1. Lecturer in Geotechnical Engineering, School of Mechanical, Aerospace, and Civil Engineering, Univ. of Manchester, Manchester M13 9PL, U.K. (corresponding author).
2. Director, Environmental Geotechnics Ltd., Adderbury, Banbury OX17 3EN, U.K.; and Visiting Professor, Dept. of Engineering Science, Univ. of Oxford, Oxford OX1 3PJ, U.K.