1. Dept. of Geological Engineering, Southwest Jiaotong Univ., Chengdu 610031, China.
2. State Key Laboratory of Coastal and Offshore Engineering, Dalian Univ. of Technology, Dalian 116024, China.
3. Key Laboratory of Transportation Tunnel Engineering of Ministry of Education, Southwest Jiaotong Univ., Chengdu 610031, China (corresponding author).