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

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

To improve the recovery for corner coal left over in mines, taking the Xin'an Mine in China as the research object, the gradual increase support mining method for recovering corner coal is proposed in this study and the evolution of the overlying strata pressure is investigated. The dynamic process of the overburden roof in the corner coal and the hydraulic support were simulated by using FLAC3D software. Results show that, under the gradual increase support mining, the abutment pressure over the mining working face is less than 21 MPa. The overlying rock over the coal seam roof forms a periodic breaking--collapse cycle with a periodic pressure step distance of 10 m and the hydraulic support load is 13-25 MPa. Based on that, the gradual increase support mining method including a scheme of three supports and three chutes adding for every 9 m is designed and the corner coal is fully recovered. The obtained conclusions provide a significant reference for predicting strata movement over the corner coal, which can help aid in designing such mining method in engineering applications. [ABSTRACT FROM AUTHOR]

Cropland is the foundation of food security. Coal is the guarantee of energy security. As China's demand for coal and grain continues to increase, so does the overlap area of their production bases. Unrestrained underground mining can cause serious damage to cropland, leading to increasing conflicts between coal mining and food production. Thus, this paper used a partial backfilling mining technology to control surface subsidence and thus protect cropland. The key to successfully implementing the technology is how to design the panel size. However, the design efficiency of the conventional enumeration method is low. Therefore, this paper proposed a design approach based on improved particle swarm optimization. The results indicated that the approach could quickly find the optimal size of the panel compared with the enumeration method and particle swarm optimization. Moreover, if the longwall panel is mined according to the size designed by the approach, the cropland will be protected, and the cost will be reduced. This study can provide technical support for the cooperative development of cropland protection and coal mining in a coal-cropland overlapping area. [ABSTRACT FROM AUTHOR]

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

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.)

This paper aims to evaluate the severities and causes of ground surface building and cropland damages after coal mining in a better way, and to clarify the correlation between the damage assessment indexes that influence mining. Against the backdrop of multi-seam mining in certain coal mines in China, the estimated results of each displacement and deformation were analyzed using GIS technology. The damage range determined for each deformation index is divided according to the displacement and deformation combined with the virtue of damage judgment threshold. The damage ranges on the ground surface based on the comprehensive value of each displacement and deformation index were obtained through superimposing those ranges delineated by each displacement and deformation index, and the law on influence from displacement indexes upon various levels of damage was analyzed in a quantitative manner accordingly. The results showed that coal mining destroyed 14 buildings and a cropland area of 11.96 hm2; among them, building damage was only associated with displacement indexes E (horizontal deformation) and T (inclined deformation). Seven buildings were solely destroyed by T alone; five buildings were solely damaged by E; two buildings were damaged jointly by E and T; and, moreover, with the aggravation in building damage level, the proportion of building damage due to E decreased while the proportion of building damage under the same level due to T increased. Regarding cropland destruction, the damage due to T accounted for 33.48% while the damage jointly caused by W (Subsidence), E and T accounted for 30.45%. Moreover, the proportion of damaged cropland area due to inclined deformation T was positively correlated with cropland damage level. These findings can provide a reference for rational judgment regarding civilian building and cropland destruction on the ground surface after coal mining. [ABSTRACT FROM AUTHOR]

Coal is the main energy source in China, and spontaneous combustion of coal is one of the main disasters in coal mines. Fully mechanized caving top coal mining technology is widely used in coal mines. Under the comprehensive action of multiple factors, gas generated by coal oxidation and low oxygen gas in goaf is easy to rush to working face, resulting in lower oxygen concentration in upper corner and exceeding harmful gas concentration. It seriously threatens the health of underground workers and the normal operation of production. If the oxygen concentration in the upper corner is changed, it is bound to cause the change of the oxygen concentration in the goaf and aggravate the threat of spontaneous combustion of coal in the goaf. In order to solve the double threat of low oxygen in upper corner and coal spontaneous combustion in goaf, based on Coulomb model, this paper uses command flow to conduct numerical simulation tests on the failure law of overlying strata, and obtains the influence of mining of the lower 1 coal seam and the lower 5 coal seam on the overlying strata subsidence and surface penetration. Based on the comprehensive consideration of atmospheric pressure, ore pressure activity, external air leakage and other factors, the mixed model of the source and emission of low oxygen gas in goaf was established, and the formation mechanism of low oxygen problem in the corner of return air of working face was defined. The use of pressure air belt to deal with low oxygen in return air corner is proposed creatively. The comprehensive fire prevention measures such as corner plugging, nitrogen injection and grouting are used to inhibit the oxidation of the left coal and the influx of low oxygen gas to the corner in the goaf, so as to achieve the goal of collaborative prevention and control of low oxygen in the corner of return air and coal spontaneous combustion. The research results have important reference significance for the mine with the risk of spontaneous combustion or the problem of low oxygen in the return air corner. [ABSTRACT FROM AUTHOR]

