For those of you who do not live on the San Mateo Coastside, you may not be tracking the $300M project that has been underway for a few years now to dig two tunnels through San Pedro Mountain between Montara and Pacifica by passing the always treacherous Devil’s Slide portion of Highway 1. This project was contemplated for decades with many options presented, finally, in 1995 the residents of San Mateo voted on Measure T giving the project a kick start. Active construction got under way in fall of 2007 and should be completed by 2011.
Thus far, two, 1,000 foot bridges and the tunnel maintenance facility have been completed and as you can see from the image above (courtesy of Caltrans) the tunneling is now at the halfway point. Rather than using one of the large tunnel boring machines, the team opted for the New Austrian tunneling method which consists of removing material (scraping, digging, and blasting as conditions dictate) and then immediately erecting a set of steel arches which are covered in concrete so that only the active digging area is the only spot unsupported at any given time.
I’ve posted some photos of the project below, enjoy!
Tunnel Entrances at the south side of San Pedro Mountain
A view of the tunnel interior
Another view of the tunnel interior
A view out of the tunnel looking south toward Montara
Array of equipment being used close to the working face
Continuous digging machine, the head breaks up the rock at the working face and arms collect the scree onto a conveyor belt which loads into a truck to send to the fill pit
Working on the arch, drainage, and concrete cover used in the New Austrian tunnel method
Digging with an excavator at the working face
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