1. Dept. of Architecture, Geology, Environment and Constructions, Belgium Univ. of Liège, National Fund for Scientific Research, Chemin des Chevreuils, 1 Bât B 52/3, Liège 4000, Belgium (corresponding author).
2. Dept. of Civil Engineering, Univ. of Minnesota, Minneapolis, 500 Pillsbury Dr. S.E., Minneapolis, MN 55455; and Commonwealth Scientific and Industrial Research Organisation, Petroleum Resources, 26 Dick Perry Ave., Kensington, WA 6151, Australia.