Ordovician limestone in North China coalfield has the characteristics of karst fissure development and strong water yield. Coal mines in North China have been threatened by Ordovician limestone water for a long time. Taking the mining of 32 coal seam in the first eastern mining area of Qianyingzi coal mine in Anhui Province in China as the engineering geological prototype, this paper uses the self-developed fluid solid coupling similarity model test device to carry out the similarity model test of overburden stress and pore water pressure response of coal mining under Ordovician limestone nappe aquifer. Based on the variation law of pore water pressure and overburden stress in a stope, it can be seen that the variation law of pore water pressure in confined aquifer is jointly affected by two factors: the vertical distance between the monitoring point and coal seam and the horizontal distance between the monitoring point and DF200 fault. According to the analysis of experimental results, the maximum height of a water flowing fracture zone in the stope is fifteen times the mining thickness. Compared with the theoretical calculation results of empirical formula, the coupling effect of seepage field and stress field and the geological structure characteristics of the stope promote the development of a water flowing fracture zone. The research results of this paper have important theoretical and practical significance not only for the safe mining of Qianyingzi coal mine but also for the safe mining of the coal mine facing the double threat of roof Ordovician limestone confined aquifer and reverse fault. [ABSTRACT FROM AUTHOR]

China has abundant coal resources, and the distribution of coal seams is complex. Thick coal seams account for more than 45% of all coal seams. Fully mechanized top coal caving mining has the advantages of large production, high efficiency, and low cost. In fully mechanized caving mining, especially in fully mechanized caving mining of extra-thick coal seams, the mining space is ample, the mine pressure is severe, and the roadway maintenance is complex. As a result, it is necessary to summarize and discuss the gob-side entry driving of fully mechanized caving in theory and technology, which will help to promote the further development of fully mechanized caving gob-side entry driving technology. First, in recent years, the research hotspots of gob-side entry driving have focused on the deformation mechanism and the control method of the roadway surrounding rock. Secondly, this paper discusses the theoretical models of the "triangle-block" and "beam" for the activity law of the overlying strata in gob-side entry driving, including the lateral breaking "large structure" model, compound key triangle block structure model in the middle and low position, the high and low right angle key block stability mechanics model, elastic foundation beam model, low-level combined cantilever beam + high-level multilayer masonry beam structure model, and the vertical triangular slip zone structure model. It introduces the "internal and external stress field theory" and the "stress limit equilibrium zone model". Thirdly, it summarizes several numerical simulation analysis methods in different conditions or research focuses and selects appropriate constitutive models and simulation software. Finally, it introduces surrounding rock control technology, including two ribs, the roof, and under challenging conditions. It provides a method reference for support in similar projects. [ABSTRACT FROM AUTHOR]

The severe deformation of surrounding rock and the easy failure of the anchoring structure of roadway under large dynamic pressure influence in the short distance are the urgent issues to be paid more attention. Based on this problem, this paper is a case study on the instability mechanism and control technology of surrounding rock in the deep roadway under dynamic mining loading in the Gubei Coal Mine of China. The vertical distance from the − 575 m roadway of 11–2 mining area and mining working face is only 68 m. Firstly, the main factors influencing the surrounding rock's severe deformation are determined by the analysis of site investigation, surrounding rock composition and structure, overlying strata failure measurement, and borehole camera detection. The stress distribution, displacement distribution, plastic zone, and lining stress distribution of roadway of three reinforcement schemes, including nine working conditions, were calculated by numerical simulation for ordinary bolt support, bolt-support + grouting of roof and two sides, and bolt-support + full section grouting. Then the combined support technology system of "36 U-shaped steel + bolt + anchor cable + grouting" was proposed. The field monitoring results showed that the deformation of two sides and roof were only 20 mm and 16 mm, respectively, during the 65 day monitoring period. Furthermore, the cracks in the surrounding rock are almost filled with grouting materials, and the overall stability of roadway surrounding rock was completely achieved. This successful case study demonstrated that the optimized supporting structure is reasonable and the deformation of surrounding rock has been effectively controlled. [ABSTRACT FROM AUTHOR]

In China, soft rock roof makes up the majority of coal mine roof, yet it is easy to break due to low strength and poor integrity. As such, it is difficult for the traditional pillar-based roadway protection means and pillarless mining techniques to effectively control the roadway roof. In order to solve the problems with pillarless mining under soft rock roof conditions, using the 1510 working face of Xinyi Coal Mine as an example, a gob-side caving roadway forming (GSCRF) technique for broken immediate roof is developed. This paper discusses the adaptability and feasibility of this technology through theoretical modeling and on-site engineering testing. A roadway rock surrounding control scheme based on "cable + steel beams + yielding prop" is further designed, and field tests and monitoring are carried out. Field tests show that, during GSCRF of the 1510 working face, the maximum subsidence of the roof remains within 200 mm. The convergence of the two sides causes stabilization. The tension on the anchor cables is gradually becoming stable. The monitoring results show that the roadway has a good stress environment and the surrounding rock is effectively controlled. Compared with the traditional pillarless mining mode, this technology has the technical advantages of achieving complete elimination of coal pillars, reduced pressure on the roadway roof, and interference-free mining of the working face. The research outcome can provide useful reference for pillarless mining by GSCRF and a solution for pillarless mining under soft rock roof conditions. [ABSTRACT FROM AUTHOR]

