| | Published September 14th, 2011
| Caldecott's 4th Bore-One Year In
| | By Andrea A. Firth |  |
| Work in progress on the east side of the Caldecott Tunnel 4th Bore Project, August, 2011. Photo Dennis Parecadan,
Caltrans Audio Visual Department |
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August 24th marked the one-year point for tunneling on the Caldecott Fourth Bore Project. Tons of dirt and rock have been excavated from both the east and west sides of the tunnel, and Caltrans expects to breakthrough-that is the two sides of the tunnel's topheading will meet-later this fall.
The topheading, the upper portion of the tunnel, will house the exhaust fans and is about 15 feet high. The lower section of the bore, known as the bench, is the section commuters will ultimately drive through.
Crews on the west side of the tunnel have begun excavating the bench, which is about 15 feet deep. Work is also underway on the seven cross-passages from the new bore to bore three, a safety feature that will allow motorists access to the adjacent tunnel if needed.
"The project is going really well. It's right on track," says Amy Worth, who in addition to her role as a member of Orinda's City Council also serves as the Vice Chair of the Metropolitan Transportation Commission. "The work is getting done efficiently and safely," she adds, noting that the Moraga Orinda Fire District has been working closely with the tunnel contractor to be sure that they are also prepared to assist if warranted.
About 2/3 of the excavation of the fourth bore has been done from the Orinda side because the rock on the east side is younger and less prone to fracture. From east to west, the fourth bore runs about 3,250 feet and spans three primary rock formations, Orinda, Claremont, and Sobrante, which date back 5 to 26 million years.
The 130-ton roadheader, which grinds through the rock face on the east side, advances about one to two meters a day, six days a week. A concrete spray is applied to the walls to provide support along the way. After breaking through on top, excavation of the bench will continue through the middle of next year. The fourth bore is expected to be open to traffic by late 2013.
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Lamorinda Weekly, Moraga CA