1. School of Mechanics and Civil Engineering, China University of Mining and Technology, Beijing100083, P. R. China
2. School of Energy and Mining Engineering, China University of Mining and Technology, Beijing100083, P. R. China
3. State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, Beijing100083, P. R. China
4. School of Science, Guizhou University of Engineering Science, Bijie551700, Guizhou, P. R. China