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

In recent years, the structural evolution characteristics of the regenerated roof of the lower coal seam have become a research hotspot when the bifurcation coal seam is mined downward. In this paper, taking the bifurcation coal seam of Xutuan Coal Mine in China as an example, the structural evolution characteristics of regenerated roof under the influence of mining in bifurcation coal seam are comprehensively studied by theoretical analysis, field measurement, and indoor similar simulation experiment. The stress transfer law in the floor after mining in the upper coal seam is also analyzed. The results show the overburden structure and stress field change caused by upper coal seam mining. The caving and fracture zones are formed in the roof, the average height of the caving zone is 8.28 m, and the one of the fracture zone is 34.91 m. The results of the field test verify the accuracy of theoretical analysis and similar simulation test results. According to the relative size of the depth of the strong failure zone of the coal seam floor and the coal seam spacing, the rock mass structure of the regenerated roof of lower coal seam is divided into three types: fractured rock mass + scattered rock mass (I), fractured rock mass + scattered rock mass + fractured rock mass (II), and fractured rock mass + bulk rock mass + fractured rock mass + layered rock mass (III), and the stability of the three types of regenerated roof structure is evaluated: III > II > I. The research in this paper can provide a theoretical basis for determining the target area of broken roof control under the mining conditions of bifurcation coal seam and provide guidance for the selection of the location and parameters of the grouting borehole for roof reinforcement. [ABSTRACT FROM AUTHOR]

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

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

Improving coal resource mining rates has long been a focus of coal industry research. The gob-side entry retaining by roof cutting (GERRC) is a new coal mining technology that has gained popularity in China due to its high mining rate and safety. Based on the GERRC technology, the precise technical procedure is elaborated, and the fundamental idea of pressure relief is explored through creating a structural mechanics model of the surrounding rock in this paper. The results of mechanical analysis show that the primary mechanism of roof pressure release is to weaken the integrity of the roof, thereby reducing the ultimate bending moment of the rock stratum. In addition, an additional strategy for pressure release is suggested in this research, involving the weakening of the roof rock by the creation of dense pressure-released holes. The results of the engineering field experimentation demonstrate that the dense pressure-released holes can completely replace the conventional blasting technology of the past to achieve the effect of releasing the roof pressure, thus avoiding the use of hazardous and challenging-to-obtain explosives and demonstrating safety, reliability, and feasibility. [ABSTRACT FROM AUTHOR]

Underground mining safety risk increases with the more complicated geological conditions in deep strata, so coal mines turn to the upper limit mining of shallow coal seams under the Cenozoic strata. Nevertheless, coal mines in the Northern China coalfield are mainly covered by thicker loose sandy layers with more abundant water. The analysis of overburdened strata deformation properties is essential for safe, efficient, and environmentally friendly production. This paper discusses the deformation and migration of overburdened strata through mechanical analysis, numerical and physical similar simulations, and in situ field measurement. A thorough understanding of overburdened strata deformation induced by mining has been obtained, and the results are as follows: The immediate roof first collapses to form the caved zone accompanied by the first weighting, and the fractured zone and bending deformation zone begin to develop in sequence; the separation layer is observed during the period of fracture development. However, the occurrence of the bending deformation subsidence results in the closure of the separation space; the ratio of fractured and mining height is quantified to 14.4:1.0 by the comparative analysis. The results may serve as technical evidence to support the mining safety of the study area and other coal mines with similar geological conditions. [ABSTRACT FROM AUTHOR]

A reliable numerical simulation method and large-scale in-situ test method for super-thick coal seams are very important to determine the failure range of mining floors, which is often the basis to protect Ordovician limestone water, an important drinking water source for people in North China. This paper takes Yushupo Coal Mine as an example; the explicit–implicit coupling simulation method and the corresponding double scalar elastic–plastic constitutive model were established to predict the failure depth of the floor numerically, and verified by the full section borehole stress–strain in-situ testing method. The results show that the explicit–implicit coupling numerical program and the double scalar elastoplastic constitutive model are suitable for predicting the floor failure depth under the condition of extra-thick coal seams. In this condition, the overburden moves violently, resulting in a loading–unloading–reloading process with large stress variation amplitude in the mining floor, which leads to serious rock failure compared with that of medium-thick coal seam conditions. In Yushupo 5105 working face, the floor failure starts to develop from 9.3–24.2 m ahead of the coal wall of working face, and the failure depth no longer increases after 35 m behind the coal wall, with the maximum failure depth of 28 m; the envelope line of the floor failure depth presents an inverted saddle distribution. The above research results lay a foundation for further protecting the Ordovician limestone water, and realizing green coal mining. [ABSTRACT FROM AUTHOR]

