On September 17, CALTRANS and Kiewit Pacific held a "tunnel excavation celebration" to kick off the start of tunnel construction on The Devil’s Slide Tunnels project on California State Route 1 (the Pacific Coast Highway) in San Mateo County between the town of Montara to the south and the city of Pacifica to the north. The project involves the creation of a separated two-lane road, one lane in each direction. This road will pass through twin tunnels, over twin bridges and connect with an existing non-separated two-lane road at each end. The new road will be approximately 6,500 feet long, made up of the roughly 4,000-foot twin tunnels, the 1,500-foot north approach road (which includes the 1000-foot parallel bridges), and the 1,000-foot south approach road. Upon completion, the new road will bypass geologically unstable portions of existing Route 1, sections of roadway subject to lengthy closures, high maintenance costs over the years, and risk of permanent failure. Thanks Geology.com for the heads up. [Read on for more background, photos, maps, and movies!] (Images by CALTRANS)

Tunnel boring will progress from south to north using the New Austrian Tunneling Method. Both tunnels will be bored at the same time, one tunnel face approximately 60 yards ahead of the other. The work schedule is 24 hours a day, 7 days a week resulting in a 24-month timetable to break through to the north portal. Estimated cost for the tunnels is between $180 and $200 million.

The project is separated into 6 separate contracts. At the southern end, there was an 85,000 cubic yard rock cut and soil nail retaining wall. That project was completed by Gordon N. Ball in June of 2006. I couldn't find mention of the dimensions for the wall, but it did say there were 1200 soil nails, 30-ft long...thats a lot of nails! They appear to have spent a fair amount of money on architectural shotcrete as well, it looks nice.

At the northern end of the project there are twin bridges that connect the north portals of the tunnels back with the PCH. This work is currently under way by Disney Construction with an expected completion date of Summer 2008.

The tunnel contract was awarded to Kiewit Pacific. The tunnels are expected to open for traffic in the Winter of 2010 with the project being completed in summer 2011.

Project Location 

Geology and History of the Landslide

This video is from shortly after the 2006 closure of the PCH due to Rockfall when Grant Wilcox, a senior engineering geologist with Caltrans gave a presentation at a Midcoast Community Council meeting  regarding the previous failure events, especially the 1995 event. There is a short commercial for something in the first 20 seconds or so.

Links and More Reading

• CALTRANS Devil's Slide Project Page
  
• ABC 7 News Story on the "tunnel excavation celebration" (includes video)
  
• Wikipedia Entry on Devil's Slide
• History of the Devil's Slide projects and attempts to construct the bypass from all the way back in the late 70's
  

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rockman said:

You probably noticed that I was using this article as a test case for a new Google Maps component I installed on the site. Hopefully you'll start seeing more of this on future posts.

Thursday September 20, 2007 01:44PM

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