The Rapid Excavation and Tunneling Conference (RETC) is sponsored by the Society for Mining, Metallurgy & Exploration (SME). Held every two years, RETC is the renowned international forum for the exchange and dissemination of developments and advances in underground construction. The RETC advances the engineering and scientific knowledge of rapid underground excavation and tunneling through interdisciplinary meetings, publications, technical-educational exhibitions and encouragement of research. It also provides innovative solutions to the unique engineering challenges associated with the tunneling industry.