In northwest China, underground mining is frequently conducted in weakly cemented rock environments, including the aquiclude that protects the aquifer from dewatering. In this context, understanding the aquiclude responses to longwall mining is significant for assessing the reliability of water-conserved mining in the weakly cemented rock environment. Taking the Jurassic and Paleogene coal measure geology in Yili Mine in Xinjiang Province, China, as a case study, the paper conducted a laboratorial three-dimensional simulation by configuring a longwall operation and induced groundwater migration. The study analysed the aquiclude depressurisation and revealed the aquiclude stability in response to longwall mining. The results indicated that the aquiclude had a significant plastic strain and self-healing ability in the ground depressurisation condition. The aquiclude experienced tension and then compression, and, accordingly, fracture initiation, propagation, and convergence, during which the aquiclude had significant bending deformation. On the aquiclude horizon, tensile fracturing dominated above the set-up and longwall stop positions. The self-healing behaviour was correlated to the high content of clay minerals and disintegration proneness. The simulation results had a good agreement with field measurements, suggesting that the aquiclude had a satisfactory water-resisting ability and that the simulation results were practically reliable. [ABSTRACT FROM AUTHOR]

Coal seam mining in the gully area easily causes ground cracks and even induces landslides, which endanger the safety of mining areas. In this paper, combined with the mining conditions of a mining area in southern Shanxi Province, China, ground crack mapping, crack width dynamic monitoring, and the numerical simulation method are used to study the static and dynamic evolution law and the formation mechanism of ground cracks in the gully area. The research shows that ground cracks mainly include dynamic in-plane cracks and boundary cracks. The dynamic in-plane cracks show the characteristics of "opening first and closing later". The boundary cracks show the characteristics of "only opening and not closing". It is found that the closure of the dynamic in-plane cracks will decrease (compared with plain areas). The development of ground cracks experiences three stages: the initial formation stage, the dynamic development stage, and the gradually stable stage. The "goaf–surface" structure model and force chain arch structure model are established to more intuitively analyze the formation mechanism of ground cracks. The research results have a specific reference value for preventing ground disasters caused by underground coal mining and land ecological restoration. [ABSTRACT FROM AUTHOR]

Cemented coal gangue paste backfill (CCGPB) containing coal gangue and fly ash is a backfilling technique newly developed in coal mines in China that allows environmentally hazardous products, such as gangue and fly ash, to be reused in underground stopes. CCGPB materials provide efficient ground support for the caving of strata and reduce surface subsidence. In this paper, field monitoring of CCGPB properties was conducted in an underground coal mine, which mainly included the measurement of the longwall face temperature, humidity, CCGPB internal hydration temperature, stress conditions inside the backfills, and displacement. First, the components of the backfills, paste technique, slurry generation procedures, coalfield geology, and mining conditions were introduced. Then, a monitoring system was designed in the field. An online monitoring system was installed. The results of the field monitoring showed that the curing temperature significantly varied, i.e., from 26°C near the main gate to 37°C near the tailgate. The curing humidity had the same trends, increasing from 60% relative humidity (RH) near the main gate to 81% RH near the tailgate. The internal hydration process of the paste was divided into four stages, i.e., the rapid hydration stage, slower hydration stage, rapid decline hydration stage, and relatively stable stage. The highest hydration temperature was 50°C, which was measured on the second day after the backfill process. The temperature approached stability at 41°C. The evolution of the roof stress applied on the CCGPB was divided into four stages: the development stage, regulation stage, rapid growth stage, and relatively stable stage. The maximum roof loading was 12 MPa in the middle of the longwall face. The deformation of the backfill experienced four stages, i.e., the rapid deformation stage, slow deformation stage, relatively stable stage, and long-term stable stage. The maximum deformation was 104.3 mm, appearing in the middle of the face. In addition, the compression ratio of the backfill was approximately 4%. The results of this study showed that the working conditions of backfills in the field were different from those in the laboratory. This paper provides guidance for the design of the CCGPB technique and the predictions of surface subsidence induced by the production process of underground mining. [ABSTRACT FROM AUTHOR]

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

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

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

The cost, complexity, lack of filling space and time create challenges in the longwall backfill operation, resulting in poor subsidence control and reduced productivity. This paper proposes an automated continuous mining and continuous backfill (CMCB) method by examining its key requirements and investigates the optimum sequence of coal panel (such as drifts) excavation to ensure ground strata control at relatively high productivity. The automated CMCB adopts the highwall mining technique underground, which enables easier automation at the workface. A numerical simulation of the Changxing coal mine in China was undertaken, and five different sequences of coal excavation were investigated, using the automated CMCB excavation parameters (assuming a 4 m width cut, 5 m mining height for a 200 m long coal slice) to determine the optimum sequence of resource excavation. The plastic zones and vertical displacement across the five models were analyzed. Simulation results of the 5 m high coal seam excavation show that the odd-even slice (OES) mining sequence, which has a vertical ground displacement of 74 mm, is the most efficient excavation method, due to its effective stress redistribution and lower induced ground displacement. [ABSTRACT FROM AUTHOR]

