1. Graduate Student, State Key Laboratory of Water Resources and Hydropower Engineering Science, Key Laboratory of Rock Mechanics in Hydraulic Structural Engineering (Ministry of Education), Wuhan Univ., Wuhan 430072, P.R. China.
2. Professor, State Key Laboratory of Water Resources and Hydropower Engineering Science, Key Laboratory of Rock Mechanics in Hydraulic Structural Engineering (Ministry of Education), Wuhan Univ., Wuhan 430072, P.R. China (corresponding author).
3. Associate Professor, State Key Laboratory of Water Resources and Hydropower Engineering Science, Key Laboratory of Rock Mechanics in Hydraulic Structural Engineering (Ministry of Education), Wuhan Univ., Wuhan 430072, P.R. China.
4. Professor, State Key Laboratory of Water Resources and Hydropower Engineering Science, Key Laboratory of Rock Mechanics in Hydraulic Structural Engineering (Ministry of Education), Wuhan Univ., Wuhan 430072, P.R. China.
5. Professor, Dept. of Civil and Environmental Engineering, National Univ. of Singapore, Singapore 117576.