Lessons Learned from the First NATM Tunnel in California, Devil’s Slide Tunnel
The Devil’s Slide tunnel is located along the California coast between Pacifica and Montara, west of the San Francisco Bay in the USA in a region with steep and unstable geological formation. The twin tubes were constructed beneath San Pedro Mountain using the New Austrian Tunneling Method (NATM). Each tube is 9m wide x 6.8m high and 1300m long making it the longest highway tunnel in California. The tunnel is constructed in one of the most complex geological setting consisting of variable rock formations, mixed ground conditions, and significant groundwater in a high seismic zone and in very sensitive environmental conditions. The paper discusses the project design and construction challenges and provides lessons learned for application of future NATM tunnel projects in the United States.