Fracture development and fractal characteristics of overburden rock under repeated mining

The purpose of this paper is to provide scientific basis for the stability evaluation overburden rock repeated mining goaf under expressway. objectives present study are reveal development fractures and identify fractal characteristics fractures. results show that (1) separation fracture vertical fissure developed in mining; (2) after lower coal seam, obviously retained general. number on both sides relatively large, while central part, it small most areas basically closed; (3) same advancing length working face dimension caving zone larger than fractured zone; (4) with increase variation trend appears from large then stable; (5) when over movement stable, ratio 1.067:1. have an important reference value ensuring safety expressways above Shanxi region similar areas.