ORINDA -- The big dig is nearly at an end. Crews building the Caldecott Tunnel's fourth bore will soon scoop out the last of the dirt to complete the outline of the giant passageway between Orinda and Oakland.
Nearly two years after starting to claw into the East Bay hills, Caltrans predicts the crew next week will finish excavating the hole to form the 3,389-foot tunnel.
The dirt may soon be gone, but the project adding two lanes to the six-lane Highway 24 tunnel is far from done. Still remaining is more than a year of concrete laying and other finishing work. The fourth bore is expected to open in late 2013 to relieve gridlock in one of the region's most infamous bottlenecks.
"We have all but finished
He added, "You never know for sure what you will find when you dig into the earth."
The project remains on schedule and within its $420 million budget, said Caltrans spokeswoman Ivy Morrison.
The latest cost estimate has risen from $391 million to $402 million because of changes needed to deal with unexpected rock and earth formations during excavation, Morrison said.
Caltrans and its project partner, the Contra Costa Transportation Authority, are pleased with the progress, she said.
The upper part of the tunnel is
Just a little more work remains to finish excavating the lower tunnel portion, called the bench, Ramirez said.
During a site visit Thursday, a bulldozer churned up earth as it came within a few hundred feet of finishing the lower tunnel section near the Orinda opening.
At the Oakland end of the new tunnel, crews have pumped into place a concrete tunnel lining that is smooth and bright.
"You're beginning to see what the tunnel will look like when it's open to traffic," said Randy Iwasaki, executive director of the Contra Costa Transportation Authority.
Contractors build the lining in 50-foot segments.
A giant hose sprays concrete into huge forms that follow the contours of the circular tunnel -- a shape that makes it stronger.
When the concrete dries over 24 hours, heavy equipment pushes the giant forms on a track 50 feet farther inside the tunnel. Then crews prepare to pump concrete into the next 50-foot segment.
On Thursday, in preparation for more concrete pumping, a worker with giant pliers snipped off wire strands and used them to tie together large metal rods that will reinforce the wall lining. The worker deftly snipped and tied the wire to the rods in a manual operation that workers will repeat hundreds of thousands of times before the project is done.
"Look how fast he is," Iwasaki said. "That is American labor using American-made steel."
Before the concrete is pumped into place, crews install a hard plastic liner that will intercept and channel groundwater away from the tunnel to protect its structural integrity.
When done, there will a 2-foot-thick layer of plastic and concrete to form the tunnel lining.
"This lining gives the tunnel more strength to withstand earthquakes," Morrison said. The tunnel is three quarters of a mile from the Hayward Fault.
Because of its strength, the Caldecott Tunnel fourth bore will be designated a "lifeline" roadway that can be counted on to transport emergency crews within 72 hours of a major earthquake, Morrison said.
She added, "The Caldecott Tunnel is a very safe place to be in a major earthquake."
Contact Denis Cuff at 925-943-8267. Follow him at Twitter.com/deniscuff.