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Coal mining is generally carried out through open pit mining methods which have an impact and become an obstacle to changes in the chemical, physical, and biological properties of the soil. Revegetation of reclaimed land is a priority in restoring ecosystems disrupted by mining activities. This study aims to assess the success of the direct planting method in accelerating the growth of Pterocarpus indicus plants in coal mining reclamation areas. Field data and observations are used to evaluate the growth of plants directly planted in reclaimed post-mining land. The growth parameters observed include plant height, stem diameter, and leaf count using both seedling and stemcutting planting materials. The research results indicate that the direct planting method has a significant impact on accelerating the growth of Pterocarpus indicus plants. The plant height, diameter, and leaf count growth from the ANOVA test results showed a significant effect or significance at p<0.05 for the interaction between planting material, fertilizer, and dosage. The Duncan test results for the average plant height, stem diameter, and leaf count indicate the optimal use of bokashi fertilizer. The effective bokashi fertilizer dosage for each variable is 3 kg/planting hole, resulting in a plant height of 102.31 cm; 3 kg/planting hole, resulting in a stem diameter of 24.26 cm; and 5 kg/planting hole, resulting in a leaf count of 41.32. [ABSTRACT FROM AUTHOR]

Sustainable development in coal mining requires a continuous and efficient method of coal extraction. Research shows that gob-side entries retained through roof cutting retained gob-side (RCGE) are vital for improving mining efficiency, enhancing coal recovery rates, and enabling continuous production. However, the mechanism of surrounding rock deformation during close-distance co-mining of coal seams with this technique is not yet clear. For the Jiaokou coal mine in China, due to an unreasonable stagger distance between upper and lower working faces, the gob-side entries retained at the 9102 tailgate and 10102 headgate experience severe rock pressure, leading to significant prop damage and a sharp reduction in the cross-section of the entry. This greatly hampers the reuse of these entries. To investigate this issue, we established a model to study the stress distribution of surrounding rocks at different stagger distances (20 m, 40 m, 60 m, 80 m, and 120 m) through numerical simulation and optimized the support parameters for the retained entries. Our research found that when the subsidence of the roof in the upper coal seam exceeds 0.74 m but is less than 1.33 m, there is sliding instability in the mining body. When the subsidence exceeds 1.33 m, the mining body will rotate and deform, causing significant mining pressure within the retained entry. A stagger distance of 40 m between the upper and lower working faces can reduce pressure on the face during the mining of the lower coal seam. Extensive field measurements of rock pressure revealed that the damage rate of the single column in the gob-side entries of the upper and lower coal seams does not exceed 5% and 1%, respectively. In summary, this study provides a practical method to reduce damage to entries during the mining process, thereby increasing the continuous production capability of the coal mine. This is critical for the sustainable development of coal mining. [ABSTRACT FROM AUTHOR]

In longwall top coal caving (LTCC) mining methods, problems such as large deformations, loss of coal resources, and excavation relay out of balance are often encountered with the increased production in single mining panels. To address these problems, a novel non‐pillar coal mining technology in LTCC was used based on the equilibrium mining theory. This approach could cut off the stress transmission, eliminate the coal pillar, and retain the gob‐side entry. In this technology, the entry is first excavated along the roof of the coal, and then four techniques are applied to control the surrounding rock of the retained entry. The constant resistance and large deformation anchor cable are used to maintain the roof stability. The directional roof split blasting technique is adopted to separate the roof between the entry and gob. The blocking‐gangue support system (BGSS) is used to form the gangue rib lagging the mining panel. The temporary support system is applied to prevent the roadway from being affected by the dynamic pressure and prevented the BGSS from falling. Finally, the field monitoring results indicate that the surrounding rock of retained entry is stabilized at 200 m behind the working face. The deformation of retained entry is within a reasonable range at 180–190 m behind the mining panel. The results provide an important reference for the thick coal seam non‐pillar coal mining technology, specifically using this technology in LTCC panels. [ABSTRACT FROM AUTHOR]

With the increasing proportion of close-distance coal seam mining in China, the problem of strong mining pressure during the mining of close-distance coal seams is becoming more and more severe. This article focuses on the complex stress environment and severe mining pressure encountered in the mining of thick coal seams under the multi-coal-seam goaf of Zhunnan Coal Mine. By using research methods, such as similar material simulation, theoretical analysis, and numerical simulation, it studies in depth the instability characteristics of the overlying rock structure of the W1701 working face, the inducing factors and mechanisms of strong mining pressure during the mining process, and control measures. The results show that the roof structure of the W1701 working face can be divided into "high-level key layer (hard rock)–giant thick soft and weak rock group–low-level key layer (hard rock)", and the law of mining pressure manifestation presents a small cycle formed by the instability of "masonry beam" structure and a main large cycle formed by the periodic penetration and step-down of the giant thick soft and weak rock group, with the load on the support during the large cycle up to 5.4 times the rated working resistance. In addition, this article proposes the strategy of using layered mining to control the manifestation of strong mining pressure under the "hard sandwiched soft" overlying rock condition of the Zhunnan Coal Mine, optimizes the thickness of the layered mining of the thick coal seam, and finally, determines the upper layer thickness of 2.8 m and the lower layer thickness of 4 m, inducing the giant thick soft and weak rock formation to undergo incremental damage and releasing the fracture energy incrementally, effectively controlling the manifestation threat of strong mining pressure in the mining of thick coal seams under the close-distance coal seam goaf. As the proportion of close-range coal seam mining increases in China, the problem of strong mining pressure during the mining of close-range coal seams becomes more severe. This article focuses on the complex stress environment and severe mining pressure in the mining of thick coal seams under multiple mined-out areas in the Zhunnan coal mine. Similar material simulation, theoretical analysis, and numerical simulation methods were used to conduct in-depth research on the unstable characteristics of the overlying rock structure of the W1701 working face, the causes and mechanisms of strong mining pressure during the mining process, and control measures. The results show that the roof structure of the W1701 working face can be divided into "high-level key layer (hard rock)–thick soft weak rock group–low-level key layer (hard rock)." The law of mining pressure manifestation presents small cycles of instability formed by "block beams" and main cycles of pressure formed by vertically cracked periodic penetration and step sinking of the thick soft weak rock group. Moreover, during the main cycle of pressure, the load-bearing capacity of the support is up to 5.4 times the rated working resistance. Furthermore, it is proposed to use hierarchical mining to control the manifestation of strong mining pressure in the "hard-inlaid soft" overlying rock condition of the Zhunnan coal mine and optimize the thickness of layered mining of thick coal seams. Ultimately, the upper layer thickness was determined as 2.8 m; the lower layer thickness was determined as 4 m, and the layered mining induced the thick soft weak rock group to undergo gradual damage and energy release, effectively controlling the threat of severe mining pressure during the mining of thick coal seams under the close-range coal seam mining. [ABSTRACT FROM AUTHOR]

