Abstract
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.
Highlights
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. e stress transfer law in the floor after mining in the upper coal seam is analyzed. e results show the overburden structure and stress field change caused by upper coal seam mining. e 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. e results of the field test verify the accuracy of theoretical analysis and similar simulation test results
Some researchers established the relationship between hydraulic support and surrounding rock, through the study of roof and interlayer rock structure in close distance coal seam, revealing the control mechanism of rock structure on stope surrounding rock [37,38,39,40]. e research results constituted a theoretical basis for the selection of hydraulic support and parameters. is paper analyzes the structural evolution characteristics of surrounding rock from the perspective of engineering geology, which can provide theoretical guidance for the treatment of roadway and surrounding rock during bifurcation coal seam mining
Summary
Xutuan Coal Mine is located in Xutuan Town, Bozhou City, Anhui Province, in China. No 7-1 (upper coal seam) and No 7-2 (lower coal seam) are the main coal seams in the mine, and the spatial form shows a bifurcation merging relationship. is paper studies 71212 and 72210 working faces in 82 mining area. 3. Theoretical Calculation of Damage Thickness of Roof and Floor Strata after No 71 Coal Seam Mining. E roof of No 7-1 coal seam in 71212 working face is medium hard rock. E Ministry of Coal Industry of China has formulated the coal pillar reservation and coal mining regulations for buildings, water bodies, railways, and main roadways (2019 Edition) and put forward the calculation formula for the height of the collapse zone and water flowing fracture zone of medium hard overburden (the average compressive strength of overburden is 20 MPa–40 MPa), as shown in formulas (1) and (2) [41]. In formula (3), r is the polar radius, θ is the polar angle, r0 is a constant, and the expression of r0 is as follows: ickness (m) Lithologic
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