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Abstract Aiming at the reasonable width of the narrow coal pillar of a fully mechanized caving face and the safety support of roadway, taking the coal pillar in the section between 110503 and 110505 face of the Yushuling Coal mine as the research background, a model of the hard basic roof fracture structure of fully mechanized caving face is established through theoretical analysis, and the roadway with narrow coal pillar is analyzed mechanically. Combined with the geological conditions of the working face, it is concluded that the low‐stress area is less than 3.29 m. When the internal stress field of the low‐stress environment is considered in the roadway layout, the influence of mining and the essential roof hardness should be considered. The reasonable size of the narrow coal pillar is 3 ~ 6 m, thinking that the load borne by the coal pillar is less than the ultimate strength of the coal pillar. The limit equilibrium theory calculates that the reasonable width of a coal pillar is at least 4 m. The stress and displacement of coal pillars with different widths of 3, 4, 5 and 6 m are analyzed by numerical simulation, and the 4 m narrow coal pillars are simulated and verified. Field industrial tests show that coal pillar and roadway surrounding rock deformation are small under asymmetric surrounding rock control. The research results have been successfully applied to engineering practice and can provide a reference for the research method of narrow coal pillar width under a hard basic roof.

Gob-side entry driving near an advancing working face can improve the recovery rate of coal resources and keep the balance between mining and development. However, the large displacement of the gob-side entry caused by the mining dynamics of abutment pressure challenges the safety and processes of coal mining. This article takes the 15102 tailentry of Xizhang Coal Mine in Changzhi City, Shanxi Province, as an example to study the stability of the coal pillar and the failure characteristics of the surrounding rock and proposes cooperative control strategies of surrounding rock stability. Field tests indicated that when the coal pillar width was 15 m, the displacements of the entry floor, roof, coal pillar side, and solid coal side were 1121 mm, 601 mm, 783 mm, and 237 mm, respectively. A meticulously validated numerical model, incorporating a double-yield model for the gob materials and calibrated parameters, was developed to investigate the stress changes and yield zone distribution across the coal pillar with different sizes. The results of the simulation indicate that the influence range of the dynamic abutment pressure caused by mining in the upper section of gob-side entry driving is 30 m ahead and 70 m behind. When the coal pillar width increases from 7 m to 20 m, the internal stress of the coal pillar increases continuously, while the internal stress of the solid coal decreases continuously. It is estimated that the reasonable coal pillar width should be 7 m, which is subjected to a lower load. The cooperative control strategies comprising a narrow coal pillar, hydraulic fracturing roof cutting for pressure relief, and entry dynamic support were proposed and applied in the 15103 tailentry. The final displacements of the floor, roof, coal pillar side, and solid coal side were 66.01%, 62.06%, 61.05%, and 63.30% lower than that of the 15102 tailentry in the same period, respectively, which effectively controlled the stability of surrounding rock. In addition, this finding for the gob-side entry driving near an advancing working face in this study can potentially be applied to other similar projects. [ABSTRACT FROM AUTHOR]

Aiming at the reasonable width of the narrow coal pillar of a fully mechanized caving face and the safety support of roadway, taking the coal pillar in the section between 110503 and 110505 face of the Yushuling Coal mine as the research background, a model of the hard basic roof fracture structure of fully mechanized caving face is established through theoretical analysis, and the roadway with narrow coal pillar is analyzed mechanically. Combined with the geological conditions of the working face, it is concluded that the low‐stress area is less than 3.29 m. When the internal stress field of the low‐stress environment is considered in the roadway layout, the influence of mining and the essential roof hardness should be considered. The reasonable size of the narrow coal pillar is 3 ~ 6 m, thinking that the load borne by the coal pillar is less than the ultimate strength of the coal pillar. The limit equilibrium theory calculates that the reasonable width of a coal pillar is at least 4 m. The stress and displacement of coal pillars with different widths of 3, 4, 5 and 6 m are analyzed by numerical simulation, and the 4 m narrow coal pillars are simulated and verified. Field industrial tests show that coal pillar and roadway surrounding rock deformation are small under asymmetric surrounding rock control. The research results have been successfully applied to engineering practice and can provide a reference for the research method of narrow coal pillar width under a hard basic roof. [ABSTRACT FROM AUTHOR]

