Search Results (521)

To overcome the deformation and failure of surrounding rock in bottom-driven roadways within thick coal seams, this paper proposes a cooperative support theory for the sides and roof of such roadways in deep thick coal seams, based on existing support theories and technologies. The haulage roadway of the 2201 working face in the Yingpanhao Coal Mine is taken as the engineering prototype. Using the proposed theory, three optimized support schemes are developed. Numerical simulations are conducted to compare the deformation and failure behavior of roadway surrounding rock under the original support scheme and the three optimized schemes. The optimal scheme identified by simulation is then implemented in field engineering. The results show that, relative to the original scheme, roof subsidence is reduced by 51.99 mm, 43.83 mm, and 21.41 mm for Optimized ^{Scheme 1}, ^{Scheme 2} and ^{Scheme 3}, respectively, corresponding to reductions of approximately 39.71%, 33.48%, and 16.35%. Under the three optimized schemes, the convergence of the two sidewalls decreases from 480.21 mm to 157.73 mm, 250.84 mm, and 424.24 mm, i.e., reductions of about 67.15%, 47.76%, and 11.66%, respectively. Under the original support scheme, the vertical stress concentration zone is located approximately 5.4 m from the roadway side. Under the three optimized schemes, this distance is reduced to 3.6 m, 3.8 m, and 4.8 m, respectively. The extent of the plastic zone is also smaller under the optimized schemes than under the original scheme, with ^{Scheme 1} exhibiting the greatest reduction. Based on a comprehensive comparison, Optimized ^{Scheme 1} is selected as the optimal support scheme. In addition, ^{Scheme 1} improves deformation asymmetry, with the left–right sidewall asymmetry index decreasing from 3.34% to 0.06% and the sidewall–roof imbalance index decreasing from 3.67 to 2.00. Field application further confirms that this scheme substantially reduces roof–floor convergence and sidewall convergence, verifying the feasibility of the proposed cooperative support theory and technology for the sides and roof in deep bottom-driven roadways of thick coal seams. Full article

Scientific studies of mine closure and ecosystem management have become very important since the rate of coal mine closures in China has increased rapidly over the last decade. This study first analyzed spatiotemporal changes in land use and ecosystem services value (ESV) during the period 2000–2020 around the Kailuan Mining Area in Tangshan City. The area has a history of over 100 years of continuous mining activities in the region. The analyses used the PLUS model, multi-scenario simulation, and ESV equivalent factor method and multi-source data on land use, mining activities, socioeconomic factors, and climatic conditions. The study then projected land-use changes and spatiotemporal ESV characteristics for the year 2030 for two alternatives: (1) the Current Development Scenario (CDS), representing the current pace of development without mine closure; and (2) the Ecological Restoration Scenario (ERS), representing mine closure and ecological restoration. Key results include: (1) during 2000–2020, cultivated land and construction land were the primary land uses, with the overall trends showing decrease in cultivated, forest, pasture, and unused lands, varying water use areas, and continuously increasing construction land; (2) the revised ESV results show that total ESV declined from 31.27 million USD in 2000 to 25.30 million USD in 2020, a net decrease of 6.19 million USD, mainly because of cropland loss and degradation of forest and grassland; and (3) for 2030, the CDS projected a continued decline in total ESV to 24.30 million USD, whereas the ERS increased total ESV to 26.50 million USD, which is 2.19 million USD higher than the CDS and 1.20 million USD higher than the 2020 baseline. Compared with the CDS, the ERS increased cropland by 13.20 km² and reduced construction land by 10.06 km², indicating that reclaiming subsided water bodies and idle construction land into cropland and restored ecological land can enhance ecosystem services while mitigating subsidence-related risks. The framework can support data-driven post-mining land-use planning and ecological management in resource-based regions. Full article

The goaf backfilling with the coal gangue is an effective strategy for mitigating the mining-induced surface subsidence and reducing the solid waste accumulation. However, the conventional backfilling methods often suffer from limited transport efficiency, poor material distribution, and high operational cost. The present paper proposes a novel technique using an inclined spiral propeller to propel the gangue particles into the goaf, aiming to improve both the backfill rate and spatial uniformity. A three-dimensional parametric model of the inclined screw conveyor is developed, and the discrete element method (DEM) is employed to simulate the dynamic transport and placement of the gangue particles. An L9 ($3^3$) orthogonal experimental design is implemented to systematically evaluate the effects of the rotational speed (240, 300, 360 r/min), inclination angle ($30°$, $45°$, $60°$), and screw pitch (180, 240, 300 mm) on the two critical performance indicators, namely, filling mass and spreading coverage area. The range analysis and matrix analysis are performed to determine the primary influencing factors and to identify the optimal parameter combination for the multi-objective performance. The results show that the inclination angle is the dominant factor for the filling mass, with a $60°$ angle yielding the highest throughput (38.60 kg). In contrast, the rotational speed is the dominant factor for the spreading coverage area, where an increase from 240 to 360 r/min nearly triples the covered area. The optimal compromise for the comprehensive backfilling performance is the rotational speed 360 r/min, inclination angle $60°$, and screw pitch 300 mm, which simultaneously achieves the high transport capacity (36.65 kg) and the largest spreading area (2.87 ${\mathrm{m}}^2$). The present study provides a theoretical and methodological foundation for the engineering design of efficient, low-cost goaf backfilling systems. Full article

