1. Institute of Mining and Special Civil Engineering, Technical University of Bergakademie Freiberg, Freiberg, 09599 Dresden, Germany
2. School of Engineering, University of Warwick, Coventry CV47AL, UK
3. West Virginia University, Morgantown 26505, USA
4. College of Energy and Mining Engineering, Shandong University of Science and Technology, Huangdao District, 266590 Qingdao, China