Abstract Though the recovery rate of coal resources can be effectively improved by adopting the gob‐side entry longwall face, which is also easy to cause tension between mining and excavation. Therefore, a new type of roadway layout, narrow coal pillar entry retained (NCPER), was invented in the study. The NCPER is excavated together with the tailgate of next longwall face before the mining of prior longwall face, which is retained and reused during the mining of the next longwall face. The layout is based on the advantages and successful experience of the double roadways excavation, the gob‐side entry retained, and the roadway driven along gob‐side and heading for adjacent advancing coal face; moreover, the NCPER significantly shortens the preparation time of the longwall face while improving the recovery rate. Taking the production geological conditions of Yushuling Mine as the engineering background, the influence of factors such as roof‐cutting pressure relief and coal pillar width on the stability of the narrow coal pillar from the perspective of improving the stress environment of the roadway and strengthening the weak structure support of the surrounding rock was studied, and reasonable suggestions for selecting parameters of roof cutting and coal pillar width were given. Furthermore, the bidirectional grouting cable and its joist were used to strengthen the narrow coal pillar and the roadway roof, respectively, and a good effect of roadway control has been obtained. The invention and application of NCPER provided a new approach for the longwall face roadway layout and effectively eased the strained relationship between mining and excavating, which has a strong popularization and application value.

Though the recovery rate of coal resources can be effectively improved by adopting the gob‐side entry longwall face, which is also easy to cause tension between mining and excavation. Therefore, a new type of roadway layout, narrow coal pillar entry retained (NCPER), was invented in the study. The NCPER is excavated together with the tailgate of next longwall face before the mining of prior longwall face, which is retained and reused during the mining of the next longwall face. The layout is based on the advantages and successful experience of the double roadways excavation, the gob‐side entry retained, and the roadway driven along gob‐side and heading for adjacent advancing coal face; moreover, the NCPER significantly shortens the preparation time of the longwall face while improving the recovery rate. Taking the production geological conditions of Yushuling Mine as the engineering background, the influence of factors such as roof‐cutting pressure relief and coal pillar width on the stability of the narrow coal pillar from the perspective of improving the stress environment of the roadway and strengthening the weak structure support of the surrounding rock was studied, and reasonable suggestions for selecting parameters of roof cutting and coal pillar width were given. Furthermore, the bidirectional grouting cable and its joist were used to strengthen the narrow coal pillar and the roadway roof, respectively, and a good effect of roadway control has been obtained. The invention and application of NCPER provided a new approach for the longwall face roadway layout and effectively eased the strained relationship between mining and excavating, which has a strong popularization and application value. [ABSTRACT FROM AUTHOR]

Underground reservoir water storage technology has become one important way to achieve efficient coal mining and water resource protection in the western mining areas of China, and the width of coal pillar dams is an important factor affecting the safe operation of underground reservoirs. In order to study the limitations on the reasonable size of a coal pillar dam, Daliuta Mine was selected as the engineering background and a theoretical formula for the reasonable width of a coal pillar dam was proposed. By combining theoretical analysis with numerical simulation analysis, the main influencing factors of the coal pillar dam were compared and analyzed. The research results indicated that changes in the mining height and coal parameters can cause a sharp change in the width of the plastic zone of the dam body. Then, mine water will have an impact on the width of the plastic zone and the width of the elastic core. Moreover, when the width of the coal pillar is smaller than the theoretically calculated width of the coal pillar dam body, the deviator stress and vertical stress inside the dam will significantly increase, and the plastic zone of the dam will significantly expand. [ABSTRACT FROM AUTHOR]

