Approximate location of the sinkhole. Graphic via Jacobs & Associates.
Approximate location of the sinkhole. Graphic via Jacobs & Associates.

A sinkhole has opened up just South of the Roosevelt Light Rail station on Sunday evening.  According to a release from Sound Transit:

Crews for Sound Transit’s Northgate Link light rail construction contractor are taking steps to fill a small sinkhole that emerged in front of a home on 12th Avenue Northeast near 62nd Street Northeast above tunneling that took place last year. The sinkhole, with an opening about six feet long, will be filled with cement this evening. Crews will conduct ground-boring tests in the area to assess whether there are other issues in the area above where one of the contractor’s tunnel boring machines passed approximately 50 feet below last fall. Sound Transit and its contractor will be working closely with the City of Seattle on follow-up.

A sinkhole opened up on Beacon Hill in 2009, just as Central Link was opening, a year or more after tunneling had completed.  Sound Transit’s contractor filled the hole at a cost of $1M.   The Times has a good graphic from that episode showing how sinkholes can occur when the tunnel boring machine hits sandy soil and too much fill is removed.  The Beacon Hill tubes were 135 feet under the surface where the sinkhole developed.

The problem-plagued Bertha, tunneling the new Highway 99, was stopped after sinking was discovered in Pioneer Square in 2015 and on the waterfront in 2016.

56 Replies to “Sinkhole Opens Above Northgate Link, Two Homes Evacuated”

    1. What? You do realize soil cannot entire the completed tunnel, right? It’s sealed. A sinkhole would have zero effect on light rail in operation. In this case, excessive sand poured through the boring machine leaving an empty cavity in the soil layers allows weight to settle all the soil above.

      1. You mean enter the completed tunnel?

        I see your point though about boring a hole through.

        Still the trains CAN cause vibrations and well, you know…

        Dammit, you know I want light rail grade separated from Everett Station to at least Tacoma.

  1. Odd that this “occurred ” so long after the tunnels were mined. Wonder if it is due to cross-passage excavation

    1. It doesn’t surprise me much. Create a hole fifty feet under the ground and it may take a while for things to settle.

    2. Highly doubtful that cross-passages are at issue here. Cross passages are excavated by hand, so over-excavation can’t happen.

  2. And we are meant to believe that it is safe to travel through these tunnels? Tens of billions for a death trap?

    1. Part of the tunnel boring machine inserts the tunnel wall before the machine moves on. It’s one of the reasons this is the safest way to tunnel in unstable soil. Unlike a trench, there is never a do get of material collapsing into the tunnel.

      Sinkholes can be caused by any number of things that alter ground water movement. Tunneling can do that, but so can improperly dealing with surface runoff from a roof.

    2. Garry, you might want to check The Seattle Times from a month or two back. It looks like most, if not all of the pillars under I-5 from Ravenna south are a long way below ‘quake standards. The ones under thousands of cars and many more people, all packed solid in traffic at this exact minute.

      Any of whom can also get killed by a drunk or a dropped cell-phone on anywhere on the rest of their commute.

      The Waterfront viaduct should have been blown up after the Nisqually quake. One just like it killed fifty people in the Bay area’s last big earthquake. Seem to remember our own most scenic death trap was supposed to come down in 2012.

      And now it’s due to open in two weeks. Whoever gives the order to re-open it ought to get one count of negligent homicide for every dead body the poor dogs have to find to be dug out. Also animal cruelty, because handlers say these animals really start to suffer when everybody they find is dead.

      You might also check online to see if this applies here: very often an earthquake’s major damage goes about 20 feet down. Making tunnel safety same as flying, in the other vertical direction. The farther from the surface, the safer you are.

      Lightning, brush fires, floods and plate tectonics-the planet won’t function without them. Though Seattle rents would be a lot lower without all those fault-line results. Which also at least guarantee that the sorrowing dogs will dig out people to whom quake conditions gave a wonderful last view.

      Mark Dublin

  3. Why is this story not in the Seattle Times or other main stream media? Is it being hidden from the public?

    1. It’s Sunday freakin’ night—on May Day. Betcha this makes the Seattle Times tomorrow, after the front-page story about today’s protests.