The re-mined face using top coal caving system is the most applicable method for recovering the remaining reserves of a previous partially-mined thick coal seam. However, this mining method may encounter the problems of low recovery and unpredicted geological conditions. A numerical model is developed using PFC2D for studying the movement of top coal mass and development of coal-rock mass interface at a longwall top coal caving re-mined face. The re-mined face advances in the lower seam below the upper solid coal pillar, previous entries and gob. A theoretical analysis according to the unsteady flow model is developed to calculate the proper time duration of caving operation. The results showed that the top coal to be recovered through the caving window before the initiation of caving operation is a partial spheroid-shaped geometry. The boundary between the coal and rock mass then develops to a funnel-shaped coal-roof interface as the caving operation continues. The top coal recovery is 98.1%, 77.1% and 70.5% for caving operations below the solid coal, entries and gob area in the upper seam, respectively. The proper timing of caving and interval of caving operation is important for obtaining a high coal recovery. Good agreement is achieved between the proposed model and the improved Boundary-Release model for short of B-R model. The study in this work may provide reference for the safety and efficiency of the extraction of the longwall top coal caving re-mined face. [ABSTRACT FROM AUTHOR]

This study reveals the hydrocarbon production potential and thermal maturity of Çilhoroz coals, which is the most important local coal field around Erzincan in the Eastern Anatolia Region. This area is one of the best examples of the continental collision zone in the world and is located in a north-south convergent collision zone between the Eurasian and Arabian Plates. The average thickness of the coal seam is about 4 m and these coals are currently mined by open pit mining methods. Coal is predominated by combined xylitic/attrital lithotypes and by huminite macerals with inertinite and minor liptinite macerals. The content of mineral matter is variable but generally low, it consists mostly of quartz, calcite, clay minerals, and pyrite. Although the Rock-Eval pyrolysis data show that the investigated coal bearing unit is represented by a significant hydrocarbon (oil and gas) potential, hydrocarbon species did not develop due to low maturation. [ABSTRACT FROM AUTHOR]

High-intensity longwall top coal caving (LTCC) mining of super-thick coal seam in high stress conditions often leads to significant movement and failure of overburden. The competent roof above the super-thick coal seam is easy to form large unstable structures, and the breaking and movement of the roof strata often induce high weighting strength and large dynamic disasters which severely affect the mine safety. The key to control the behavior of competent roof is to understand the fracturing law of the roof strata. In this paper, a case study based on microseismic (MS) monitoring was performed at LW8309 working face in Tongxin coal mine, where super-thick coal seam under competent sandstone roof in high stress conditions was mined by LTCC method. The spatial distribution characteristics of MS events were studied and four impact zones in the horizontal direction and 'four-zones' in the vertical direction were identified. Multifractal analysis of MS events was carried out to study the multifractal characteristics of the fracturing of competent overburden. In addition, a large and small periodic law of fracturing of competent roof was revealed from the temporal distribution of MS events and on-site monitoring of hydraulic support pressure. A key stratum (KS) structural model was then proposed to explain the strong behaviors of competent strata during high-intensity mining. The research results are of great significance for safe and efficient mining of super-thick coal seam under competent roof in high stress conditions. Highlights: The impact zones in front of the mining face and four vertical zones were identified and the fracture characteristics of the competent overburden in the impact zones and the vertical zones were revealed. Multifractal characteristics of the fracture of the competent overburden were obtained. A large and small periodic law of fracture of competent overburden was revealed from the temporal distribution of MS events and on-site monitoring of hydraulic support pressure. A key stratum (KS) structural model was proposed to explain the behavior of the fracture of competent overburden. [ABSTRACT FROM AUTHOR]

To study the fracture law of different overlying strata during mining of the lower protective seam under a close distance coal seam at a depth of 1000 m, roof bed‐separation and fissure imaging monitoring were carried out in the inlet roadway ahead of the working face of the JI15‐31040 lower protective seam in the Pingdingshan XII coal mine. The results show that with the overlying strata of the lower protective seam being affected by mining, the displacement of the overlying strata in the roof of 0–4 m was relatively large, and the fissure development was very significant. The displacement of the overlying strata in the roof of 4–12 m was relatively small, the fissures in this range were mostly randomly closed fissures, and this area was stable. Bed separation occurred in the roof of 12–16 m, and the bed‐separating fissures were mostly located at the coal–rock junction. During the mining process, the fractal dimension of the roof gradually increased, and the fissure network developed continuously. The changing process of the fractal dimension of the roof can be roughly divided into three typical change areas: less influence area (distance from the working face > 70 m), rapid increase area (15 m < distance from the working face < 70 m), and stable area (distance from the working face < 15 m), and the area within 70 m in front of the working face was the key supporting area. Under the influence of mining, the roof fissures showed an overall change trend of "from zero to some, from short to long, from small to large, and from narrow to wide." This study can provide a reference for mining of the protective seam in deep coal seams. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology 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 Coal Science & Technology (0253-2336) is the property of Coal Science & Technology 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.)

