California Department of Transportation
I-710 North Tunnel Feasibility Study
The California Department of Transportation (Caltrans) performed a feasibility study for constructing one of the world’s largest highway tunnels in order to ease traffic congestion in Los Angeles. Depending on the final tunnel alignment selected, it is envisaged that the twin-bore tunnels could be in excess of 60 feet (18.3 m) and 4.5 to 11 miles (7.2 to 17.7 km) in length. Preliminary construction costs are estimated at over $3.5 billion. If constructed, this would be the largest bored highway tunnel (in both diameter and length) in the U.S., comparable to some of the Trans-Alps tunnels in Europe.
Jacobs Associates was part of a CH2M HILL–led team, supporting the Caltrans feasibility analysis through a series of technical studies. The initial focus of these studies was on characterization of the geotechnical conditions along several potential tunnel routes. This was achieved by a carefully planned geotechnical exploration program consisting of surface mapping, geophysical surveys, exploratory borings, and associated laboratory testing. Results were used to evaluate the feasibility of constructing tunnels in the corridors studied. We led the feasibility analysis with respect to the geotechnical conditions.
The feasibility study started in late 2008 and completed in 2010. During this time, the CH2M HILL team completed its detailed technical studies, better characterizing the physical and environmental nature of the study area. Caltrans will use this information to make informed decisions in subsequent studies for selecting potential alignment alternatives for further analysis and design.