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Copyright of Mine Water & the Environment is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

Cropland is the foundation of food security. Coal is the guarantee of energy security. As China's demand for coal and grain continues to increase, so does the overlap area of their production bases. Unrestrained underground mining can cause serious damage to cropland, leading to increasing conflicts between coal mining and food production. Thus, this paper used a partial backfilling mining technology to control surface subsidence and thus protect cropland. The key to successfully implementing the technology is how to design the panel size. However, the design efficiency of the conventional enumeration method is low. Therefore, this paper proposed a design approach based on improved particle swarm optimization. The results indicated that the approach could quickly find the optimal size of the panel compared with the enumeration method and particle swarm optimization. Moreover, if the longwall panel is mined according to the size designed by the approach, the cropland will be protected, and the cost will be reduced. This study can provide technical support for the cooperative development of cropland protection and coal mining in a coal-cropland overlapping area. [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 severe deformation of surrounding rock and the easy failure of the anchoring structure of roadway under large dynamic pressure influence in the short distance are the urgent issues to be paid more attention. Based on this problem, this paper is a case study on the instability mechanism and control technology of surrounding rock in the deep roadway under dynamic mining loading in the Gubei Coal Mine of China. The vertical distance from the − 575 m roadway of 11–2 mining area and mining working face is only 68 m. Firstly, the main factors influencing the surrounding rock's severe deformation are determined by the analysis of site investigation, surrounding rock composition and structure, overlying strata failure measurement, and borehole camera detection. The stress distribution, displacement distribution, plastic zone, and lining stress distribution of roadway of three reinforcement schemes, including nine working conditions, were calculated by numerical simulation for ordinary bolt support, bolt-support + grouting of roof and two sides, and bolt-support + full section grouting. Then the combined support technology system of "36 U-shaped steel + bolt + anchor cable + grouting" was proposed. The field monitoring results showed that the deformation of two sides and roof were only 20 mm and 16 mm, respectively, during the 65 day monitoring period. Furthermore, the cracks in the surrounding rock are almost filled with grouting materials, and the overall stability of roadway surrounding rock was completely achieved. This successful case study demonstrated that the optimized supporting structure is reasonable and the deformation of surrounding rock has been effectively controlled. [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]

Combined mining is when two working faces separated by a certain distance simultaneously advance in the same direction, which commonly results in stress concentration and rockburst. This paper investigates the rockburst mechanism due to inclined coal seam combined mining under complex geological conditions in the Da'anshan Coal Mine, China. Based on the experimental analysis, there is an impact tendency of the No.10 coal seam. A theoretical model is established to evaluate rockburst risk due to combined mining. In addition, a 3D multifactor numerical model of inclined coal seam combined mining is established. The novel "PyFlac-Exc" calculation code and the "PyFlac-Eng" elastic strain energy calculation script are compiled. The evolution of elastic strain energy is obtained during combined mining. Theoretical and numerical results show that a rockburst occurs in the western fourth working face of the No. 10 coal seam, which is consistent with the on-site rockburst accident. In addition, the kernel density estimation method is proposed to reduce stress concentration by changing the coal pillar widths and misalignment distances. Numerical results show that the elastic strain energy levels are low for the same coal pillar width, and the misalignment distance is arranged from 50 to 80 m. With the same misalignment distance, a coal pillar width greater than 45 m can effectively reduce the rockburst risk. [ABSTRACT FROM AUTHOR]

The characteristics of overlying strata movement and the evolution of surface subsidence-related parameters are essential in preventing geological hazards and environmental alterations. This paper comprehensively analyses surface subsidence, overlying strata movements, and dynamic surface characteristics above the No. 24213 working face of the 1930 Coal Mine in Xinjiang, China. A numerical simulation model was established to predict the surface subsidence under a larger dip angle. Various time functions were used to determine the suitable function to predict subsidence speed. The in situ surface subsidence results showed prominent asymmetric characteristics. The tilt value was larger toward the footwall than in the opposite direction. However, the curvature evolution was not overly asymmetric and fluctuates greatly. The maximum surface subsidence value in tendency and inclination were 1800 mm and 433 mm, respectively. Moreover, the movement and advance angles were 77.4° and 66°, respectively. The numerical results were in good agreement with the on-site results; the overlying strata movement shape from underground to the surface was similar to an inclined funnel, and the stable draw angles of both sides were 41° and 82°, respectively. The logistics time function can describe the dynamic subsidence characteristics well for a representative point under large dip angle conditions. The parameters in the logistics time function were related to the rapid deformation stage duration time and initial subsidence speed. This study can offer guidance in predicting asymmetric characteristics in inclined coal seams. [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]