Aiming at the problem of stability control of surrounding rock in the process of upward mining of inclined coal seam gob-side entry retaining, the gob-side entry retaining of 5449 working face in Beipingdong coal mine is taken as the research background. Based on the study of theoretical model of gob-side entry retaining, the law of overburden movement and surrounding rock deformation in the process of gob-side entry retaining is obtained through similar simulation experiment and numerical simulation analysis, and the optimal optimization scheme of supporting structure is put forward. The main research results are as follows: in the process of coal seam mining, the center of gravity of the overlying strata on the whole working face will shift to the side of the goaf, and the supporting structure composed of roadside filling body and bolt effectively inhibits the deformation of the roadway, in which the roadside filling body plays a key role; the top bolt bears greater stress than the side bolt in the process of mining, so the top bolt mainly maintains the stability of the roadway, and the side bolt plays the role of strengthening the side and preventing the extrusion. The width of the roadside filling body should be about 2.5 m, and the plastic failure range can be well controlled under this width. [ABSTRACT FROM AUTHOR]

The more complex the hydrogeological conditions of a mine, the more likely the coal seam is to experience water inrush during the mining process, and the greater the degree of the water inrush hazard. The scientific and reasonable prediction of water inrush in mines with complex hydrogeological conditions is of great significance to the safe and efficient operation of coal mines. Taking the roof water inrush problem of the No. 3 lower coal seam in the Jisan Coal Mine as the research object, the factors affecting the roof water inrush of the coal seam were comprehensively considered from three aspects: the aquifer property, the mining fracture development and the geological structure. The evaluation index system was constructed by selecting 10 factors, including the aquifer depth and thickness, core recovery rate, brittle–plastic rock thickness ratio, number of water-resisting layers, development height of the water-conducting fracture zone, fault density, frequency density, scale index and variation coefficient of the coal seam floor dip angle. At the same time, based on the dual influence of subjective and objective weighting, the scientific and reasonable weight of each factor was ensured. The AHP-CRITIC composite weighting method was used to calculate the comprehensive weight of each factor. Finally, the roof water inrush risk prediction model was constructed. According to the prediction results, the study area was divided into a low-risk area, medium-risk area and high-risk area. Compared with the actual situation, the prediction results were basically consistent with the actual situation, and the prediction results can provide the basis for the prevention and control of water in a coal mine. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Mine Automation is the property of Industry & Mine Automation Editorial Department 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 Coal Science & Technology (0253-2336) is the property of Coal Science & Technology 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.)

Background: To optimize the layout position of the residual coal pillar return roadway when mining a close coal seam group and to clarify the optimization mechanism, a roadway optimization layout analysis was conducted on the Tashan coal mine. Methods: Surface displacement monitoring was conducted using field tests, and the main stress magnitude, plastic zone morphology, deformation variables, and connectivity between the plastic zone of the roadway and the plastic zone of the residual coal pillar were analyzed at different locations with the help of FLAC3D numerical simulation software. Results: It was found that, in the process of close coal seam group mining, the residual coal pillar of the overlying coal seam seriously affects the stress state and plastic zone distribution of the lower coal seam roadway. The roadway is arranged in a position that is relatively far away from the residual coal pillar, which could reduce the stress influence of the residual coal pillar on the roadway and guarantee the stability of the roadway. Conclusion: Since the Tashan Mine uses the top release method for mining, the stability of the roadway can be better ensured by placing the roadway in the middle and lower regions of the coal seam and using the layout method to retain small coal pillars. [ABSTRACT FROM AUTHOR]

With the increasing improvement of national ecological standards, the eco-environmental problems caused by super thick coal seam mining in western China are becoming more and more serious. The failure law of weak overburden stratum is an important factor affecting the safe mining of coal. The failure characteristics of weakly cemented overburden under high-intensity mining in the mining area of western China were studied. For this purpose, a case study was conducted in the 1101 working face of the Baituyao Coal Mine in Ürümqi County. Based on the analysis of geological conditions in the study area, we combined empirical calculations with engineering analogy, physical simulation, and numerical simulation to comprehensively analyze the characteristics of mining-induced overburden failure. The study showed that the overburden in the study area had several unfavorable engineering geological characteristics, including ease of softening in the presence of water. The Middle Jurassic Xishanyao Formation is a directly recharged aquifer with a weak water-retaining property. Overburden failure mainly occurred at the two ends of the open-off cut. During the mining process, vertical fissures and bed-separated fissures were periodically developed and closed, and the fissures were interconnected. The overburden was fractured, and the fractured zone showed a trapezoidal shape, tapering off from bottom to top. The heights of the caving zone and the water-conducting fracture zone were 25 and 280 m, respectively, in the 1101 working face of the Baituyao Coal Mine, and the ratio of fracturing to mining height was 14.0. Due to the weakly cemented overburden and the presence of the Neogene weak aquifer, the risk of water and sand bursts still exists in this working face under high-intensity mining. Our findings shed light on the safe mining and environmental protection of the ground surface in coal mine shafts in western China. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology 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 problem needs to be solved about stability control of small coal pillars along goaf in the coal mining process. In this paper, the effects of water reducer, accelerator and expansion agent on the fluidity, setting time, expansion ratio and stone body strength of grouting materials were analyzed through orthogonal experiments, and the optimal ratio of grouting materials was obtained, and it is applied to the engineering site to obtain the reinforcement effect of the coal pillar grouting material on the coal pillar. The results of the study show that: When the dosage of the accelerating agent is 4%, the amount of water-reducer is 0.3%, and the amount of the expansive agent is 6%, the comprehensive performance of the grouting material is the best. After using the new coal pillar grouting material to strengthen the coal pillars, 30 days of monitoring were conducted to determine the deformation of the surrounding rock of the roadway. The shallow separation layer of the surrounding rock of the roadway was about 39.6~52.5 mm, and the accumulated separation layer of the deep rock was 28.5~29.5 mm, which were kept within the safe control range. The coal pillar grouting material can well fill the surrounding rock fissures and coupling and cement the broken rock mass, improve the bearing capacity of the narrow coal pillar, and enhance the overall stability of the surrounding rock of the roadway. The research results have important reference significance for similar coal pillar grouting. [ABSTRACT FROM AUTHOR]

In the mining process, protective-seam mining is one of the most effective measures to prevent and control coal and gas outburst accidents across the world. To accurately obtain the fracture development characteristics for protected coal in a similar physical simulation (to two-dimensional (2D) protective-seam mining), a novel and similar material to coal was developed. The similar material was prepared by mixing pulverized coal with a certain particle-size distribution and a water solution of sodium humate, which were separately taken as the aggregate and binder, followed by pressing and drying. Numerous orthogonal proportioning tests revealed that, under the molding pressure of 15 MPa, the unit weight and porosity of the similar material tended to be stable and approach that of raw coal. The similar material has a high compressive strength that is regulatable over a range as wide as 0.5~2.8 MPa and has an approximately linear direct proportional relation with the binder concentration. The adsorption and desorption tests revealed that the similar material features favorable adsorption properties, and its adsorption isotherm agrees with that of raw coal. The similar material is also characterized by a low price for its raw materials, no toxic or side effects, simple proportioning, stable properties, and the convenient regulation of various physical and mechanical parameters. Therefore, it can be used to simulate raw coal with different strengths. [ABSTRACT FROM AUTHOR]

