Slog
News & ArtsThursday, April 5, 2012
Transportation Sound Transit Tunnels Three Months Ahead of Schedule
Posted by Dominic Holden on Thu, Apr 5, 2012 at 2:14 PM
Our regional transit agency is getting better at building subways.
Two tunnel boring machines digging routes for a future light-rail line between Capitol Hill and Husky Stadium "have finished their tunneling three months ahead of their original schedule," says Sound Transit spokesman Bruce Gray. The second machine broke through soil and cement at the future Capitol Hill station late last month, as was widely reported, but a Sound Transit schedule from February shows the tunnels weren't slated to be done until June 30.
"Mining is always the always the highest risk part of the project in terms of cost and unknowns," Gray says. It speaks well for the project "any time you can get the tricky part out of the way."
The advanced schedule doesn't yet change the project's overall timeline or guarantee taxpayer savings—Gray explains that many other project components must fall into place before the line is expected to be open in 2016—but it bodes well for accelerating the project's pace.
"The sooner they are done mining, the sooner the contractor building the station can get to work," Gray says. Currently, three of the four 21-foot-wide tunnels that terminate in the Capitol Hill station are complete: both lines to the University District, northbound and southbound, and one of two lines to downtown. The second tunnel between downtown and Capitol Hill, being dug by a machine named Brenda, is arguably less risky now that the parallel line is complete and engineers are familiar with the soil conditions.
Indiana-based tunnel contractor Traylor/Frontier-Kemper, which has a $339 million deal with Sound Transit, has had a "very smooth operation and had very few hiccups," Gray says.
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@3) It's funny, that project was totally different from this one (financing, need, soil conditions, traffic diversion, demand, tolls). Not to mention, that 57-foot-wide tunnel, the biggest of its kind, is more than seven times the area of this 21-foot-wide tunnel, a standard size for light-rail tunnels all over the country. My coverage never said the downtown tunnel was impossible, just that it was a risky, impractical, stupidly expensive replacement for the viaduct. This project is far, far less risky and subways have an obvious, proven benefit in high-density cities.
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I didn't get that at all. The coverage revolved around the necessity for that specific implementation over other options. Do you seriously recall anything being said about "impossibility"?
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And SR-520 is still mostly unfunded on the Seattle side.
UW Husky Stadium station ftw!
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@6, the coverage continually harped on the size of the shield, as if that was a particularly difficult hurdle to clear, as if the maximum size of shields hasn't been continually increasing for decades without problems. The coverage repeatedly threw up examples of tunnels with problems, while ignoring the far, far greater number of tunnels with none.
This is what annoyed me about the coverage: it wasn't just blatantly partisan -- I expect that -- but it was biased to the point of dishonesty -- and to the point of ignoring the real arguments against the thing, which were and are persuasive enough.
We haven't given any money for the stadium yet. Even if we do, it's not like we are taking money out of the general or transportation fund to pay for it. We're issuing bonds. Unless those bonds somehow hurt our credit rating it doesn't change the math of paying for the other projects at all.
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The problem with the tunnel solution was that it was UNNECESSARY to spend that much money, there were cheaper just as viable solutions.
When toll diversions and other current viaduct users for whom a downtown bypass is useless were factored in, we were told to expect 40,000 daily trips through the 99 tunnel, right? The majority of which are likely to contain a single passenger.
The downtown-UW light rail segment, meanwhile, will be the most heavily-packed stretch of subway we'll ever build, handling 125,000 daily trips by most estimates.
That is more than 40,000.
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I would also like to withdraw and apologize for the word "dishonesty". Dominic's coverage was not dishonest. I'll try again, with the word "overzealous" in its place, and hope that doesn't sting as much. Overall the Stranger's opposition to the tunnel was a correct opinion; I just take extreme issue with the engineering scaremongering, if that's not too much again. I apologize for being a dick. "Overzealous" is a significant part of my arsenal too.
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Maybe the region is just better now at picking contractors for this sort of thing.
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So why build in low density Seattle?
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One of the mitigating factors in this case is the extensive drilling that has been done on and around the Viaduct alignment because of the known problems with the shallow fill/tideflat soils. More information is always better. Remember, though, that all soil profiles are interpolations. Drilling results even every 500 feet still aren't perfect information. You never really know where the transitions are from sand to till to clay to silt; you can only make estimates based on what you found in the boreholes.
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