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]

Gas is one of the main factors causing coal mine accidents in China. Understanding the mechanism of the influence of mine pressure on coal seam gas emission has important theoretical guiding significance for coal mine enterprises to be able to control gas. This paper chose the 72,909 working face in the Du'erping coal mine as the engineering background, analyzed the characteristics of the mine pressure in the working face and the driving face through numerical simulation, and found that the power of the gas emission in the working face is the mine pressure, while that of gas emission in the driving face is the gas pressure gradient. Based on the field monitoring data of the hydraulic support in the working face and the single pillar in the mining roadway, the law of mine pressure was obtained. Combined with the monitoring data of the number of drill cuttings and gas in different positions of the mining roadway and the gas concentration change in the upper corner of the working face during mining, the influence of the advanced support pressure and periodic pressure on the gas emission of the coal seam was analyzed. The results show that the advanced support pressure affects the coal seam gas emission by affecting the coal seam permeability coefficient. With the increase in the support pressure, the coal seam permeability coefficient decreases, and the coal seam gas emission decreases. During the period of periodic pressure, the advanced support pressure moves forward, forming a pressure relief zone in front of the working face, which is conducive to the emission of coal seam gas, and periodic pressure provides power for the gas emission. [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]

The slow excavation speed of coal roadways has always been a key factor restricting the safe and efficient production of large-scale coal mines in China, and the problem of unbalanced mining replacement caused by this is widespread. This paper takes the S1231 heading face of the Ningtiaota coal mine of Shaanxi Coal and Chemical Industry Group as the research object, analyzes the characteristics of the stress evolution of coal roadway driving, reveals the principle of low-density cross-border support, and proposes a low-density cross-border support plan. Using FLAC3D to study the roadway stress-displacement evolution law of the new support scheme during the driving and mining phases, the results show that the peak stress during the driving is 5.3 MPa, and the coal pillar side stress concentration is the most obvious during the mining period, with the peak value being 7.9 MPa. The moving distances of the two banks are both 10 mm, which verifies the feasibility of low-density cross-border support. Field application shows that during roadway excavation, the amount of roof subsidence and the displacement of the two sides are 9 mm and 11 mm, respectively, and the development depth of roof cracks is controlled within 0.5 m. The overall control effect is good, and the speed of coal roadway driving is increased by 77.19% compared with the original. The new support builds a thick roof anchor structure to ensure the safety and stability of the roadway. At the same time, by reducing the number of bolts, the bolt support time has been greatly reduced, effectively alleviating the tight situation of mining replacement, and providing solutions for mines under the same conditions. [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]

The determination of propulsive abutment pressure and deformation characteristics of roadway surrounding rock mass in top-coal caving mining is of great significance for further research on mining stress, roadway support and equipment selection. This paper adopts the method of combining theoretical analysis and field test, taking Helin coal mine j7401 working face as the research object. The relationship between abutment support pressure and roadway surrounding rock mass deformation is revealed by monitoring the stress of transportation and ventilation roadway and observing the deformation of mining roadway. The main conclusions are as follows: when the distance between top-coal caving mining and borehole is about 65 m, the borehole stress begins to exceed the original rock stress, and the peak of the abutment pressure is 15–22 m in front of the working face, ranging from 33 to 39 MPa, which is 3.2–3.8 times the original rock stress. The intersection of propulsive abutment pressure curve and original rock stress curve is located at 8.1 m in front of the working face, the boundary of roadway rapid deformation stage and deceleration deformation stage is 8.9 m ahead of the working face, the distance between the two stages is 0.8 m, and the peak position of propulsive abutment pressure is 19.8 m. The boundary of roadway decelerative deformation stage and stationary small deformation stage is 20.1 m, and the distance between the two stages is 0.3 m. The boundary between the fracture zone and the limit equilibrium zone is the intersection of the propulsive abutment pressure curve and the original rock stress curve. The plastic zone is constituted by the damage zone and the limit equilibrium zone, and the boundary between the plastic zone and the elastic zone is located at the peak of the propulsive abutment pressure. The above study results provide a basis for roadway support and efficient coal mining. [ABSTRACT FROM AUTHOR]