Geological disasters are frequently triggered in steep mountainous mining areas due to the coupling effects of underground excavation and slope stability, yet the applicability of traditional rock movement theories in such terrains remains unclear. This study investigates an extremely steep coal mine in southwestern China, integrating engineering geological surveys, unmanned aerial vehicle (UAV) measurements, InSAR monitoring, and rock movement theoretical calculations to analyze the impact of mining on mountain deformation and slope stability. The results show that the study area exhibits steep slopes (55–85°) and gently inclined, reverse-layered rock masses controlled by structural fracture zones, creating a geological environment prone to mining-induced landslides. The 1151 working face lies at a depth of 286–470 m, with a protective coal pillar of approximately 160 m left between the excavation and the cliff zone. InSAR monitoring indicates cumulative LOS deformation rates of −0.98 to 0.55 cm/a, with subsidence concentrated above the working face, while existing landslides in the cliff zone show no significant deformation. Comparison between theoretical calculations and InSAR inversion reveals that InSAR boundary angles (downslope 61–68°, upslope 67–73°) exceed theoretical predictions (downslope 48–52°, upslope 55°), indicating that complex topography and rock mass structure constrain mining-induced deformation propagation. The findings demonstrate that appropriately designed protective coal pillars and avoidance of unstable slopes can effectively mitigate the impact of mining-induced disturbances on existing hazards. This study provides valuable reference for landslide risk assessment and disaster prevention in extremely steep mining regions. Full article

Shallow-buried coal seams in western China are commonly overlain by deeply incised gully terrain, where mining is often accompanied by coal-wall spalling and abnormal increases in support resistance, which affect safe and efficient production. To investigate overburden failure during shallow-buried coal seam mining under gully terrain and to clarify the support–resistance mechanism, a typical working face was selected as the engineering background. Physical similarity simulation, 3DEC numerical simulation, and theoretical analysis were used to analyze overburden failure characteristics and the coupled evolution of the stress, displacement, and fracture fields. Mechanical models of key-stratum fracture and a support–resistance estimation model were established to reveal the influence of overburden-thickness variation on key-stratum fracture and support resistance. The results show that overburden failure in gully areas exhibits pronounced stage-dependent and asymmetric characteristics. In the similarity simulation, the initial fracture intervals of the key stratum in the downhill section were 32 m and 36 m, indicating an asymmetric fracture pattern with a shorter span on the left side and a longer span on the right side. In the uphill section, the periodic fracture interval of the key stratum decreased from 30 m to 24 m as the overburden thickness increased. During overburden failure in gully areas, the three fields exhibited a coupled relationship: stress concentration at the working face caused overburden failure and subsidence, which promoted fracture propagation, whereas stress redistribution in the goaf compacted the fractured overburden and promoted fracture closure. The overburden failure characteristics differed significantly between mining stages. During downhill mining, the key stratum behaved as a fixed-ended beam with a relatively large fracture interval, whereas during uphill mining, it formed a cantilever beam, and its fracture interval decreased with increasing overburden thickness. The loading mechanism of support resistance was shown to be jointly controlled by variations in gully overburden thickness and key-stratum fracture. During downhill mining, support loading increased gradually under the support of the fixed-ended beam key stratum. During uphill mining, support loading exhibited periodic abrupt increases under the combined effects of increasing overburden thickness and periodic fracture of the cantilever-beam key stratum. These findings provide a theoretical basis for strata pressure control at working faces in gully areas. Full article

