Abstract
Severe dynamic disturbance in extrathick coal seam mining has become one of the main factors threatening the stability of roadway surrounding rock. In this article, the #6 thick coal seam of Buliangou mine in Inner Mongolia, China, is taken as the engineering background. A mechanical model of the roadway roof structure is established to obtain an analytic formula of the key block subsidence. A three-dimensional discrete element model is established and used to verify the field measurement results. The fracture characteristics of the main roof above the F6104 transport roadway and the deformation and damage evolution law of the surrounding rock during thick coal seam mining are analyzed. The results show that because of the long-term breaking and falling of the roof rocks during extrathick coal seam mining, the F6104 transport roadway will undergo two severe mining disturbances at the locations of 10∼30 m and 50∼70 m ahead of the F6103 working face. During the two disturbance periods, the roadway roof displacement settles to 300∼350 mm and 750∼800 mm, and the deformation of the solid coal wall reaches 650∼700 mm and 1350∼1450 mm, respectively. The energy change curve of the total length of the fractured key roof is obtained, and when mining at 50 m, the basic roof is close to its tensile strength, and the strain energy can reach the peak value of 5.2 × 10 4 kJ, which easily leads to rock burst. The plastic damage zones on both sides of the roadway develop to the roof central area and eventually coalesce, and the deformation of the surrounding rock is obvious. When mining at 50∼70 m, the basic roof breaks and unloads, and elastic strain energy of 3.57 × 10 4 kJ is instantaneously released. These two dynamic disturbances are the main reasons for the instability of the roadway surrounding rock. The results clarify that the failure mechanism investigation of roadways in thick coal seam mining conditions can be effectively applied to control the stability of the roadway surrounding rock under strong mining disturbance.
Highlights
China’s energy base is gradually moving west to Inner Mongolia, Xinjiang, and other western regions of China. e coal in these areas is widely distributed in extrathick seams.e single-layer thickness can be up to 10 m or even dozens of meters, and in China, the proportion of coal produced from these extrathick coal seams is increasing yearly [1,2,3]
S2 X0 · sin θ, where is the coal seam mining height, m; T is the height below which working face should not be placed when mining, m; Km is the expansion coefficient of the coal body, taken as 1.3; η is the mining recovery rate, taken as 0.8; K1 is the failure parameter of the overlying strata in the roadway, taken as 1.2; H1 is the thickness of the basic roof, m; X0 is the distance between the top failure location and the mining side above the roadway, m; θ is the rotation angle of block B at the top of the roadway in contact with the filling material in the goaf area, θ arcsin(S1/l); l is the length of basic roof block B, m
Due to the large mined-out space produced by extrathick coal seam mining, the slope of the displacement curve abruptly increases for long-term dynamic loading action on the F6104 transport roadway and the pillar. e settlement at the surface is 650∼700 mm, and that at the side of the coal pillar reaches 1350∼1450 mm
Summary
China’s energy base is gradually moving west to Inner Mongolia, Xinjiang, and other western regions of China. e coal in these areas is widely distributed in extrathick seams. The dynamic influence of the roadway depends on the lateral stress concentration, the height of the mining coal seam, the fracture strata structure, and the properties of the rock mass [4,5,6]. In traditional mechanized top-coal caving mining, the working face lateral roof caving is rather extensive, and the caved gangue provides support for the overlying strata, which reduces the occurrences of collapse and the lateral stress in the roof strata, thereby reducing the disturbance on the surrounding rock [7]. E dynamic influence of strong mining on the roadway surrounding rock has become one of the main disasters in coal mine safety when mining is arranged in extrathick coal seams. E deformation and stress distribution characteristics of the surrounding rock are determined by the influence of mining on the coal seam and the caving conditions of the overlying strata. Coring data suggest that the basic roof conditions are better than those of other parts of the roofs and play the role of key strata. e field data show that the roadway displacement during extrathick coal seam mining is 3–5 times greater than that of roadways in solid coal
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