Search Results (70)

Mining-induced ground fissures in the Ordos Basin pose critical threats to coal mine safety and ecological stability. This study integrated multi-source monitoring data (improves data acquisition efficiency by 60%) with theoretical models to elucidate the dynamic response mechanism between overlying strata failure and ground fissure development. The results demonstrate that: (1) Two rock beam structural models for initial and periodic fracturing of thick, hard rock strata are established, demonstrating that both failure modes are dominated by tensile–shear mechanisms. (2) Ground fissures exhibit distinct zonal characteristics, displaying a gradient pattern of “strong disturbance in the near field and weak response in the far field.” Quantitative data support this pattern: average fissure density is 36/hm², with a maximum of 45/hm² recorded in the immediate vicinity of the working face, declining steadily outward. (3) Overlying strata failure forms three distinct zones—caving zone (42 m), fissure zone (158 m), and longitudinal penetrating zone—reflecting the heterogeneous fracture characteristics of medium-hard rock strata under mining influence. (3) The proposed “virtual main arch—virtual auxiliary arch” equivalent support system theory elucidates the mechanistic differences between step fissures (attributed to local support system instability) and collapse fissures (driven by global support system instability) from a mechanical perspective. The developed chain response theory fills a critical theoretical gap and provides a novel method for predicting and preventing geological disasters in mining areas. Full article

Underground coal mining can induce substantial surface deformation and trigger associated geological hazards. However, the quantitative links between mining-induced deformation, stress redistribution, and the spatial pattern of landslide occurrence remain insufficiently understood, particularly in loess-covered mining regions. Taking the Hecaogou Coal Mine in the Zichang mining area of the Loess Plateau, China, as an example, this study uses a coupled framework that integrates multi-temporal Interferometric Synthetic Aperture Radar (InSAR) observations with three-dimensional FLAC3D numerical simulation. We found that surface deformation is primarily concentrated above and adjacent to the mined-out zones, with maximum cumulative deformation of −169.3 mm during March 2017 and December 2023. The stepwise excavation simulations reveal that vertical displacement and vertical compressive stress in the overlying strata increase continuously as mining advances, thereby promoting tensile–shear failure and surface subsidence, with the subsidence magnitude quantitatively increasing from 3.7 mm at 200 m depth to 162 mm at 1000 m depth. A strong agreement between InSAR-derived deformation and simulated deformation fields is demonstrated, confirming the reliability of the modeled deformation process. We also found that the landslide density exhibits a strong spatial correlation with surface deformation, with high-density zones clustering near the mined-out areas. These findings enhance our understanding of how underground coal mining reshapes surface stability and influences the spatial pattern of landslide occurrences in coal mining regions. Full article

Underground coal gasification (UCG) is a controlled combustion process of in situ coal that produces combustible gases through thermal and chemical reactions. In order to investigate the UCG induced multi-physical field evolution and overlying strata fracture propagation of deep steeply inclined coal seam (SICS), which play a vital role in safety and sustainable UCG project, this study established a finite element model based on the actual geological conditions of SICS and the controlled retracting injection point (CRIP) technology. The results are listed as follows: (1) the temperature field influence ranges of the shallow and deep parts of SICS expanded from 15.56 m to 17.78 m and from 26.67 m to 28.89 m, respectively, when the burnout cavity length increased from 100 m to 400 m along the dip direction; (2) the floor mudstone exhibited uplift displacement as a result of thermal expansion, while the roof and overlying strata showed stepwise-increasing subsidence displacement over time, which was caused by stress concentration and fracture propagation, reaching a maximum subsidence of 3.29 m when gasification ended; (3) overlying strata rock damages occurred with induced fractures developing and propagating during UCG. These overlying strata fractures can reach a maximum height of 204.44 m that may result in groundwater influx and gasification failure; (4) considering the significant asymmetry in the evolution of multi-physical fields of SICS, it is suggested that the dip-direction length of a single UCG channel be limited to 200 m. The conclusions of this study can provide theoretical guidance and technical support for the design of UCG of SICS. Full article

