1. Lect., Dept. of Civ. Engrg., Facu. of Engrg., Univ. of Tokushima, 2-1, Minami-Jyosanjima, Tokushima 770-8506, Japan. E-mail: ueno@ce.tokushima-u.ac.jp
2. Assoc. Prof., GeoMechanics Group, School of Civ. Engrg., Asian Inst. of Technol., Bangkok 10120, Thailand. E-mail: kmiura@ait.ac.th
3. Prof., Div. of Civ. Engrg., Tokyo Inst. of Technol., 2-12-1, Ookayama, Meguro-ku, Tokyo 152-8552, Japan. E-mail: kusakabe@geotech.cv.titech.ac.jp
4. Engr., Geological Engrg. Div., KAIHATSU Koei Co. Ltd., 13F, Asty 45 Build., Kita 4, Nishi 5, Kita-ku, Sapporo 060-0004, Japan. E-mail: nishimura@kai-koei.co.jp