1. Research Associate, Dept. of Civil Engineering, Fukushima National College of Technology, Taira, Iwaki, Fukushima 970-8034, Japan.
2. Professor, Dept. of Civil and Environ. Engineering, Nagaoka Univ. of Tech., Nagaoka, Niigata 940-2188, Japan.
3. Research Fellow, Nagaoka Institute of Snow and Ice Studies, NIED, Suyoshi, Nagaoka, Niigata 940-0821, Japan.