Height Prediction of Water Flowing Fractured Zone and Thickness Effect of Long Wall Caving in Thick Loose Seam with Weak Cementation

Based on the transfer rock beam theory and the mining overburden movement theory, the height prediction methods of collapse zone and fracture zone under different lithologic conditions are deduced according to the characteristics of rock mass dilatation and rock strata combined motion. Furthermore, the predicted height of water-conducting fracture zone of a shallow soft rock thick coal seam is 10-12.5 times of mining height. The mechanical parameters of each rock layer are obtained by field coring and laboratory mechanical tests. The mechanical properties of different rock layers are tested by configuring similar simulated materials according to different ratios. The rock mixture ratio is selected by similarity criterion, and the similarity simulation experiment is carried out. The relationship between the height of the water-conducting fissure zone and the mining thickness is obtained by simulating the development of the height of the water-conducting fissure zone with different mining thickness, and the accuracy of the predicted height is verified. In this paper, the mining thickness effect of the water-conducting fractured zone in thick coal seam mining is further analyzed, and the three stages of the collapse zone, which increase with the mining thickness, namely, the waiting stage, the increasing stage and the stable stage, are obtained under the specific geological conditions. The fracture zone shows linear growth and the collapse zone presents a step growth pattern.