1. Senior Engineer, State Key Laboratory of Shield Machine and Boring Technology, Zhengzhou 450001, China.
2. Graduate Student, Dept. of Structural Engineering, Univ. of California at San Diego, La Jolla, CA 92093.
3. Professor, Dept. of Geotechnical Engineering, Southwest Jiaotong Univ., Chengdu 610031, China (corresponding author).
4. Professor, Dept. of Civil Engineering, Shanghai Jiaotong Univ., Shanghai 200240, China.
5. Professor, Dept. of Civil and Environmental Engineering, Hong Kong Univ. of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China.