Study on the mechanism of coal pillar breaking and fracture development under repeated mining in a close seam group

The study show the influence of coal mining on pillar under a repeated mining, in close seam group, fracture and instability process mechanism development oxidation pillars. In this paper, FLAC 3D numerical simulation software is used to simulate dynamic evolution characteristics stress, displacement upper pillar. results that 1) theoretical length along strike obtained by establishing mechanical model pillar, which consistent with results. 3) according stress divided into “step subsidence area”, “fracture compaction area” “reverse high risk area spontaneous combustion determined.