Abstract
In Northwest China, rainfall is low, water resources are scarce, and the ecological environment is fragile. For shallow‐buried and close‐spaced coal seams with a thickness of upper coal bed >60∼70 m, the water‐conducting fissures of the overlying rock will not penetrate the water‐isolating layer after the upper coal seam is mined; the internal and external gap angles of the water‐conducting fissures are not generated from the water‐isolating layer. We set out to explore the critical internal and external dislocations for the second significant development of water‐conducting fissures in the overlying rock after coal mining under control. A calculation model for the critical internal and external staggered distances of coal mining face in shallow‐buried and close‐spaced coal seams is established, the calculation formula is given, and the calculation formula for the critical seam mining ratio under the condition of internal staggered mining mode is given. Numerical simulation performed by UDEC methods: taking the overburden strata in the shallow‐buried and close‐spaced coal seam mining area of Shigetai Coal Mine as a prototype, it was verified that the critical internal and external offsets of the coal mining face in shallow‐buried and close‐spaced coal seams have a significant effect on the overlying water flow cracks in the mining of the lower coal seam. For the feasibility of developmental control, according to the engineering geological conditions of Shigetai, through the calculation method of external staggered distance, it is concluded that the distance of the open cut of the lower coal face and the upper coal face is only 21∼27 m, which is much smaller than the water barrier. It does not produce the critical distance of the water‐conducting cracks. Therefore, in the process of mining the lower coal seam, the water‐proof layer will produce water‐conducting cracks, lose its water‐proof performance, and cause water loss. This is also the cause of the water inrush accident in Shigetai Coal Mine.
Highlights
Taking the geological parameters that affect the development of water-conducting fissures in the overlying rock as the basic conditions, starting with the mining parameters, find the control methods. ere is a soft rock water barrier in the shallow-buried and close-spaced Shendong coal mining area
For the second type of shallow-buried and close-spaced coal seams, when the full-thickness long-wall mining method is adopted to mine the coal seam, after the upper coal seam is mined, due to the expansion of the water-resistant layer existence, the waterconducting cracks in the overlying rock will not penetrate the water-impermeable layer in the end
When mining the lower coal seam, whether the water-conducting cracks in the overlying rock will penetrate the water-resistant layer is mainly related to the control method adopted. erefore, exploring the control methods for the development of watertransmitting fissures in the overlying rock in shallow-buried and close-spaced coal seams will be carried out for the second type of shallow-buried and close-spaced coal seams
Summary
Taking the geological parameters that affect the development of water-conducting fissures in the overlying rock as the basic conditions, starting with the mining parameters, find the control methods. ere is a soft rock water barrier in the shallow-buried and close-spaced Shendong coal mining area. When the shallow-buried and short-distance coal seam adopts the external staggered layout, if the boundary point of the nodeformation zone of the sinking basin of the lower coal seam is located at the boundary point of the water-resisting layer movement during the mining of the upper coal seam (the boundary line of the rock layer movement and the water barrier except for the intersection point of the top surface of the seam), the mining of the lower coal seam will not cause the secondary development of water-conducting fissures in the upper coal seam on the side of the cut.
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