Taking Yujialiang Coal Mine as the engineering background, aiming at the actual demand of 5-2 coal seam mining and 4-4 coal seam upward mining, the temporal evolution and spatial distribution characteristics of overburden failure height after 5-2 coal seam mining are systematically investigated by using multi-source field detection technology such as ground drilling, logging, and borehole peeping, combined with a numerical simulation method. The field detection results show that after the 5-2 coal seam is mined, the development height of the water-conducting fracture zone (WCFZ) is 116.25–129.92 m, and the height of the caving zone is 9.32–21.56 m. The 4-4 coal seam is located within the fracture zone, 15.99–22.88 m above the caving zone. The strength of the 4-4 coal seam and its surrounding rock affected by mining is reduced, with a more significant decrease in the middle of the goaf. The numerical simulation further reveals the law of overburden movement and deformation. After the 5-2 coal seam mining, the maximum subsidence of the 4-4 coal seam floor reaches 4.57 m, and there is stress concentration above the remaining coal pillars. The maximum vertical stress after mining all three working faces (52,204, 52,205, 52,206) is 4.10 MPa, and the stress environment above the goaf is better. The results show that the average distance between the 4-4 coal seam and 5-2 coal seam is about 39.45 m, and the upward mining is feasible, but the stability of the rock strata in the fracture zone should be paid more attention to. Based on the movement law of overlying strata and the characteristics of stress distribution, it is suggested that the mining gateway of the 4-4 coal seam should be arranged in the middle of the remaining coal pillar of the 5-2 coal seam or the corresponding area in the middle of the goaf so as to ensure the stability of the roadway surrounding the rock during mining. The research results provide a reliable theoretical basis and technical support for the upward mining design of the 4-4 coal seam in Yujialiang Coal Mine and have important reference value for the upward mining projects of coal mines under similar conditions. Full article

The accurate real-time delineation of overburden failure zones, specifically the caved and water-conducted fracture zones, remains a significant challenge in longwall mining, as conventional monitoring methods often lack the spatial continuity and resolution for precise, full-profile strain measurement. Based on the hydrogeological data of the E9103 working face in Hengjin Coal Mine, a numerical calculation model for the overburden strata of the E9103 working face was established to simulate and analyze the stress distribution, failure characteristics, and development height of the water-conducting fracture zones in the overburden strata of the working face. To address this problem, this study presents the application of a distributed optical fiber sensing (DOFS) system, centering on an innovative fiber installation technology. The methodology involves embedding the sensing fiber into boreholes within the overlying strata and employing grouting to achieve effective coupling with the rock mass, a critical step that restores the in situ geological environment and ensures measurement reliability. Field validation at the E9103 longwall face successfully captured the dynamic evolution of the strain field during mining. The results quantitatively identified the caved zone at a height of 13.1–16.33 m and the water-conducted fracture zone at 58–60.6 m. By detecting abrupt strain changes, the system enables the back-analysis of fracture propagation paths and the identification of potential seepage channels. This work demonstrates that the proposed DOFS-based monitoring system, with its precise spatial resolution and real-time capability, provides a robust scientific basis for the early warning of roof hazards, such as water inrushes, thereby contributing to the advancement of intelligent and safe mining practices. Full article

When constructing subway tunnels in composite strata consisting of overlying soil and underlying rock, placing the tunnel within the overburden rock strata and setting a certain thickness of safety cover rock on top is an effective way to ensure the safety of tunnel construction and the stability of the surrounding rock. However, there is currently no unified understanding or standard regarding the safe overburden thickness of the tunnel and its general rules. To investigate the effect of changes in the roof overlying rock thickness on the surrounding rock stability of subway tunnels, this study is based on the typical soil–rock strata of an underground tunnel section of Jinan Metro Line 4 in China. A total of 4 different conditions for the thickness of the overlying soil layer were considered, and 48 comparison schemes were designed. A systematic study of numerical simulation comparisons of tunnel excavation under different cover rock thicknesses was conducted. The deformation and plastic zone evolution characteristics of the surrounding rock were revealed under different cover rock thicknesses, and the existence of an optimal cover rock thickness range for tunnel crowns in soil–rock strata was identified. Based on this, a theoretical analysis model for the failure of the tunnel roof overlying rock was constructed. Using the upper-bound approach limit analysis method, the theoretical formula for the critical overburden thickness of the tunnel crown was derived. The influence of different rock mechanical parameters and tunnel design parameters on the critical overburden thickness was analyzed. The results were compared with numerical simulation results to verify the effectiveness of the proposed method. The research findings provide theoretical references for selecting reasonable buried depths and support designs for mining-bored tunnels in soil–rock composite strata. Full article

