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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.)

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]

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 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]

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]

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]

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.)

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]

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.)

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.)

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.)

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]

Coal seam mining is one of the most widely participated engineering activities in China. This study examined the failure process induced by underground thin coal seam mining of Wangxia perilous rock in Chongqing, China. Numerical simulation was conducted on the stress, displacement and plastic deformation with Fast Lagrangian Analysis of Continua 3D (FLAC3D). Results show that tensile stress is dominant and it keeps increasing during coal mining. The stability failure process experiences four stages from the perspective of crack propagation. A new simplified subsidence prediction method was proposed for quick engineering applications. The relationship between mining geometric parameters and rock mass stability was established and the ultimate mining dimensions were suggested. The simplified method was demonstrated to be reliable. [ABSTRACT FROM AUTHOR]

In order to study the fracture evolution regularity of surrounding rock under different interlaminar strata structure in short-distance coal seams group, based on the background of the coal seam group in a Shendong Coal Mine, the interlayer structure was classified using key strata theory. Four UDEC numerical models were established according to the distance between two coal seams and the number of inferior key strata, the main conclusions were drawn as follows: when there was only one inferior key stratum between the two coal seams, the increase of the distance between these two coal seams has little effect on the fracture evolution of the overburden rock mass; the location and number of inferior key strata affect the dynamic development and distribution of overburden fractures, while it would not affect the height of fracture distribution; the two inferior key strata with same properties and thickness would decrease the range of fracture distribution. The conclusion of this study is of great theoretical significance for coal mine gas drainage and water hazard control. [ABSTRACT FROM AUTHOR]

The mismatch of speed of mining and excavating is the main contradiction of high efficiency production in China, improving the excavating speed of coal roadway is an effective way to solve the problem. According to the engineering geological conditions of the main haulage roadway 21205 in Hulusu Coal Mine, the technical problems existing in the original support scheme were analyzed, increased the excavating speed of roadway through improve support efficiency of single bolt and reducing density of bolt, a rapid excavation technology based on anchoring method of critical high efficiency and low density on roof of coal roadway was proposed. The influence of different bolt length and different pre-tightening force on the stability of roadway roof was studied by FLAC3D simulation, the results showed: (1) increasing the length and pre-tightening force can control the development of the roof vertical strain with a certain range; (2) as the length of bolt increases, the compressive stress zone of the rock layer between the two bolts increases and the compressive stress in the rock layer area of the anchorage section tends to increase; (3) with the increase of pre-tightening force, the effective, compressive stress zones between the two bolts overlap with each other, forming a whole, and the compressive stress values in the near zero stress zone increase. Decided the scheme that, bolt length is 4 m, pre-tightening force is 200 kN, and the support density is 0.5 root/m2, industrial experiments were carried out. The mine pressure monitoring showed that the roof of the roadway has almost no ionosphere, and the deep ionosphere was well controlled. The monthly excavating progress of the roadway was increased from 520 to 825 m, with a rise of 58.7%, the technical and economical effects were significant. It was proved that the scheme is in line with the actual. It can provide reference for roadway rapid excavating support technology for similar conditions. [ABSTRACT FROM AUTHOR]

Coal bump refers to a sudden catastrophic failure of coal seam and coal burst into underground mining roadway, while typical shallow-focus coal bumps in China generally happened under a three-hard strata structure. In order to clarify the mechanism of coal bumps caused by mining effect under the condition of hard coal-rock strata structure, a modified structural slip model is built considering coordinated deformation of roof and floor. The practical parameters of the Xinzhouyao coal mine are used to prove the validity of the model, then the vertical stress and the state of plastic zone under high stress are discussed with different strength reduction coefficients. The results show that the length of plastic zone is 1.5 m, 1.8 m, 2.3 m, 2.9 m respectively when the lateral pressure coefficient is 0.6, 0.9, 1.2, 1.5, with vertical peak stress ranging from 21.5 to 14.1 MPa, and that the model could well reflect the stress distribution and bump risk with stress status. By discussing the effect of weakening of coal seam, the structural slip mode of coal seam induced by mining effect are evaluated, the model can provide support for following risk evaluation and control. [ABSTRACT FROM AUTHOR]

Thick hard rock strata (THRS) are widely distributed among coal-bearing strata in China. The dynamic THRS failure may induce the coal-rock dynamic hazards during underground coal mining. In this study, the size, stress and energy characteristics of dynamic THRS failure were analyzed; the Yangliu coal mine, Huaibei coal basin, China, was taken as a case study. Then the apparent-depth effects of the dynamic THRS failure on the underlying coal mining were researched. The results revealed that the rock roof would be caved, fractured and deformed and even develop the bed separation during underlying coal mining. A large quantity of elastic energy is stored in the bent and compressed THRS, the amount and scope of the vertical stress concentration in front of the working face increases significantly before THRS breaking. THRS generally exhibit the square-form structure failure (SSF), after which the elastic and kinetic energy is attenuated in power form with the energy spreading distance. The shock force and energy effects of the dynamic THRS failure on the underlying coal mass were greater than those observed for the common lithological rock strata. Thus the mining coal mass below THRS bears similar mechanical conditions as the deeper coal mass and is of greater apparent depth, which is called the apparent-depth effects of the dynamic THRS failure. The apparent-depth effects of the dynamic THRS failure significantly influenced the coal-rock dynamic hazards according to in situ measurements of the mine earthquake energy, in situ stress, roof pressure and gas emission parameters. As a result, reasonable measures should be taken to avoid stress concentration and energy accumulation and to reduce the apparent depth of the mining-disturbed coal mass for preventing coal-rock dynamic hazards. The research results provide significant value for the control of coal-rock dynamic hazards below THRS. [ABSTRACT FROM AUTHOR]

As coal mining is extended to ever-greater depths, the factors affecting the safe mining of coal seams are becoming increasingly complicated. High-pressure confined water in the coal seam floor can pose a major threat to the safety of coal mining. Therefore, based on the analysis of various factors that affect water inrush from coal seam floors, this study develops a geological engineering model of high-pressure confined water damage assessment for coal mine face floors. The model adopts six evaluation factors: coal mining depth, coal seam thickness, thickness of the aquiclude, hydrostatic pressure, brittle-rock thickness, and the distribution of faults and folds. The comprehensive weight of the six factors is obtained through analytic hierarchy processing (AHP) and the entropy weight method (EWM) to establish an AHP–EW risk index model (AEM). AEM is applied for the evaluation of two coalfaces in a study area in North China, and the water inrush risk zonation of the coalface floors is determined. Finally, the results given with AEM are compared with those from the traditional water inrush coefficient method, and its applicability in other mining areas is also validated. The results show that the proposed model provides more accurate evaluation results than the traditional method and that its application is more practical. [ABSTRACT FROM AUTHOR]