In order to explore the influence of coal pillar width on the principal stress deflection and plastic zone form of surrounding rock in deep roadway excavation, taking 11030 working face transportation roadway of Zhaogu No. 2 Coal Mine as engineering background, theoretical analysis, numerical simulation, and field detection were used to study the effect of coal pillar width on principal stress deflection and plastic zone form and field detection and verification of plastic zone form of surrounding rock in 11030 transportation roadway. The results show that the maximum principal stress is deflected in the vertical direction, which in roadway surrounding rock excavation. The coal pillar width effect of principal stress deflection on both sides of roadway roof and floor and inside coal pillar are more obvious than that of middle roof and floor, coal pillar edge and coal wall position. The deflection of the principal stress affects the morphological distribution of the plastic zone of the surrounding rock, which led to the width effect of coal pillar in roof, and two sides plastic zone are more obvious than that in floor. The principal stress deflection of roadway surrounding rock is highly consistent with the maximum damage depth of plastic zone, and at the same time, the drilling peep results of surrounding rock are basically consistent with the form characteristics of plastic zone in numerical simulation. On this basis, the surrounding rock reinforcement support scheme of 11030 working face transportation roadway was proposed.
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.
In this study, the nonuniform deformation and failure of the goaf retaining roadway in an inclined coal seam due to repeated mining have been investigated by field verification, theoretical analysis and numerical simulation. As a case study, 3131 headentry of a coal mine in Sichuan province was considered. The deformation characteristics of the surrounding rock along the gob of inclined coal seam and the distribution characteristics and evolution of the plastic zone and stress field direction of gob-side entry retaining (GER) in 3131 coal faces during the service period were also studied. Based on the mechanical model of the plastic zone of surrounding rock, the stress field direction effect of nonuniform expansion of the plastic zone is explained, and the nonuniform deformation damage mechanism of the inclined coal seam along the empty tunnel is revealed. The results show that the plastic zone of the side always expands along the coal seam towards the side affected by mining during the whole service period of GER in the inclined coal seam, and the plastic zone of the roof and floor expands to the deep surrounding rock; and the expansion degree of the soft coal (rock) seam position of the roadway is the highest. At the same time, the direction of the surrounding rock stress field will be deflected during the service period of GER, and the plastic zone expands unevenly under the action of the coal seam dip angle and stress direction. The nonuniform expansion degree of the plastic zone is the largest when the angle between the maximum principal stress and the coal (rock) layer is 45° (±5°). A collaborative support method with “supporting and reducing span” as the core in GER is also proposed in this work. Field tests were also carried out. During the retaining period, the displacement of the roof and floor was reduced from 250 mm to 125 mm.
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