadway, and substantially improved stability of the surrounding rock. Third, under a backfill ratio of 95%, the evolution of the abutment stress during face advancement was investigated. It was found that as the working face advanced, the backfill material and the overlying strata gradually formed a stable composite structure, with the abutment stress in the mining area stabilizing over time. Finally, to address the issue of insufficient initial strength and limited support capacity of the paste backfill material, a comprehensive control system for surrounding rock stability was proposed. This system integrates a basic bolt-mesh-cable support structure with localized reinforcement using portal hydraulic supports. Field industrial practices demonstrated that after applying this comprehensive control technology, the convergence of roof and floor was approximately 190 mm and the convergence of two ribs was about 140 mm, effectively ensuring the stability of surrounding rock in GER with paste backfill working face. Full article

Aiming to address the challenges of determining the coal pillar’s width and managing the significant deformation of the surrounding rock in the deep gob-side entry driving, the limiting equilibrium zone theory, employing the operational area of Dongpang Mine 21110 as the engineering setting, states that a coal pillar’s appropriate width in the gob-side entry driving falls between 7.9 and 9.8 m. The pattern of vertical stress distribution and the extent of the plastic zone in the roadway for coal pillar widths of 7.0 m, 8.0 m, 9.0 m, and 10.0 m are analyzed, respectively, investigated using the numerical simulation method of FLAC^3D. The acceptable coal pillar width in the deep gob-side entry driving is 8.0 m. Combined with the roadway surrounding rock borehole inspection results, the fracture development condition of the roadway’s full-face surrounding rock is determined, and the asymmetric aberration characteristics, with significant surrounding rock damage depth at the coal pillar flank location, are obtained. Based on the theoretical calculations, an integrated proposal for a “non-symmetrical bolt and cable anchor” coupling support scheme for the surrounding rock in the gob-side entry driving is put forward. This was applied at the Dongpang coal mine site. Engineering practice shows that leaving an 8.0 m coal pillar width and adopting the “non-symmetrical bolt and cable anchor” support system design can control the deformation of the surrounding rock in the track entry at a reasonable range, which ensures the stability of the surrounding rock in the gob-side entry driving. Full article

The gob-side entry driving in deep mines with soft rock exhibits a complex deformation and instability mechanism. This complexity leads to challenges in roadway stability control which greatly affects the coal mine production succession and safe and efficient mining. This paper takes the gob-side entry in Liuzhuang Coal Mine as the background. By adopting the method of theoretical analysis, a dynamic model of the roof subsidence in the goaf is established. The calculation indicates that achieving the stable subsidence of the basic roof and the equilibrium of the lateral abutment stress within the goaf requires a minimum of 108.9 days, offering a theoretical foundation for selecting an optimal driving time for the gob-side entry. The control technologies and methods of gob-side entry through grouting modification and high-strength support are proposed. Enhancing the length of anchor ropes and the density of bolt (cable) support to improve the role of the roadway support components can be better utilized, so the role of the support components of the roadway can be better exerted. The method of grouting and the reinforcement of coal pillars can effectively improve the carrying capacity of coal pillars. The numerical simulation is used to analyze the deformation law of gob-side entry. The study reveals significant deformation in the coal pillar and substantial roof subsidence, highlighting that maintaining the stability of the coal pillar is crucial for ensuring roadway safety. Following the grouting process, the deformation of the coal pillar and roof subsidence decreased by 16.7% and 7.1%, respectively. This demonstrates that coal pillar grouting not only mitigates pillar deformation but also provides effective control over roof subsidence. This study offers a quantitative calculation method to ascertain the excavation time of gob-side entry, and suggests that the application of high-strength support and the practice of coal pillar grouting can effectively maintain the steadiness of gob-side entry in deep mines with soft rock. Full article