ORINDA -- Crews carving out the Caldecott Tunnel's fourth bore have shifted from a big dig to fine finish work three years after breaking ground on the Highway 24 tunnel widening.

Construction began Jan. 22, 2010, and the new bore is expected to open by the end of the year.

These days, crews inside the tunnel are pouring concrete curbs to form the edge of the road, and sidewalks for stranded drivers to escape to during emergencies.

Contractors also are installing wires and conduits to power the permanent tunnel lights, fans, warning lights and air quality sensors. Carpenters are building wooden forms for pouring concrete walls for exterior portals at the Orinda and Oakland openings of the fourth bore.

Carpenter Leonardo Lucero carries lumber for forms being built near the East Portal of the Caldecott Tunnel fourth-bore project on Jan. 18, 2013, near
Carpenter Leonardo Lucero carries lumber for forms being built near the East Portal of the Caldecott Tunnel fourth-bore project on Jan. 18, 2013, near Orinda. The long-awaited project expects to open later this year. (Karl Mondon/Staff)

"You see a big transformation in the fourth bore in the last half year," said Randy Iwasaki, executive director of the Contra Costa Transportation Authority, a partner with Caltrans in the $402 million project. "You see finished tunnel lining. The cross passages (for emergency escapes) are dug."

Carpenters, ironworkers, electricians and laborers are busy inside the tunnel on precise work using metal, wires and cables.

About six months ago, giant earth-digging machines were still clawing and scraping away several truckloads of earth per day.

The digging machines are gone. Some of the miners who excavated the dirt and rock to create the new 3,389-foot-long cavity in the East Bay hills have moved on or are preparing to move on to tunnel digs elsewhere.

"When the road bed is built in spring," Iwasaki said, "you will look at it and say, 'When is this tunnel going to open'"?

But more work still will need to be done. Iwasaki and Caltrans spokeswoman Ivy Morrison said they expect the new two-lane forth bore will open in late 2013. No precise date has been scheduled, though, they added.

"There are still some challenges ahead," Iwasaki said, "but we're looking good for late in this calendar year."

A visit to the work site Friday showed how the nature of the work is more focused on the finish, rather than the rough tearing out of raw earth and rock.

Just north of the fourth bore opening in Orinda, crews are creating a steep, permanent retaining wall to anchor the hillside.

Near the Oakland side of the bore, carpenters have built structures where concrete will be poured to form the Art Deco outer walls of the tunnel portal. The structures have small diamond-shaped gaps where student-designed architectural medallions will be installed to add a grass-roots decorative flair to the fourth bore.

Inside the new tunnel last week, contractors were pouring concrete for curbs and sidewalks.

"There is concrete pouring most every day now," said Bill Monahan, a veteran tunnel builder for Tutor Saliba Corp., the lead contractor for the project.

The tunnel interior still has the feel of a primitive, otherworldly place.

Parts of the floor are covered in thick, muddy pools. Loud clanking from air and water pumps makes it hard to hear. Lighting is dim in spots, and portable lights cast an eerie glow.

Lighting will improve soon, though. Permanent LED lights in the tunnel will be ready to switch on in one to three weeks, said Ivan Ramirez, a senior engineer with the Contra Costa Transportation Authority.

"Turning on lights will be a milestone," Ramirez said. "It will make it easier for the workers to see to do their jobs."

Construction of the road bed with aggregate is scheduled to be completed in spring. After that, the road can be paved.

Unlike the first three bores, which are much narrower, the fourth bore will have a shoulder beside the road for motorists with car problems to pull out of traffic.

Opening of the fourth bore will give the Caldecott Tunnel four lanes in each direction permanently, eliminating the daily direction reversal for the second bore that causes traffic weaving and delays.

"It will make traffic much more predictable and reliable in the reverse commute," Ramirez said.

Contact Denis Cuff at 925-943-8267. Follow him at Twitter.com/deniscuff.