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Intelligent computing is transforming safety inspection methods and response strategies in coal mines. Due to the significant safety hazards associated with mining excavation, this study proposes a multi-source data based predictive model for assessing gas risk and implementing countermeasures. By examining the patterns of gas dispersion at the longwall face, utilizing both temporal and spatial correlation, a predictive model is crafted that incorporates safety thresholds for gas concentrations, four-level early warning method and response strategy are devised by integrating weighted predictive confidence with these correlations. Initially tested using a public dataset from Poland, this method was later verified in coal mine in China. This paper discusses the validity and correlation of multi-source monitoring data in temporal and spatial correlation and proposes a risk warning mechanism based on it, which can be applied not only for safety warning but also for regulatory management. [ABSTRACT FROM AUTHOR]

To solve various extraction-related problems existing in the deep Jurassic mines in the Inner Mongolia-Shaanxi (IM-S) mining area, this paper puts forward a method to control roof water hazards based on the sedimentary facies pattern of the aquifers. The problems we addressed are: high volumes of goaf water, mixing of coal-based water in the stope, the proximity of the upper coal seam to water-enriched aquifers, and the inability for safe excavation and stoping. We first investigated the spatial distribution patterns of the aquifers and their related storage properties. A zone model of water yield compatible with the hydrogeological characteristics of a deep Jurassic mine was evaluated for the aquifers in the roof of the 3–1 coal mine, and a "low-position and lateral interception" control method was proposed based on the water yield zonation. The results demonstrated that the depositional environment for the sandstone aquifer in the first member of the Zhiluo Formation had a channel bar paleoenvironment that was characterized by a varying water table. This proved to be the key layer for preventing and controlling the water hazards. The method described in this paper effectively mitigated the water hazards associated with that aquifer in the study area and thus provide a theoretical and practical basis for controlling mine water hazards in the IM-S mining area. [ABSTRACT FROM AUTHOR]

The instability control of deep mining roadway is currently dominated by ejection and grouting, as well as floor support, which contradicts the economic and excavation efficiency of production. Taking the failure site of Xin'an Coal Mine in China as an example, this paper systematically analyzes the failure characteristics of supporting components, crack propagation, and surrounding rock deformation in situ, and the impact of failure on the rights and interests of staff, enterprise benefits, and low-carbon environmental protection. Then, a three-way continuous anchorage theory and the derived control technology are proposed based on the exploration of the instability mechanism. Besides, the UDEC Trigon model is adopted to reproduce the instability process and demonstrate the effect of the proposed control technology. According to the subsequent industrial test, the plastic deformation developing from shallow to deep parts leads to the bending, subsiding, swelling, and deformation of rock mass within 5.5 m of the roof, and the surrounding rock failure mainly features the shear failure in the middle of the tail of the supporting components and anchorage relaxation. Meanwhile, it wrecks huge havoc on the rights and interests of staff, enterprise benefits, and CO 2 emission. Following the smooth application of the new technology to roadway excavation, the roof subsidence and two side displacements are reduced by 91.18% and 58.5%, respectively, compared with the original scheme, the rock mass fractures within 1.71 ~ 3.92 m of the roof is effectively sealed, the evolution depth of bed separation is down by 78.6%, and the excavation efficiency rises by 50% while ensuring the supporting cost. In addition, the defects of the new technology in engineering application are also discussed. Accordingly, the R&D and application of this new technology provide a positive reference for the efficiency control of deep mining roadway. Highlights: A three-way continuous anchorage theory and relevant technique are proposed. Multiscale original position analyses are conducted on the failure features of deep coal roadway. The impact of surrounding rock instability on sustainability was considered for the first time. The new scheme reduces roof subsidence by 91.2% and sides' displacement by 58.5%. [ABSTRACT FROM AUTHOR]

