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Caldecott closing in on breakthrough Oct 2011
Paula Wallis, TunnelTalk
The California Department of Transportation (Caltrans) is nearing a milestone on the Caldecott Tunnel Fourth Bore Project in the hills east of Oakland, California. After 14 months of excavation, the contractor, Tutor Saliba, is nearing breakthrough of the top heading in the NATM-construction highway tunnel.
Surveyor checks alignment of top heading

Surveyor checks alignment of top heading
Photo by Caltrans

"In total almost 890m of top heading is completed with another 100m to go until we break through," said Axel Nitschke, of Gall Zeidler Consultants, which holds the construction management contract in JV with Parsons Brinckerhoff.
Tutor Saliba secured the Caltrans contract to add a fourth bore to the three existing tunnels on State Route 24, with a bid of $215 million, which was 20% below the Engineer's Estimate. The contractor is about 730m into the top heading from the East Portal, while its subcontractor, FoxFire, is about 160m in from the West Portal.
NATM excavation on the 990m long, two-lane tunnel began at the East Portal in August 2010.
Since then, Tutor Saliba has tunneled through the Orinda formation and is currently in the Claremont formation (Second Sandstone), where crews are installing support category 1A, the lightest support category on the entire project. The Orinda Formation required primarily support categories of IB, IIA. Additional support measures were installed in these areas, 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.
Excavation progress as of Oct 1, 2011

Excavation progress as of Oct 1, 2011

Foxfire started from the West Portal on the Oakland side in March 2011 - beginning in the Sobrante formation. Currently, the subcontractor is in Shaly Sandstone and installing support category IIA and IIB, with adjusted pre-support measures as needed.
"At the West Portal the contractor is alternating top heading with bench excavation, and has finished roughly 60m of bench so far," said Nitschke.
Excavation of seven cross passages between bores four and three is also under way.
Foxfire has completed boring cross passage No.7 at the eastern end of the tunnel and is currently excavating cross passage No.6.
"We have not experienced any significant technical problems and the project is on schedule and within budget," said Nitschke.
  • Tunnelers adjust the shotcrete machine

    Tunnelers adjust the shotcrete machine
    Photo by Caltrans

  • Excavation of cross passages under way

    Excavation of cross passages under way
    Photo by Caltrans

The project has received significant federal funding, as well as substantial funds through Measure J, a local half-cent sales tax measure administered by the Contra Costa Transportation Authority. The project is also receiving funding through regional bridge tolls and state funds.
The $391 million fourth bore is expected to open to traffic in late 2013.
References
Caldecott second heading underway - TunnelTalk, Mar 2011
Caldecott fourth bore progress - TunnelTalk, Jan 2011
Caldecott fourth bore groundgreaking - TunnelCast, Jan 2010

           

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