Cramped, dark and wet: Tunnel boring ain’t much fun

Fed up with the crappy coffee and cramped cubicle at work?

Count your blessings.

At the deepest reaches of a tunnel 600 feet beneath the shore of Lake Mead, workers have spent the past few weeks swapping out parts and repairing damage to the business end of a massive tunneling machine.

Their work area is an alcove, 10 feet wide and 3 feet deep, cut from solid rock.

Their background music is the ceaseless gush of water pouring into the tunnel with the force of two fire hydrants running wide-open.

Crews are wrapping up their first maintenance stop on a 23-foot-tall, 1,500-ton tunnel-boring machine specially built and shipped from Germany to dig the Southern Nevada Water Authority’s new 3-mile straw into Lake Mead.

The $800 million project known as the third intake is expected to keep water flowing to Las Vegas even if the lake shrinks low enough to shut down one of the authority’s two existing pipes.

The valley draws 90 percent of its drinking water from the reservoir formed by Hoover Dam.

Despite the “cramped, dark and wet conditions,” the maintenance work should be finished with the tunneling machine up and running again within the next week or two, said Marc Jensen, director of engineering for the water authority.

But like a lot of things about this complex and risky project, the repair stop has not gone as smoothly as planned.

Workers had to inspect the 48 cutter disks that dot the front of the $25 million machine and switch out the ones showing wear.

“These are the disks that do the heavy work of cutting on the rock,” Jensen said.

And the damage was more extensive than expected. Though the disks are made from a hardened steel alloy, some of them had been “destroyed or disintegrated,” exposing the face of the machine to damage from the rock.

During a presentation to the water authority board Thursday, Jensen showed a picture of one disk that had been ground almost in half in the first 1,500 feet of tunnelling.

The machine has another 13,000 feet of digging before the intake pipe is finished.

Jensen said workers had planned to swap out the cutter disks from inside the front of the machine, but the plan changed when they discovered the additional damage. That forced them to carve out a work area in front of the machine large enough for two workers to stand and weld steel plates over the damaged areas.

First, though, general contractor Vegas Tunnel Constructors had to stabilize the area ahead of the machine so the workers wouldn’t be crushed by falling rock or drown.

The tunnel has not yet crossed directly beneath Lake Mead, but water from the reservoir is already finding its way into the work area.

The machine stopped digging in late September in preparation for maintenance. Workers then spent months drilling holes in the surrounding rock and injecting grout into the cracks in hopes of stemming the flow of water into the tunnel.

The result was a work space safe enough to put people in but far from dry. As welders worked on the front of the machine, heavy tarps and boards shielded them from water still flooding in at 3,800 gallons a minute.

Despite the longer-than-expected repair stop, water authority officials insist the project remains on track for completion in the summer of 2014.

Construction began in 2008 with the excavation of a vertical access shaft to the intake’s proposed alignment roughly 60 stories underground.

The third intake suffered its biggest setback on June 11, when laborer Thomas Albert Turner, 44, was killed in a construction accident in the tunnel.

By then, the project had already seen its budget swell and its schedule slip by about 20 months after a series of underground floods in 2010 and 2011 forced the contractor to abandon its first tunnel and excavate a new one in a different direction.

The third intake is the single largest and most expensive construction project in water authority history.

Contact reporter Henry Brean at hbrean@reviewjournal.com or 702-383-0350.