1. Research Fellow, Centre for Geomechanics and Railway Engineering, Faculty of Engineering and Information Sciences, Univ. of Wollongong, Wollongong City, NSW 2522, Australia.
2. Professor of Civil Engineering and Research Director, Centre for Geomechanics and Railway Engineering; Program Leader, ARC Centre of Excellence in Geotechnical Science and Engineering, Faculty of Engineering and Information Sciences, Univ. of Wollongong, Wollongong City, NSW 2522, Australia (corresponding author).