The mining disturbance between multiple working faces will induce rock burst disaster, and regional harmonic mining is one of the key means to prevent this kind of rock burst. In order to verify the rationality and effectiveness of regional harmonic mining to prevent rock burst, taking Yima Mining Area where rock burst occurs frequently as an example, based on the harmonic mining principles and parameter values obtained from simulation, the harmonic mining scheme in the area between Yuejin and Changcun coal mines is formulated, and the effect of harmonic mining is evaluated by comparing the stress transfer characteristics and rock burst characteristics in the area with different harmonic degrees. The results show that the thickness of coal seam and huge thick conglomerate of Yuejin 23092 face and Changcun 21162 face are smaller in the area between Yuejin and Changcun coal mines. The width of coal pillar between 23092-21162 and 21170-21162 working faces are larger, and the horizontal distance and vertical offset between the two faces are further, so the 23092 and 21162 working faces between the two coal mines are the optimal continuous working faces. The degree of harmonic mining in the area between Yuejin and Changcun coal mines is higher than that of Gengcun and Qianqiu coal mines. The frequency and intensity of stress transfer caused by rock burst and mining among working faces are all significantly reduced with harmonic mining, and the range of stress transfer significantly is reduced, so the effect of harmonic mining is obvious.

The water accumulation in goaf and coal rock interaction will weaken the strength of the coal pillar in the section and cause gradual destruction and failure of the coal pillar. The interaction of water and rock is the key factor that must be considered in the design of the reasonable width of the coal pillar. The uniaxial compression experiment and theoretical analysis are carried out based on the engineering background of the coal pillar design between mining area 31 and 33 of a mine in Xinjie mining area, Ordos, Inner Mongolia. The results show that water-rock interaction has a significant impact on the weakening of coal strength parameters. The width of the plastic zone at the side of the water accumulation in the section coal pillar expands with the increase of the weakening degree of the coal body strength. Based on the basic conditions for the stability of the section coal pillar, the reasonable theoretical width of the section coal pillar is 53.62 m. Using FLAC3D to simulate the process of water-rock interaction, the paper analyzes the stability characteristics of coal pillar with different widths. The results show that when the width of the coal pillar is small, the weakening effect of water accumulation in goaf has stronger destructive capability to the elastic core area with higher stress concentration. With the increase of coal pillar width, the stress concentration degree in the elastic core area decreases. The area where the vertical stress at the water accumulation side of the goaf is lower than that of the original rock increases. The stress concentration distribution on both sides of the coal pillar tends to be uniform, and the weakening effect of water accumulation in the goaf on the elastic core area is no longer significant. Based on the results of theoretical calculation and numerical simulation, the width of coal pillar is determined to be 70 m. The engineering application results show that the coal pillar with width of 70 m can effectively bear the roof pressure. The deformation of the roadway surrounding rock is small, the stress of the anchor cable is stable, and the safety production of the mine is guaranteed.

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.)

The goaf water accumulation of abandoned mine will damage the strength of boundary coal pillar, cause coal pillar failure, and pose a threat to the safety of adjacent production mine. The research on the safety limit of goaf water level after mining damage of coal pillar at mine boundary is not comprehensive. In order to solve the problem, taking East Shaft of Shuoshi Mining Industry of Huaibei Mining Group(Shuoshi East Shaft) and Huaibei Shuanglong Mining Co., Ltd.(Shuanglong Company) as the research objects, this paper analyzes the impact of goaf water in abandoned mine of Shuoshi East Shaft on Shuanglong Company, and puts forward corresponding water disaster prevention measures. The mining damage of coal pillar at mine boundary is studied by theoretical calculation and numerical simulation, and the safety limit of goaf water level is calculated according to the damage results. Based on the Bernoulli equation and the Darcy-Weisbach pipeline flow theory, the drainage capacity of the existing drainage boreholes is calculated and the safety is evaluated. The research results show that under the impact of mining, the damaged width of coal pillar at the mine boundary is about 19 m, the effective width is only 21 m, and the maximum water level difference that can be borne is 33 m. When the water level in the abandoned mine of Shuoshi East Shaft rises to −398 m, the coal pillar may be unstable. The drainage capacity of the existing drainage boreholes in the mine is about 89 m3/h, which is less than the actual abandoned mine water inflow of 160 m3/h. After reaching the limit water level, the goaf water level may continue to rise, and there is a threat of water disaster. The water disaster prevention and control measures such as enlarging the borehole diameter and adding drainage boreholes are proposed. The research results can provide reference for the water disaster prevention and control of abandoned mine under similar conditions.

