Three-dimensional physical model experiment of mining-induced deformation and failure characteristics of roof and floor in deep underground coal seams

Abstract Underground mining engineering causes complex changes in the three-dimensional stress near the working face of a mine, resulting in deformation and failure of the roof and floor rocks, as well as ground subsidence. To study the stress, deformation, and fracture field characteristics of the roof and floor strata due to mining, an indoor large-scale three-dimensional physical similarity model was developed. A novel method was used to simulate the mining process of coal seams. The results show that coal seam mining disrupted the original stress balance; consequently, a bearing pressure was generated in front of the working face, and a significant pressure relief state appeared in a particular area. The collapsed rock blocks of the overburden strata filled the goaf and played a supporting role, causing the overburden stress to increases again to a value close to the original rock stress. After complete mining, the overburden strata subsided, and the floor strata bulged. With an increasing vertical distance from the working face, the deformation of the rock formation gradually decreased. Evident fractured fields were formed in the surrounding rock of the goaf. In the horizontal section of the overburden rock layer, the cracks were distributed in a “rounded rectangular” shape. As the distance from the coal seam increased, the “rounded rectangular” boundary became smoother; the coverage area decreased; and the degree of crack opening and development in the plane decreased. The fractal dimensions of fractures with different overburden heights and different strike positions are calculated using the fractal geometry theory. We found that as the distance from the excavation face increased, the fractal dimensions of the fractures gradually became stable. In addition, numerical simulation methods were used to verify the correctness of the physical similarity model experiments. The research results can provide important references for the stability of deep underground projects such as coal mining process, tunnel excavation process, nuclear waste storage and other engineering stability.