1. Graduate Research Assistant, Dept. of Civil and Environmental Engineering, Univ. of Illinois at Urbana-Champaign, 205 North Mathews Ave., Room 2220, Urbana, IL 61801 (corresponding author).
2. Professor, Dept. of Civil and Environmental Engineering, Univ. of Illinois at Urbana-Champaign, 205 North Mathews Ave., Urbana, IL 61801.
3. Senior Geotechnical Engineer, Arup, 560 Mission St., San Francisco, CA 94105.
4. Director, Arup, 560 Mission St., San Francisco, CA 94105.
5. Adjunct Professor, Dept. of Civil and Environmental Engineering, Davis Hall, Univ. of California, Berkeley, CA 94720.