1. Highway School of Chang'an Univ., South Erhuan Middle Section, Xi'an City, Shaanxi Province, 710064, CN, e-mail: gfychd@yahoo.com
2. Highway School of Chang'an Univ., South Erhuan Middle Section, Xi'an City, Shaanxi Province, 710064, CN, (Corresponding author), e-mail: yul@chd.edu.cn
3. Dept. of Civil & Environmental Engineering, Michigan Technological Univ., 1400 Townsend Dr., Houghton, MI, 49931, US, e-mail: zyou@mtu.edu
4. Highway School of Chang'an Univ., South Erhuan Middle Section, Xi'an City, Shaanxi Province, 710064, CN, e-mail: yaoshun.chd@foxmail.com