1. School of Resources and Civil Engineering, Suzhou University, Suzhou 234000, P. R. China
2. Institute of Energy, Hefei Comprehensive National Science Center, Hefei 230031, P. R. China
3. National Engineering Research Center of Coal Mine Water Hazard Controlling, Anhui 234000, P. R. China
4. School of Earth and Environment, Anhui University of Science and Technology, Huainan 232001, P. R. China