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Caldecott second heading underway Mar 2011
Paula Wallis, TunnelTalk
Excavation at Caldecott is now advancing from both portals of the fourth bore. Work started at the west portal this week with breaking in through the secant pile support wall. Top heading excavation will then continue into the mined tunnel using a CAT 330 excavator with an Alpine roadheader attachment.
Shotcrete support of the west portal break-in

Shotcrete support of the west portal break-in

The machine joins a much larger Aker Wirth T3.20 roadheader progressing from the east portal of the vital highway tunnel's additional capacity just east of Oakland in Northern California. The west portal start served as a media opportunity yesterday (17 March) to update the surrounding communities on the tunnel's progress.
NATM excavation began from the east portal in August 2010 and contractor Tutor-Saliba is currently about 353m (1,158ft) into the two-lane tunnel top heading. "About 36% of the 990m (3,248ft) long mined section of the tunnel has been advanced," said Axel Nitschke, senior NATM engineer with Gall Zeidler Consultants, part of the construction management team in joint venture with Parsons Brinkerhoff.
"Bench and cross passage excavations are also to start shortly, beginning with excavation of cross passage 7." West portal advance is being carried out by Tutor-Saiba's subcontractor, FoxFire Constructors of San Clemente, California. Foxfire will be starting in some of the most difficult ground on the project.
Excavator with jackhammer demolished the secant pile wall

Excavator with jackhammer demolished the secant pile wall

The contractor is expected to be in the Sobrante Formation for about 330m or a third of the tunnel length. FoxFire is also excavating the cross passages.
Nitschke said ground conditions from the east portal generally have been as predicted. In the first week of March, the east portal top heading excavation passed from the Orinda Formation into the Claremont Formation. The Orinda Formation required support categories of IB, IIA, and IIB, with a small section of support category IIIA. Additional support measures were installed, including spiles, face dowels, and rock dowels, to address local overbreaks at the tunnel crown as well as instabilities at the tunnel face, and partially higher convergences.
Construction is a little behind schedule, but the contractor hopes to make up the time now that excavation is progressing from both sides. The $420 million fourth bore is expected to open to traffic late 2013.
References
Caldecott progresses - TunnelTalk, Jan 2011
Caldecott groundbreaking - TunnelTalk, Jan 2010
Caldecott bid opening - TunnelTalk, Oct 2009

           

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