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Abstract Automatic roadway formation by roof cutting is a sustainable nonpillar mining method that has the potential to increase coal recovery, reduce roadway excavation and improve mining safety. In this method, roof cutting is the key process for stress relief, which significantly affects the stability of the formed roadway. This paper presents a directionally single cracking (DSC) technique for roof cutting with considerations of rock properties. The mechanism of the DSC technique was investigated by explicit finite element analyses. The DSC technique and roof cutting parameters were evaluated by discrete element simulation and field experiment. On this basis, the optimized DSC technique was tested in the field. The results indicate that the DSC technique could effectively control the blast-induced stress distribution and crack propagation in the roof rock, thus, achieve directionally single cracking on the roadway roof. The DSC technique for roof cutting with optimized parameters could effectively reduce the deformation and improve the stability of the formed roadway. Field engineering application verified the feasibility and effectiveness of the evaluated DSC technique for roof cutting.

Automatic roadway formation by roof cutting is a sustainable nonpillar mining method that has the potential to increase coal recovery, reduce roadway excavation and improve mining safety. In this method, roof cutting is the key process for stress relief, which significantly affects the stability of the formed roadway. This paper presents a directionally single cracking (DSC) technique for roof cutting with considerations of rock properties. The mechanism of the DSC technique was investigated by explicit finite element analyses. The DSC technique and roof cutting parameters were evaluated by discrete element simulation and field experiment. On this basis, the optimized DSC technique was tested in the field. The results indicate that the DSC technique could effectively control the blast-induced stress distribution and crack propagation in the roof rock, thus, achieve directionally single cracking on the roadway roof. The DSC technique for roof cutting with optimized parameters could effectively reduce the deformation and improve the stability of the formed roadway. Field engineering application verified the feasibility and effectiveness of the evaluated DSC technique for roof cutting. Highlights: A directionally single cracking (DSC) technique for roof cutting in automatic roadway formation of the non-pillar mining method is proposed. The mechanism of the DSC technique to achieve single cracking relies on effective control of the blast-induced stress. DEM simulation and field experiments are effective methods to evaluate the DSC and roof cutting parameters to improve the stability of the roadway surroundings. [ABSTRACT FROM AUTHOR]

Longwall mining with large cutting height serves as one of main methods for extracting thick coal seam. Face failure gradually becomes a critical phenomenon due to significant increase of the cutting height, which drastically influences the mining efficiency in such longwall faces. In order to improve surrounding rock stability and mining efficiency of such faces, the influence of support stiffness on face stability is thoroughly investigated by using theoretical analysis, laboratory testing and field measurements. The results show that three kinds of face failure patterns commonly appear in longwall face with large cutting height, including splitting pattern of hard coal seam, shearing pattern of relatively hard coal seam and plastic flow pattern in soft coal seam. A safety factor is proposed for longwall face, which is defined as the ratio of the difference between load-bearing capacity of the face and roof load applied on the face to the referred roof load. The influence of roof load on distribution of the safety factor is obtained. A model is developed for roof impact phenomenon, determination method of the load exerting on the face by roof is deduced. The relation between support stiffness and face stability coefficient is achieved. With the increase in support stiffness, the load applied on the face decreases and the face stability is strengthened. However, the sensitivity of the load and face stability to support stiffness decreases gradually. Physical modeling of the influence provided by support stiffness on face stability is carried out. With the support stiffness of 1.0, 1.5 and 2.0 MN/m, load-bearing capacity of the face increases from 17 to 19 and then to 20 kN. The largest horizontal displacement decreases from 40 to 30 and then to 25 mm. After failure, the broken areas are about 0.41, 0.32 and 0.21 m2, respectively, in the referred scenarios. At last, the face stability of 31402 longwall face in Wulanmulun coal mine is effectively improved by increasing the support stiffness.

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Taking No.12051 fully-mechanized coal face of Zhaogu No.1 Coal Mine as research object, thin bedrock deformation and strata behavior in coal seam mining under ultra-thick unconsolidated strata were studied by use of UDEC numerical simulation software. The results show that the first weighting interval and periodical weighting interval of the coal face is 55 m and 15 m respectively. Caving zone and fractured zone appear in overlying strata after mining. The height of caving zone and fractured zone is 12.4 m and 36.7 m respectively. Ratio of caving zone height to mining height is 3.54 and ratio of fractured zone height to mining height is 10.48. Affected zone range of front abutment pressure, peak of front abutment pressure and plastic zone range increase with increase of coal face advancing distance. The front abutment pressure is stable after the first weighting at basic roof, which manifests in the maximum stress concentration factor and plastic zone range basically remain unchanged. The research results can provide basis for surrounding rock stability control of fully-mechanized coal face under the similar geological condition.

On the basis of analyzing the current situation and definition of high-intensity mining in coalmine, the main technical characteristics of high-intensity mining in thick coal seam were systematically studied from the aspects of geological and mining condition, working lace size, technical equipment, advance speed,high production and efficiency, ratio of depth to thickness, overburden strata and ground surface destruction. Based on the concept of green mining,the main technical indexes and evaluation system of high-intensity mining had been established from the aspects of geological and mining technology,and mining influence and failure. Meanwhile, the analytic hierarchy process ( AHP) was used to analyze the mining influence and failure index. The results demonstrate that geological and mining technical factor and mining influence and failure factor are important parts of high-intensity mining of thick coal seam. Moreover, mining influence and failure factor is an important characteristic that cannot be ignored in high-intensity mining of thick coal seam. The research results provide a theoretical and technical basis for safe and efficient green production, mining damage and protection in coalmine. [ABSTRACT FROM AUTHOR]

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

Abstract: Caving of top coal behind the face is the key factor affecting the efficiency of production at thick coal seams. During production of top coal by caving behind the face not only is a significant amount of coal lost in the goaf but also the coal drawn by means of caving is usually diluted considerably with surrounding rock. Therefore, it is not possible to carry out an efficient production operation unless caving of top coal behind the face is optimized. In this paper, results of 3-D modelling of the top coal caving mechanism at the M3 longwall panel of Omerler Underground Mine located at Tuncbilek (Turkey) are presented by using a finite difference code called FLAC3D. According to modelling results, a 1.5–2.0-m-thick layer of coal just above the shield supports is well fractured. However, 3.0–3.5-m-thick layer of coal above the well-fractured part is either not fractured or fractured in the form of large blocks leading to obstruction of windows of shields during coal drawing. It is concluded that, in order to decrease dilution and increase extraction ratio and production efficiency, the top coal should be as uniformly fractured as much as possible. Hence, an efficient and continuous coal flowing behind the face can be maintained. A special pre-fracture blasting strategy just sufficient enough to form cracks in the top coal is suggested by means of comparing results from numerical modelling. [Copyright &y& Elsevier]