1. Associate Professor, Dept. of Road Engineering, School of Civil Engineering, Central South Univ., Changsha 410075, P.R. China.
2. Professor, Dept. of Civil and Environmental Engineering, Univ. of Tennessee, Knoxville, TN 37996 (corresponding author).
3. Research Assistant Professor, Dept. of Civil and Environmental Engineering, Univ. of Tennessee, Knoxville, TN 37996.