Water inrush mechanism of thick alluvium aquifer with high pressure based on the "bidirectional fractures" model in Huainan and Huaibei Mining Area

The coal reserves under Quaternary thick alluvium with high pressure are huge in Huainan and Huaibei Mining Areas. In the process of increasing the upper limit mining near the alluvium, water inrush accidents often occur. However, it is difficult to reasonably explain the mechanism of such accidents by using the traditional aupper three zonesa theory. In this paper, the hydrogeological and engineering geological conditions of thick alluvium with high pressure are analyzed, and the abidirectional fracturesa model is established. Laboratory experiment, numerical simulation, theoretical analysis, and engineering application inspection are used to study the development law of downward infiltration zone and upward cracks and reveal the water inrush mechanism under thick alluvium with high pressure in Huainan and Huaibei Mining Areas. The results show that the ratio of height of water conducting fractured zone to mining height increases linearly with the water pressure of the fourth aquifer, and the height of aupward fracturea in overburden increases with the water pressure action. The calculation formula of primary fracture propagation depth in bedrock weathering zone is derived by fracture stress analysis, which shows that the splitting effect of high confined unconsolidated aquifer on weathering fracture is the main factor for the formation of adownward fracturea. The comprehensive effect of abidirectional fracturesa makes the working face more prone to water inrush accident. The research results provide scientific bases for the reasonable retention of safe coal (rock) pillars for mining near the thick alluvium with high pressure.