To solve the low-precision prediction problem of noisy non-stationary goaf subsidence sequences, this study aims to establish a high-accuracy hybrid prediction model for mining surface deformation monitoring. The Global Navigation Satellite System (GNSS) monitoring data of surface subsidence in goaf areas exhibits non-stationary and noisy characteristics, which limits the accuracy of traditional prediction models. In this paper, a hybrid prediction model, namely the Improved Radial Movement Optimization–Variational Mode Decomposition–Gated Recurrent Unit (IRMO-VMD-GRU) model, is proposed. The IRMO algorithm is employed to globally optimize the key parameters of VMD, achieving adaptive and stable decomposition of the settlement sequences. The obtained Intrinsic Mode Function (IMF) sub-sequences are input into the GRU network for independent training and prediction, followed by superposition and reconstruction. The model is validated using the GNSS monitoring data from three monitoring points at a coal mine in Shaanxi Province, China. The results show that the proposed model outperforms the comparison models in all four evaluation indicators, namely Mean Absolute Error (MAE), Root Mean Square Error (RMSE), Mean Absolute Percentage Error (MAPE), and Coefficient of Determination (R²), with all R² values exceeding 0.8. The model demonstrates superior fitting performance, correlation, and generalization ability, which provides important practical technical support for goaf subsidence early warning, geological disaster prevention and engineering safety management in mining areas. Full article

To determine a rational, narrow coal-pillar width and support scheme for gob-side entry driving in thick coal seams, the 4904 return airway of the No. 9 coal seam at Zhongshui Coal Mine was investigated using limit-equilibrium analysis, FLAC3D numerical simulation, and field monitoring. The theoretical pillar width was calculated as 6.73–7.90 m, and sensitivity analysis showed that the selected 7 m pillar remained within the reasonable range under variations in key empirical and mechanical parameters. Numerical results indicated that a 7 m pillar could form a relatively complete central load-bearing core and effectively control surrounding-rock deformation, whereas further increasing the pillar width provided limited additional deformation reduction but caused greater coal loss. Compared with the 7 m pillar, the 9 m and 11 m schemes would cause additional coal losses of approximately 9.09 × 10³ t and 1.82 × 10⁴ t, respectively. A hierarchical synergistic support scheme consisting of high-strength bolts, long and short roof cables, and pillar-rib reinforcement cables was proposed. Compared with the equal-length roof-cable-plus-bolt scheme, the proposed scheme provided better control of roof subsidence and rib convergence. Field monitoring showed that roadway deformation gradually stabilized after support installation and remained within a controllable range under the monitored engineering conditions. Full article

To address the large deformation and instability of gob-side entry roofs in soft, thick coal seams induced by residual cavities left by hydraulic flushing, the 1609 working face of Jiulishan Coal Mine was selected as the engineering background. Field investigation, numerical simulation, and industrial field testing were combined to investigate the deformation and failure characteristics of surrounding rock and the corresponding control technology for gob-side entries with cavity-bearing roofs. The results indicate that residual cavities created by hydraulic flushing disrupt the stress transfer path within the roof, causing stress field distortion and expansion of tensile stress zones, thereby significantly weakening the roof load-bearing capacity. As the cavity size increases, the surrounding rock deformation and plastic zone continuously expand. When the cavity size exceeds 1.0 m, roof subsidence exhibits a nonlinear increase, and the fractured zone around the cavity connects with the roof plastic zone, forming a continuous failure band that serves as the key factor leading to surrounding rock instability. Based on the deformation characteristics of the cavity-bearing roof, namely shallow fragmentation, deep-seated separation, and structural instability, a collaborative control technology consisting of multi-level cable bolts, steel-beam reinforcement, and grouting through injection pipes was proposed. By establishing a shallow–intermediate–deep hierarchical load-bearing structure and reinforcing the fractured cavity zone through grouting, the technology reconstructs the surrounding rock load-bearing system and optimizes the stress environment. Field application results show that, for a roof containing a 1.5 m cavity, the maximum roof subsidence and separation were controlled within 102 mm and 55 mm, respectively, and the roadway maintained a stable condition throughout the monitoring period. The findings provide both a theoretical basis and engineering guidance for surrounding rock control of gob-side entries with cavity-bearing roofs in soft, thick coal seams. Full article

