“About a dozen” Montlake homeowners have complained about noise and vibration in the area of the light rail tunnels being bored from the University of Washington’s Husky Stadium to Capitol Hill. But engineers for Sound Transit say the giant tunnel boring machines aren’t at fault. Instead, a rep tells CHS, the likely culprits are the supply trains that run up and down the growing tunnel delivering the components used to assemble the 2-mile route.

Here’s one post about the situation from a community message board:

We are on Eaton Place (across from the Greek Orthodox Church more or less) and I guess the tunnel must have just reached us because about every half hour or so the noise is very noticeable and the house shakes, windows rattle and pictures swing around on the wall. Is this normal or should we worry? I know the tunnel is closest to the surface in our neighborhood, just before it starts under Capitol Hill itself, but this is disturbing.

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Sound Transit says it has been told the same thing by others in Montlake — even with the tunnel boring machines already well beyond the area.

“We’ve been contacted by about a dozen homeowners from the two areas where our tunnels are at their shallowest points (60′ to 85′) between UW and Capitol Hill with concerns about noise or vibration,” Sound Transit spokesperson Bruce Gray tells CHS via email about the situation in Montlake. “This is essentially in the Shelby/Hamlin area and in what we call the ‘Boyer Basin’ just before we head under Interlaken Park.”

 Both Sound Transit and residents on the message board agree — these are the first significant reports of noise and vibration during the U-Link tunneling that has been underway since early summer and the reports aren’t coming from the area where the boring is currently underway.

Progress (Image: Sound Transit)

So, if it’s not the tunnel boring machines — or TBMs —  causing the hum and shake, what is it? Sound Transit officials believe they’ve identified a cause — and a way to fix it.

Sound Transit engineers believe that the trains carrying 100+-ton loads that run back and forth between the TBM and Husky Stadium delivering giant cement tunnel segments are creating the noise and the vibrations that have residents of the area on edge. 

“These supply trains run on rails and ties that are directly attached to the tunnel liners,” Gray writes. “As expected, the underground conditions in these areas is very hard-packed clay. That’s good for maintaining surface integrity during mining, but it may be a contributor to the noise and vibration traveling to the surface instead of dissipating underground.”

Gray says Sound Transit is working with contractors to install new rail in the tunnels for the supply trains, replacing steel ties with wood rail ties and adding rubber mats between the rail ties and rail fasteners. Grays says crews have already installed new ties in about 1,500 feet of the tunnels under the neighborhood. Sound Transit believes the work has already reduced some of the noise but says more work is required to eliminate it.

 

While Sound Transit’s projects to create its light rail system involve incredible levels of precision, there have been plenty of examples of engineering screw-ups and course corrections. In Beacon Hill, the agency ended up on the hook for a home damaged by collapsing “sandy voids.” Tukwila residents had to raise a stink to battle noise created by light rail trains. Flubs on Capitol Hill have been limited to issues like this fountain of foamy gray water that spouted from E Pike in October.

As for worries that noise and vibrations from the twin U-Link tunnels could also be an issue with passenger trains once service starts in 2016, Gray says the rails for light rail are significantly different.

“The biggest difference will be the new continuously-welded rail that our passenger trains will run on,” Gray says. “Without getting too technical, there will also be several other differences in the way that rail is affixed to the tunnel than how the supply train rail is attached. We’ll essentially have a new concrete bed between the rail and the tunnel liners and special fasteners holding the rail in place.”

In the meantime, as the work area moves its way up under the Hill to Broadway, residents and business owners can let Sound Transit know if they see or hear anything peculiar by contacting the agency’s Jeff Munnoch at 206-398-5131 or [email protected]. In Montlake, residents are also making sure to take care of themselves. “I’ve been advised to take lots of ‘before’ pictures of your exterior and interior walls,” one person writes.