With the increasing tension of current coal resources and the increasing depth of coal mining in China, Non Coal Pillar Gob-side Entry Retaining Technology has become a preferred coal mining method in underground coal mines. In the current study of the non coal pillar gob-side entry retaining mining with roof cutting and pressure releasing, the theory and design of roof cutting under near-level conditions have formed a certain system. However, there is a lack of systematic research on the design of the roof cutting and the connection requirement of the cutting seam and other aspects about the inclined coal seam. Therefore, choosing the concrete representative target mines as the research foundation, using mechanics analysis, geometric analysis, numerical simulation and other means, on the basis of considering the change of mining height, this paper mainly studies about the effect of coal seam inclination on roof slit depth and angle, then get the three steps of the cutting height design, the three considerations of the roof cutting angle design and the connection rate requirement of the roof cutting. At last the key roof cutting parameters of the three target mines are calculated accordingly. Based on the existing research, this paper puts forward the concept and design method of roof cutting connectivity rate. The design system of roof cutting seam parameters of non coal pillar gob-side entry retaining mining with roof cutting and pressure releasing is further improved, and the corresponding calculation method is deduced for the design of the key parameters of the inclined coal seam and the gently inclined coal seam, and proposing the second roof cutting scheme of the upper side gob-side entry retaining. [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]

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]

The Jurassic coalfield in northern Shaanxi, China is one of the seven largest coalfields in the world. It is located in an arid region of northwestern China, with poor water resources and fragile ecological environment. Due to coal mining, the rock layers on the coal seam will be slumped and fractured to produce fissures. The penetrated fissures will cause a mine water burst disaster and cause damage to groundwater and surface water. The strip filling method can control the expansion of the diversion fissure zone and protect the groundwater and surface water from the underground mining of coal. In this paper, the effects of different strip filling conditions on the diversion fissure zone are studied by discrete element numerical experiments. The study indicates that the upward-fissure and the downward-fissure penetrations are the direct causes of the instability of the water-blocking rock group. After the upward fissure extends to a certain extent, there will be a downward fissure. Under the condition of controlling the width of the filling strip and the compressive strength, the strip filling method can effectively prevent the upward and downward fissures of the water-blocking rock group from penetrating and can ensure that the surface water system is not affected by the underground coal mining activities. [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]

The hydrogeological conditions of Weibei coalfield in China are complex; the main mining No. 5 coal seam is seriously threatened by Ordovician limestone karst water disaster at the bottom of coal measures. Chenghe No. 2 Mine is a typical example. With the increase of mining depth, confined water pressure increases year by year. To find out the law of floor deformation and failure caused by No. 5 coal seam mining in Chenghe No. 2 Coal Mine, this paper takes 24,508 working face of Chenghe No. 2 Coal Mine as engineering geological background, and carries out research by numerical simulation and field test methods. The stress field, displacement field distribution law and plastic zone evolution characteristics of No. 5 coal seam roof and floor varying with the advancing degree of mining face are obtained by simulation calculation. The progressive failure process of the whole floor stratum is reproduced dynamically, and the development height of the water conducting fracture zone of overburden is given. The maximum failure depth of the floor occurs at the mining distance of about 1.5 times the mining width, at which time "the saddle shape" supporting pressure arch reaches its maximum. At the same time, the multi-point separated layer displacement meter is used to carry out field measurements. The results show that the maximum failure depth of floor occurs in the goaf, and the maximum range of the relative displacement of the floor is 8.0–8.5 m, which is close to − 6.1 m from the coal mining surface, consistent with the results of the numerical simulation. Comprehensive analysis shows that the maximum failure depth of coal seam floor in Chenghe No. 2 Coal Mine is 8.3 m. The conclusion provides a favorable basis for the rational formulation of water disaster control countermeasures. It provides reference and experience for mining under safe water pressure of aquifuge for prevention and cure water of similar working face in Chenghe mining area in the future. [ABSTRACT FROM AUTHOR]