In northern Shaanxi province, the coal seam deposit conditions are generally characterized by large thickness and shallow depth of burial, the phenomenon of coal pillar sloughing is serious in the process of working face retrieval, which brings great potential danger to mine safety production. In this paper, by monitoring the stress and damage of the coal pillar in the field section, the stress changes and damage degree of the working face in different mine stages are determined. A new mechanical model of coal pillar in a thick coal seam is constructed and the stress changes and structural breakage law of each section are obtained, the stress transfers mechanism of overburden structure and the stress damage to coal pillar during the mining process of upper and lower section comprehensive mining working face is analyzed. The stress, microscopic damage, and the degree of sloughing in the coal pillar were significantly reduced by monitoring through the top plate hydraulic cracking pressure relief control program. The results of the study show that the extent of sloughing coal pillar and internal damage is closely related to the length of key block B of the masonry beam formed by the overlying rock layer and the position of the break line, by changing the orientation of the overlying masonry beam rock layer and the position and length of the tendency to break line, the sloughing coal pillar is effectively controlled and its stress and damage are reduced. We have achieved good results in control of the sloughing in the Hanjiawan coal mine and similar mines in northern Shaanxi. [ABSTRACT FROM AUTHOR]

• True triaxial loading restores the airside roadway stress state. • Though coal and rock failure mechanisms are similar, variations are distinct per stage. • Coal and rock shift from progressive stability to sudden failure. • The journey from coal and rock microfractures to total damage is clarified. The airside roadway is frequently identified as the predominant site for dynamical disasters involving coal and rock. For the assurance of safety in mining zones, it becomes imperative to understand the mechanical response and energy characteristics of the coal and rock system within the airside roadway during mining processes. A triaxial static and dynamic load test system was used to conduct compression experiments on coal and rock samples under single-free-face true triaxial loading at different loading rates. The research findings are summarized as follows: (1) The damage and failure of the samples gradually propagate from the free face to the deeper sections of the samples and evident stage characteristics. Revealed that the damage mechanism was "microfracture localization – localized region development through – overall instability." (2) A rising loading rate impedes the coal and rock's ability to make adaptive adjustments, thereby amplifying the sample's resistance against crack development, and playing a positive role in stimulating coal and rock failure, and the coal and rock system changed from progressive stable failure to sudden instability failure. The mesoscopic failure pattern gradually evolves into inadequacy and irregularity. (3) Throughout the entire failure episodes of coal and rock samples, the predominant mode of failure is tensile. However, influenced by the loading rate, the principal failure mechanism transitions from tensile to shear during the Ⅳ stage of failure. (4) There is noteworthy congruence between the macrofracture sites and the spatial positioning of high-energy fracture episodes. This furnishing pivotal insights for preempting and control deep impact disasters. [ABSTRACT FROM AUTHOR]

The rockburst dynamic disasters in the process of deep coal mining become more and more serious. Taking the rockburst occurred in the 23130 working face of Yuejin Coal Mine as the engineering background, we study the characteristics of mining stress field around roadway, the plastic failure morphological characteristics of surrounding rock and the accumulation/release law of elastic energy before and after burst. An analysis model quantitatively describing the physical process of rockburst in the mining roadway is established, and the calculation method of dynamic release of elastic energy in the physical process of rockburst is educed. The mechanism of rockburst in mining roadway is revealed. The results show that an "L-shaped" stress concentration zone is formed within 100 m of the 23130 working face, and the principal stress ratio of the surrounding rock of the transportation roadway is 2.59–4.26. The change of the direction of the maximum principal stress has a significant effect on the burst appearance characteristics. The failure strength of different sections of the mining roadway is characterized by the elastic energy release value. With the increase of the working face distance, the elastic energy released by burst failure and the expansion variation of failure boundary radius show a nonlinear variation law that tends to decrease steadily after sharp fluctuation. The closer to the working face, the higher the burst risk. At a distance of 10 m from the working surface, the maximum principal stress reaches its maximum value. The butterfly-shaped failure system generated by the surrounding rock of the roadway has energy self-sustainability, and the elastic energy released by the sudden expansion of the butterfly leaf is enough to cause a burst damage of 1.9 magnitude. This work could provide theoretical support for the prediction and prevention of rockburst. [ABSTRACT FROM AUTHOR]