Since the western region of China, which is typical of extraordinary resource endowments, has gradually emerged as the major mining zone in China, the mining of thick coal seams and roadways with coal-rock composite roof have become more and more common in this region. However, it is extremely difficult to realize safe and effective maintenance and control of such roadways due to the differences in natural endowments of coal-rock masses. With the roadway with coal-rock composite roof of Hulusu Coal Mine in western China as the engineering background, experiment research on large-scale similarity model was conducted through comprehensive measures such as the pneumatic loading system, the surrounding rock stress monitoring system, the roadway deformation monitoring system, the bolt load monitoring system, and the displacement field monitoring system in this paper. According to the results of the experiment, the control effects of the three support systems on the roadway with coal-rock composite roof were significantly different. When the single support of short anchor bolts was applied, the comparatively low initial anchor-hold failed to constrain the initial micro deformation of the roof. Consequently, wide-range fractures of the roof were triggered at a loading pressure of 0.8 MPa. In the meanwhile, the deep surrounding rocks witnessed a downward inflection point in stress, accompanied by the possibility of the collapse of the thin-layer anchorage zone at any time. As for the support combining both short anchor bolts and long anchor cables, though a reinforced effect on the bolt anchorage zone could be achieved with the help of the cables, the active reinforcement capacity of the bolt was limited. The bolt anchorage zone was the first to be damaged at a loading pressure of 0.9 MPa, which would subsequently affect the effective bearing capacity of the deep surrounding rocks. In the application of the single support of high-strength long anchor bolts, the long bolts with high pre-tightening force were able to lock multiple groups of coal-rock strata to form a thick-layer anchorage bearing structure capable of withstanding a load as high as 1.0 MPa. The crash and collapse of the coal wall eventually caused the subsidence of the roof. Based on the intense dynamic load experiment and the feedbacks of engineering application outcomes in the field, it was concluded that the high-pretension thick-layer (HPTL) anchoring technology can effectively constrain the deformation of roadways with coal-rock composite roof with favorable application outcomes. [ABSTRACT FROM AUTHOR]

Longwall top coal caving technology is one of the main methods of thick coal seam mining in China, and the classification evaluation of top coal cavability in longwall top coal caving working face is of great significance for improving coal recovery. However, the empirical or numerical simulation method currently used to evaluate the top coal cavability has high cost and low-efficiency problems. Therefore, in order to improve the evaluation efficiency and reduce evaluation the cost of top coal cavability, according to the characteristics of classification evaluation of top coal cavability, this paper improved and optimized the fuzzy neural network developed by Nauck and Kruse and establishes the fuzzy neural network prediction model for classification evaluation of top coal cavability. At the same time, in order to ensure that the optimized and improved fuzzy neural network has the ability of global approximation that a neural network should have, its global approximation is verified. Then use the data in the database of published papers from CNKI as sample data to train, verify and test the established fuzzy neural network model. After that, the tested model is applied to the classification evaluation of the top coal cavability in 61,107 longwall top coal caving working face in Liuwan Coal Mine. The final evaluation result is that the top coal cavability grade of the 61,107 longwall top coal caving working face in Liuwan Coal Mine is grade II, consistent with the engineering practice. [ABSTRACT FROM AUTHOR]

The study of water-conducting fracture zone development height is key to the scientific prevention and control of water damage in mines. Based on the geological conditions of the Wenjiapo coal mine in Binchang, China, this paper investigates the development of water-conducting fracture zone in overlying bedrock during mining under large buried depth and huge thick aquifer by combining on-site well-location microseismic monitoring and laboratory similar material simulation. To overcome the limitation of the " limited outlook " of water-conducting fracture zone investigation, the spatial development characteristics of roof fissures in coal seam mining were determined by on-site " the underground - ground" combined microseismic monitoring and follow-up monitoring, and the development of overlying rock fracture under the large depth of burial was concluded. The fractures were mainly distributed in the upper part of the protective coal pillar on both sides of the working face, but less in the upper part of the working face, and primarily distributed in the protective coal pillar on the side of the working face and the adjacent mining area. To verify the accuracy of the conclusion, the overlying bedrock movement and deformation characteristics and the development process of the hydraulic fracture zone during coal seam mining were analyzed by simulating similar materials in the laboratory, using the monitored area as a prototype. The results show that the development height of the mining fracture zone obtained from microseismic monitoring is basically consistent with the simulation results of similar materials. The research finding have significant implications for the study of fracture distribution characteristics and the evolution law of mining overburden, and provide a foundation for scientific prevention and control of water damage on the roof. [ABSTRACT FROM AUTHOR]