Copyright of Mine Water & the Environment is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

Coal brittleness is one of the important indexes to characterize the post-peak characteristics of coal, which is closely related to the efficiency of underground coal mining and the degree of coal disaster. In this paper, the compression characteristics of coal are studied by laboratory experiment, which is characterized by relatively long nonlinear elastic stage, smaller plastic stage and stress drops in post-peak stage. On this basis, the existing brittleness evaluation methods are summarized, and the applicability of 11 indexes of 6 physical parameters to the quantitative evaluation methods of coal brittleness are analyzed and discussed. The results show that: (1) for the coal is a complexity heterogeneous medium with hole and fracture, there are different degrees of limitation on the methods of coal brittleness quantitative evaluation,which can be used to roughly estimate the brittleness of coal, but it can not accurately characterize its brittle characteristics. (2) Based on the whole process stress–strain curve, the brittleness degree index B5 is more suitable for the brittleness characterization of coal by quantitatively considering the relative size and absolute rate of post-peak stress drop. [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]

To form a kind of support technology that was universally applicable to all kinds of dynamic pressure roadways, This paper proposes asymmetrical support technology for dynamic pressure roadway. Firstly, the asymmetry characteristics of surrounding rock structure and stress distribution in dynamic pressure roadway were analyzed. The mechanism of asymmetric support technology for dynamic pressure roadway was preliminarily explored. Taking the 1303 dynamic pressure roadway in Guotun Coal Mine as the engineering background, the coal pillar width and support parameter were determined by numerical simulation and theoretical analysis. In the asymmetric support scheme, the roof bolts and the side bolts are respectively Φ20 × 2200 and Φ20 × 2000 mm, the spacing-discharge distance of roof bolts, coal pillar side bolts and coal body side bolts are respectively 800 × 900, 600 × 900 and 800 × 900 mm. Through field observation, the overall deformation of roadway surrounding rock supported by the asymmetric support scheme was not large and the deformation of the roof, coal pillar side and coal body side were basically equal. So, this asymmetric support technology can effectively control the deformation of surrounding rock in dynamic pressure roadway. [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 major environmental consequence of coal mining is anthropogenic land subsidence. In particular, mine subsidence can cause damage to public and private infrastructure such as railroads, roads, pipelines and buildings. What is more, it is an engineering problem which troubles engineering construction and safety. Ground surface deformation is related to the measure of mining and the deformation mechanism of overlying strata above the gob. In this paper, a physical and numerical model on the subsidence of longwall mining within a geotechnical setting is presented. The physical model is developed within the framework of physical similar law and geological model in Henan Province, China. The numerical solution is developed within continuum poromechanics and finite element setting. The law of overlying strata deformation is obtained according to physical model experiment and numerical simulation. [ABSTRACT FROM AUTHOR]

Water inrush at floor area is a natural hazard during coal mining. Especially in the northern coalfield of China, more than 55% of coal mines are threatened by water inrush at floor area. The hazard of water inrush is becoming more serious with increasing mining depth. In this paper, the deformation and failure behavior at floor area in deep longwall mining site were analyzed. The correlation between the floor failure and main roof breakage was studied using kinematics theory. Meanwhile, the impact loads of cantilever beam breakage on the floor area at both longwall face and gob area were calculated. Combining with "Pressure arch hypothesis", the compression and unloading mechanics processes at floor area were analyzed, and the unloading deformation model of floor structure after the breakage of main roof was established as well. In addition, the correlation between unloading deformation at floor area and the main roof breakage, mining depth and unloading stresses were also obtained. Finally, these studies have been verified by using micro-seismic monitoring data in deep longwall mining site. The results show that the impact loads are proportional to the span and loads of cantilever beam. After the breakage of cantilever beam, the impact loads were transferred to the floor area at longwall face side and gob side, and the rock masses at both sides were failed in compression. Consequently, the position of back arch foot of the pressure arch was rapidly transformed into the contact gangue zone at gob area from the last breakage position of main roof. While as the unloading stress of rock masses inside of the floor pressure arch is increasing, the depth of unloading fracture and heave below longwall face are greater than those before cantilever beam breakage. In addition, the unloading deformation at surface floor increases nonlinearly with the increase in mining depth and unloading stresses. [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]

