(1. Geoteehnical and Structural Engineering Research Institute, Shandong University, Jinan 250061;
2. Research Institute of Highway, Ministry of Transport, Beijing 100088;
3. Department of Electricity Generating & New Energy Resources, State Grid Technology College, Jinan 250061;
4. Shandong University of Science and Technology, Qingdao Shandong 266510, China)