Abstract When highwall mining technology is applied to recover large amounts of residual coal left under the highwall of a big open-pit mine, a reasonable coal pillar width is required to ensure the stability of the web pillars. Using numerical simulations, this paper studied the characteristics of the abutment stress distribution in the web pillars under different slope angles and mining depths, and established a relation describing the stress distribution in the web pillar. The relationship between the abutment stress and the ultimate strength of the web pillar under different pillar widths was also analyzed. In combination with the failure characteristics of the pillar yield zone, this relationship was used to explore the instability mechanism of web pillars. Finally, the optimal retaining widths of the web pillars were determined. Based on the modeling results, a mechanical bearing model of the web pillar was established and a cusp catastrophe model of pillar-overburden was constructed. Additionally, the web pillar instability criterion was derived. By analyzing the ultimate strength of the web pillars, a formula for calculating the yield zone width either side of the pillars was established. Using the instability criterion of web pillars in highwall mining, a reasonable pillar width can be deduced theoretically, providing significant guidance on the application of highwall mining technology.

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At present, the research on the coal pillar width of gob-side entry retaining focuses on the coal pillar strength, coal pillar load and coal pillar stability. There are few researches on the impact of rock heterogeneity and damage effects on the coal pillar width. Taking the gob-side entry retaining of No.12 coal in the fourth panel of Wulanmulun Coal Mine as the engineering background, the coal pillar width is studied in the context of rock heterogeneity-damage effect and the comprehensive use of theoretical analysis, numerical calculation and field measurement. The research results show that the rock heterogeneity-damage effect model can better reflect the fracture characteristics of the rock. Only a small number of particles are damaged in the elastic stage. Fractures begin to develop and penetrate in the plastic stage. Macro shear fractures along the diagonal direction are formed in the damage stage. As the coal pillar width increases, the overall deformation of the roadway first decreases and then increases. When the coal pillar width is 6 m, a sudden change occurs. The range and degree of damage around the coal pillar continue to decrease. The deformation of the roadway gang on the mining side is larger than that on the non-mining side. However, the amount of change with the coal pillar width is smaller than that of the non-mining side, and the surrounding rock damage distribution on the goaf side is larger than that of the solid coal side. According to the theoretical analysis and numerical calculation, it is proposed that the coal pillar width of gob-side entry retaining is 5 m. The result is applied to the engineering site. The overall deformation of the roadway in front of the working face is not large, and the movement and deformation of the overburden rock after 60 m behind the working face are basically stable, which verify the reasonableness of the coal pillar width of gob-side entry retaining.

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.)

At present, in most coal mines, the coal pillar width of goaf-side roadway driving is determined by the average mining thickness. However, the thickness of the same coal seam could be varied greatly by various factors during the formation process. The large variation of mining thickness in the fully mechanized working face leads to large difference of surrounding rock deformation and complex damage mechanism of the goaf-side roadway driving. In order to solve the above problems, FLAC3D software is used to establish a roadway model so as to analyze the surrounding rock deformation and damage law under the average mining thickness, and determine the reasonable coal pillar width. When the average mining thickness is 18 m, on the side of the solid coal, the peak supporting pressure in the coal is positively correlated with the coal pillar width. Moreover, when the coal pillar width is greater than 8 m, the growth rate of the supporting pressure slows down. Therefore, the reasonable coal pillar width should be 8 m. This paper studies the influence of mining thickness on the stability of the surrounding rock of goaf-side roadway driving in the context of determined coal pillar width. The results show that when the coal pillar width is 8 m, with the increase of mining thickness, the shear damage area of roof increases, and the rock deformation range and the roof subsidence increase. However, the shear damage area of two sides and the distance between the two sides decrease. When the mining thickness is less than 18 m, the peak support pressure in the coal pillar is negatively correlated with the mining thickness. When the mining thickness is greater than 18 m, the peak support pressure in the coal pillar is positively correlated with the mining thickness, but the growth is small. According to the simulation analysis results, it is concluded that the increase of mining thickness is beneficial to the control of the surrounding rock along the two sides of the goaf roadway, but not beneficial to the roof maintenance. For areas with large mining thickness, anchor rods should be added to strengthen support in time. The actual application on site verifies the reliability and validity of the research in this paper.

