1. Key Laboratory of Road Construction Technology and Equipment of Ministry of Education, Chang′an University, Middle-Section of Nan′er Huan Road, Xi′an 710064, China
2. School of Construction Machinery, Chang′an University, Middle-Section of Nan′er Huan Road, Xi′an 710064, China
3. School of Mechanical and Precision Instrument Engineering, Xi′an University of Technology, NO.5 South Jinhua Road, Xi′an 710048, China