There is complex air leakage in the mining of shallow buried close distance coal seam group, which affects the generation and migration of CO in the goaf, and easily leads to exceeding safety limits of CO in the return corner of the working face, which threatens the safety of underground production. To examine this problem, taking Lijiahao Coal Mine as an example, this study analyses the generation law of CO gas, the distribution law of overburden fractures, the characteristics of air leakage in the goaf, the sources of CO in the return corner, and the migration and accumulation law of CO in the goaf under multi-source air leakage in the mining of shallow buried close distance coal seam group through experiment tests, numerical simulations, observations and theoretical analyses. The results indicated that there is an exponential growth relationship between the CO generation rate and the coal temperature, and the critical temperature for rapid oxidation of coal samples is between 70 and 80 °C. The 31,115 working face has complicated air leakage from the working face and ground surface and the goaf of this coal seam. The surface air converges to the return corner through the mining fissure of overburden and 2–2 coal goaf, and the air leakage of the working face flows out from the return roadway through the goaf. The gas leakage in the overlying goaf and the oxidation of residual coal are the main sources of CO in the return corner. The CO generated during the coal mining process and the CO generated by the trackless rubber-tired vehicle operation will increase the CO concentration in the return corner to varying degrees. Under the effect of multi-source air leakage, CO from the overlying goaf and the residual coal in the goaf of this coal seam are migrated to the air return side of the goaf, resulting in the accumulation of CO in the return corner, and both of them have a linear positive correlation with the CO concentration in the return corner. The results of the study have scientific guidance for the control of air leakage and the prevention of CO excess in the goaf. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology 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 mining areas in Western China are characterized by water shortage and ecological fragility, and the coal resources in these areas are extracted in a large-scale and highly intensive manner, which is highly likely to induce ecological problems, such as soil erosion and grassland degradation. In addition, there is a secondary protection zone of Hongshixia water source near Guojiatan minefield. If the water resources loss of Salawusu Formation is too large, it will affect the normal water supply of Yulin city. To reasonably coordinate coal exploitation and water protection, the development characteristics of water-conducted fissures with different backfill ratios are obtained in combination with theoretical analysis, field test, and numerical modelling. The panel layout of the layered-backfill-based water protection working face and the parallel operation of mining and backfilling are designed, and a feedback regulation system integrating hydrological monitoring and backfill ratios is established, which assists in evaluating the effectiveness of water protection. The results indicated that when the slicing mining method was adopted with the roof naturally caving, the maximum development height of the water conducted fracture zone was 220.0 m (developed to the Yan'an Formation), and the water conducted fracture zone could only develop to the Yan'an Formation without crossing the Zhiluo Formation when the backfill ratio reached 80%. The water emission rates in the west of the field testing area reduced from 334.95 m3/h to 60.60 m3/h, dropping by 86.86%. Compared to the scene prior to the layered backfill mining, the shallow water outflow was reduced by 72.74 m3/h, and it helped annually reduce the shallow water loss of 637200 m3, which was equivalent to 1.74% of the actual water supply to Yunli city every year. The results of this study can provide guidance on effectively avoiding the loss of shallow water resources that are regarded as indispensable sources of domestic water. [ABSTRACT FROM AUTHOR]

The short-distance coal seam group refers to the coal seams which has obvious mining influence on the adjacent coal seam during mining process. In the process of short-distance coal seam mining, there are a large number of cracks around the stope due to the mining stress, resulting in serious air leakage and high risk of spontaneous combustion. To mining the working face under the condition of overlying close goaf in Xutuan Coal Mine in Huaibei Mining area, the distribution of spontaneous combustion dangerous area in goaf was studied systematically with the help of engineering test, laboratory research and numerical simulation. Results show that a "Γ" distribution of high oxygen concentration area was found above the roadway of the goaf due to the effect of air leakage and coal seam space, the high spontaneous combustion risk area is close to the return airway. A three-dimensional distribution of the high spontaneous combustion risk area was formed in the composite goaf after mining in the lower coal seam face, the spontaneous combustion risk of the upper position is higher than that of the lower position. Besides, based on the pyrolysis-room temperature oxidation experiments of coal sample, it is considered that the inert environment and high temperature promote the production of active groups in coal and thus enhanced the oxidation ability of coal, mechanism of spontaneous combustion of residual coal in the overlying goaf was further revealed. Accordingly, the comprehensive fire prevention and fire extinguishing measures of nitrogen injection, leakage plugging and inhibitor injection are put forward. With the method of numerical simulation, it was found that nitrogen injection at the position of 50 m in the goaf can effectively reduce the spontaneous combustion risk in the compound goaf, and the injection of TEMPO inhibitor was put forward based on the secondary oxidation characteristics of residual coal. The research conclusion can provide theoretical guidance for the fire prevention technology of coal seam mining in the overlying close goaf. [ABSTRACT FROM AUTHOR]

Coal use exacerbates several major environmental problems including build-up of greenhouse gases and air quality deterioration. Although Kuzbass (Siberia) is one of the largest exploited coal basins worldwide, the role of regional coal mining and processing in atmospheric pollution is unknown. We outlined the Kuzbass coal basin by spaceborne night-lights and revealed a regional, long-term tropospheric NO2 anomaly (2005–2018) by spaceborne NO2 column observations (hereafter ‒ NO2). The spatial agreement between NO2 and night-lights indicates that the anomaly is attributable to an agglomeration of coal quarries and the cities in Kuzbass, that are heavily reliant on coal. A positive relationship between NO2 and interannual coal production suggested that the anomaly was related to coal in Kuzbass; ~ 1.0% of annual coal production increase induced ~ 0.5–0.6% of NO2 enhancement. As coal production accelerated since 2010, NO2 exhibited strikingly similar annual increases over Kuzbass in 2010–2014 (7%) and 2015–2019 (15%), compared to 2005–2009. Conversely, Siberian cities lacking a coal industry followed the global trend of reducing NO2 for the same periods (−5% and −14%, respectively), driven by fuel combustion improvements. Overall, we demonstrated that coal mining, processing and utilization can induce distinct tropospheric NO2 anomalies, detectable from space. [ABSTRACT FROM AUTHOR]

The working face is the most dangerous place of coal mines, and it is difficult (even impossible) to replenish energy by replacing batteries of sensor nodes in the working faces. This paper presents a wireless charging method for this scenario that is composed of two sub methods called mining charging and maintaining charging, respectively. Mining charging provides opportunistic charging services during the process of coal cutting through two airborne Mobile Chargers (MCs) installed on the two ends of the shearer and two portable MCs carried by shearer drivers. Maintaining charging provides opportunistic charging services for nodes in the charging radius when scraper conveyor repairmen and hydraulic support repairmen check or repair equipment, with each repairman carrying one portable MC. Simulation results show that both mining charging and maintaining charging can give energy replenishment for nodes in coal faces. When charging power of MCs is greater than or equal to 5.2 W, the first row of nodes can work sustainably. If the energy requirements of the second row of nodes are also met, the charging power of MCs cannot be less than 12 W. [ABSTRACT FROM AUTHOR]