    2. The four top stories on Kiro7.com right now: May Day, May Day, death at the ice caves, the sinkhole. Coverage is exactly what it should be.

      1. Same as with wars and electing the government of our country, Kacie. The part of the entertainment industry that used to be called the news media stays in business by not telling people what they themselves don’t want to hear. Balance sheet proves it.

        Mark Dublin

      2. I’ve been to those ice caves once. There is sign after sign saying they are dangerous and to not only stay out of them but to not even get close to them (and there are numerous “do not go beyond this point” signs so it’s clear just how close is “too close”).

        Yet despite the history of tragedy at that location people still choose to ignore the signs. You can’t fix stupid.

        That child’s parents should be prosecuted for negligent homicide.

      3. My bad. Every time I hear about a death at the Big Four Ice Caves I assume it’s another fatality caused by an “unexpected” cave collapse. There have been so many of those over the years.

    3. Ya, it is a big giant, secret conspiracy. Which is why you see it published here and you are commenting on it.

      You’re not making much sense…..

    4. No, like other posters have said, it will be there tomorrow in the newspapers. Also, sinkholes are a pretty normal part of using machines to dig tunnels and there is no safety issue in the tunnel or/and stations themsleves, thanks to the tunnel wall.

    1. Talk about things that’ll put rescue dogs on prozac if they find Dori! They’ll probably just kick some more dirt over him, and go back to work that gives them more moderate depression.

      But by the way, Frank, thanks for the section drawing- exactly what I’ve been saying we need for any discussion of route from Ballard to West Seattle. Any chance Jacobs & Associates can help us out?

      Mark

  4. Latest blockbuster disaster movie released today – Bertha II. (dateline Seattle 2024)
    A legislature drunk with power is the setting for launching the worlds largest TBM at 100 feet across, designed to replace I-5 from Georgetown to Roanoke with 8 lanes in each direction.
    All progresses as planned until Bertha II crosses under City Hall, when unexpected losses of recycling trucks is noticed, causing little concern.
    Things take a real turn for the worse, when large chunks of government begin falling into an abyss after the Mayors office tries to assure everyone to calm down.
    Coming to a theater near you.

    1. I guess there’s not enough time for a second female mayor to be likely by then. But the one who decides it should own it.

      As for I-5, if rebuilding it goes through, I think we can just put a lid on it downtown. On the west side of Beacon Hill it doesn’t seem to be bothering anybody much, and the adjacent area is industrial so it kind of blends in. In SLU I don’t really know: could a lid work? But where it rises up to the bridge you can’t really lid or wall that. And putting I-5 under the Ship Canal seems like overkill. There have been calls to decommission it and turn it into two smaller state highways (north and south), but I don’t quite see how that would work since a lot of people do travel through between north and south Seattle so you can’t really break it in the middle.

  5. Sink holes are very common in this town. If you live on a steep hill, you will see a bunch of them. While walking around the other day I saw one. It was pretty tiny, and will probably get filled in quickly by the city. Of course, there are sinkhole and their are sinkholes. A sinkhole in someone’s back yard is a pain, but not that big of a deal. If it damages a house — or worse, a building or freeway — then it can be very expensive to deal with (which is what they are worried about with Bertha).

    1. If anyone questions the concept that Seattle has had sinkholes before and will probably have them again, I suggest they Google the Great Ravenna Sinkhole of 1957.

      Now that’s something to get worried about.

      1. I did Google it, thanks. Wow, that’s amazing. FYI – This small sinkhole isn’t all that far from that really big one.

    2. It may be that tunnel boring was the cause of this sink hole. It also may be completely unrelated. Let’s not assume. Could be a broken pipe, improper drainage, construction uphill, or any number of known causes. Or unknown causes.

    3. Sinkholes happen here, but on the whole they’re pretty rare, at least compared to places with lots of limestone.

      To those saying let’s not jump to conclusions, it’s much more likely that a sinkhole above a recently bored tunnel is caused by said boring than that it is the product of chance.

      But that’s fine – it’s an inevitable hazard of boring tunnels, and it’s an acceptable price to pay to have the infrastructure. It’s a heck of a lot better here, under some low-density neighborhoods, than, say, downtown, like Bertha. But we do have to prepare for the possibility of a sinkhole downtown with ST3 – that’s one reason to stick to the street grid where possible. Also it’s a big advantage is small diameter light rail tunnels over the massive Bertha tunnel – commensurately smaller sinkhole possibilities.