Coal is one of the fundamental fossil energy supporting the world's economy. The synergistic development between efficient coal mining and ecological environment protection is the inevitable requirement for the preservation of global harmony. As the world's largest coal producer, China has conducted a strategic shift from east to west in terms of the exploitation of its energy resources, posing a serious threat to the fragile ecological environment of the western region. In particular, the surface subsidence caused by coal mining is the root of the ecological deteriotation and the destruction of ground structures. However, it is difficult to reveal the law of large-scale surface subsidence in western mining areas merely by conventional measurement methods such as leveling, on account of the high intensity of coal seam mining, the weakness of the lithology of overlying rock and the large thickness of wind-blown sand strata. In view of this, small baseline subset interferometric synthetic aperture radar (SBAS-InSAR) technology was used in this study to obtain the time series of surface vertical displacement during the whole mining process of the 2401 working face in the Yingpanhao coal mine, Inner Mongolia. Based on the deformation data, the dynamic evolution characteristics of surface subsidence under high intensity mining in the western mining area were analyzed exhaustively. It was found that the surface subsidence is characterized by an extensive coverage range (48.52 km2) with minimal ground settlement (250 mm) in the study area. Meanwhile, the boundary shape of the subsidence basin followed a "circular-parallelogram-trapezoid" changeable process and the coverage area of the basin experienced three stages: a linear increasing period, a temporary stagnation period, and a re-expansion period. Furthermore, there existed an abnormal uplift phenomenon on the east side of the open-off cut in the 2401 working face. Combined with the structure of overlying strata, this paper carried out a preliminary analysis on the reasons of the abovementioned phenomenon. The research results are of vital realistic significance for ground buildings and ecological environmental protection in the aeolian sand mining area in Western China. [ABSTRACT FROM AUTHOR]

With the exploitation of the lower coal seams of the Taiyuan Formation, the Ordovician limestone water inrush in the floor became more serious. This paper considers the 162 and 163 mining areas of the Jiangzhuang Coal Mine, in Shandong Province, China. A comprehensive analysis of the geological and hydrogeological conditions of the mining area revealed the following: water pressure and water richness provide the water source and power for the floor water inrush; the thickness of the effective aquifer and the ratio of brittle rock can restrain floor water inrush; fault structures provide water inrush channels; and mining damage is an artificial interference and increases the probability of water inrush. Therefore, six factors: the water pressure of the Ordovician limestone aquifer, water abundance of the Ordovician limestone aquifer, equivalent thickness of effective aquifuge, brittle rock ratio, fracture structure, and mining destruction were selected as the influencing factors on water penetration of the bottom plate, and drawing software was used to establish a mining area map of related factors. The improved fuzzy hierarchical analysis method is more suitable for analyzing multi-objective decisions than the traditional hierarchical analysis method, but the weighting of results is influenced by expert experience. The entropy weight method is data-driven, and the empowerment results are objective. The improved fuzzy analytic hierarchy process and entropy weight method were coupled together, to determine the weight of each factor. The new method is not only data driven, but also takes empirical experience into consideration, making the empowerment results more reasonable. An evaluation of coal floor water inrush was established using MapGIS10.6, which is a general tool-type geographic information system software developed by the China University of Geosciences; and the risk of Ordovician limestone water inrush in the floor of the study area was classified into four levels: dangerous, relatively dangerous, relatively safe, and safe. The whole evaluation process is simple, but the evaluation results have practical importance and are very efficient, providing theoretical support for coal mine water prevention and control engineering. [ABSTRACT FROM AUTHOR]

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

Due to the complex geostress and mining conditions in the coal seam with depth of 800 m, stability of surrounding rock for gob‐side entry retaining is very difficult to achieve. In this paper, we firstly propose an innovative bolt‐grouting controlled roof‐cutting for gob‐side entry retaining (BCR‐GER) approach for deep coal mines. Secondly, a mechanical model of "surrounding rock‐supporting body" for BCR‐GER is constructed, which consists of coal wall, roadside props, and gangues in gob (the whole supporting body). Thirdly, the key parameters (ie, cutting height, cutting angle, grouting cable length, and row of roadside props) are designed. Finally, field practice was applied at the No. 31120 haulage roadway of the Suncun coal mine in China, and in situ investigations were conducted for verification. Field measurement results show that maximum convergences of roof‐to‐floor and side‐to‐side were 264 mm and 113 mm, respectively. What is more, the maximum support resistance of roadside props was reduced by approximately 58%. The deformation and failure of surrounding rock were effectively controlled, and the pressure on roadside props was greatly reduced. This research fully considers the bearing properties of gangues in gob, eliminates the secondary disasters caused by borehole blasting, and provides guidance and reference for deep surrounding rock control of the same or similar gob‐side entry. [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]

