1. Department of Civil and Environmental Engineering, Yamaguchi University, Tokiwadai, Ube, 755-8611 Japan
2. Oyo Corporation, Miyahara-cho 1-66-2, Omiya, 330-0038 Japan
3. Department of Civil Engineering, Sojo University, Ikeda, Kumamoto, 860-0082 Japan
4. Mewbourne School of Petroleum and Geological Engineering, The University of Oklahoma, 100 East Boyd, Norman, Oklahoma, 73019-1014