1. Assistant Professor, College of Environment and Civil Engineering, Chengdu Univ. of Technology, Chengdu 610059, P. R. China (corresponding author).
2. Professor, Key Laboratory of High-Speed Railway Engineering of Ministry of Education School of Civil Engineering, Southwest Jiaotong Univ., Chengdu 610031, P. R. China.
3. Professor, College of Environment and Civil Engineering, Chengdu Univ. of Technology, Chengdu 610059, P. R. China.