Yunwei Li, Tianhe Xu, Shandong University, China; Kegen Yu, China University of Mining and Technology, China; Meng Wang, Shandong Provincial Lunan Geology and Exploration Institute (Shandong Provincial Bureau of Geology and Mineral Resources No.2 Geological Brigade), China; Fengjian Liu, Dongtan Coal Mine, Yankuang Energy Group Co., Ltd., China; Chao Sun, Inner Mongolia Haosheng Coal Industry Co., Ltd., China