1. Ph.D. Student, Dept. of Civil and Environmental Engineering, Univ. of California, 2217 Academic Surge, 1 Shields Ave., Davis, CA 95616.
2. Professor, Key Laboratory of Geotechnical and Underground Engineering of Minister of Education and Dept. of Geotechnical Engineering, Tongji Univ., Geotechnical Bldg., Siping Rd. 1239, Shanghai 200092, China.
3. Ph.D. Candidate, Dept. of Civil and Environmental Engineering, Univ. of California, 2221 Academic Surge, 1 Shields Ave., Davis, CA 95616.
4. Assistant Professor, Key Laboratory of Geotechnical and Underground Engineering of Minister of Education and Dept. of Geotechnical Engineering, Tongji Univ., Geotechnical Bldg., Siping Rd. 1239, Shanghai 200092, China (corresponding author).