1. Faculty of Geosciences and Environmental EngineeringSouthwest Jiaotong Univ. Chengdu 611756 China
2. Dep. of Civil and Environmental Engineering, Geological Engineering ProgramUniversity of Wisconsin–Madison Madison WI 53706 USA
3. Dep. of Civil and Environmental EngineeringUniv. of Wisconsin–Madison Madison WI 53706 USA
4. Dep. of Civil and Environmental Engineering, Geological Engineering and Environmental Chemistry and Technology ProgramsUniv. of Wisconsin–Madison Madison WI 53706 USA