1. State Key Laboratory for Geomechanics and Deep Underground Engineering, School of Mechanics and Civil Engineering, China University of Mining and Technology, Xuzhou 221116, P. R. China
2. School of Vehicle and Energy, Yanshan University, Qinhuangdao 066004, P. R. China
3. Faculty of Engineering and the Environment, University of Southampton, Southampton SO17 1BJ, U.K.
4. Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of Education, Dalian University of Technology, Dalian 116024, P. R. China