Abstract
Most hilly areas are dotted with gullies, some of which contain plenty of water, especially in rainy seasons. Once surface water penetrates the underground working face, it will lead to an increased water inflow of the working face. Even worse, it may induce water and sand burst accidents. To prevent geological disasters such as water and sand burst and ensure the safe production in coal mines, it is necessary to reveal the development law of “two zones” in the overburden caused by shallow-seam fully mechanized top coal caving high-intensity mining in hilly areas with exposed bedrock and timely grasp the communication between the water-flowing fractured zone (WFFZ) and the water in surface gullies. In this study, the working face P2 of the exposed bedrock surface in the Coal Mine DN is taken as the research object. First, the characteristics of overburden movement and the law of exposed bedrock surface movement in areas with exposed bedrock were investigated through similar simulation. Meanwhile, the temporal–spatial evolution of overburden movement caused by shallow-seam fully mechanized top coal caving high-intensity mining was clarified, and the mode of overburden movement was revealed. Moreover, the reason why the water inflow of the underground working face increases suddenly was theoretically explained. The following conclusions were drawn: Under shallow-seam fully mechanized top coal caving high-intensity mining, the WFFZ of the working face P2 is directly connected to the exposed bedrock surface, and the movement of the overburden is subject to the typical “two-zone” mode. The development height of the WFFZ is greater than the value in the traditional “three-zone” mode calculated according to the empirical formulas. The ratio of the WFFZ height to the mining thickness is 43.75. Under the “two-zone” mode, a water-flowing channel exists in the overburden near the open-off cut and the stopping line. When the surface water source is in the right position, the water inflow of the underground working face will increase suddenly.
Highlights
Underground coal mining often induces large-scale damage to overburden and surface movement, further accelerating the occurrence of mine geological disasters such as water and sand burst under the condition of shallow-seam mining (Kratzsch, 1983; Gray, 1990)
High-intensity mining is characterized by shallow seam, large mining thickness, and high advancing speed
When there are water-containing gullies near Positions A and B, the water will flow into the working face, increasing its water inflow
Summary
Underground coal mining often induces large-scale damage to overburden and surface movement, further accelerating the occurrence of mine geological disasters such as water and sand burst under the condition of shallow-seam mining (Kratzsch, 1983; Gray, 1990). The key to preventing water and sand burst is to reveal the height of “two zones” (i.e., the caved zone and the fractured zone) in the overburden (Sun et al, 2011; Author Anonymous, 2014). The prediction of the height of the “two zones” in China is mainly based on the calculation formulas concluded with reference to the conventional mining and fully mechanized mining faces in the 1950s and 1990s. Relevant scholars have found the limitations of the calculation formulas for the height of “two zones” in the Code and conducted studies on the height of “two zones” under large mining height, thin bedrock, small buried depth, and fully mechanized top coal caving mining (Minggao and Xiexing, 1995; Baobin and Xiaolei, 2013; Jianjun et al, 2008; Xiaoqian and Zhenquan, 2015; Duan et al, 2011; Qingxian et al, 2013; Yiqiong, 2008), following which some conclusions have been put forward
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