This paper presents a study on the stability of a mine entry of an innovative approach to non-pillar coal mining—gob-side entry retaining using cantilever beam theory (GERMC). This method is on the rise in China and it has shown to increase the coal seam rate of recycling and mining productivity. The method utilizes the caved-in material resulting from the mining activities to fill the gob area and ensure the stability of the roof of the already mined area. The caved-in material will form the gob-side wall of the retained entry. This characteristic is unique to this method. Thus, there are not many studies that analyze the stability of the filling material and of the gob-side entry wall under these circumstances, which is a vital element for the safety of the mining operations. This paper studies the stability of the gob-side retained entry of the Hongjingta underground coal mine in China. The authors perform the analysis using a discrete fracture network (DFN) model developed by the Massachusetts Institute of Technology (MIT), GEOFRAC, in combination with the discrete-element method (DEM) software UDEC. GEOFRAC estimates the rock blocks (fracture networks) in the filling body, from fracture traces measured along the gob-side wall of the entry. Statistical methods are used to estimate the fracture intensity and the mean fracture areas, which are inputs to the DFN. The generated fracture networks are then inputted into the DEM code, UDEC, to evaluate the stability of the mine-retained entry. For this study, we developed two types of models in UDEC, one considering the fractures generated by the DFN model and another considering the gob-filling material as a continuum. This methodology—combined DFN–DEM—is unique and provides a more realistic representation of the gob-filling material by considering the fractures in the filling body and by estimating those fractures (interfaces between rock blocks) using field data. In addition to this, we also considered the effects of uncertainties that are associated with estimating three-dimensional (3-D) fractures' networks/rock blocks from two-dimensional (2-D) field data. Finally, the results of the simulations were compared with the measurements from the mine and are in good agreement. [ABSTRACT FROM AUTHOR]

Deep coal seam mining often leads to water resource loss due to bedrock water entering the workings of the mine and is discharged adjacent to the mining area. Using the geological conditions of the Maiduoshan coal mine, this paper applied a physical simulation experiment. The specified rock above the coal seam was hydraulically fractured in advance to form a postmining grouted fracture network, followed by grouting to construct a flexible isolation layer that blocked the infiltration of groundwater from the aquifer into the water-conducting fracture zone. Stress sensors, flow sensors and strata displacement monitoring technology were deployed inside the experimental material to study the spatial distribution characteristics and evolution law of the water-conducting fracture zone in the overlying rocks. Analysis of the water-conducting fracture zone development law, stress variation, overburden evolution characteristics, fracturing and grouting sequence of the flexible isolation layer and the effect of postmining grouting on the water barrier was conducted. These experiments verified the feasibility of fracture and grouting of the flexible isolation layer. These research results will provide practical guidance for the transition from the current safe and efficient mining methods to safe and green mining methods of deep coal mining in the western mining areas of China. [ABSTRACT FROM AUTHOR]

China is rich in primary energy resources. Due to specific terrain conditions, different types of problems may occur in the process of development. When the coal seams are located under the oil layers, due to the physical characteristics of oil, the exploitation of coal seams will cause losses to the oil layers, and the volatile oil may also cause threats to coal mining. To analyze the fracture development and leakage characteristics of overburden strata for this type of geological conditions, we have carried out physical simulation experiments and performed a further numerical simulation to study and verify the evolution of fractures. Based on numerical simulation results, methods have been proposed that may effectively reduce the air leakage in the working face and control the parameters, including viscous resistance, distance, and the construction period of the blocking. In this paper, based on the 30100 face in the Nanliang coal mine as an example, we have proved that the proposed measures can provide good theoretical guidance for the prevention of spontaneous combustion of residual coal and control of water in coal mine production. The developed method offers good economic benefits for safe production in coal mines. [ABSTRACT FROM AUTHOR]

High-intensity coal mining activities in China's western mining area are damaging fragile ecological environments. The key to coordinating ecological protection and coal mining is to understand the law of overlying strata migration in high-intensity mining. However, it is difficult for conventional monitoring methods to efficiently monitor overburden movement in high-intensity mining areas in real time. In this paper, a space-sky-surface (3S) integrated system is proposed to conquer this challenge. This monitoring system consists of three parts: a space monitoring component (a combination of a global navigation satellite system (GNSS) and interferometric synthetic aperture radar (InSAR)), a sky observation component (an unmanned aerial vehicle (UAV) equipped with a measuring camera (MC)), and a surface exploration component (ground-penetrating radar (GPR) and high-density electricity method (HDEM)). This system was successfully applied to the 12,401 longwall face in the Shangwan coal mine (the maximum mining height is 8.8 m). The deformation cloud map of the entire mining area was obtained through InSAR monitoring technology accompanying the 3D laser scanning to improve the accuracy in the local region of 12,401 longwall face. The distribution characteristics and dynamic evolution of surface fractures were obtained using UAV and MC (visible light camera + infrared camera). Using the HDEM and GPR technologies, the fracture development was well detected. Based on the strata movement theory, combined with the monitoring results, a three-dimensional model of overburden rock fracture after 12,401 longwall face mining was constructed. Monitoring results and the fracture model provide a basis for controlling air leakage in the goaf and remediation of surface fracture. [ABSTRACT FROM AUTHOR]

