The Formation of The "Upper Three Belts" in The Collapse of Rock Formations and Water Inrush Studies

In order to study the formation of the "upper three belts" by the collapse of the overlying rock layer in coal mining and communicate the influence of the overlying aquifer on the water inrush of the working face, the process of the overlying rock layer crossing to form a complete "upper three belts" and the occurrence of roof water inrush occurred was simulated based on FLAC3D software. The development law of water conduction fracture channel and the change law of permeability coefficient of roof rock mass and the water inflow of roof rock mass were studied by numerical simulation method. The results show that: (1) The disturbance of coal seam mining activities leads to the collapse of the overlying rock layer, which makes the overlying rock layer form the distribution characteristics of "upper three belts"; (2) The development form of the water conduction fracture zone after the working face is advanced by 140m is "saddle-shaped". Four dominant water fracture zones from left to right are formed in the "curved zone", which are located at 15m, 70m, 100m and 150m respectively in the model. The "fracture zone" and "falling zone" formed four dominant water fracture zones at 20m, 80m, 140m and 158m of the working face. A separation zone is formed between the "bending zone" and the "fracture zone", and the maximum development height of the separation zone is 2.3m, and the average height is 0.8m; (3) The detection points on the roof showed that the maximum water inrush was located at the monitoring points with coordinates of (78,2) to (78,8) and (80,2) to (80,8), and the maximum water inrush at the monitoring points was 1.024m3/h. After the seepage simulation started, the maximum water inrush from the roof was 54.9m3/h.