The strong disturbance of upward mining of the short-distance multiseam results in frequent fractures in the coal seam to be mined, jeopardizing the operation safety due to the instability of the surrounding rock of the overlying stope and risks of coal and gas outburst. A lucrative alternative is the downward mining of multiseam, which wide implementation is limited by the lack of reliable data on stress evolution characteristics. In this paper, the evolution, nonlinear interaction, and superposition characteristics of mining-induced stress after multiple pressure relief in the short-distance multi-seam were investigated by the numerical simulation and physical simulation, taking the endowment and mining technology characteristics of group B short-distance multiseam in Pan'er Coal Mine in Anhui Province of China as an example. The numerical and physical models of multiple (2—5 times) mining activities in pressure relief multiseam (with five main coal layers) under downward mining are constructed and implemented with the FLAC3D software and 1 : 100 scaling, respectively. The results showed that a pressure relief arch, which bears and transfers stresses, is formed on the coal seam's roof and floor. In downward mining, the local arch expands to the long arch, which bearing capacity within the influence range of multiple mining disturbances is weak, and the arch structure is prone to instability. If a coal pillar is left in the upper coal seam after its mining, the lower coal seam mining will switch from the large-scale low-stress area under the goaf to the small-scale high-stress area of nonlinear interaction of the multiple mining stresses with the stress under the coal pillar. [ABSTRACT FROM AUTHOR]

The bed separation backfill grouting (BSBG) is commonly used to mitigate the surface subsidence caused by coal mining. The distribution characteristics of bed separation and its dynamic evolving process are crucial for BSBG design. This paper utilizes the continuum-discontinuum element method (CDEM) to study the distribution characteristics of bed separation for a longwall top coal caving (LTCC) panel of Longquan coal mine. Numerical results indicate that in addition to the bed separation below the primary key stratum, several small bed separations may also occurred in the strata between the primary key stratum and the subordinate key stratum. The bed separations in the overburden could be classified into three classes: the upper bed separation, the middle bed separation, and the lower bed separation. The upper bed separation has the longest duration time, and the middle bed separation has the shortest duration time. And the BSBG should be started before the closure of the middle bed separation. Based on the actual geological information, the BSBG scheme for 4203 LTCC panel is proposed to mitigate the surface subsidence by taken the results of numerical simulation into consideration. In addition, the case study of the BSBG is introduced in detail. By using gangue power slurry, BSBG could not only effectively mitigate the surface subsidence but also solve the problems of environmental pollution and land occupation caused by traditional gangue stacking. The present study could provide technical support for surface subsidence mitigation and coal gangue disposal for LTCC mining with similar conditions. [ABSTRACT FROM AUTHOR]

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

In order to study the influence of roof stress and fracture distribution characteristics on the stability of stope surrounding rock under repeated mining in close-distance coal seams, the research background of this paper is the close-distance coal seam mining of a mine in Guizhou province, China. The dynamic evolution characteristics of stope roof caving and the stress environment change law under repeated mining are studied by using the method of similar simulation experiment, numerical simulation, and field verification. The results show that the roof stage under repeated mining can be divided into four stages: normal mining, roof deterioration, end face roof leaks, and support crushing. The tip-to-face distance, support height, and support working condition are the main influencing factors in end face roof control. The main reason for the support crushing is that the roof above the support is broken, the main roof cannot form the self-stable structure, and the support force is insufficient. The roof dynamic load is high, and the subsidence of the end face roof is large, which is prone to roof caving during the stope roof weighting. Moreover, the roof weighting is frequent under repeated mining, which leads to the broken roof and the support cannot be supported, resulting in the occurrence of the support crushing accident. The control strategies for stope roof under repeated mining are provided based on the thorough study findings. The working face 17101 roof is successfully controlled by the aforesaid procedures, which provides the foundation for the management of stope surrounding rock under repeated loading. [ABSTRACT FROM AUTHOR]

Solid waste backfill mining can effectively deal with gangue and other mining wastes, as well as control the movement and damage of rock strata. In this paper, the RFPA2D rock failure process analysis software is used to study the fracture evolution and seepage response mechanism of the key aquiclude strata (KAS) under the conditions of different structural characteristics, interlayer rock thickness, and backfilling ratios in backfill mining. The simulation results show that, in backfill mining, soft rock plays a crucial role in the fracture repair of KAS with different structural characteristics. An increase in the KAS thickness from 15 to 35 m is shown to results in a continuously improved repair of KAS fractures. At the advancing distance of the working face of 50~100 m and the KAS thickness of 35 m, the minimum vertical seepage velocity of 0.06 ‐ 0.78 × 10 − 2 m / s is reached. An increase in the backfilling ratio from 45 to 80% improves the control effect on the overlying strata. A case study of backfill mining in the Wugou Coal Mine located in the Anhui Province of China was conducted. At the goaf backfilling ratio of 80%, the composite KAS's good control effect was achieved, which minimized seepage and avoided the water in rush phenomena. The above engineering application ensured the safe backfill mining of coal resources. [ABSTRACT FROM AUTHOR]

