1. Department of Geotechnical Engineering; Tongji University; Shanghai 200092 China
2. School of Civil Engineering; Purdue University; West Lafayette IN 47907 U.S.A.
3. Department of Civil Engineering; Shanghai Jiaotong University; Shanghai 20030 China
4. Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education; Tongji University; Shanghai 200092 China