1. College of Mining Engineering; Taiyuan University of Technology; West Yingze St., Taiyuan Shanxi 030024 China
2. Key Laboratory of In-situ Property-improving Mining of Ministry of Education; Taiyuan University of Technology; West Yingze St., Taiyuan 030024 China
3. Key Laboratory of Coal Science and Technology of Ministry of Education and Shanxi Province; Taiyuan University of Technology; West Yingze St., Taiyuan 030024 China