1. Railway and Geotechnical Engineer, Scott Wilson Pavement Engineering, Nottingham, U.K.; formerly, Research Student, Dept. of Civil Engineering, School of Engineering, Univ. of Birmingham, Edgbaston, Birmingham B15 2TT, U.K.
2. Professor of Geotechnical Engineering and Head of the Infrastructure Engineering and Management Research Centre, Dept. of Civil Engineering, School of Engineering, Univ. of Birmingham, Edgbaston, Birmingham, B15 2TT, U.K. (corresponding author).
3. Research Fellow, Dept. of Civil Engineering, School of Engineering, Univ. of Birmingham, Edgbaston, Birmingham B15 2TT, U.K.