The continuous downward mining of close-distance coal seam groups faces severe challenges, yet existing research rarely addresses the structural failure mechanisms in groups with three or more layers. To address this, a two-dimensional physical similarity simulation combined with non-contact digital image correlation (DIC) technology and fractal geometry theory was conducted based on the geological conditions of Donghuantuo Coal Mine. This multi-method approach ensured the high-precision capture and validity of the spatiotemporal deformation data. The evolution of overlying strata and fracture networks during the extraction of four close-distance coal seams was quantified. The results indicate that underlying seam mining triggers severe secondary activation of upper goafs, which transforms the classic vertical three-zone structure into a composite trapezoidal failure zone. Driven by structural instability, the maximum subsidence of the overlying strata exhibits a step-like nonlinear growth, increasing dramatically from an initial 0.44 m to 8.70 m. Simultaneously, the topological evolution of the fracture network exhibits an overall nonlinear increase. Specifically, the fractal dimension rose from an initial value of 1.234 to a more stable value of 1.437, featuring two significant surges with growth rates of 8.34% and 3.79% that directly corresponded to spatial goaf connectivity. The mutual verification between the macroscopic displacement jumps and the fracture network evolution confirms the reliability of the obtained results. Ultimately, the mechanical model of the interlayer rock transitions from a rigid load-bearing beam to a loose buffer layer. Based on these mechanisms, a differentiated interlayer support strategy is proposed. High pre-tension and impact-resistant supports must be applied to the upper seams, whereas pressure-relief and flexible yielding supports are required for the lower seams. This study provides theoretical guidance for disaster prevention in close-distance coal seam groups mining. Full article

Surface deformation induced by underground coal mining shows a clear time-lag effect, with persistent residual deformation in old goafs under strip pillar mining conditions, drawing significant research attention. This study focuses on the Gucheng mining area, where 210 Sentinel-1A SAR images (May 2017–January 2025) were processed using SBAS-InSAR to derive 7.5 years of time-series surface deformation. Based on these results, five strip pillar mining panels with different cessation times were selected. Through comparative analysis, a time-progressive sequence was constructed to identify post-mining residual deformation and stage-wise stabilization characteristics, and to reveal long-term deformation responses occurring years after cessation, thereby reconstructing the long-term evolution of surface deformation in old goafs. Furthermore, a stacking ensemble prediction model was developed to predict subsidence trends at representative feature points. The results indicate that subsidence mainly ranges from −20 to −10 mm/a, with a maximum of approximately −64 mm/a and cumulative subsidence of about −515 mm. Surface deformation follows a stage-wise evolution pattern of “residual subsidence—stage-wise stabilization—secondary subsidence—deformation stabilization”, with durations of approximately 2, 2, and 14 years, respectively, and overall stabilization occurring after approximately 18 years. The predicted results from the stacking model are highly consistent with the SBAS-InSAR monitoring data and can reliably describe the evolution trend of surface subsidence. The findings provide important evidence for understanding long-term surface deformation in old goafs of strip pillar mining areas. Full article

Gob-side roadways driven along the floor while retaining top coal in thick soft coal seams are prone to instability under strong mining-induced dynamic loading. To clarify the instability mechanism and develop an effective control method, the 1609 return airway of Jiulishan Mine was investigated using field survey, borehole imaging, FLAC3D numerical simulation, industrial testing, and field monitoring. The results show that, under the combined effects of large mining height, insufficient filling of the gob by the caved immediate roof, weak retained top coal, and low coal strength, shear failure planes tend to develop within the narrow coal pillar and extend from the gob-side roof toward the floor. Once the dominant shear plane cuts through the pillar, the overall bearing structure is destroyed, leading to shear slip, asymmetric rib deformation, roof subsidence toward the coal-pillar side, and rib–roof coupled instability. Based on a multi-index evaluation of pillar load-bearing capacity, plastic zone development, stress concentration, roadway deformation, and coal recovery, a 3 m coal pillar was determined as the rational width. A coordinated “narrow coal pillar + cross-rib anchorage” scheme was proposed, and field verification confirmed its effectiveness in controlling roof separation, roadway surface displacement, and internal surrounding-rock damage. Full article

Rock bolt corrosion can weaken support systems and affect the long-term stability of water-flooded roadways. This study investigates the symmetry evolution of roadway deformation induced by bolt deterioration in alkaline water-flooded roadways, using Sanxin Coal Mine, Xinjiang, as a case. Electrochemical accelerated corrosion tests were conducted in 10% Na₂SO₄ solutions at pH = 9, 11, and 13 for 3, 6, and 9 d, followed by uniaxial tensile tests and FLAC3D numerical simulations. Under the controlled accelerated electrochemical conditions, the mass loss rate and corrosion rate generally increased with corrosion duration, with the greatest deterioration observed in the pH = 13 group after 9 d. The tensile curves of corroded bolts still exhibited elastic deformation, yielding, strain hardening, and post-peak softening stages. However, the yield load decreased with increasing mass loss rate, with fitted slopes of −0.1842, −0.07531, and −0.04998 kN/% for pH = 9, 11, and 13, respectively. Numerical results showed that bolt deterioration intensified roadway deformation and stress redistribution. Under severe corrosion, the horizontal displacement of the two sidewalls reached approximately −153.7 mm and 155.4 mm, while the maximum roof subsidence and floor heave reached about −188.7 mm and 191.3 mm, respectively. The shallow stress release zone expanded, and the deep stress concentration became more pronounced. Moreover, bolt deterioration intensified the roadway response while largely preserving its left–right symmetry. The numerical results incorporating the experimentally derived bolt deterioration showed increased roadway deformation and stress redistribution, indicating that bolt-capacity degradation can adversely affect roadway stability. These findings provide a reference for evaluating residual support performance and designing reinforcement measures for water-flooded roadways. Full article

