1. Faculty of Safety Engineering, China University of Mining & Technology, Xuzhou, Jiangsu 221116, China
2. State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, No. 1 University Road, Xuzhou, Jiangsu 221116, China
3. Yang Changwan Mine, Ningxia Coal, China Energy, Yinchuan, Ningxia 750011, China