Fracture law of different overlying strata in mining of protective seam under close distance coal seam

To study the fracture law of different overlying strata during mining lower protective seam under a close distance coal at depth 1000 m, roof bed-separation and fissure imaging monitoring were carried out in inlet roadway ahead working face JI15-31040 Pingdingshan XII mine. The results show that with being affected by mining, displacement 0–4 m was relatively large, development very significant. 4–12 small, fissures this range mostly randomly closed fissures, area stable. Bed separation occurred 12–16 bed-separating located coal–rock junction. During process, fractal dimension gradually increased, network developed continuously. changing process can be roughly divided into three typical change areas: less influence (distance from > 70 m), rapid increase (15 < stable 15 within front key supporting area. Under showed an overall trend “from zero to some, short long, small narrow wide.” This provide reference for deep seams.