Experiment research on overburden mining-induced fracture evolution and its fractal characteristics in ascending mining

The simulated material model was used to simulate the formation and distribution of overburden fractures induced by ascending mining. The fracture evolution law was revealed. The fractal geometry theory and MATLAB software were applied to analyze fractal characteristics of fracture network of overburden stratum. The results showed that the overburden failure evolution is trapezoidal, accompanied with collapse in layer group and the developing height of fractures discontinuously jumps; as the mining width increased, the fractal dimension of fracture network showed an overall ascending trend, presenting three stages, namely, fast dimension rising stage, slow dimension rising stage, and stable stage. In the caving zone, fracture zone, and bending zone, the development, propagation, and closure of fractures were asynchronous and inner similar. These achievements are important to roof roadway stability control and layout of gas drainage system and contribute to the simultaneous extraction theory of coal and gas by pressure relief.