Real-time evolution and connectivity of mined crack network

Based on the field conditions of coal mining face No. 15-14120 at No. 8 Mine of Pingdingshan Coal Mining Group, the information for real-time evolution of coal-rock crack network with advancement of working face was collected by using improved intrinsically safe borehole video instrument. Fractal theory and projective arithmetic for the two-dimensional connectivity of cracked rock mass were employed to characterize the evolution of crack network and variation of connectivity caused by mining. The results show that the influenced domain of crack network ahead of the working face is 50 m approximately in the condition of coal mining face No. 15-14120 at No. 8 Mine of Pingdingshan Coal Mining Group, and the calculated fractal dimension of crack network increases as the distance between the monitoring hole and the mining face decreases, which exhibites a good agreement with the variation of pressure at overburden strata. Moreover, the calculated connectivity of mining-induced crack network increases obviously with the advancing of mining-face and the increasing process can be divided into linear phase, exponential phase and constant phase.