1. Researcher, Research Centre for Geotechnology-Indonesia Inst. of Sciences, Jl. Sangkuriang, Bandung 40135, Indonesia.
2. Professor, Dept. of Environmental and Civil Engineering, Okayama Univ., Tsushimanaka 3-1-1, Okayama 700-0082, Japan.
3. Assistant Professor, Dept. of Environmental and Civil Engineering, Okayama Univ., Tsushimanaka 3-1-1Okayama 700-0082, Japan.