It was a non-negligible problem in the reserve of section coal pillar in coal mining. Reasonable section coal pillar width and support parameters can not only ensure the stability of surrounding rock of roadway but also produce more coal resources and save support cost. In this paper, the mining of 9106 workface of Linfen Tianyu Hengsheng Coal Industry of Wanbei Coal Power Group was taken as the research engineering background. FLAC3D numerical simulation software was used to simulate and analyze the laws of deformation failure of 6 m, 7 m, 8 m, 9 m, and 10 m coal pillars and surrounding rock of roadway along goaf without support conditions during the mining of 9106 workface. On this basis, the deformation failure law of 7 m and 8 m coal pillars and surrounding rock of roadway along goaf under different supporting conditions (bolt and cable with different row spacing) were further simulated and analyzed. The results showed that when 7 m coal pillars were reserved in 9106 roadway along goaf, the optimal bolt row spacing was 800 mm. When 8 m coal pillars were reserved, the bolt row spacing was preferred to be 900 mm. At this time, the width of coal pillar and support parameters can ensure the stability of roadway surrounding rock during the mining process of 9106 workface and can produce more coal resources and save support cost. [ABSTRACT FROM AUTHOR]

In order to solve the problem that the gas in the upper corner is easy to exceed the limit in the mining process of the deep outburst coal seam. Based on the theory of "O-ring" and the distribution of stratigraphy in the field, the development law of mining fissures in the overlying rock layer during the workface retrieval was studied by combining theoretical calculation and FLAC3D numerical modeling. The research results show that the range of fissure development zone in 2913 working face is 14.2 to 33 m from the coal seam roof, and the high drilling arrangement can be in the stable rock layer of the roof. For siltstone-fine sandstone interaction stratum, measures such as opening branches to adjust the layer and lowering the casing to protect the hole wall can be taken to ensure the stability of the borehole and the smooth flow of gas extraction channels. Field application shows that the high directional long borehole has the advantages of long extension distance and wide coverage, the average value of extraction mix is 34.3 m3/min, and the average value of extraction pure is 0.4 mm3/min, which helps to prevent the gas overlimit in the upper corner during the workface recovery. The high directional long borehole has obvious economic and safety benefits over the traditional high hole and has important promotion value in coal mine gas management. [ABSTRACT FROM AUTHOR]

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Copyright of Journal of Mine Automation is the property of Industry & Mine Automation Editorial Department 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.)

Roof-breaking characteristics and ground pressure behavior of the coalface are instrumental in guiding deep Jurassic coal seam mining, in particular in the Shaanxi and Inner Mongolia regions of China. A thick-plate mechanical model (TPMM) of the main roof was developed and applied to the case study of 21102 first-mined coalface (FMC) of the Hulusu Coal Mine (HCM) in the Hujirt Mining Area (HMA), China. A theoretical analysis performed via the developed model revealed that the first and periodic breaking intervals of the main roof were 40.6 and 25.0 m, respectively. The roof failure occurred in the tensile mode, was controlled by the internal stress σ x in the rock strata, and started from the center of the long side with the fixed support in the goaf. The field measurement of roof weighting was also performed for the coalface advance from zero to 400 m. The measurement results showed that the first weighting average interval was 41.4 m, and the average interval of periodic weighting was 22.0 m, which agreed with the theoretical calculation and proved the proposed model's feasibility. Finally, the frequency distribution features of the hydraulic support working resistance in the FMC were analyzed statistically. The results showed that the ZY10000-16/32D supports could adapt to the mining geological conditions of the FMC. However, the margin of the rated working resistance of supports was still small. Thus, roof management enhancement during the mining process was strongly recommended. These research findings could offer theoretical guidance for safe and high-efficiency production in the coal mines under similar geological conditions. [ABSTRACT FROM AUTHOR]

Karst water may break into coal tunnels through the rock fissures and cause severe coal mine disasters. The direct current resistivity (DCR) is sensitive to underground water and can be used to detect fissures during the coal mining process. However, the three-dimensional (3-D) measurement of the DCR is still a challenging task and has not been applied to the practical coal mining dynamic process. To bridge this research gap, this study proposes a new 3-D cross-borehole method by monitoring the DCR at multiple points to analyze the geoelectrical field evolution in the underground coal mining process. Based on the forward and inversion theoretical analysis, a DCR observation system is developed for a real unground coal mine to evaluate the cross-borehole points. The 3-D resistivity distributions at different positions in the coal mining process are calculated. The analysis result demonstrates obvious resistivity changes with the evolution of the Karst water zone during the coal mining, and the location and movement of the Karst water can be well estimated. As a result, the proposed 3-D cross-borehole method is very effective for monitoring the DCR and is able to accurately detect the underground water. [ABSTRACT FROM AUTHOR]

In order to prevent the occurrence of rockburst accident caused by the stress concentration of the middle rock pillar in the near-vertical coal seam and affect the mining of the lower coal seam in the known goaf, taking Wudong coal mine in Xinjiang as an example, based on the special geological and mining conditions of the mine, through the simulation experiment and numerical analysis of similar materials, the variation law of the stress distribution of the middle rock pillar with the increase in mining depth is analyzed. A presplitting blasting pressure relief technology of drilling a construction chamber in the middle of the rock column is proposed to form a buffer layer in the rock wall and effectively prevent the continuous downward movement of stress. In order to achieve the optimal blasting effect, the finite element numerical simulation software GTS NX is used to carry out the chamber rock mass hole blasting simulation experiment, the three influencing factors of blasting effect, such as charge quantity, blast hole diameter, and blast hole row spacing, are comprehensively considered, and the optimal pressure relief blasting parameters with the radius of borehole blasting crack circle and the width of plastic zone as the index are determined. The experimental results show that under the condition of determining the physical and mechanical parameters of coal and rock, the blast hole diameter has become the main control factor affecting the blasting pressure relief effect, followed by the charge amount. Through 9 groups of orthogonal tests, the optimal combination of the three indexes is 6 kg charge, 150 mm hole diameter and 10 m hole row spacing. The practical engineering application results of the combination are tested by downhole transient electromagnetic detection (TEM), and it is found that the pressure relief effect is obvious. The preliminary conclusions of the study have guiding significance for the pressure relief and erosion prevention of the middle rock pillar in Wudong mine and provide experimental methods and theoretical basis for the determination of blasting pressure relief parameters in other mines. [ABSTRACT FROM AUTHOR]

