1. Research Fellow, Center for Geomechanics and Railway Engineering, Univ. of Wollongong, Wollongong, NSW 2522, Australia.
2. Professor of Civil Engineering and Research Director, Center for Geomechanics and Railway Engineering, Univ. of Wollongong, Wollongong, NSW 2522, Australia (corresponding author).
3. Senior Lecturer, Center for Geomechanics and Railway Engineering, Univ. of Wollongong, Wollongong, NSW 2522, Australia.