1. Associate Professor, Dept. of Geotechnical Engineering, Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education, Tongji Univ., Shanghai 200092, P. R. China.
2. Dept. of Geotechnical Engineering, Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education, Tongji Univ., Shanghai 200092, P. R. China (corresponding author).
3. Dept. of Geotechnical Engineering, Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education, Tongji Univ., Shanghai 200092, P. R. China.