1. Dr. Eng., Professor, Graduate School of Engineering, Muroran Institute of Technology, 27-1 Mizumoto-cho, Muroran 050-8585, Japan (corresponding author).
2. Dr. Eng., Emeritus Professor, Hokkaido Univ., Kita 13 Nishi 8, Kita-ku, Sapporo 060-8264, Japan.
3. Dr. Eng., Senior Researcher, Dept. of Geotechnical Engineering, Port and Airport Research Institute, 3-1-1 Nagase, Yokosuka 239-0826, Japan.