High rate of dust generation and serious dust diffusion in dry directional drilling in soft and broken coal seams (SBCS) have long been critical problems in the mining process. To solve these problems, in this study, a dust hood was designed and applied to realize non-contact dust control in drilling holes. The optimal performance of the dust hood was achieved when different technical parameters, including the gap width between the dust hood and the drill pipe, the air-slot width of the sealing device, the slag discharge pressure, and the air curtain pressure were controlled at 2 mm, 0.2 mm, 0.3 MPa, and 0.5 MPa, respectively. As a result, the dust concentration was reduced from 540 mg/m3 to 15 mg/m3, with dust control efficiency reaching 97.2%. The in situ test results confirmed good dust control effects, as the dust control efficiency reached 98.3% after using the dust hood. [ABSTRACT FROM AUTHOR]

Gas disasters, such as coal and gas outburst and gas overflow, always occur during the mining of the steep and extra-thick coal seam in the horizontal, fully mechanized, top coal slice caving (HFMTCSC) method. To solve these issues and guarantee the safe and efficient mining in the Yaojie No. 3 coal mine, 3DEC software was used in this work to investigate the overburden movement and collapse law as well as the stress redistribution and coal-seam deformation characteristics below the goaf. The results show that a pressure arch structure and a hinge structure are formed in succession in the overburden rock, which induces stress redistribution in the coal below the goaf. During the mining of the upper slice, more than 75% of the coal in the lower slice is located at the effective pressure relief zone; therefore, the steep and extra-thick coal seam can then be protected slice by slice. Meanwhile, with the increase of mining depth, the efficient pressure relief range expands. Based on this pressure relief mechanism, crossing boreholes and bedding boreholes were reasonably designed to efficiently extract the pressure relief gas during the mining of the steep and extra-thick coal seam in the Yaojie No. 3 coal mine. [ABSTRACT FROM AUTHOR]

A larger mining height leads to easy caving of the coal wall in the working face. The flexible reinforcement method during the mining period of the working face affects the normal mining of the working face, and the high strength of the traditional bolt/cable material affects the operation of the shearer drum, so it is necessary to seek a reinforcement material which does not affect the production and the drum coal cutting. This paper proposed a technical scheme of coal wall reinforcement by pre-grouting with a cuttable aluminum–plastic composite pipe which is easy to cut during mining in the working face, tested the mechanical properties of the "grouting + flexible pipe" specimen, and obtained the optimal support spacing by numerical simulation and carrying out an industrial test. The results show that the tensile strength of aluminum–plastic composite pipe is much higher than that of coal spalling and the elongation is much higher than that of the anchor rod. When double-row composite grouting holes are arranged 1.5 and 3.0 m away from the roof, the supporting effect is better. Underground grouting shows that pre-grouting before mining according to the advancing speed of the working face 10–14 days in advance can effectively fill the coal cracks and significantly improve the integrity of the coal wall. [ABSTRACT FROM AUTHOR]

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Backfill mining is an effective measure to control surface subsidence and restrain floor water inrush. It is an essential part of green mining technology. To solve the problem of confined water in mines under buildings, this study was carried out by combining theoretical analysis, laboratory simulation, and numerical simulation, taking the Liangbei coal mine as the research area. The coal seam floor failure characteristics of traditional longwall caving and paste filling mining methods were compared and analyzed. Based on the relevant mining theory, the key parameters, such as mining thickness and filling rate under the critical state of water inrush, were obtained. Then, the feasibility of backfill mining was expounded, and the surface subsidence of paste backfill mining was predicted and measured on site. The results demonstrated that the longwall caving mining method not only had the risk of water inrush, but also the possibility of step cracks at the surface, with the potential to result in serious damage to buildings. However, the backfill mining method reduced the floor damage depth of the coal seam from 12 m to 7 m, which reduced the water inrush coefficient by 12%, the maximum vertical concentrated stress by 42.1%, and the displacement subsidence value by 78.8%. These parameters correlated negatively with backfill strength. Meanwhile, the maximum subsidence, maximum inclined deformation, and horizontal displacement deformation were estimated as 730 mm, 2.5 mm/m, and 1.1 mm/m, respectively, consistent with the measured values (608 mm, 2.1 mm/m, and 0.9 mm/m, respectively). More relevantly, there were no obvious cracks found in the surface buildings, ensuring the safety of mining above confined water on the working face, and realizing the effective protection of surface buildings. [ABSTRACT FROM AUTHOR]

Identification of the coal layer is the primary technical issue that guides CBM exploration and development. Conventional well logs are now generally used by mining geoscientist for identification of coal layer. The aim of this study is to identify coal layers and investigate physical properties by cross-plot and qualitative inspection of log curves methods in 9 wells from Ordos basin, China. The result confirmed that Gamma ray and density logs are most sensitive followed by neutron, resistivity and acoustic logs to the coal formation in the Ordos Basin. Combining the information from multiple conventional geophysical log types can provide important information, in terms of understanding coal litho-units in the area for its future exploitation. [ABSTRACT FROM AUTHOR]

Results of the investigation of polycyclic aromatic hydrocarbons (PAHs) content in fine coal powders prepared according to a special procedure within size classes (-0.2+0.1) mm, (-0.1+0.063) mm, (-0.063+0.04) mm, (-0.04) mm for ten different coal ranks (B, D, G, Zh, K, KS, OS, SS, T, A) from the Kuznetsk coal basin are presented. The qualitative and quantitative PAHs content in coal samples was determined by means of GC-MS using a SCION SQ SELECT instrument (Bruker, USA). The maximal ∑14 PAHs content is observed for A rank coal (224.3 mg/kg), KS (201.9 mg/kg) and T (197.8 mg/kg), and the minimal ∑14 PAHs content is detected for B rank (2.2 mg/kg) for the size fraction (-0.04) mm. The concentration of benz(a)pyrene, which is a strong carcinogen, is within the range of 0.026-103.1 mg/kg in coal samples under investigation. At the same time, the fraction of benz(a)pyrene is less than 45% of the total amount of detected PAHs, and it is less stable to the effect of the environment than other PAHs. The most stable component in PAHs series is phenanthrene, which was detected in the series of studied coal samples of different fractions (0.061-43.7 mg/kg). Phenanthrene may be considered a PAHs of priority, and it may be used as a reference compound to evaluate the influence of coal mining and processing on the environment. The group composition of hydrocarbons in coal extracts was determined by means of two-dimensional gas chromatography with flame ionization detection. [ABSTRACT FROM AUTHOR]

