Brightwater tunnel inches through toughest stretch toward finish

On a good day, 100 feet below ground, you can see progress as a 3,000-ton machine slowly bores the tunnel for King County's Brightwater sewage-treatment plant.

Not so on one recent day, as the behemoth churned away in rigid clay and its propulsive hydraulic jacks seemed to stand still.

Machine operator Mike Allen grumbled about the rock-hard earth as he held back the machine to one-tenth the speed it can go in soft soil. "If you put too much pressure on it," he said, "you'll bust the bearings like anything."

During two working shifts, the machine mined 20 feet of the 13-mile tunnel that will connect the plant north of Woodinville to Puget Sound.

If tunneling is completed by September, as now scheduled, the tunnel could begin carrying treated wastewater to Puget Sound in July 2012 — a year and a half past the original target date.

Earthworming its way under Ballinger Way Northeast in Shoreline, the tunnel-boring machine rounded the curve onto Northeast 195th Street in Lake Forest Park last week. It now is approaching the last, most difficult segment of the entire $1.8 billion Brightwater project.

With less than a mile and a half of digging left to go, county officials say they're confident in the contractor, even though its machine is an unusual type for the job and a prior contractor abandoned its damaged machine far underground.

Since that slow day Jan. 13, the pace has speeded up and county officials say work is on schedule. Still, the recent slowdown is a reminder that timely completion of the job is far from assured.

The mining monolith is going downhill — not a desirable direction — which means workers must pump water uphill and be alert to any sign of flooding. Then there's the unusually jumbled, glaciated geology that can change in an instant from hard clay to unstable sand.

But the biggest challenge is to come: the high water and ground pressure that the machine will encounter as it grinds through saturated soils as much as 400 feet underground.

Troublesome segment

That problematic stretch is right in the middle of a tunneling project that was divided among three sets of joint-venture contractors, who were assigned the east, central and west tunnel sections.

The east and west sections were completed without a major hitch. The trouble came in the center, where most of the high-pressure ground lies and where the Vinci/Parsons RCI/Frontier-Kemper team lowered two machines into the North Kenmore portal.

One machine headed east, the other west. Both ran into trouble and needed extensive repairs in spots where workers couldn't work safely without special measures to prevent the soil from collapsing on them.

After months drilling wells and pumping out groundwater, the eastbound machine went back into action and successfully completed its drive to Bothell.

Vinci's westbound machine lies abandoned beneath Lake Forest Park, where it will be dismantled.

After Vinci said that, for safety reasons, it couldn't finish the job on a schedule or budget acceptable to the county, County Executive Dow Constantine brought in a different team.

Jay Dee and Coluccio, part of a team that successfully tunneled four miles from Point Wells to Shoreline, were hired to modify their machine and send it east to finish the tunnel.

Using a machine like Jay Dee's is unconventional, said the team's project manager, Greg Hauser, explaining that "slurry" machines such as the one abandoned by Vinci are the standard choice for mining in extremely high-pressure areas — often sandy soil saturated with water.

"We're doing things that haven't been done before. Taking an earth-pressure-balance machine to these pressures isn't done," Hauser said.

Slurry and earth-pressure-balance machines use different techniques for equalizing pressure on the outside and inside faces of the machine.

County officials said they were impressed by Jay Dee's work on the western end of the tunnel. And Gunars Sreibers, the county's Brightwater project manager, noted that Jay Dee worked with the machine manufacturer to retrofit the machine for the high-pressure Lake Forest Park tunnel segment.

Hauser said he will try to avoid stopping for maintenance in high-pressure spots like Vinci did, but is prepared to do so, if necessary.

"They're looking for every opportunity they can to do this under atmospheric conditions because it's just more efficient to do it that way and also it's a safe way to do changeouts to the front of the machine," Sreibers said.

High-pressure areas present two kinds of challenges. One is to maintain a proper pressure balance and keep the machine in good operating condition. Under high pressure, friction on a machine's cutter head "increases astronomically," Hauser said.

The other challenge is to maintain or repair the face of a machine under high pressure. Short of a months-long process of sinking wells to freeze or dewater the soil, standard practice is to counter the outside pressure with compressed air. Workers, typically divers, can spend only limited time working under those conditions and then must decompress in a hyperbaric chamber.

The Vinci group ran into trouble at pressures under six bars, or six times atmospheric pressure, and the Jay Dee team has been told to prepare for pressures in excess of seven bars.

During boring for the 57-foot-wide tunnel that will replace the Alaskan Way Viaduct, the state Department of Transportation predicts pressures approaching five bars for only a short stretch.

Court fight continues

While Jay Dee continues to tunnel, King County and Vinci are in court, fighting over who was responsible for the contractor's difficulties and who should pay Jay Dee's bills, part of more than $178 million in disputed costs.

The county claimed Vinci defaulted on its contract when it said it couldn't finish tunneling until the end of 2012, putting the overall project three years behind schedule.

Even though Jay Dee didn't guarantee a fixed price — or even that it could complete the job — county officials said it offered a greater likelihood of finishing the tunnel sooner and at lower cost.

Vinci said soil conditions and pressure were different from what the county's bid documents stated. After the two boring machines were damaged, an expert panel set up by the county and the contractor recommended drilling test holes and creating "artificial safe havens" where crews could perform maintenance at or near atmospheric pressure, Vinci's lawyers claimed in pleadings in King County Superior Court.

Neither recommendation was carried out after Vinci asked the county to pay for that work and the county refused, according to pleadings from both sides.

Inside Jay Dee's machine, damp chunks of gray muck — clay that had been "conditioned" with water and foam — plopped from a conveyor belt into small rail cars. Rubbed between two fingers, it felt like modeling clay.

Said Sreibers, watching the slow-going work: "My focus and everybody on this part of the job is, 'Let's get this part moving.' The lawyers will work out their piece of it."

Keith Ervin: 206-464-2105 or kervin@seattletimes.com