Failure Process of Rock Strata Due to Multi-seam Coal Mining: Insights from Physical Modelling

Abstract

With an increasing number of multi-seam mining projects, the problem of strata movement caused by multi-seam mining has attracted increasing attention. Previous studies have shown that the rock failure mechanism for multi-seam mining is obviously different from single-seam mining. When a lower coal seam is being mined, two issues are apparent: the activation that the upper goaf will suffer and the difference in the break mechanism of the stratum between single-seam and multi-seam mining. The research regarding these two issues is still inadequate. In this paper, a physical model experiment was used to simulate the full longwall mining process of multiple seams. Then, the failure mechanics of the stratum and the influence of mining the lower coal seam on the activation of the upper goaf are discussed under the condition that the upper coal seam has been fully mined. The results show that a part of the fracture zone that formed by mining the upper coal seam will be converted into a caving zone when the lower coal seam is mined. In multi-seam mining, the cracks in the overlying fractured rock mass will widen and propagate upward. During the process of mining the lower coal seam, the interburden rock mass presents a typical plate bending failure, and the break location is greatly affected by the distribution of the periodic weighting in the upper coal seam mining. Multi-seam mining will cause the surface subsidence trough produced by upper coal mining to move towards the end of the mining panel. The mechanism of rock stratum movement revealed by the test has a certain practical guidance for the control of roof pressure in multi-seam mining and the subsidence of surface.