1. Department of Mechanics, Northeastern University, Shenyang 110819, P. R. China
2. Key Laboratory of Ministry of Education on Safe Mining of Deep Metal Mines, Northeastern University, Shenyang 110819, P. R. China
3. Center for Rock Instability and Seismicity Research, School of Resources and Civil Engineering, Northeastern University, Shenyang 110819, P. R. China