For fully mechanized caving face with high gas and fault occurrence, coal pillar with reasonable reserved width can not only support overlying strata pressure, but also isolate gas in goaf and reduce gas diffusion. However, there is a lack of research on distribution characteristics of surrounding rock stress under the condition of reasonable reserved width of different coal pillars at present, and it is difficult to accurately determine the basis for calculating reserved width of coal pillars because factors affecting coal pillar width in different mines are different. For the above problems, taking M9 -10 coal seam on fully mechanized caving face of Tunbao Coal Mine as engineering background, the minimum width of coal pillar is obtained by theoretical calculation, and stress distribution characteristics around coal pillars with different width are studied by numerical simulation. The results show that: reasonable coal pillar width is 30 -40 m; horizontal stress in coal pillar tends to goaf side with the increase of coal pillar width, which verifies that the increase of coal pillar width can transfer influence of horizontal stress on roadway, so as to improve roadway stability; vertical stress of coal pillar has characteristics of double wave peaks,and the vertical stress peak and stress concentration coefficient at roadway side and goaf side decrease with the increase of coal pillar width; location of stress peak at roadway side is 2.5 m away from the roadway, then as the distance from the roadway increases, the vertical stress first decreases rapidly and then increases slowly, and then slowly decreases after the stress peak appears on the goaf side. In order to verify rationality of 40 m coal pillar width, field monitoring of drilling stress and gas concentration is carried out on the fully mechanized caving face. The result shows that the coal pillar width of 40 m can meet actual requirements of roadway support strength and gas diffusion.

Abstract The principles of mining pressure in extra‐thick coal seams are different from those of medium‐thick and thick coal seams. Field investigation, laboratory test, and simulation analysis methods were used to study the correlation between the gob‐side entry (GSE) stability and coal pillar width during longwall top coal caving mining in extra‐thick coal seams. The test site is in Datong City, Shanxi Province, China. The mining pressure in N5209 tailgate with coal pillar of 30 m is severe based on the field investigations during the N5209 panel retreat. Global constitutive double‐yield and strain‐softening models were built to study the abutment pressures and plastic failure ranges of coal seams with different thicknesses and coal pillar widths. The simulation results show that the GSE with an 8‐m coal pillar is destressed and minimal GSE deformation occurs. In addition, the abutment stress in the coal pillar decreases with increasing coal seam thickness. The field tests indicate that the GSE with an 8‐m‐wide coal pillar is stable in extra‐thick coal seams. This study provides a reference for the coal pillar design in coal mines with similar geological and mining conditions.

Selecting reasonable coal pillar size is the premise of success and safety of gob side entry driving. Taking 30503 working face of a coal mine as the background, the reasonable size of narrow coal pillar in gob driving roadway under the condition of overlying residual coal pillar and adjacent goaf of the coal seam is studied by using the methods of theoretical analysis, numerical simulation and field practice. Results have shown that: through theoretical analysis of the stress change law of the remaining coal pillars along the floor, it is determined that the size range of the narrow coal pillars should be between 7 m and 10 m; numerical simulation is used to analyze the stress, deformation and failure law of coal pillar under different widths of coal pillar. Comprehensive theoretical analysis and numerical simulation show that 8 m coal pillar is suitable. Field monitoring results show that when 8 m coal pillars are left, the maximum deformation of the roof of the goaf roadway is 359 mm, the deformation of the two sides is 66 mm, and the surrounding rock deformation of the roadway is stable, which can meet the actual production requirements on site.

