1. College of Mining, Guizhou Univ., Guiyang 550025, China.
2. Professor, College of Mining, Guizhou Univ., Guiyang 550025, China.
3. Professor, College of Mining, Guizhou Univ., Guiyang 550025, China (corresponding author).
4. China Coal Technology and Engineering Group Shenyang Research Institute, Fushun 113122, China.