Experimental study on overburden strata fracture evolution law in three dimensional mine-induced stress conditions

Using self-developed “ multi-field coupling coal mine dynamic disaster simulation test system”,a three-di- mensional simulation excavating experiment was conducted based on the geological data from 24080 working face in Pingdingshan Coal Mine,China. Depending on the stress monitoring,pigment tracer,photographic sketch means,the statistics of fracture morphology,number and distribution characteristics in horizontal and vertical sections were ana- lyzed,then the overburden strata fracture network model was constructed. The research results show that:under true tri- axial stress condition,the fracture network in strata above the goaf presents a “ similar-trapezoidal platform” form in space,in the lower strata,presents a rounded rectangle shape,while in higher strata it tends to an “O shape” morphol- ogy. According to the degree of difficulty of gas migration,the overburden rock fracture network can be divided into primary and secondary flow channels.