In order to comprehend the dynamic disaster mechanism induced by overburden rock caving during the advancement of a coal mining face, a physical simulation model is constructed basing on the geological condition of the 21221 mining face at Qianqiu coal mine in Henan Province, China. This study established, a comprehensive monitoring system to investigate the interrelations and evolutionary characteristics among multiple mechanical parameters, including mining-induced stress, displacement, temperature, and acoustic emission events during overburden rock caving. It is suggested that, despite the uniformity of the overburden rock caving interval, the main characteristic of overburden rock lies in its uneven caving strength. The mining-induced stress exhibits a reasonable interrelation with the displacement, temperature, and acoustic emission events of the rock strata. With the advancement of the coal seam, the mining-induced stress undergoes four successive stages: gentle stability, gradual accumulation, high-level mutation, and a return to stability. The variations in other mechanical parameters does not synchronize with the significant changes in mining-induced stress. Before the collapse of overburden rock occurs, rock strata temperature increment decreases and the acoustic emission ringing counts surges with the increase of rock strata displacement and mining-induced stress. Therefore, the collaborative characteristics of mining-induced stress, displacement, temperature, and acoustic emission ringing counts can be identified as the precursor information or overburden rock caving. These results are in good consistent with on-site situation in the coal mine. [ABSTRACT FROM AUTHOR]

Background: The mining-induced stress in the surrounding rock after coal seam mining is the primary cause of damage and failure of the surrounding rock in the mining area. However, the magnitude and direction of the stress field induced by mining in the overburden strata during the excavation process of deep and adjacent coal seams are not yet clear, and it is difficult to determine how adjacent working faces interact with each other. Results: In this study, a large-scale numerical model was built using FLAC3D (Fast Lagrange Analysis Continua) to simulate the sequential mining process of three adjacent working faces (No.1, No.2, and No.3) in Liuzhuang Coal Mine located in southern China. The results showed that the maximum height of plastic zone development after mining in the No.1 working face was 41 m, and the maximum height of plastic zone development was 33.8 m away from the 13 coal seam. It did not affect the top and bottom of the No.3 working face. The development height of the plastic zone on the roof of the No.2 working face after mining was 52m, and the top and bottom plates of the No.3 working face remained intact. The plastic zone of the floor of the No.3 working face after mining was not communicated with the plastic zone of the roof of the No.1 and No.2 working faces. There was a complete rock layer between the two coal seams, and there was not the mutual influence of the mining activities. During the mining process of working faces No.1 and No.2, the range of dynamic pressure influence was extended up to 100m ahead of the working face. During the mining process of the No.3 working face, the range of dynamic pressure influence was 120 m ahead of the working face. The No.1 working face goaf and the mining of No.2 working face had not disturbance to the No.3 working face. Conclusions: After the mining of No.1 and No.2 working faces, the stress in the goaf significantly decreased, and the lateral support stress concentration area of No.1 and No.2 working faces had a relatively small impact on the 13 coal seam. Therefore, the No.1 goaf and mining of No.2 working faces had not disturbance to No.3 working face. [ABSTRACT FROM AUTHOR]

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Land subsidence is a typical geological disaster that will produce many secondary disasters and negatively impact human production and life. Human engineering activities (underground mining and coal mining) are the leading causes of land subsidence. This study takes Jining, a typical land subsidence city in eastern China, as a case study to investigate the features and control of land subsidence under the combined action of groundwater extraction and coal mining. A three-dimensional numerical model of land subsidence considering groundwater extraction and coal mining is established. The evolution process of land subsidence in the study area from 2000 to 2020 under the action of groundwater extraction and coal mining was obtained through numerical simulation. Results showed that coal mining was the main cause of land subsidence compared to groundwater extraction in the study area. Different groundwater extraction schemes were proposed to try to control the land subsidence, and the land subsidence features of different schemes from 2021 to 2030 were also investigated. Results showed that the ground rebound phenomenon occurred during the first few years, and the rate and amount of ground rebound decreased over time. After that, land subsidence continued, and its rate gradually slowed. The more mining wells are shut down, the smaller the final cumulative land subsidence will be. According to the comparison of these schemes, the land subsidence is basically stable when the amount of groundwater exploitation wells is closed by 50%, which is a more reasonable and practical exploitation scheme. [ABSTRACT FROM AUTHOR]

