Evolution of mining-induced crack network in overburden strata of longwall face

On the basis of geological conditions of coal mining face No.1122(1) at Zhangji Coal Mine,Huainan Mining Group Corporation,a physical model was constructed.A fractal theory was introduced to characterize distribution and growth of mining-induced cracks in overburden strata.A relation between fractal dimensions of length-number of mining-induced cracks and advancing lengths of coal mining face was investigated.It is indicated that the total number of mining-induced cracks increases with the increasing of advanced lengths of mining face.Moreover,the number of mining-induced cracks increases gradually before breaking of the main key stratum.In addition,the breaking of the main key stratum results in the closing of some cracks in the center of the goaf and the generating of new cracks.