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

In the mining stage of shallow thick coal seam in the western mining area of China, there is often severe mine pressure and serious surface subsidence and damage. In this paper, theoretical analysis and PFC (Particle Flow Code) numerical simulation are combined to study the caving characteristics and force chain evolution characteristics of the overlying strata of stope. We analyze the stability of the structure of the "inclined step cutting body" on the overlying strata and obtain the calculation formula of the support force of the working face based on the instability of the structure. The force chain arch curve equation is modified according to the evolution law of force chains, from which the force chain can be the basis for judging the large area damage of the surface. The results demonstrate that the rock mass i1 ≤ 0.86, the structure of "inclined step cutting body," is not prone to sliding and instability. Considering that i = 1.0~1.4 under the condition of shallow buried thick coal seam, the structure of the "inclined step cutting body" is prone to being destroyed leading to instability, resulting in severe rock pressure.The minimum supporting force to maintain structural stability is 0.2Fn, which is in line with the actual support force in the mining process of the working face. Taking the mining technical parameters of the nearby working face into the force chain arch formula, it can be concluded that, when the working face advances to 175 m, large-scale subsidence damage begins to appear on the surface, which agrees with the survey results. Therefore, the force chain is the main force system to bear the load of the overlying strata. PFC has unique advantages in simulating discontinuous deformation of overburden rock. The results of the study reasonably explain the phenomena of severe mine pressure and serious surface damage caused by the mining of the shallow thick coal seam working face, which has a certain reference value for preventing ground disasters caused by underground mining and land ecological restoration. [ABSTRACT FROM AUTHOR]

As coal mining gradually extends deeper, coal seams in China generally show high stress, high gas pressure and low permeability, bringing more difficulty to coal mining. Therefore, in order to strengthen gas extraction, it is necessary to carry out reservoir reconstruction after deep coal seams reached. In this paper, the distribution and evolution laws of fracture zone overlaying strata of J15 seam in Pingdingshan No. 10 coal mine after excavation were studied by combining similar simulation and numerical simulation, meanwhile, the gas transport law within fracture zone was numerically simulated. The results show that the fracture zone reaches a maximum of 350 mm in the vertical direction and is 75 mm away from W9,10 coal seams in vertical distance. Since W9,10 coal seams are in an area greatly affected by the bending zone of J15 coal seam under the influence of mining, the mining of J15 coal seam will exert a strong permeability enhancement effect on W9,10 coal seams. The J15 coal seam can act as a long-distance protective layer of W9,10 coal seams to eliminate the outburst danger of the long-distance coal seams in bending zone with coal and gas outburst danger, thereby achieving safe, productive and efficient integrated mining of coal and gas resources. The gas flux of mining-induced fractures in the trapezoidal stage of mining-induced fracture field is far greater than that in the overlaying stratum matrix. The horizontal separation fractures and vertical broken fractures within the mining-induced fracture field act as passages for gas-flow. Compared with gas transport in the overlaying stratum matrix, the horizontal separation fractures and vertical broken fractures within the mining-induced fracture field play a role in guiding gas-flow. The research results can provide theoretical support for the arrangement of high-level gas extraction boreholes in roof fracture zones. [ABSTRACT FROM AUTHOR]

The compressive strength of coal in Yanlong mine area of China is less than 3 MPa. Basically, it is powdery. The roof and floor rocks are mudstone. Therefore, this coal seam is a typical "three soft" coal seam. Anchor and cable cannot be used due to low anchoring force. This paper describes how to support this type of soft coal roadway. The deformation characteristics of soft coal roadway were investigated. Results show the conventional U-shaped steel support is not subjected to uniform load, which bearing capacity can be improved by structural compensation, such as addition of horizontal and vertical beams made of U-shaped steel. In addition, by drilling pressure-relief holes in the ribs of a soft coal roadway, the stress distribution of surround rock in the roadway can be improved, which can transfer the high stress in the surrounding rock to deeper parts and reduce the pressure on the artificial support. A support method is to combine the strengthened U-shaped steel support with pressure-relieving drill holes, providing an economic and efficient way to support the very soft coal roadways. [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]

Coal mine pillar burst frequently occurs in Western China, which seriously restricts safe production. This paper takes the 35 m coal pillar of the 3102 working face of MKQ coal mine as the engineering background. The mechanism and evolution control of pillar bursts in multithick key strata are studied using field investigation, theoretical analysis, and numerical simulation. The mechanism of dynamic and static stress-induced pillar bursts was revealed combining the "O-X" broken features for key strata and numerical simulation of pillar stress evolution. A prevention scheme is put forward for strata presplit blasting and adjusting coal pillar width to minimize the dynamic and static stresses. The results demonstrate the following. (1) In the multithick strata, the first and second near-field subkey strata have perpendicular "O-X" broken features, whereas the third far-field subkey has parallel "O-X" broken features. The working face has three kinds of periodic weighting phenomena: long, medium, and short. (2) The simulated vertical stress curve of 35 m coal pillar goes through three states: two-peak, asymmetric trapezoidal and symmetrical trapezoidal shape with the different advancing position of working face. The stress concentration is extensively promoting a high-risk area for rock burst. (3) The coal pillar burst was induced by the superposition of energy released by the key strata breaking and the elastic energy accumulated in the wide coal pillar. (4) The monitoring data showed that the long, medium, and short periodic weighting steps of multithick key strata are 141.6 m, 43.2–49.6 m, and 17.6–27.2 m, respectively. The microseismic events energy, frequency, and stress of hydraulic support increment are the highest during the long periodic weighting, and the spatial distribution of microseismic events coincides with the stress concentration area. The theoretical analysis is confirmed with the field practice. [ABSTRACT FROM AUTHOR]