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The optimum design of deep-coal pillar width at the gob-side entry is the key to control surrounding rocks. Existing studies on this issue are based on the distribution law of mining abutment pressure without considering the principal stress difference distribution, which is related to the shear failure of surrounding rock. This study aimed to optimize the design of deep-coal pillar width at gob-side entry based on the distribution law of the principal stress difference. With FLAC 3D numerical simulation, the distribution characteristics of principal stress difference in the side mining stress field of the deep mining face and the distribution laws of the principal stress difference of the surrounding rock at the gob-side entry under different coal pillar width were explored. According to the distribution characteristics of the principal stress difference, the coal and rock mass on the goaf side in the deep mining face could be divided into three zones, i.e., decreasing, increasing and stable zones. Results show that the principal stress differences of the deep surrounding rock on the roof, floor, and coal wall rib at the gob-side entry present a single-peak curve distribution under different coal pillar width. However, the principal stress difference of the surrounding rock on the coal pillar rib displays a single-peak curve when the coal pillar width is less than or equal to 8 m, but a double-peak curve appears when the coal pillar width is greater than 8 m. The peak value of the shallow surrounding rock is obviously smaller than that of the deep surrounding rock. The width of the coal pillar of the gob-side entry in 11030-tunnel was optimized according to the theoretical calculation. This work provides a novel idea and method for the arrangement of deep coal pillars of gob-side entry.

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To study the problem of leaving a narrow coal pillar under the conditions of high soft rock, the mining of 2# coal seam in Shuguang Mine is taken as the engineering background. Using the methods of theoretical analysis, numerical calculation, we obtained a certain method of reasonable width of narrow coal pillars along an empty roadway with external-misaligned stagger arrangement, which considers four aspects for the pillar width from distribution laws of lateral support stress in upper goaf, the theoretical calculation of coal pillar width in retaining roadway, vertical stress and plastic zone distribution of coal pillar. Theoretical calculations show that the fracture zone is 3.35 m and the plastic zone is 5.76 m and the numerical simulation shows that the reasonable retention width of the coal pillar is 3.37 to 5.13 m. The numerical analysis of the surrounding rock stress distribution of the roadway under different coal pillar widths shows that when the coal pillar width is 4 m, the surrounding rock deformation of the roadway is small.

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.)

The principles of mining pressure in extra‐thick coal seams are different from those of medium‐thick and thick coal seams. Field investigation, laboratory test, and simulation analysis methods were used to study the correlation between the gob‐side entry (GSE) stability and coal pillar width during longwall top coal caving mining in extra‐thick coal seams. The test site is in Datong City, Shanxi Province, China. The mining pressure in N5209 tailgate with coal pillar of 30 m is severe based on the field investigations during the N5209 panel retreat. Global constitutive double‐yield and strain‐softening models were built to study the abutment pressures and plastic failure ranges of coal seams with different thicknesses and coal pillar widths. The simulation results show that the GSE with an 8‐m coal pillar is destressed and minimal GSE deformation occurs. In addition, the abutment stress in the coal pillar decreases with increasing coal seam thickness. The field tests indicate that the GSE with an 8‐m‐wide coal pillar is stable in extra‐thick coal seams. This study provides a reference for the coal pillar design in coal mines with similar geological and mining conditions. [ABSTRACT FROM AUTHOR]

