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Fixing a 7,000-Ton Drill
An anonymous reader writes: At the end of last year, we discussed Bertha, the world's largest tunnel boring machine. During an effort to drill a viaduct beneath downtown Seattle, the machine — clocking in at 7,000 tons, 57.5 feet in diameter, and 326 feet long — got hamstrung by an 8-inch-diameter steel pipe. The complexity and scope of the repair plan rivals that of the project itself. "The rescue operation (workers call it "the intervention") began in late spring with construction on the shaft to reach Bertha. Workers have been sinking pilings in a ring to prevent the shaft from collapsing, using 24,000 cubic yards of concrete — enough for a medium-size office building. Once that ring is complete, digging on the shaft will start. When the shaft is ready, Bertha, which is damaged but still operational, will be turned back on so she can chew through the concrete pilings to reach the center of the shaft. There, the machine will rest on a cradle where workers can detach the front end and hoist it out." That detachable front end? It weighs about 2,000 tons by itself. The repair bill is estimated at about $125 million.
Actually, something else is causing the seals to fail on the bearings and master bearing. The sampling pipe was the original theory but it could not account for the damage being done.
FTFA “Contractors are not entirely sure what’s happening to the seals. They’re letting sand in, which is not good,” said Matt Preedy, deputy Highway 99 administrator for the state Department of Transportation (DOT). “Either you’ve got gaps somewhere, or you’ve got cracks in the seals.”
http://seattletimes.com/html/l...
Basically, our water front soil make up is not ideal. Much of the Seattle water front is fill dirt from various late 19th century and early 20th century projects around Seattle. Much of the path Bertha is taking underground is lined with caissons to keep the liquid dirt at bay.
What could possibly go wrong?
>"During an effort to drill a viaduct beneath downtown Seattle"
Viaduct? How is digging/drilling a tunnel a viaduct? "A viaduct is a bridge composed of several small spans for crossing a valley or a gorge." http://en.wikipedia.org/wiki/V... You cannot drill a viaduct.
They are digging a TUNNEL under Seattle for a car highway as an alternative to an old, damaged viaduct.
http://www.nytimes.com/2013/12...
Whether or not Mitsubishi fucked up their cutter head bearing design, or Seattle Tunnel Partners forgot to read the documents that described the exact location of the previous exploratory bore pipe, regardless of if it's even possible to sucessfully extract the cutter head without sinking the current viaduct with all the additional excavation and ground water pumping, this virtual video flythrough from four years ago is my favorite thing to come out of the project.
And if you enjoy crappy flash web cam software, you can watch the current progress on the cutter head replacement shaft here.
The contractors are on the hook for the bill, not the taxpayers. No idea whether or not they have insurance that might or might not cover it.
Ignore the tea-baggers who are claiming this is a government failure. This one's all about how private industry isn't getting it done.
By "Republicans that rule this city" do you mean the City Council, or do you mean Ed Murray, the Mayor? Perhaps you mean the overall populace with its highly one-sided voting record?
Browsing at +1 - no ACs, I ignore their posts. So refreshing!
Likewise yourself. A mostly lifelong (until the last 3 years) resident, born and raised in Ballard. And I can tell you unequivocally that Seattle is extremely Democrat biased, and the city leans heavily to the left - exceedingly so. Puget Sound as a whole closely mirrors Seattle, and that makes the entire State lean so far Democrat that it exceeds the national margin of GOP/DEM voting results by several points. Washington is one of the most solidly Democrat states there are. Outside the rural districts in Eastern Washington (with extremely limited population), Washington is a guaranteed Democrat win - every election.
Browsing at +1 - no ACs, I ignore their posts. So refreshing!
The problem is that the drill head diameter is larger than the inside tunnel diameter. The tunnel gets built out of cast concrete sections which are installed behind the cutter head. You might be able to disconnect the cutter head and back the TBM out, but you still have the head to deal with.
I suspect that the complexity (that is, cost) of using a collapsible head would outweigh the potential benefits, especially since this is hardly a common occurrence.
BTW, a pretty neat animation of the project can be found here.