Devils Slide bridge showing progress

February 19, 2008 8:23:20 PM PST
On the San Mateo County coast, the new Devil's Slide tunnel has a second part that's received less attention but is no less important.

However, a new bridge is going up in Pacifica that will link Highway 1 and the tunnel. That bridge is well on its way to being finished. It soars across the valley at Pacifica's Shamrock Ranch and it's really two bridges -- north and southbound.

The bridges are being built one 16-foot-segment at a time. The individual segments can be made out by faint horizontal lines dividing different colored concrete.

Workers and machinery were not allowed to touch the valley floor to protect an endangered frog, so the segments were added-on one at a time, from opposite sides, to meet at the middle. The last segment of the southbound deck was poured two weeks ago.

"Everything lined up perfectly in the end. We were within about 5 -10 millimeters in elevation and horizontal, when the two ends came together," says Rick Disney, contractor.

Each of the segments is slightly different from the other. The bridge curves and slopes and Disney says the biggest challenge is what he calls "geometry control."

"The depth changes, and also it's on a curve so there's super-elevation. It starts on a 2 percent slope and ends on a 10 percent slope, so there's elevation differences, horizontal differences and curving on a tight radius," says Disney.

This blue structure is holding the mold for the last segment and will take workers weeks to remove it. The northbound side is scheduled to be completed in the summer and the finished bridge should appear to float over the valley.

"I think Caltrans did a nice job on the design. It's architecturally satisfying to the eye. Could have been easier to build, but we knew what we were getting in to when we came out here," says Disney.

The bridge and tunnel projects have been on time and on budget, despite weather delays like the last big storm in January that closed Highway 1 at Montara. Slides like during that storm are a constant reminder of the need for a bridge and tunnel to bypass the treacherous and unstable Devil's Slide section of the highway.

At the southern entrance to the tunnel, Caltrans took us as close as you can get to the portals Without being a part of the work crew. Giant pipes are part of a fan system, ventilating the air inside. The bores are being dug with specialized tunneling machines or where the mountain material is harder,

"It's the contractor's choice really, which method to use depending on what's most efficient," says John Cunliffe, Caltrans.

The tunnel and bridge are scheduled to be open to traffic in late 2010.