## 2 Water Inrush Type and Mode Classification in Fengfeng Mining Area
### Division of Water Intrusion Modes  
The occurrence conditions of mine water inrush include various factors such as water inrush source, water inrush channel, mining disturbance, etc. It is a manifestation of structural damage to the rock mass of the aquifer caused by the comprehensive action of mine pressure, confined water pressure, and regional hydrogeological conditions. Based on the data of water inrush accidents in the Fengfeng Mining area from 2011 to 2023, the causes of the disaster were systematically summarized, and the manifestations of water inrush were analyzed from multiple perspectives. Four water inrush modes were summarized: composite structure water inrush mode, through-type fault water inrush mode, roof crack expansion water inrush mode, and floor vertical crack expansion water inrush mode. 1. Composite structure water inrush mode  
The composite structure water inrush mode refers to the water inrush channel composed of multiple composite structures when a mine water inrush accident occurs. The structure of the Fengfeng mining area is relatively developed, with a large number of faults and collapse columns that run through or hide beneath the coal seam. Under the combined action of strong mining disturbance conditions and high confined water, mining-induced fractures are interconnected with faults and collapse columns and jointly develop into the Ordovician limestone water inrush channel. The composite structure water inrush mode includes: through fault + collapse column water inrush mode, hidden fault + collapse column water inrush mode, through fault + hidden collapse column water inrush mode, hidden fault + through collapse column water inrush mode, primary fracture + fault (through, hidden) + collapse column (through, hidden) water inrush mode of the aquifer, and mining fracture + fault (through, hidden) + collapse column (through, hidden) water inrush mode. At 4:15 a.m. on 11 December 2011, during the process of mining 2 # coal in the 112,106 working face of the Xin'an Coal Mine, a large range of tensile cracks were generated in the floor waterproof layer under the combined action of concentrated stress and high pressure water, and expanded along the original joints and cracks. Under the combined effect of mining disturbance and high water pressure in the Ordovician limestone aquifer, the water resistance of the complete rock layer zone of the coal seam floor was reduced, the degree of internal cementation in the collapse column was weakened, and the external water conductivity was improved. The existence of hidden faults has raised the water pressure of the high Ordovician limestone by 68 m, and the remaining 60 m of floor water barrier layer is difficult to block the high water pressure of the Ordovician limestone. Under the combined action of mining pressure and high water pressure wedge splitting, softening, and scouring, the cracks at the top of the collapse column connect with the failure zone of the working face floor to form a concentrated water inrush channel, which leads to delayed water inrush from the goat floor, as shown in Figure 4. The water inrush channel is a typical representative of composite structural water inrush patterns, consisting of hidden collapse columns, hidden faults, and mining-induced fractures. 2. Through-type fault water inrush mode  
The through-type fault water intrusion mode refers to the water inrush channel being a fault that runs through the coal seam. In deep coal mining, the fault fracture zone is connected with the goat, and mining disturbance causes rock mass destruction near the fault zone, releasing local crustal stress, and inducing the floor-confined water to break through the key water barrier layer, causing water inrush in the mine. During the excavation process of the 112,124 working face of the Xin'an Mine, the F\({}_{55\text{-}1}\) fault with a drop of 120 m was subjected to periodic pressure from the roof at 4:42 am on 19 November 2010.