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Due to technological and safety limitations, there are considerable amounts of coal resources pressed under end slopes in open-pit coal mines. In recent years, this problem has gradually attracted the attention of researchers. How to realize the efficient recovery of side overburden resources while ensuring the stability and safety of slopes has become an important topic for the development of mining technology in China. A 2D/3D integrated simulation experimental device for end slope coal mining is developed. Based on the geological engineering conditions of the Ordos mining area in China, a typical geological engineering model of a near-horizontal slope condition is constructed to simulate the whole process of "roadway group formation—supporting coal pillar failure—slope rock mass instability". By tracking and monitoring the movement and failure processes of slope rock masses in an end-slope mining field, the yield failure characteristics of coal pillars and the movement and deformation laws of slope rock masses are revealed, and the deformation and failure zoning method of overburden rock in an end-slope mining field is proposed; in addition, the key stages, trigger conditions and key positions of slope deformation and instability are defined. The results show that under the coupling action of the "slope stress field" and "roadway group stress field", the actual stress of a supporting coal pillar in the deep part of a geometric centre along the slope of a roadway group is greater than the ultimate stress, and then large discontinuous deformations of multiple adjacent coal pillars around the central coal pillar are caused by compressive shear failure, which is the triggering condition of deformation and instability around the mining slope. The key position of yield failure of the supporting coal pillar is located in the deep part of the geometric centre along the slope of the roadway group. At the end of the mining adit, the supporting coal pillar within a width of 2.5–3 times the mining adit will not be destroyed. The boundary of the final collapse plane range of the roadway group is approximately a closed curve formed by two paraboloids, which are axisymmetric with the central pillar and open oppositely; the parabola opening in the shallow part of the slope area is small, and the parabola opening in the deep part of the slope area is large. There is a significant space–time correspondence between the failure of supporting coal pillars and the deformation of the slope surface. According to the failure process of the rock mass structure and the movement and deformation characteristics of the slope surface, the slope after failure can be divided into three areas, and the upper part of the slope is the key area of deformation and instability of the overlying rock mass in the end-slope mining field. These research results provide a theoretical basis for the scientific monitoring and stability control of slopes in an end-slope mining field. [ABSTRACT FROM AUTHOR]

To find out the characteristics of geological structure exposed in the mining process of 12,318 working face in Pansan Mine and grasp its influence law on subsequent coal seams mining, the structure was first determined as the collapse column by means of 3D seismic, transient electromagnetic detection, SYT detection and other methods, and its development characteristics, conductivity and water enrichment were identified. FLAC3D numerical simulation software was used to analyze the characteristics of vertical stress and plastic failure zone in different coal seams during mining. Finally, by comparing the ultimate failure depth of floor and the thickness of waterproof layer in the process of each coal seam directly pushing through the collapse column, the risk of water inrush and the prevention are analyzed. The results show that the exposed geological structure is characterized by weak water-rich collapse column. Under the influence of the mining of the previous coal seam and the activation of the collapse column, the subsequent coal seam is in the low-stress area before mining, which increases the floor failure and causes the activation of the collapse column more easily during mining. [ABSTRACT FROM AUTHOR]

