1. Senior Specialist, Deltares, P.O. Box 177, NL-2600 MH Delft, Netherlands (corresponding author).
2. Professor, Head of Civil Engineering Division, Cambridge Univ., Trumpington St., Cambridge CB2 1PZ, U.K.
3. Professor of Foundation Engineering, Delft Univ. of Technology, Netherlands and Member of Scientific Board Deltares, P.O. Box 177, NL-2600 MH, Delft, Netherlands.