1. Assistant Professor, Dept. of Civil Engineering, Zhejiang Univ., Hangzhou 310058, China.
2. Professor and Director, Rock Mass Modeling and Computational Rock Mechanics Laboratories, Univ. of Arizona, Tucson, AZ 85721 (corresponding author).
3. Graduate Research Assistant, Rock Mass Modeling and Computational Rock Mechanics Laboratories, Univ. of Arizona, Tucson, AZ 85721.