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The mining depth of most coal mines in North China has exceeded 1 km. The high seepage water pressure caused by high ground stress leads to the increasingly serious threat of water disaster in the mine. To explore the relationship and mechanism between water inrush from deep mining floor and grouting prevention, single-level grouting and multi-level cooperative grouting methods were carried out in Ordovician limestone confined aquifer of coal seam floor in Xingdong coal mine. Meanwhile, the temporal and spatial characteristics of rock fracture in the floor of deep mining face are revealed through the law of rock fracture microseismic. It is noteworthy that the occurrence time of water inrush and microseismic events have lag characteristics, that is, the occurrence time of microseismic events is earlier than that of water inrush. The multi-level cooperative grouting method can effectively control the non-uniform dissolution Ordovician limestone aquifer in-plane and vertical plane. Furthermore, single-level grouting and multi-level cooperative grouting methods are assumed to be unstable grouting and stable grouting. Besides, the flow pattern transformation characteristics of Ordovician limestone water in unstable to stable grouting are simulated by the finite element method. The results show that the energy inoculation level of fracture expansion around the aquifer decreases after stable grouting reinforcement. In other words, the multi-level cooperative grouting method can effectively strengthen and fill the water inrush channel and reduce the damage of high osmotic pressure to the aquiclude. It is of great significance to reduce the probability of water inrush in deep coal seam and ensure the mining safety of deep coal seam. Highlights: The Ordovician limestone rock mass damage and dissolution are characterized by layered failure and non-uniform dissolution in horizontal and vertical directions. The occurrence time of water inrush and microseismic events in Xingdong mining area have the lag characteristics. A continuous multi-level collaborative grouting method in karst aquifer is proposed through segmenting, sequencing, and grouting pressure strengthening. Multi-level cooperative grouting method in Ordovician limestone aquifer with high water pressure and uneven dissolution can effectively strengthen and fill the water inrush channel and reduce the probability of water inrush. [ABSTRACT FROM AUTHOR]

The water-conducting fractured zone induced by mining under aquifers is channels for water and sand inrushes. A method based on multiple regression analysis and a geographic information system (GIS) is proposed to predict the height of the water-conducting fractured zone in this paper. Five main indicators are found to control the height of the water-conducting fractured zone during fully mechanized caving mining under aquifers in which the thickness of the coal seam is more than 3 m: thickness of the coal seam, proportion of hard rock, length of the panel, mined depth and dip angle. The height of water-conducting fractured zone and the predictive variables from eighteen coal mines in China are investigated. Based on information entropy theory, a nonlinear multiple regression model and the weight of the indicators are considered, and the nonlinear multiple regression model is used in the GIS. Then, the approach is validated with a case study of the Xiegou Coalmine in the Shanxi province of China, in which the thickness of the coal seam which is under aquifers is more than 3 m. Error analysis of the approach is calculated with different hydrogeology classification. The results indicate that this model is a useful tool for predicting and analyzing the height of the water-conducting fractured zone, since the height of the water-conducting fractured zone can be quantitatively calculated and visualized. [ABSTRACT FROM AUTHOR]

This paper presents an investigation on the effect of grouting into multi-bed-separation to control mining-induced surface subsidence. In the overburden without obvious thick-and-hard strata for generating large-scale bed separation, overburden grouting is carried out by increasing the number of boreholes and grouting strata. The scale model test, numerical simulation, and field measurements are used to study distribution and process of bed separation and to compare the overburden failure with surface subsidence due to pre- and post-overburden grouting, with a case study of the Qi'nan Coal Mine, Anhui Province, China. The scale model test and numerical simulation results of the overburden grouting process are in close agreement with those obtained from the field measurements. Filling masses with different diffusion radii are commonly formed in the different bed separation, which are overlaid to control the surface subsidence. It is proven that overburden grouting can successfully mitigate overburden failure and subsidence without obvious hard strata and bed separations. This provides an effective and cost-efficient approach for addressing the surface subsidence and overburden deformation problems due to mining. [ABSTRACT FROM AUTHOR]

Height identification of water-permeable fractured zone (WPFZ) is one of the decisive influence factors for mining safety, especially in some specific conditions, such as mining under aquifer. In order to demonstrate the formation process of the WPFZ, the scaling model experiment is carried out. Through the analysis of movement and breaking in overlying strata, the WPFZ height is significantly affected by mining range, movement characteristics of key strata and its follow-up strata. Based on the research findings, a new theoretical method, " overlying strata synchronous movement method " (OSSM) is established to predict the WPFZ height. Taking 3301 mining face of Zhujiamao Coal Mine in China as the engineering background, the WPFZ height is estimated by OSSM. Additionally, the field detection is carried out by the downhole segmented water injection method combined with borehole camera method. By comparing the results of different methods, the accuracy of OSSM is verified and the WPFZ height is determined finally. What´s more, various methods for determining WPFZ height are evaluated. [ABSTRACT FROM AUTHOR]