Most prediction methods used to calculate mining-induced subsidence do not involve the formation of overburden, and therefore cannot explain the mechanism of fundamental rock strata movement. Due to the differences of the overburden's formation in different mining areas, to develop a feasible method for determining the movement of overburden is significant. This paper presents an original method for determining the movement of overburden, which is based on the key stratum theory and Mohr–Coulomb failure criteria. The mining-induced movement of overburden is described by two major theoretical models: the Analogous Funnel Model (AFM) and the Analogous Hyperbola Model (AHM). The theoretical predictions of movement boundary of overburden and surface subsidence are given in each model. The Distinct Element Method was used to assess the performance of the theoretical models using a case study of the Antaibao coal mine in Western China. The theoretical and numerical subsidence of the primary key stratum was validated by field measurements, most of which are in good agreement. The theoretical predictions of surface subsidence and the movement boundary of the overburden also match well with the numerical results during supercritical mining. The primary key stratum damages the least in the overlying strata in the Analogous Hyperbola Model. [ABSTRACT FROM AUTHOR]

This paper focuses on the first work face under a thick loose layer of sediment and thin bedrock in the No. 8 Mining District of the Baodian Coal Mine in the Yanzhou mining area of China. Due to mining, the hydrogeological conditions in the aquifers at the bottom of the thick, loose sediment layers have been greatly changed in the shallow areas in this area. The main problem is a low-pressure, water-rich aquifer. However, this problem could be remedied by modifying the coal pillars to prevent sand flow instead of water seepage. To do so, measurements of the first work face were obtained from drilling data, and the stress distribution and plastic zone were determined by examining the mining of the upper part of the no. 3 coal seam using FLAC3D numerical analysis software. The simulated results were also compared with the empirically calculated results. Comprehensive analysis indicates that modifying the coal pillars from preventing water seepage or inrush to preventing sand flow appears feasible, and provides an important reference for increasing mining areas and recovery of coal resources. [ABSTRACT FROM AUTHOR]

The demand for gob-side entry retaining (GSER) technology is extensive in Chinese coal mines because of its outstanding advantages. However, due to the occurrence of long-term roof movement disturbances, maintaining the conventional GSER over long distances is difficult. The urgent demand for this technology and its difficult maintenance are prominent contradictions faced in its application. In this paper, two characteristics of strata movement after mining that have great influence on GSER are determined in a physical simulation experiment. One is that the roof layers, which are dominated by the key strata (KS), collapse in multiple groups to form two-directional periodic pressures and superposed disturbances. The other is that the movement of the main roof will experience three stages of deformation, as follows: bending subsidence before collapse, sinking deformation at collapse and compressive deformation after collapse. In particular, the gradual compression of the bulging gangue in the gob extends the disturbance cycle. Therefore, it is difficult to maintain the GSER over long distances because of the long-term and multiple breaking disturbances of the roof layers. Mechanical models of KS breaking and GSER are established, and a method to determine the timing and strength of KS disturbances are proposed. Making use of the characteristics of staged collapse and fluctuating weighting of the overlying strata, an innovative technology named short-staged GSER is proposed. This technology maintains the maximum length of GSER within the optimal length, which ensures that the entry avoids superposed disturbances, and reduces the maintenance difficulty. The method for determining the key technical parameters is discussed, and an engineering case in panel 24202 of the Shaqu Mine in China is presented. From a back-calculation of measurements, the engineering practice demonstrates that the surrounding rock mass is stable, and the deformed entry size is safe when the length of the short-staged GSER does not exceed 100 m. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive analysis of roof strata conditions, shield pressure, and ground surface subsidence above Panel 42105 of the Buertai Coal Mine in Inner Mongolia, China. A 3D geological model and a 2D numerical simulation model are established to examine the roof strata structures with varying strata conditions. Numerical simulation results demonstrate that the hard rock 1 and 2 roof layers are, on average, likely to break 20 m and 57 m behind the coal face, respectively. It is concluded that when the immediate roof is relatively thin, a cantilever beam is formed, whereas a Voussoir beam is formed when the immediate roof is relatively thick. The patterns of shield pressure and surface subsidence under different roof conditions are also examined. The shield working pressure under the Voussoir beam structure appears to be lower than that under the cantilever beam structure. The average horizontal distance behind the working coal face at which the maximum surface subsidence occurs is 92.1 m. On-site monitoring data are used to explain the causes of the unusual shield pressure and its relation to surface subsidence. Finally, guidelines to predict the shield pressure under similar conditions are provided. [ABSTRACT FROM AUTHOR]