With the deepening implementation of the coordinated development strategy for energy exploitation and ecological conservation, green coal mining technology has become a critical pathway to achieve balanced resource development and environmental protection. This study investigates the stress field evolution and dynamic fracture propagation mechanisms in overlying strata during shallow coal seam mining in the Shenfu mining area. By employing a multidisciplinary approach combining triaxial compression tests (0–15 MPa confining pressure), scanning electron microscopy (SEM) microstructural characterization, elastoplastic theoretical modeling, and FLAC3D numerical simulations, the synergistic failure mechanisms of overlying strata were systematically revealed. Gradient-controlled triaxial tests demonstrated significant variations in stress-strain responses across lithological types. Notably, Class IV sandstone exhibited exceptional uniaxial compressive strength of 106.7 MPa under zero confining pressure, surpassing the average strength of Class I–III sandstones (86.2 MPa) by 23.6%, attributable to its highly compacted grain structure. A nonlinear regression-derived linear strengthening model quantified that each 1 MPa increase in confining pressure enhanced axial peak stress by 4.2%. SEM microstructural analysis established critical linkages between microcrack networks/grain-boundary slippage at the mesoscale and macroscopic brittle failure patterns. Numerical simulations demonstrated that strata failure manifests as tensile-shear composite fractures, with lateral crack propagation inducing bed separation spaces. The stress field exhibited spatiotemporal heterogeneity, with maximum principal stress concentrating near the initial mining cut during early excavation. Fractures propagated obliquely at angles of 55–65° to the horizontal plane in an ‘inverted V’ pattern from the goaf boundaries, extending vertically 12–18 m before transitioning to the bent zone, ultimately forming a characteristic three-zone structure. Experimental and simulated vertical stress distributions showed minimal deviation (≤2.8%), confirming constitutive model reliability. This research quantitatively characterizes the spatiotemporal synergy of strata failure mechanisms in ecologically vulnerable northwestern China, proposing a confining pressure-effect quantification model for support parameter optimization. The revealed fracture dynamics provide critical insights for determining ecological restoration timelines, while establishing a novel theoretical framework for optimizing green mining systems and mitigating ecological damage in the Shenfu mining area. Full article