There is a high potential for coal spontaneous combustion (CSC) above the roof beams of supports during the mining-stopped period. Early detection of temperature abnormal zones and corresponding measures are necessary to prevent CSC. In this work, a top-coal temperature measurement method was proposed, combining the coal surface temperature detection and the drilling temperature observation. Furthermore, an apparatus was developed that dramatically increases the rate of dry ice sublimation, resulting in the rapid release of cryogenic carbon dioxide gas. The device utilizes water from firefighting pipes in underground coal mines as a heat source for dry ice sublimation without electrical energy and has been applied and validated taking Silaogou Coal Mine in China as a field test site. Specifically, we found that during the stoppage period, the coal above the supports near the air inlet tunnel is more likely to appear hot spots; the carbon dioxide gas generated by the dry ice phase change device can quickly reduce the hot spots temperature, and the coal temperature does not rebound after the gas injection is stopped. Based on the above analysis, this work can effectively prevent the early top-coal spontaneous combustion during the stop mining period. [ABSTRACT FROM AUTHOR]

Research on land subsidence is a global topic. In recent years, the environmental problems caused by coal mining have received great attention. In particular, mining land subsidence caused damage to villages, buildings, farmland, etc., which seriously threatened the mining area's living environment and ecological environment. This study proposes a pressure-state-response concept model based on mining land subsidence to build an evaluation index system in coal mines. Based on this index system, given the uncertainty in the evaluation process, the cloud model is used to represent the index weight and comprehensive evaluation calculations, which fully consider the randomness and ambiguity in the evaluation process. The mining land subsidence of several mining areas in China was evaluated and classified into three grades (slight-medium-strong). The cloud model assessment results are compared with the result of the probability integration method and the actual situation. The assessment results of the cloud model are closer to the actual situation than the probability integration method. This shows that the established mining land subsidence evaluation method based on the cloud model in this study is reasonable and feasible. The mining width and height ratio, depth and height ratio, and coal seam dip angle affect mining land subsidence. Therefore, improving the mining method to deal with the goaf reasonably and optimizing the mining design to control the influence range of mining are essential measures to reduce mining land subsidence and protect the ecological environment of mining areas. [ABSTRACT FROM AUTHOR]

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To better understand water inrushes originating from shaft-freezing holes, the hydrogeological conditions and water source were analyzed for a typical inrush case in the Yingpanhao coal mine in western China. The mechanism of this new type of water inrush was identified by considering the stratum movement caused by mining, the concentric annular channels of freezing holes, and the dynamic recharge of multiple aquifers. A new risk assessment model and corresponding grouting method were developed and the problems involving the prediction of water inrush and selection of the optimum grouting position were described. Detailed guidelines for grouting, including the layout of injection boreholes, slurries, grouting pressure and stopping criteria, were proposed. A grouting case targeting this type of water inrush in the Yingpanhao coal mine was introduced. Field studies indicated that open, concentric annular freezing hole channels provide favorable conditions for groundwater migration. The proposed method may effectively inhibit groundwater migration in multiple aquifers and prevent water inrushes through shaft freezing holes and provides an appropriate framework for water inrush prevention for similar mining areas in western China. [ABSTRACT FROM AUTHOR]

Gob-side roadway excavating could not only notably reduce the loss of coal resources and improve the coal recovery rates, but also greatly mitigate the imbalance between excavation speed and production needs. However, it is difficult to determine the coal pillar reasonable width of gob-side roadway under the condition of deep buried high stress and multiple key strata superimposed disturbance in the West. With Auxiliary transportation roadway 30207 (ATR 30207) in Muduchaideng Coal Mine as the research background, in situ investigation, theoretical calculation were carried out to study the reasonable width of coal pillar in gob-side roadway under the condition of deep buried high stress multi key seam mining. Results showed that, based on the width of stress reduction zone, two factor control of stress intensity, ratio optimization of width and height and effective anchor width, the optimal width of coal pillar of ATR 30207 is 5.5– 7.7 m. The stability of coal pillar and roadway under different width of coal pillar was simulated and analyzed by using UDEC numerical calculation. The calculation results showed that 6 m width coal pillar was the inflection point of vertical stress, plastic zone and displacement distribution, that is, 6 m width coal pillar was the best width of coal pillar, which verified the theoretical calculation results. This study provides a reference for the scientific mining under the condition of strong mining and high stress mining in Western China. [ABSTRACT FROM AUTHOR]

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