Inside the Caldecott Tunnel – 511 Contra Costa

Inside the Caldecott Tunnel


Most of us will only see the new Caldecott Tunnel from our car windows, but new pictures of the ongoing construction give a glimpse of the construction process now five months underway.
ABC Local News reports that miners are working around the clock to pull 1,500 tons of rock and mud out of the hills each day. Every day, the tunnel gets 10-15 feet closer to its 4,000 foot goal. After every five feet, workers reinforce the tunnel by spraying a thick coat of shotcrete onto the new walls, drilling holes for new support bolts, and layering another six inches of shotcrete.
All of this digging, spraying, and drilling pushes the tunnel deeper into the hills and into occasional pockets of poisonous and flammable methane gas. Something as innocuous as a cell phone could produce enough electrostatic spark to ignite the methane and produce a deadly fireball.
The risk of ignition is so great that workers are “brassing in and out.” The term refers to using brass tags to tell who is “in and out” of the bore. Why brass? Should something go wrong, brass will survive heat up to 1,700 degrees.
As if methane fireballs weren’t bad enough, the slick walls and layers of shotcrete post risks. Redundant safety measures generally protect workers from fluctuations in temperature and leaking mountain water, but last November, a 5’x3′ section of shotcrete broke off and injured two workers.
It’s enough to make someone appreciate the boring view from the other three tunnels.

In other news, the Caldecott Tunnel’s official website recently launched a new page to help the project’s neighbors understand what to expect in each phase of construction. The page explains each stage, as well as any noise or schedule implications.
The installation of pipe canopy is expected to wind down this month. Next, tunnel excavation will begin and continue into early 2012. Noise will be highest during the first 60 feet, but will diminish as the activity moves further into the hills. More than 50 truckloads of material will be removed form the site each week, but hauling will be restricted to 7 am to 9 pm.
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