Roadways in thick coal seams are widely distributed in China. However, due to the relatively developed cracks and brittleness of coal, the support failure of thick-coal-seam roadways frequently occurs. Therefore, the study of bolt failure characteristics and new anchoring technology is very important for the safety control of thick-coal-seam roadways. Based on field observations, the failure mechanism of selected roadway failures under distinct conditions at three representative coal mines in eastern and western China was analyzed. Recommendations are provided for roadway safety control. The results show that the strength and dimension of the anchoring structure in the coal roof of thick-coal-seam roadways are the decisive factors for the resistance of the roadway convergence and stress disturbance. The thick anchoring structure in the roof constructed by flexible long bolts can effectively solve the problem of support failure caused by insufficient support length of traditional rebar bolts under the condition of extra-thick coal roof and thick coal roof with weak interlayers. The concepts and techniques presented in the paper provide a reference for the design of roadway support under similar geological conditions and dynamic load. [ABSTRACT FROM AUTHOR]

Coalbed methane (CBM), which is extremely rich in deep coal reserves in China, is not only the material cause of gas explosion and coal‐gas outburst disasters but also a clean and environmentally friendly energy source. Gas drainage must be carried out during deep coal mining to avoid gas accidents while obtaining clean energy. The low‐level roadway is an effective gas drainage measure for coal seams with high coal‐gas outburst risk and low‐permeability, and it can simultaneously realize the functions of gas drainage before and during mining. Roadway tunneling has a strong influence on the stress and permeability properties of the adjusted coal seams, and further determines the gas drainage efficiency and the layout of the air‐return roadway. Taking the Pingshu Coal Mine as an example, this paper analyzes the influence of the vertical distance between the low‐level roadway and the underlying coal seam, and the influence of the width and height of the low‐level roadway on the stress relief and deformation characteristics. The results indicate that the low‐level roadway tunneling results in a nonuniform stress disturbance of coal seam #15. And a reasonable layout and size parameters of the air‐return roadway in coal seam #15 were proposed based on which gas drainage practices were carried out with good effects in panel #15211. The research can effectively guide the elimination of coal and gas outburst in return air roadway, and achieve the purpose of safe and rapid tunneling coal roadway under the environment of highly‐gassy coal seam. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

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With the characteristic of less roadway excavation and high resource recovery, gob-side entry retaining (GER) technology is a safe and efficient green mining technology. Many experts and scholars have done extensive research on its principle and application. However, GERs are rarely used in thick soft coal seams. In this paper, based on the geological conditions of a coal mine in China, we propose a novelty approach of GER in thick three-soft coal seam (it means a single seam with a soft roof and a soft floor). The engineering scheme includes roadway expansion, large section roadway support, cutting roof to relieve pressure, and road-inside backfill body construction. The established mechanical and numerical calculation models effectively guide the engineering practice. Field observations showed that all the processes met the requirements of field production. The research results could provide theoretical guidance for the application of GER under similar geological conditions. [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]

Most of the coal mining in China is underground, which will inevitably cause surface deformation and trigger a series of geological disasters. Therefore, it is essential to find a suitable method to forecast the ground sinking caused by underground mining. The most commonly used prediction model in China is the probability integral model (PIM). But when this model is used in the geological condition of mining under thick loose layers, the predicted edge of the sinking basin will converge faster than the actual measured sinking situation. A geometric model (GM) with a similar model shape as the PIM but with a larger boundary value was established in this paper to solve this problem. Then an improved cuckoo search algorithm (ICSA) was proposed in this paper to calculate the GM parameters. The stability and reliability of the ICSA were verified through a simulated working face. At last, the ICSA, in combination with the GM and the PIM, was used to fit 6 working faces with the geological mining condition of thick loose layers in the Huainan mining area. The results prove that GM can solve the above-mentioned PIM problem when it is used in geological mining conditions of thick loose layers. And it was obtained through comparative analysis that the GM and the PIM parameters can take the same value except for the main influence radius. [ABSTRACT FROM AUTHOR]

Backfill mining has become an important part of coal mine green mining technology. In this paper, the spatiotemporal characteristics of coupling effect between the roof and dense backfill body were analyzed by theoretical analysis and similar simulation test, and Xingtai Mine in China was taken as an engineering case for verification. The results show that the larger subsidence of the roof is, the stronger the supporting capacity of the backfill body is, and the interaction between the two is more obvious, thus showing a coupling effect. This coupling effect presents a regular variation with the increase of backfill distance and time, that is, the coupling degree of roof and backfill body is high in the middle of goaf and low in the vicinity of the coal pillar in spatial distribution, and the coupling behavior of roof and backfill body continues to occur slowly with time. Through the monitoring of stress and displacement in the engineering site and the analysis of borehole observation results, the spatiotemporal coupling effect between roof subsidence and backfill support is fully verified. The research results are of great significance to the control of surrounding rock in backfill mining, the study of the mechanical aging characteristics of backfilling materials, and the optimization of backfill body support performance. [ABSTRACT FROM AUTHOR]