1. Distinguished Professor of Civil Engineering and Director of Centre for Geomechanics and Railway Engineering, School of Civil, Mining and Environmental Engineering, Univ. of Wollongong, Wollongong City, NSW 2522, Australia (corresponding author).
2. Research Fellow, Centre for Geomechanics and Railway Engineering, Univ. of Wollongong, Wollongong City, NSW 2522, Australia.
3. Professor, Department Head, John A. and Harriette K. Shaw Professor, Dept. of Civil and Environmental Engineering, Pennsylvania State Univ., 212 Sackett, University Park, PA 16802.
4. Associate Professor, Centre for Geomechanics and Railway Engineering, School of Civil, Mining and Environmental Engineering, Univ. of Wollongong, Wollongong City, NSW 2522, Australia.