With concern about vibrations and noise peaking at the surface along Broadway as the first of two tunnel boring machines traveling from Montlake prepares to bust through a concrete wall and end its two-mile, 10-month journey Tuesday, Sound Transit says it is studying a much larger concern — worries that the vibrations felt by residents and businesses created by track-use during construction will continue when the U-Link light rail line becomes operational in 2016.

“We’ll be talking to the community later this spring or summer when that study is complete,” Sound Transit’s Bruce Gray tells CHS. “As we’ve talked about, the operating tracks will be new, continuously welded rails set on a permanent concrete slab with different fasteners designed for long term use.  The design is completely different than what the supply trains are running on.”

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What’s happening now is less of a concern for the agency — though any damage proven to be caused by the vibrations could be costly. The noise and vibrations now felt around the end-target for the “holethrough” expected later today are the same that shook a much quieter part of Seattle — we first reported about the Montlake Murmur late last year. Described as everything from the deepest bass you’ve ever heard to sounds of raspy, rhythmic scraping, the sounds and vibrations have followed the line up from Montlake, under Volunteer Park and up to Broadway. We reported on families near Volunteer Park affected by the issue in January as the worst of the rumbling seemed to have moved through that area.

But, due to a variety of factors ranging from how fast the trains moving spoils along the construction rails are traveling to where, precisely, along or near the light rail route a building is located, the vibrations from construction and boring activities continues. Here’s an email CHS received last week from KS, a neighbor who lives just south of Volunteer Park:

Hi – was at a neighborhood meeting yesterday that was attended by the neighborhood liason from Sound Transit. – Roger Pence.  As you may be aware, the Sound Transit tunnel project under Montlake caused that neighborhood many headaches due to noise from the tunneling and supply trains running.  Neighbors on Capitol Hill have been complaining too.  

Some residents are hearing the trains running at all hours.  It’s a low rumbling noise – I’ve heard it myself. The house has also vibrated at times.  Two nights ago I felt my bed shaking a bit.  In any case, we, as a neighborhood, are very concerned as to whether Sound Transit will spend the money to mitigate the noise.  Unless people directly complain to Sound Transit, they will not be motivated to spend the money.  I myself, was guilty of only talking to my neighbors, not letting Sound Transit know that I was concerned until I attended this meeting yesterday.

Personally, I’m concerned that when construction is finished, I will continue to hear the noise of the trains running, and that, in turn, will diminish my property values.

It would be great if you did a blog post and see if it is being heard, felt or disturbing other people on Capitol Hill.

The final arrival on Broadway of the two machines from Montlake — one expected today, the other in about 4 weeks —  won’t end the tunneling work. “[W]ork continues for several months after the machines arrive at their destinations, because of the need to build “cross-passages” that connect the southbound tunnel to the northbound tunnel, and install concrete floors, emergency walkways, and utility conduits,” Sound Transit said in a recent bulletin. Meanwhile, possibly due to the types of buildings and structures its moving beneath, the trips made by the third tunnel boring machine working the 7/10ths of a mile between Broadway and downtown have been relatively silent. Nice job, Brenda.

For as much of an irritation the line has occasionally been at the surface, the project has also been an on-time, on-budget engineering marvel. We’ve included on this post some pictures of the work crews building the tunnels recently provided by Sound Transit and wrote about the nitty gritty of the engineering in this post last year. Still, for all the engineering, there are also human elements at the surface as well as the economic and development impact of the project including this recent piece by the Tacoma News Tribune about what the end of tunneling will mean for the plant that produces the concrete tunnel segments.

Sound Transit’s Gray said that, in the meantime, tests are underway on the light rail trains to determine if the line’s tracks will produce similar problems when the system becomes operational in late 2016. “[W]e’re wrapping up more light rail vehicle fleet tests now to get a more complete picture of conditions during train operations,” Gray said. “The results will inform our North Link (UW-Northgate) final designs and could also influence the final U-Link (downtown to UW) installation.”