1. Professor, Dept. of Civil Engineering, National Taiwan Univ., Taipei 10466, Taiwan.
2. Research Assistant, National Center for Research on Earthquake Engineering, Roosevelt St., Taipei 10466, Taiwan.
3. Graduate Student, Dept. of Geotechnical Engineering, College of Civil Engineering, Hunan Univ., Changsha 40010, China.
4. Formerly, Graduate Student, Dept. of Civil Engineering, National Taiwan Univ., Taipei 10466, Taiwan.
5. Professor, Dept. of Geotechnical Engineering, College of Civil Engineering, Hunan Univ., Changsha 40010, China.
6. Professor, Dept. of Geotechnical Engineering, College of Civil Engineering, Hunan Univ., Changsha 40010, China (corresponding author).