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Posted Sep 8, 2009, 7:26 AM
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Join Date: Jul 2001
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2 Seattle TBMs are damaged — and 300 feet deep
On the issue of tunnel boring machines:
Quote:
2 tunneling machines on Brightwater sewer project are damaged — and 300 feet deep
2 tunneling machines on Brightwater sewer project are damaged — and 300 feet deep
By Jack Broom
Seattle Times staff reporter
Helene and Rainier are huge, expensive and slow-moving, but they certainly aren't boring.
And that's precisely the problem.
"Helene" and "Rainier" are the nicknames of two 17.5-foot-diameter, German-made machines that are supposed to be hard at work boring sections of a 13-mile tunnel to take wastewater to Puget Sound from the Brightwater sewage-treatment plant King County is building north of Woodinville.
If things were going well, each of the $10 million Herrenknecht machines would be working round-the-clock, cutting through compacted wet dirt at up to five feet an hour.
But instead, they're damaged and awaiting costly repairs more than 300 feet underground.
More than 120 workers on the tunnel job have been laid off until the machines are fixed, and each day's delay adds to Brightwater's escalating $1.8 billion price tag.
"We've got a long way to go, and we need to make sure these machines are in tiptop shape before they continue," said Gunars Sreibers, King County's project manager on the job.
Two other boring machines on the project, built by Toronto-based Lovat, have fared better: "Luminita" has finished the eastern end of the tunnel, and "Elizabeth" is still working on the western section.
But even if repair work goes according to plan, Helene likely won't be moving again until the middle or end of next month. Rainier wouldn't be restarted until December.
Millions of dollars will be at stake — with claims and court cases likely — as a determination is made, possibly years from now, about who should bear the costs of the delay.
How the machines work
For now, Sreibers said, the county, the contractor and the machines' manufacturer are working together on "getting the fix in place and getting these tunnel-boring machines moving again ... It's in everybody's interest to complete this job as quickly as possible."
That will be no easy task.
Helene and Rainier — named for Mount St. Helens and Mount Rainier — had been working in some of the most difficult conditions expected along the tunnel route, which roughly follows the King/Snohomish county line.
"Ten thousand years ago we were under glaciers that moved dirt every which way," Sreibers said, and the result is "a mix of open pockets of water, sand, gravel and mixed faces that are continually changing as you go along."
The two damaged machines, operated by the contracting consortum Vinci/Parsons RCI/Frontier-Kemper, munched their way though the soggy underground environment behind spinning faces lined with metal discs and teeth.
A slurry of water and clay bits was injected in front of the blades as lubricant, and as the wet dirt was carved away, it was piped back through the machine and up to the surface.
"You could look at it as a big disc-sander," Sreibers said. "It's continually pressing against the dirt surface in front of it and griding it away."
Once the material gets above ground, the soil and rocks are removed, and the water and clay bits are pumped back to the machine, to be used again.
As the machine advances, concrete rings are put in place behind it. In effect, the equipment is simultaneously digging a tunnel and building a concrete pipeline.
How things went wrong
Trouble was detected in May, when workers saw that the material Helene pumped to the surface contained not just water, rock and sand, but fragments of the machine itself, some up to seven inches long. "Some wear would be expected, but this was way too much," Sreibers said.
Adding to the problem, rocks the size of softballs were getting lodged in the gaps where the rim broke away. The rocks, in turn, banged around on the machine, causing further damage.
Because of the extent of damage to Helene, project managers decided in June to inspect Rainier, working in similar conditions. It, too, had sustained damage, though not as severely.
To get an idea of what conditions the machines would face, core samples were taken from the ground, down to the depth of the tunnel, before the project started.
"Obviously you can't bore a hole over the whole length of it, foot by foot," Sreibers said. "But we did it at 500-foot intervals to get a good sense of what type of general materials we were encountering."
In some areas, additional samples were taken for a more detailed look.
As the cost of the delay becomes known, a determination will have to be made about who'll bear what portion of that expense, with the county, contractor and machine manufacturer each having a large stake in the outcome.
Among the questions that could wind up in court: Was the contractor given sufficient information about the conditions? Were the machines properly operated? Were the machines themselves flawed in some way?
In the meantime, the process of repairing the machines is prolonged by the high groundwater pressure around them.
Divers have done some work on the cutting heads, not working underwater, but in high-pressurized, sealed air pockets in front of the machines.
But in those conditions, Sreibers said, a worker can only spend about an hour or two on the job and then has to go through six to seven hours of decompression, in chambers inside the machine.
To allow workers more prolonged access to the machines, groundwater above the tunnel is being pumped away through a series of 8-inch-wide wells drilled down from the surface.
For Helene, wells were drilled from the parking lot of Bothell's Maywood Elementary School. For Rainier, the county is seeking permits to drill wells down from the 19500 block of 53rd Avenue Northeast in Lake Forest Park.
Once workers access the machine, they can weld the damaged rim. In addition, Herrenknecht engineers flown in from Germany have designed tools to add to the machine to keep rocks from catching in the gap between the cutter face and the outer rim.
Tunnel is expensive
Because of its inland location, Brightwater requires the longest tunnel of any of the five sites King County studied for the treatment plant, in the planning for more than a decade.
About half of Brightwater's $1.8 billion price stems from its "conveyance system," which includes the tunnel, pump station, outfall facility, engineering, design, environmental studies and related costs.
Even before the difficulties with the tunnel, the target date for opening the plant had slipped from 2010 to August 2011.
Sreibers said the county hopes to stick to that opening for the treatment plant, even though the tunnel won't be finished.
Until the tunnel is complete, treated effluent from Brightwater will be routed along existing pipelines to treatment sites at Renton and Seattle's West Point. But Sreibers said those plants can't handle the growing volume of wastewater on a long-term basis.
Jack Broom: 206-464-2222 or jbroom@seattletimes.com
Copyright © The Seattle Times Company
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