To solve the high-stress hazard faced in the process of deep mining process, the pressure relief characteristics of gas bearing coal and the deformation characteristics of surrounding rock in deep roadway are studied by means of laboratory test, similar simulation analysis, and field investigation. The investigation results and engineering application showed that the specimens could more easily reach the failure point due to the axial pressure relief under high confining pressure. In addition, the deformation and failure degree of the surrounding rock was higher due to the disturbance from the deep high-stress roadway. The scope of the height affected by the pressure relief of the overlying strata reached above 10 m. Moreover, the initial gas emission could reach 4.41–14.39 times that of the original coal seam by drilling a hole in the coal seam at 10 m from the roof. Thus, the short-distance floor roadway exerted an obvious pressure relief effect on the overlying coal seam. [ABSTRACT FROM AUTHOR]

The key to safe and efficient longwall mining of steeply dipping seams lies in the stability control of the "support-surrounding rock" system. This study analyzes the difficulties encountered when controlling the stability of the support during the longwall mining process of steeply dipping coal seams in terms of the characteristics of the nonuniform filled-in gob using a combination of physical tests, theoretical analyzes, and field measurements. Considering the floor as an elastic foundation, we built a "support-surrounding rock" mechanical model using data obtained on support-surrounding rock systems in different regions and the laws of support motion under different load conditions. Our findings are summarized as follows: first, depending on the angle of the coal seam, the caving gangue rolls (slide) downward along the inclined direction, resulting in the formation of a nonuniform filling zone in the deep gob where the lower, middle, and upper sections are filled, half-filled, and empty, respectively. In addition, an inverted triangular hollow surface is formed on the floor of the gob in the middle and upper sections behind the support. Furthermore, as the angle of the coal seam, length of the working face, and mining height increase, the characteristics of the nonuniform filled-in gob are enhanced. Second, we found that because of the gangue support, the "support-surrounding rock" system is relatively stable in the lower part of the working face; however, in the middle and upper sections of the working face, the contact method and loading characteristics of the support are more complicated, making stability control difficult. Third, the magnitude and direction of the load, action point, and mining height affect the stability of the support to varying degrees, with the tangential load and action position of the roof load having the most significant impacts on the stability of the support. Under loading by the roof, rotation and subsidence of the support inevitably occur, with gradually increasing amplitudes and effects on the intersupport and sliding forces. Finally, we found that overall stability can be achieved by adopting measures involving "sliding advancement of supports" and applying a "down-up" removal order. These research results serve as a significant reference and guidance for longwall mining applications. [ABSTRACT FROM AUTHOR]

The separation of coal and gangue is an important aspect of coal production, which can improve coal quality, save energy, reduce consumption, and enable the rational use of resources. At present, manual selection remains widely implemented, but the working environment is harsh, labour intensity is high, and efficiency is low. With the continual developments in artificial intelligence and image technology, in this paper, a new method is proposed to separate gangue from coal based on image processing, the visual differences between the coal and gangue are analysed, and the supplementary texture is extracted based on morphology. Pre-treatments of coal and gangue images, including filtering, sharpening, and segmentation, are also introduced. Owing to the differences in physicochemical properties, coal and gangue exhibit different visual traces in the process of mining and transportation, but the traces appear to be irregular. Thus, the morphological method is applied to seek the region of interest where the coal or gangue body is exposed, and then the supplementary texture is extracted to establish the coal and gangue classifier. The effect of this classifier is evaluated and compared to the traditional texture classifier, and it is found that the recognition accuracy is significantly improved without special treatment (wash or blow). [ABSTRACT FROM AUTHOR]

The gangue filling mining method is used to reduce the occurrence of dynamic disasters on the roof of a steeply dipping coal seam (SDCS) effectively and improve the stability of the overburden structure. To comprehensively study the movement law of the overburden under different filling quantities, the 3221 working face of the Lvshuidong coal mine was taken as the research site. The vertical displacement, vertical stress, and plastic zone of the overburden under different filling quantities were analyzed by using FLAC3D numerical simulation and physical similarity simulations. The results show that the maximum stress in the stress concentration zone decreased with the increase of filling size. The vertical stress range of the overburden and floor in the filling zone increased significantly. The affected zones of the vertical displacement of the roof and floor and the vertical displacement of the overburden were reduced to varying degrees. The overall plastic zone was shrinking. The movement of overburden was well-controlled as the proportion of the fillings increased. The results of this study can provide an important reference for the stability control of the roof of SDCS filling mining. [ABSTRACT FROM AUTHOR]

Taking roadway along gob with narrow coal pillar in fully mechanized top coal caving face for extra thick coal seam as the research object, this paper systematically studies two key problems of asymmetric failure mechanism and control technology of gob side entry driving in extra thick coal seam by using comprehensive research methods such as theoretical analysis, numerical simulation and field measurement. Firstly, by establishing the mechanical model of overlying strata of gob side entry in fully mechanized top coal caving face of extra thick coal seam, the mechanical source of roof asymmetric failure of gob side entry is obtained. Secondly, the deflection stress invariant is selected to analyze the temporal and spatial evolution law of surrounding rock deformation and failure in the whole process of mining. Finally, the concept of asymmetric control and support technology of gob side entry in fully mechanized top coal caving face of extra thick coal seam are proposed, and the field engineering test is carried out. The research results show that: during the mining of extra thick coal seam, the overlying strata of gob side entry form a composite structure of "low cantilever beam + high hinged rock beam", and the subsidence and rotation of cantilever beam is the fundamental reason for the roof asymmetric settlement and two sides asymmetric failure of gob side entry. During the mining, the bearing capacity of the narrow coal pillar and the roadway near the narrow coal pillar decreases, and the storage capacity of the distortion energy also further decreases, forcing the deviator stress to transfer to the deep part of the solid coal wall, resulting in more significant asymmetric deformation and failure on both sides of the roadway with the center line as the axis; The asymmetric control concept with asymmetric anchor cable truss and anchor cable channel steel composite structure as the core is constructed, and the supporting scheme of "anchor cable channel steel composite structure + asymmetric anchor cable truss structure + high strength anchor cable structure at the side" is put forward, and the field application effect is remarkable. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Mine Automation is the property of Industry & Mine Automation Editorial Department 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 Journal of Mine Automation is the property of Industry & Mine Automation Editorial Department 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.)