1. Research Assistant Professor, Center for Underground Construction and Tunneling, Colorado School of Mines, Golden, CO 80401; formerly, Ph.D. Candidate, Dept. of Energy and Mineral Engineering, Pennsylvania State Univ., University Park, PA 16802.
2. Assistant Professor, Dept. of Civil and Environmental Engineering, Pennsylvania State Univ., University Park, PA 16802 (corresponding author).
3. Associate Professor, Dept. of Energy and Mineral Engineering, Pennsylvania State Univ., University Park, PA 16802.