Deep multi-coal seam mining is plagued by intense mining pressure, significant impacts of multi-working face mining on system roadways, and difficult surrounding rock deformation control—these issues severely threaten the safe and normal operation of roadways, creating an urgent need for effective dynamic disaster control technologies. Taking the 131,105 working face of Liuzhuang Mine (burial depth up to 740 m) as an example, this study addresses a critical research gap; existing roof cutting pressure relief technologies mostly focus on shallow/thin-coal-seam mining and fail to tackle secondary dynamic pressure induced by repeated mining in deep multi-coal seams—where the superposition of mining stress, ground stress, and goaf stress severely threatens system roadways. To fill this gap, three novel contributions are made. (1) A hierarchical “upper break and middle cut” deep-hole blasting design is proposed, distinct from single-mode roof cutting in existing studies. It achieves directional roof failure by “upper break” (damaging overlying hard rock) and “middle cut” (creating fissures between goaf and protective coal pillars), blocking stress transmission to roadways. (2) Numerical simulations specifically for deep strata (740 m) optimize key parameters: 25 m as the optimal cutting height and 35° as the optimal cutting angle, quantifying their effects on pressure relief (a gap in existing parameter optimization for deep mining). (3) A rapid sealing scheme combining AB material grouting with high-strength detonator pins is developed, solving the problem of slow hardening and poor sealing in traditional deep-hole processes (e.g., cement-only sealing), enabling blasting within 10 min after sealing. This cut off the integrity of the roof, blocked the pressure transmission of the roof stress to the existing system roadway, and achieved a 43.7% reduction in roadway surrounding rock stress (from 32 MPa to 18 MPa) and a 46.7% reduction in maximum roadway deformation (from the pre-blasting 15 cm to 8 cm). This study provides a reference for similar deep multi-coal seam projects. Field monitoring and numerical simulation results show the following. (1) The maximum deformation of the protected East Third Concentrated main roadway is only 8 cm, fully meeting normal operation requirements. (2) The “upper break and middle cut” technology effectively reduces the mining influence range (from 156 m without roof cutting to 125 m with 25 m roof cutting) and weakens roof stress transfer to roadways. This study verifies the feasibility and effectiveness of deep hole blasting for roof cutting, pressure relief, and roadway protection in deep multi-coal seam mining. It provides direct technical references and engineering application templates for similar projects facing roadway protection and dynamic disaster control challenges, contributing to the safe and efficient mining of deep coal resources. Full article

This work aimed to address the severe deformation and uncontrollable instability of surrounding rocks in gob-side roadways of ultra-thick coal seams under intense mining disturbances. Theoretical analysis, numerical simulation, and field practice were used to investigate the reasonable width of deteriorated coal pillars and surrounding rock control technology. The following items were clarified, including the structural characteristics of the overlying strata, the fracture location of main roof, and the stress, failure, and deformation patterns of surrounding rocks based on coal pillar width. In terms of the load-bearing characteristics of coal pillars, the reasonable width of deteriorated coal pillars in roadways was determined. According to the differential deformation characteristics of roadway roof and sides, an adaptive and targeted asymmetric control scheme was proposed for surrounding rocks. Key strata above the ultra-thick coal seam working face formed a structure of low-level cantilever beam and high-level articulated rock beam. The fracture position of the main roof cantilever beam was located 15.4 m from the coal wall of the goaf. When the pillar width reached 8 m during roadway excavation, the internal stress exceeded the original rock stress. The lateral deterioration range of the coal seam extended to 25 m from the coal wall after mining the upper working face. The protective coal pillars within the reasonable width range were all in a fully plastic failure state. The plastic-bearing zone within the deteriorated coal pillar occupied a high proportion when the coal pillar width ranged from 8 to 10 m, demonstrating convenient load-bearing capacity. Considering economic and safety factors, the reasonable width for deteriorated coal pillars was determined to be 8 m. The deformation of roof and side on the coal pillar side of the roadway was greater than that on the solid coal side, showing obvious asymmetric characteristics. A targeted asymmetric support scheme using truss anchor cables was proposed for surrounding rocks. This scheme formed an effective prestress field in the surrounding rocks, enabling enhanced control of severely deformed areas. Field practice has verified the rationality of the designed deteriorated coal pillar width and support system, ensuring safe production in the working face. This provides reference and inspiration for the reasonable width and surrounding rock control technology of deteriorated coal pillars under similar geological conditions. Full article