Intensive extraction in shallow coal seam groups poses a severe threat to regional hydrogeological stability. This study investigates the evolutionary laws of water-conducting fracture zone (WCFZ) height and phreatic level response at the Wanli No. 1 Mine. Although limited to a two-dimensional physical model and a single-case study, the research integrates field monitoring with similarity simulations to evaluate the efficacy of gangue grouting backfilling (GGB). The results reveal a significant superposition effect in dual-seam mining, where cumulative disturbances trigger the reactivation of upper-seam fractures, causing the WCFZ to penetrate the surface (170 m)—a phenomenon absent in single-seam mining. Scientifically, this work identifies a dual-threshold effect for ecological and structural preservation. While an equivalent filling rate (η) of 35% is sufficient to maintain the ecological water level in single-seam mining, dual-seam extraction requires a minimum η of 65% to restrict phreatic drawdown within the 1.5 m ecological threshold. Notably, while the laboratory model suggests a higher mechanical safety limit of η = 80% to prevent fracture propagation, the 65% threshold provides a balance between backfilling efficiency and environmental protection. The primary scientific contribution of this study is the quantification of the coupling relationship between overburden mechanical stability and long-term ecological functions. By shifting the overburden failure mode from “surface-penetrating fracturing” to “controlled bending subsidence,” this research provides a robust theoretical foundation for decoupling mining intensity from hydrogeological degradation in fragile multi-seam environments. Full article

Bed-separation grouting filling mining is a damage-mitigation mining technology characterized by non-interfering mining and filling operations, low cost, and high efficiency. To recover coal resources from the 3801 working face located beneath a surface gas station in a Shanxi coal mine, this study first analyzed the maximum allowable deformation values for the gas station’s canopy, business hall, and oil storage tanks. Second, the feasibility and safety of bed-separation grouting filling mining at the 3801 working face were investigated using physical similarity modeling and the probability integral method. Finally, a field application of this technology was carried out at the 3801 working face. The results show that: (1) After the successive mining of the 3802, 3803 and 3801 working faces, the No. 17 bed separation was finally preserved above the 3801 working face. It is located in the upper part of the water-conducting fracture zone and has a thick impermeable isolation layer. (2) Physical similarity simulation and numerical simulation (3UDEC) of bed-separation grouting filling mining at the 3801 working face indicate that the underlying strata are effectively compacted after mining, and both overlying strata movement and surface subsidence above the grouting zone are significantly reduced. (3) The probability integral method was adopted to predict surface movement and deformation induced by mining at the 3801 working face (bed-separation grouting filling mining), the 3802 working face (fully mechanized top-coal caving mining) and the 3803 working face (full-seam mining in a single lift). All surface movement and deformation indices satisfy the surface deformation control requirements for the gas station. (4) After completion of the overburden bed-separation grouting filling project at the 3801 working face, the measured surface movement and deformation values during and after mining are all below the allowable deformation limits. No large deformations or cracks occurred in gas station structures including the canopy, business hall and oil tank farm. The protection effect is satisfactory, and the gas station has maintained normal operation throughout the mining period. Full article

Coal roadway support design still relies heavily on engineering analogy and simplified analytical rules, which limits transferability across sites with different geological and geometric conditions. This study develops a theory-constrained machine learning workflow for roof bolt-cable support design and evaluates the generated scheme through FLAC3D simulation. A hybrid dataset containing 80 samples, including 30 real engineering cases and 50 constrained augmented samples, was established. Twelve geological and roadway descriptors were used to predict eight roof-support parameters with weighted single-target models based on random forest, XGBoost, support vector regression, and Gaussian process regression. The optimal regressor differed among targets, confirming strong parameter heterogeneity. The 11104 return-air roadway of Jingu Mine was selected as the main validation case, and the Sanxia 1008 material roadway of Fucun Mine was used as an external consistency case. For the 11104 return-air roadway, the workflow predominantly recommended increasing the roof bolt length from 2.00 m to 2.64 m. FLAC3D results showed reduced roof subsidence and slightly lower local stress peaks, but no improvement in rib convergence. The proposed workflow is therefore better interpreted as a roof-priority optimization tool that integrates data-driven prediction, theoretical correction, and numerical verification. Full article