1. School of Highway, Chang’an Univ., Xi’an 710064, China.
2. Dept. of Civil and Environmental Engineering, Univ. of Wisconsin–Madison, Madison, WI 53706.
3. Lecturer, School of Highway, Chang’an Univ., Xi’an 710064, China.
4. Professor, School of Highway, Chang’an Univ., Xi’an 710064, China.
5. Professor, School of Highway, Chang’an Univ., Xi’an 710064, China (corresponding author).