1. Associate Professor, Engineering Faculty, China Univ. of Geosciences (Wuhan), 388 Lu-mo Rd., Hongshan District, Wuhan City, Hubei Province 430074, P.R. China (corresponding author).
2. Researcher Laboratory for Rock Mechanics (LMR), School of Architecture, Civil and Environmental Engineering (ENAC), École Polytechnique Fédérale de Lausanne (EPFL), Station 18, CH-1015 Lausanne, Switzerland.