Coal pillars are formed by excavation and mining activities in an intact coal seam and play a key role in underground coal mines. Most previous investigations of pillars have mainly focused on existing coal pillar failures. However, few scholars have investigated the failure mechanisms of coal pillars during their formation process. This paper focuses on the failure of a 7 m-wide coal pillar that caused the large deformation of a tailgate in the Sijiazhuang coal mine in China. Field tests and numerical modeling were used to study the initiation, propagation, and failure of cracks within this gob-side coal pillar during its formation. Field monitoring revealed that the maximum roof-to-floor and rib-to-rib convergence reached 860 mm and 1460 mm, respectively. The coal pillar became a yield pillar with substantial fractures. A numerical model was built using UDEC Trigon logic and calibrated with laboratory tests and RQD methods. Both the natural roadway deformation and crack distribution in the coal pillar were simulated. A FISH function was used to document the propagation of shear and tensile cracks in pillars with different W/H ratios, and a damage parameter was adopted to evaluate the failure of these pillars. The results suggest that the most appropriate pillar width is 10 m. Field trials prove that a 10 m-wide coal pillar combined with optimized support measures can effectively control deformation around the tailgate. [ABSTRACT FROM AUTHOR]

The paper investigates groundwater inflow into a longwall working face of the Xiegou Coal Mine located in the northwest of the Shanxi province, China. Three modelling approaches, including basic Darcy modelling, full poroelastic modelling using Biot's classical theory, and the full Biot poroelastic modelling that takes into account permeability alterations of the coal seam and strata due to alterations in the mining-induced stress state, are used to estimate the fluid flow into the underground longwall coal mine as the excavation progresses. Based on plausible assumptions of hydrogeological structure, boundary conditions and mining conditions, a three-dimensional finite element model of the simplified geological setting is developed using the COMSOL software. The permeability changes in both the strata and the coal seam due to the mining are associated with the mining-induced stress changes and water pressure, and the correlation between them accords with the exponential relationship. The differences in the modelling results of three approaches were analyzed, and the simulation results are compared with the field measurements. [ABSTRACT FROM AUTHOR]

The selection of a mining method is one of the most important decisions made by mining engineers. An appropriate fully mechanized mining method is of great importance to mining design and capacity planning for thin coal seams. Therefore, the comprehensive evaluation of alternative mining methods is an important part of mining design. Several parameters should be considered in that evaluation, and the evaluation is therefore complex and must be compliant with a set of criteria. In this paper, a comprehensive method that combines two multi-criteria decision-making methods, the analytic hierarchy process and the technique for order of preference by similarity to ideal solution, was adopted for the evaluation. The most appropriate mining method, which involved a shearer, was then selected for panel 43101 in the Liangshuijing coal mine in China. [ABSTRACT FROM AUTHOR]

This paper investigates the abutment pressure distribution in coal mines with extremely thick alluvium stratum (ETAS), which is a typical kind of mines encountering frequent intense rockbursts in China. This occurs due to poor understanding to abutment pressure distribution pattern and the consequent inappropriate mine design. In this study, a theoretical computational model of abutment pressure for ETAS longwall panels is proposed based on the analysis of load transfer mechanisms of key stratum (KS) and ETAS. The model was applied to determine the abutment pressure distribution of LW2302S in Xinjulong Coal Mine; the results of stress and microseismic monitoring verified the rationality of this model. The calculated abutment pressure of LW2302S was also used in the terminal mining line design of LW2301N for rockburst prevention, successfully protecting the main roadway from the adverse influence of the abutment pressure. [ABSTRACT FROM AUTHOR]