1. Senior Researcher, Soil Mechanics and Geo-Environment Division, Port and Airport Research Institute, 3-1-1, Nagase, Yokosuka, Kanagawa 239-0826, Japan.
2. Head, Soil Mechanics and Geo-Environment Division, Port and Airport Research Institute, 3-1-1, Nagase, Yokosuka, Kanagawa 239-0826, Japan.
3. Professor, Dept. of Civil Engineering, Shibaura Institute of Technology, 3-9-14, Shibaura, Minato-ku, Tokyo 108-8548, Japan.