Investigation of overburden failure characteristics due to combined mining: case study, Henan Province, China

The evolution of fractures in overburden is quantitatively investigated to characterize the effect of mining activity. Scale model testing and numerical modeling were used based on the engineering geological and mining environments of Panel 11050 in the Quandian Coalmine in Henan Province, China. The maximum vertical displacement is 62.76 m, which is 140 m from the initial mining in the scale model test. Based on the fractal geometric theory, the fractal dimensions of the fractures in the overburden are calculated and visualized. The results reveal that if two coal seams are mined at the same time, the fractal dimension of the fracture network in the overburden increase with the progression of mining, but the rate of increase gradually slows. The relationships between the fractal dimension and the maximum height of the overburden failure and maximum overburden subsidence are nonlinear. The structural characteristics of the overburden are represented by the network of fractures. With increasing distance from the coal seam roof, the mining stress is gradually transferred upward to the overlying strata, and the scale of this stress transfer gradually reduces. The variation in the vertical stress gradually weakens and shows a delayed change with the mining process. The maximum principal stress is compressive stress and is distributed in an "arch" shape. The stress on both sides of the "arch" is high, and the intermediate stress is low. The stress within the "arch" shows an opposite trend.