1. School of Mechanics and Civil Engineering, State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology, Xuzhou, Jiangsu 221116, China
2. LNM, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China e-mail: ;
3. School of Sciences, China University of Mining and Technology, Xuzhou, Jiangsu 221116, China