1. Key Laboratory of Transportation Tunnel Engineering, Ministry of Education, School of Civil Engineering, Southwest Jiaotong University, Chengdu 610031, China; School of Civil and Environmental Engineering, Nanyang Technological University, Singapore 639789, Singapore
2. School of Civil, Mining and Environmental Engineering, University of Wollongong, Wollongong, Australia (Corresponding author), e-mail: naj@uow.edu.au
3. School of Civil, Mining and Environmental Engineering, University of Wollongong, Australia