1. Professor, College of Civil Engineering and Architecture, Lanzhou Railway Univ., Lanzhou 730070, P. R. China; and State Key Laboratory of Frozen Soil Engineering, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, P. R. China.
2. Professor, College of Civil Engineering and Architecture, Lanzhou Railway Univ., Lanzhou 730070, P. R. China.
3. Professor, State Key Laboratory of Frozen Soil Engineering, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, P. R. China.