NATM was developed in Austria between 1957-1965 by Rabcewicz, Müller, and Pacher. Method gained attention in 1960s as a cost-effective alternative to traditional tunneling. Originally designed for deep Alps tunnels with high in situ stress
Shotcrete was invented by Carl Akeley in 1907 for repairing Field Columbian Museum. Initially called gunite, it was trademarked in 1909. Dry-mix process was used until wet-mix was developed in 1950s
Phase 1 connects San Francisco to Los Angeles via Central Valley, totaling 494 miles. Phase 2 planned to extend to Sacramento and San Diego, totaling 776 miles. Initial Operating Segment (IOS) spans 171 miles from Merced to Bakersfield
Tunnel is an underground or undersea passageway with common portals at ends. Used for road, rail, water, utility, and military purposes. Length often exceeds twice diameter, with various construction methods
Tunnels are categorized based on ground conditions: soft ground, hard rock, soft rock, and subaqueous. All tunneling operations involve investigation, excavation, support, and environmental control. Geologic conditions significantly influence tunnel design and construction methods
TBMs are advanced equipment for tunneling through rock and soft ground. TBMs reduce disturbance and produce smooth tunnel walls. Various TBM types include Slurry, EPB, Grippers and Single Shield. Microtunnel TBMs allow fast excavation without surface disturbance