To reveal the fracture mechanism of overburden aquifers during mining under anticlinal structural zones in western mining areas, this study takes Panel 1309 of the Guojiahe Coal Mine as the engineering background and employs field investigations, physical similarity simulation, and numerical simulation methods to systematically investigate the overburden fracture and crack evolution laws during extra-thick coal seam mining in anticlinal zones. The research results demonstrate the following: (1) The large slope angle of the anticlinal zone and significant elevation difference between slope initiation points and the axis constitute the primary causes of water inrush-induced support failures in working face 1309. The conglomerate of the Yijun Formation serves as the critical aquifer responsible for water inrush, while the coarse sandstone in the Anding Formation acts as the key aquiclude. (2) Influenced by the slope angle, both overburden fractures and maximum bed separation zones during rise mining predominantly develop toward the goaf side. The water-conducting fracture zone initially extends in the advance direction, when its width is greater than its height, and changes to a height greater than its width when the key aquifer fractures and connects to the main aquifer. (3) The height of the collapse zone of the working face is 65 m, and the distribution of broken rock blocks in the collapse zone is disordered; after the fracture of the water-insulating key layer, the upper rock layer is synchronously fractured and activated, and the water-conducting fissure leads to the water-conducting layer of the Yijun Formation. (4) Compared to the periodic ruptures of the main roof, the number of fractures and their propagation speed are greater during the initial ruptures of each stratum. Notably, the key aquiclude’s fracture triggers synchronous collapse of overlying strata, generating the most extensive and rapidly developing fracture networks. (5) The fracture surface on the mining face side and the overlying strata separation zone jointly form a “saddle-shaped” high-porosity area, whose distribution range shows a positive correlation with the working face advance distance. During the mining process, the porosity variation in the key aquiclude undergoes three distinct phases with advancing distance: first remaining stable, then increasing, and finally decreasing, with porosity reaching its peak when the key stratum fractures upon attaining its ultimate caving interval. Full article

Coal mining can cause the rupture of the overlying strata, and the energy released by large-scale fractures can therefore induce earthquake disasters, which in turn can cause more secondary disasters. In the past 50 years, countless earthquakes induced by coal mining have been reported. In this paper, the main factors relating to the mining-induced seismicity, including the mechanical properties, geometry of the space, excavation advance, and excavation rate, are investigated using both experimental and numerical methods. The sensitivity of these factors behaves differently with regard to the stress distribution and failure mode. Space geometry and excavation advances have the highest impact on the surface settlement and the failure, while the excavation rate in practical engineering projects has the least impact on the failure mode. The numerical study coincides well with the experimental observation. The result indicates that the mechanical properties given by the geological survey report can be effectively used to assess the risk of mining-induced seismicity, and the proper adjustment of the tunnel geometry can largely reduce the surface settlement and improve the safety of mining. Full article

In order to examine the fracture development law of overlying strata in goafs and to reasonably lay out a high gas-drainage roadway under gob-side entry retaining with roadside filling, the 91–105 working face of the Wangzhuang Coal Mine was selected as the engineering case study. The failure laws and fracture development characteristics of the overlying strata in both the strike and dip directions using gob-side entry retaining and roadside filling were studied through rock mechanic tests and PFC numerical simulations. The optimal layout of the high gas-drainage roadway was determined through theoretical analysis and coupled Fluent–PFC numerical simulations, and on-site monitoring was conducted to evaluate the extraction effects. The results indicate that the first weighting interval of the 91–105 working face was 40 m, while the periodic weighting interval was approximately 14 m. The height of the falling zone was 14.4 m, and the height of the gas-conducting fracture zone was 40.7 m. In the dip direction, compared with coal pillar retaining, gob-side entry retaining with roadside filling formed an inverted trapezoid secondary breaking zone above the retaining roadway. Using this method, the span of the separation zone increased to 30 m, and the collapse angle decreased to 52°, resulting in a shift in the separation zone—the primary space for gas migration—toward the goaf. It was determined that the optimal location of the high gas-drainage roadway was 28 m above the coal roof and 30 m horizontally from the return air roadway. Compared with the 8105 working face, this position was 10 m closer toward the goaf. On-site gas extraction monitoring data indicate that, at this optimized position, the gas concentration in the high gas-drainage roadway increased by 22%, and the net gas flow increased by 18%. Full article

