Tunnel Excavation
Feb. 2011 to early 2012

The tunneling machinery at the West Portal will be smaller, but more versatile than at the East Portal. First, an excavator will break-up the concrete on the wall, creating an entryway for the tunnel. The steel within the concrete wall will be cut with blow torches.

After a tunnel-sized hole is made in the portal wall, the excavator, now equipped with a cutting head, will begin tunneling. The cutting head spins rapidly, gouging out chunks of dirt and rock from the face of the tunnel. Afterwards, the walls are sprayed with concrete. Steel girders are installed and sprayed with concrete. The excavator is rolled into position again and the process repeats as the work crews advance in this manner through the tunnel.

Hauling Away Tunnel Spoils

After a section is tunneled, front-end loaders will scoop the tunnel spoils and drop them into mining dump trucks. The trucks will off-load the spoils outside the tunnel portal.

All spoils will be tested for hazardous materials prior to being taken to a designated site. Loaders will fill much larger dump trucks with clean spoils that will be off-hauled to Treasure Island in San Francisco. Any spoils contaminated with naturally occuring hazardous material will be loaded into trucks and transported to an appropriate disposal site.

WHAT TO EXPECT:

Noise levels will be highest during the first 60 feet of excavation when there are no tunnel walls to baffle the noise. However, the hillside to the north of the portal and the 30-foot high temporary soundwall will block the most of the sound and noise levels are not expected to impact local residents.

More than fifty truckloads of tunnel spoils will be off-hauled from the site each week. In compliance with the legal agreement between Caltrans and the local residents, no excavated material may be removed from the tunnel between the hours of 9:00 p.m. and 7:00 a.m, except during the first 200 feet of tunneling, when the tunnel is not long enough to store the excavated material. Additionally, no tunnel spoils will be off-hauled from the project site between the hours of 9:00 p.m. – 7:00 a.m.

Extensive dust control procedures will be employed by the construction contractor. All trucks carrying tunnel spoils will be required to cover their loads. If any dust is visible on the work site, the contractor is required to take measures to mitiagate it, such as by spraying with water or by covering exposed stockpiles with plastic tarps.

Caltrans will work with the contractor to mimimize any disruptions or delays to public traffic on Caldecott Lane and other nearby roadways.

East Portal

The graphic shows mining of the topheading at the eastern and western portals of the tunnel. Tunneling on the east began in August 2010 and on the west in March 2011.