Study on mechanism of water inrush and sand inrush in mining of coal seam with thick overlying bedrock

To reveal the formation mechanism of water inrush and sand inrush disasters from the roof when mining coal seams with thick overlying bedrock, this paper takes the intrusion accident of water and sand in Zhaojin Coal Mine as an example. Combined with the latest supplementary geological data, a comprehensive analysis was conducted on the mechanism of this disaster from many aspects such as channel, water source, source, water storage space, power source and geological structure. The results show that under the influence of mining conditions, the Luohe Formation aquifers with weak and medium water-rich may also suffer from great water accidents. The intrusion of water and sand from the roof when mining the coal seam with thick overlying bedrock is not caused by a single factor. In fact, it is caused by the interaction of multiple factors, which ultimately leads to movement and collapse of the mixed water and sand flowing. The water flowing fractured zone generated during the fully mechanized caving mining of the No.202 longwall face causes the aquifer water of Luohe Formation to enter the separated cavity between Yijun Formation and Zhiluo Formation. As the amount of accumulated water increases, the water in the separated cavity penetrates into the coal measures aquifer and the ancient riverbed phase loose body to form a mud-like fluid. The mud-like fluid instantaneously breaks into the longwall surface along the concentrated channel generated by cutting the longwall face. This leads to the invasion of water and sand in the coal seam roof with a thick bedrock.