Based on Brillouin optical time-domain reflectometry (BOTDR) technology, this study integrates laboratory tensile tests and similarity simulation experiments to systematically investigate the relationship between overlying strata collapse and fiber strain during coal seam mining. An analytical expression was established to describe the correlation between overlying strata displacement and fiber strain. The horizontal fiber monitoring results indicate that fiber strain accurately captures the evolution of overlying strata collapse and exhibits strong agreement with actual displacement height. When the working face advanced to 115 m and 155 m, the rock strata primarily underwent stress adjustment with minimal failure. At 195 m, the collapse zone expanded significantly, resulting in a notable increase in fiber strain. By 240 m, severe roof failure occurred, forming a complete caving zone in the goaf. The fiber strain curve exhibited a characteristic “double convex peak” pattern, with peak positions closely corresponding to rock fracture locations, further validating the feasibility of fiber monitoring in coal seam mining. Vertical fiber monitoring clearly delineated the evolution of the “three-zone” structure (caving zone, fracture zone, and bending subsidence zone) in the overlying strata. The fiber strain underwent a staged transformation from compressive strain to tensile strain, followed by stable compaction. The “stepped” characteristics of the strain curve effectively represented the heights of the three zones, highlighting the progressive and synchronized nature of rock failure. These findings demonstrate that fiber strain effectively characterizes the collapse height and evolution of overlying strata, enabling precise identification of rock fracture locations. This research provides scientific insights and technical support for roof stability assessment and mine safety management in coal seam mining. Full article

The gob-side roadway technique is extensively utilized in coal extraction due to its capacity to enhance coal resource recovery efficiency and mitigate mining sequence conflicts. Nevertheless, increasing mining depths lead to progressively intricate stress conditions, posing challenges for maintaining gob-adjacent roadway surrounding rock stability. Taking the belt haulage roadway 1513 (BHR 1513) at Xinyi Coal Mine as an engineering case, this research investigates the application of narrow-pillar gob-side roadway construction under remote working face mining conditions. By integrating field observations, analytical modeling, and computational simulations, the cross-goaf pressure transfer phenomenon and its formation mechanism in narrow-pillar roadways under distant mining operations are systematically examined. Key findings reveal that during the alternating extraction of wide and narrow working faces, the caving angle terminates roof collapse within the narrow working face goaf at the second key stratum (KS2). The subsequent mining of the adjacent wide working face induces stress accumulation in the overlying “T”-shaped strata zone, triggering the instability of the inter-working face island pillar. This pillar failure merges the two goafs into an expanded void, initiating sequential fracture, collapse, and rotational displacement across all overlying key strata (KS). Consequently, previously intact KS above the narrow working face goaf undergo fracturing and rotation, amplifying lateral main roof block subsidence toward the goaf. This kinematic process generates substantial deformation in the narrow-pillar gob-side roadway. Full article

Pre-drilled composite planted piles are a commonly used construction method, but there is currently limited research on the load-bearing characteristics of piles penetrating boulders. Therefore, a new type of pre-drilled composite planted pile suitable for sites with isolated boulders has been developed. Using transparent soil technology, vertical uplift bearing capacity tests were conducted on pre-drilled piles to investigate the uplift capacity and load transfer mechanism of piles with boulders. Additionally, a discrete–continuous coupled 3D numerical model was employed to analyze the influence of boulder position on the pile’s uplift bearing capacity. The results indicate that the ultimate uplift bearing capacity of piles with boulders in the pile body is approximately twice that of piles without boulders, and this difference decreases with the increase of the distance between boulder and the pile end; under ultimate uplift loading, the pile end of a pile containing boulders contributes approximately 32% of the uplift bearing capacity, whereas the pile end without boulders contributes almost no uplift capacity; the presence of boulders increases the cross-sectional diameter of the pile, providing additional vertical support from the overlying soil, thereby significantly enhancing the ultimate uplift bearing capacity of the pile. Additionally, the boulder also increases the pathways for load transfer to the surrounding soil, further expanding the impact area on the soil surrounding the piles. Parameter analysis of the position of the boulder in the pile body reveals that under various conditions (boulder distances from the pile tip of 0, 50, 100, and 150 mm), both the ultimate uplift bearing capacity and the angle of the sliding failure surface decrease gradually as the depth of boulder decreases. This study provides a novel solution for pile foundation construction in similar boulder strata. Full article