1. Associate Professor, Dept. of Geotechnical and Geoenvironmental Engineering, School of Civil Engineering, Beijing Jiaotong Univ., Beijing 100044, China (corresponding author).
2. Ph.D. Student, State Key Laboratory of Hydroscience and Engineering, Dept. of Hydraulic Engineering, Tsinghua Univ., Beijing 100084, China.
3. Professor, State Key Laboratory of Hydroscience and Engineering, Dept. of Hydraulic Engineering, Tsinghua Univ., Beijing 100084, China.
4. Professor, Dept. of Civil and Environmental Engineering, National University of Singapore, Singapore 117576.