1. Associate Professor, Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education, Dept. of Geotechnical Engineering, College of Civil Engineering, Tongji Univ., 1239 Siping Rd., Shanghai 200092, P.R. China.
2. Associate Professor, Dept. of Civil Engineering, Shanghai Univ., 149 Yanchang Rd., Shanghai 200072, P.R. China (corresponding author).