  6. This area has one of the most challenging geologies I’ve ever seen. We have a mix of outwash, glacial till, and ice-contact layers, not to mention fault lines and a nearby plate subduction zone. I’ll say this: given my minimal background in soil mechanics and knowledge of the issues facing the design team: 1. They are doing a great job with approach, budget, and schedule. 2. When completed, not only will I feel comfortable and safe riding the light rail, I’ll probably be one of those people who makes a trip exclusively to try it out. 3. I feel terrible for the homeowners/renters involved in this and hope that Sound Transit compensates them adequately for their troubles. This is expected and should have been built into the budget.

    1. Most likely the way it was “built into the budget” was that ST purchased an insurance policy in case this sort of thing happened. As I understand it, such things are pretty much SOP whenever one tunnels under an urban area.

    2. Would you feel comfortable living on top of light rail?

      In a worst-case scenario, if the houses are uninhabitable and ST buys the lots from the homeowners, then it could, um, build affordable housing there. The city could cooperate by zoning it multifamily if it’s not already.

      1. That brings new meaning to “Eminent Domain”.
        Your house rides atop a TBM gnawing at the earth below, where sudden disaster is Imminent.
        OK, close enough. Do you wish to sell?

      2. Let’s put it this way. If I owned a home atop a light rail tunnel under construction, I’d be getting an appraisal ASAP, and doing every cheap/free project I could think of to increase the value of my home in preparation of the appraisal. Actual home improvements that aren’t free or cheap would go on hold until after construction. And I might tuck away a few irreplaceable valuables in storage or a safe deposit box. But, given the inflation of real estate values in Seattle, I would be in no rush to sell, and I wouldn’t be worried about dying – no more so than when I get in a car and get on a freeway.

      3. RE: eminent domain (mic): Eminent domain was historically used to build roads and other public facilities for the benefit of the public. This would be no different. The thing is, this tunnel isn’t dislocating entire neighborhoods as I-5 did. Disaster is not imminent. It’s possible. We have one sinkhole on this tunnel so far, out of how many homes? I don’t see a huge swath of homes in Capital Hill that got annihilated by that tunnel. Your hyperbole is not helpful.

      4. BNSF owns a tunnel under a lot of very valuable real estate in downtown Seattle. There’s no guarantee that, even after 100 years of settling, there isn’t some unforeseen underground earth movement going on under there.

        Panic and demolish downtown Seattle and move downtown Seattle elsewhere?
        Or let things sit for now and hope for the best?

  7. I would be interested to know if anyone who voted against any of the ST ballot measures lives above these “accidental” sinkholes.

      1. Payback is real. Bing the George Washington bridge scandal if you don’t believe me.

      2. My attorney, Victor Sifuentes, just informed me that I should add the disclaimer that I am in no way suggesting that these sinkholes were purposely created.

  8. If it was caused by the TBM (and it almost surely was), they should be able to tell from the drilling/boring logs.

    If you’re boring in a sandy spot and the roof collapses, so you end up with a tunnel with airspace above it, you should see that you removed more material than the size of the hole for that stretch. And more sand in the rock that comes out.

    There’s no way to predict if you’ll end up with a stable cavern or if the roof will keep collapsing until it reaches the surface and you’ll have a sinkhole – but they hopefully are keeping track of where this stuff is happening.

  9. Too bad “Almost Live” went off the air, Sam. Otherwise, “CSI Seattle” would trace rash of sink-holes to an annual animal-impersonating perverts’ convention that couldn’t get a hotel in ‘Vegas, and ended up at the Weston.

    Resulting in the detectives finding a guy in a dog suit run over by a semi after being shot by a rancher who thought he was a coyote while he was throwing up in the on what’s left of the Viaduct.

    And finally solving the case when they find a victim with his head cut off by LINK while wearing a Confederate uniform over a corset.

    Note that program title is in quotes too. “Sam.”

    “Mark”

    1. I’ll add that the suspect was sitting in a tree throwing sticks at people.

  10. I knew I could come to this blog and find people saying the sinkhole above the new tunnel is unrelated to the new tunnel.

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