Devil's Slide Tunnel

The Tom Lantos or Devil’s Slide Tunnel is a 30 ft. diameter twin bored tunnel connecting the cities of Montara and Pacifica, CA, along US Highway 1.  The approximately 4,000 ft. long tunnels – among the longest in California – opened in 2013 as a bypass to the coastal highway.

SC Solutions performed seismic analysis of the Devil’s Slide Tunnel section to evaluate vulnerabilities of the concrete structure during the design seismic event. Additionally, excavation analysis was carried out to validate the design construction sequence process.  The technical scope of work was carried out by dynamic time history analysis that accounted for nonlinear effects including representation of the construction sequence, global geometric effects, and liner / soil interaction. The main tunnel liner, cross-passage, and the surrounding soil continuum were modeled using high-order solid elements.  Connection between the liner and the soil mass was characterized by a series of tangential and longitudinal nonlinear springs.

Seismic loading was applied as displacement time history records at the boundaries of the soil continuum model. Specifically, effects of the seismic wave passage on the structural integrity of the tunnel were thoroughly examined.

Results were computed and evaluated at each tunnel segment, as well as the tunnel to cross-passage connection.  SC Solutions worked closely with the design team to optimize and validate the final design.

Caltrans, SC Solutions, and our consultant partners were recognized with engineering excellence awards from the California Transportation Foundation (CTF) and the American Council of Engineering Companies (ACEC).