1. Lecturer, Laing O'Rourke Centre for Construction Engineering and Technology, Dept. of Engineering, Univ. of Cambridge, Trumpington St., Cambridge CB2 1PZ, GB (Corresponding author), e-mail: me254@cam.ac.uk
2. Geotechnical Engineer, Geotechnical Consulting Group LLP, 52A Cromwell Rd., London, SW7 5BE, GB, e-mail: g.choy@gcg.co.uk
3. Sir Kirby Laing Professor of Civil Engineering, Dept. of Engineering, Univ. of Cambridge, Trumpington St., Cambridge CB2 1PZ, GB, e-mail: rjm50@cam.ac.uk