Digging begins at Caldecott
Digging begins at Caldecott Aug 2010
Patrick Reynolds, Freelance Reporter
Excavation of the fourth bore for the Caldecott highway tunnel on the SR24 east of San Francisco starts in earnest next week with a heavy weight Aker Wirth roadheader set to carve through the secant pile wall and advance into the exposed face of weak sedimentary strata.
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  • The first of two heavy-duty Aker Wirth roadheaders has made a start from the east portal at Caldecott

The tunnel has a horseshoe-shaped section of 50ft wide x 32ft high (15.2m x 9.7m) and will be connected to the existing third bore by seven cross passages. A number of major and minor faults intersect the alignment and ribs, bolts and shotcrete will support the sedimentary geology of sandstone, siltstone, conglomerate, chert, shale and mudstone. The roadheaders are expected to advance at about 6ft-10ft (1.8m-3m) per day to complete excavation in about 18.5 months.
A final, concrete lining with a waterproofing membrane between it and the initial shotcrete support will finish the two-lane highway tunnel.
Pic 3

Fig 1. A fourth bore at Caldecott will ease serious bottleneck traffic at the highway tunnel facility

Excavation will be undertaken by Foxfire, a subcontractor to main contractor Tutor-Saliba. Tutor-Saliba secured the project in 2009 with a bid of US$214.8 million. The bid was less than the Engineer’s Estimate and Tutor-Saliba offered to build the tunnel in less time than predicted. Preparatory work at site has included construction of a sound barrier to shield local residents from construction noise.
California Department of Transportation (Caltrans) is developing the US$420 million scheme in partnership with the transport agencies of Alameda and Contra Costa counties. The initial twin tunnels were built in the 1930s and the third tube was added in the 1960s. Construction of the new fourth bore is to be completed by mid-2014.
The partnership authorities are being advised on the project by Parsons Transportation, Jacobs Associates and ILF.
Celebrating Caldecott groundbreaking (video report) - TunnelTalk, Jan 2010
Competition produces wide spread for Caldecott - TunnelTalk, Oct 2009

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