The key to the selection of coal pillar width lies in the stability of the roadway space and the stability of the coal pillar itself. Based on the theory of coal pillar stress distribution, the reasonable retention width of the coal pillar in the deep buried thick coal seam is discussed. Reasonable coal pillar width and scientific roadway support parameters can maximize the bearing capacity of the surrounding rock, improve the stability of the roadway and reduce the coal mining loss. Reducing the size of existing large coal pillars in a stable stress interval is of great significance for coal mines to increase production and green mining. Through theoretical analysis, numerical simulation and on-site measurement, the stress, strain and displacement of the coal pillar are analyzed, and the width of the section coal pillar is reduced to a safe and scientific scope, supplemented by engineering verification. Therefore, it provides a reference for the narrow coal pillar mining in thick coal seam; learn from the meaning. [ABSTRACT FROM AUTHOR]

Extraction of a 10-m-thick coal seam in one single lift using the longwall top coal caving method caused severe deformations in underground roadways in Majialiang coal mine in Shanxi Province, China. Field monitoring of stress changes in the roof and in the coal pillar, and deformation of the 14202 tailgate, were carried out. The deformation monitoring found that the maximum floor heave of the 14202 tailgate was 1.85 m when the monitoring point was 250 m behind the longwall working face, while the maximum roof subsidence and the maximum rib-rib convergence was 0.93 and 1.14 m, respectively. The deformation rate of the 14202 tailgate increased dramatically when the monitoring point was at distances of 100-150 m behind the longwall working face, which reflected the fact that the tailgate underwent sharply increased loads within this range. Field monitoring of stress changes and the displacement of the 14202 tailgate revealed that the impact range of the mining-induced stresses in longitudinal direction (the same as the mining direction) was from 60 m ahead of the longwall face to 250 m behind the longwall face. Additionally, the mining impact range in transverse direction was more than 45 m, indicating that the coal pillar width should be larger than 45 m to avoid significant influences of mining-induced stresses. This finding was applied to the 14103 tailgate, which was subjected to similar mining and geological conditions as the 14202 tailgate. A coal pillar with width of 56 m was adopted in the 14103 tailgate, and displacement monitoring showed that large deformation was successfully controlled. The field investigations in this study provide a basis for design of a proper coal pillar width of underground roadways when subjected to large stresses induced by mining of thick coal seams in a single lift. [ABSTRACT FROM AUTHOR]

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Different from the traditional goaf-side entry in the mining face, a goaf-side entry driving heading mining face can greatly alleviate the problem of mining and excavation replacement tension under the high-intensity mining condition of a single-wing mine, withstanding the whole process of the fracture, rotation, and sinking of key blocks in the overlying rock layer, which is extremely difficult to maintain. Taking the roadway layout in a single-wing mining face of a coal mine in Neimenggu, China as the research background, first, the stress environment and structural stability characteristics of a goaf-side entry driving heading mining face is qualitatively analyzed with the theoretical analysis method according to five different stages. Secondly, the distribution and evolution law of stress and displacement with a goaf-side entry driving heading mining face are systematically studied during the whole process of advanced mining, excavation, and mining with the numerical simulation method, and the reasonable width of the section of the coal pillar is determined to be 6.0 m. Finally, the deformation laws of a goaf-side entry driving heading mining face are revealed with the field survey method: (1) the stage of advanced mining—the function relation between the distance of the excavation and mining face and roadway displacement is approximately the logistic function; (2) the stage of goaf-side entry driving—the function relation between roadway displacement and the driving distance basically forms the exponential function. Based on the above research, the dynamic segmentation control principle of "high-resistance support, dynamic monitoring, sectional control, consolidation coal sides, and stable roof control" and the dynamic segmentation control technology of "section combined strong support of anchor, net, cable, and beam, narrow coal pillar grouting and reinforcement in key periods, strengthening support of the roof with a single pillar π steel beam", and industrial tests are carried out on site. The monitoring results of the underground pressure show that the deformation failure of the goaf-side entry driving heading mining face is effectively controlled with the control principle and technology, the difficult problem of mining and excavation replacement tension is alleviated with the single-wing mine, and the useful reference and reference for the engineering practice under similar conditions are provided. [ABSTRACT FROM AUTHOR]