On Wednesday, Sound Transit gave a brief media tour of the active construction site where the future Capitol Hill Link station will be.  So far, construction crews have excavated roughly 90,000 cubic yards of dirt, creating an enormous hole or “station box” which requires a conveyor belt for the removal of all the fill.  According to Rick Capka, ST construction manager, roughly 10,000 more cubic yards, or ten feet in depth, have to be excavated before crews will put in a ten-foot thick concrete invert slab at the bottom of the box.  The box will eventually be 80 feet deep, 80 feet wide, and 540 feet long.

The concrete slab will help the transition into the next phase of construction in mid-2011 when a TBM (tunnel-boring machine) will begin boring its way south to the Pine Street Stub Tunnel, roughly 3,800 feet.  Two more TBMs will also be tunneling toward Capitol Hill simultaneously from the University Station site.  According to Capka, crews haven’t encountered any significant delays apart from a few recent weather-related issues.

Thanks to Oran, we have a video of the tour above for your viewing pleasure.  You can also view pictures in our Flickr pool.

37 Replies to “Capitol Hill Construction Update”

  1. Will the Capital Hill station be opened for service before the UW station (and tunnels to it) are completed?

      1. Maybe you should switch to Bing…


        “3. Invert Types
        The invert of a tunnel is the slab on which the roadway or track bed is supported. There are two main methods for supporting the roadway or track bed; one is by placing the roadway or track bed directly on grade at the bottom of the tunnel structure, and the other is to span the roadway between sidewalls to provide space under the roadway for ventilation and utilities. The first method is used in most rail transit tunnels because their ventilation systems rarely use supply ductwork under the slab. This method is also employed in many highway tunnels over land where ventilation is supplied from above the roadway level.

        The second method is commonly found in circular highway tunnels that must provide a horizontal roadway surface that is wide enough for at least two lanes of traffic and therefore the roadway slab is suspended off the tunnel bottom a particular distance. The void is then used for a ventilation plenum and other utilities. The roadway slab in many of the older highway tunnels in New York City is supported by placing structural steel beams, encased in concrete, that span transversely to the tunnel length, and are spaced between 750 mm (30 in) and 1,500 mm (60 in) on centers. Newer tunnels, similar to the second Hampton Roads Tunnel in Virginia, provide structural reinforced concrete slabs that span the required distance between supports.”

  2. Two more TBMs will also be tunneling toward Capitol Hill simultaneously from the University Station site.

    I thought one machine was going to go in each direction and then be turned around to dig the second tunnel?

    1. Bernie,

      The two UW TBM’s will be mining at the same time. The single one will start on the Northbound tunnel from CHS to Pine Street, be disassembled then will return to CHS then do the Southbound tunnel.

      All three machines (unless the contractors are selected for UW to Northgate) will be sold/auctioned off, just like the Beacon Hill TBM was.

      Kinda of a shame we can’t just keep a hold of these TBM’s (at least two) for future projects since all of the bores will be 21 feet in dia.

      1. Bah.. need an edit feature..

        “The two UW TBM’s will be mining at the same time Southbound towards CHS. CHS is where all of the equipment will be removed and sent back to storage since it is the closet and less disruptive route, plus, they do not have to contend with the Montlake Bridge.

      2. OK, that sounds right. It’s much easier to deal with all the dirt removal at Montlake. I’d think they’d want to load it on a barge and take it to oh say Vason Island where they’ve been hauling out gravel and sand for decades. If I’m remembering correctly now they needed two machines on the CHS to UW section because it’s twice as long as the DT to CHS segment. I don’t understand the economics of TBMs but even if it’s the same size bore they seem to be custom built for every job. I think the majority of the expense is in the cutting heads which are pretty much used up at the end of a job. I suspect the rest of the equipment would have to be disassembled and completely rebuilt at the factory before starting a new project anyway. You really don’t want one of these things to break down and get stuck! Plus tunneling technology is still advancing pretty rapidly so a machine that’s a 5-10 year old design is going to be slower and more costly to operate.

      3. I thought after the second tunnel was built, a part of the TBM from Capitol Hill was going to be abandoned in-place in the vicinity of the PSST. I’m not sure why that needs to be done, because they obviously need to recover the entire machine after boring the first tunnel. Maybe it’s just more economical that way.

      4. It’s possible they’ll abandon the outer shell of the TBM, because it’s easiest to just leave it there around the end of the tunnel rather than digging a big hole to lift it out, and you can’t really take it back out through the tunnel since it’s a) bigger than the tunnel diameter (it’s what holds the dirt while the tunnel lining) is being assembled and b) you can’t easily cut it up to take it back through the tunnel, since it’s holding the dirt while the tunnel is being assembled, so removing it while building the tunnel would be painstaking work to keep things from collapsing.

      5. Yeah the outer shell of the TBM is going to be encased in the tunnel. I wonder if you’ll be able to tell when you’re going through there…

      6. As a tugboater I’m probably more than a little biased, but I’m surprised they decided to truck the TBM spoils away from Montlake rather than barge them out. Maybe building a conveyor over to Union Bay wasn’t feasible. You’ve got to think the idea occurred to them at least, so there must have been some compelling reason to go with the trucks.

  3. Did they really need to level an entire block to build that station? I was looking at the Granville station on the Vancouver Sky Train and they built the entire thing with the confines of the street. We on the other hand remove Capital hill, put in the tracks and then dump the hill back on top. Seems to be excessive. Although I think Granville was a “dig a trench and cover it back up when done” type of tunnel.

    1. Grant, if I recall correctly, Skytrain used an existing tunnel for the original downtown alignment.

      1. Clearing up some mis-information.

        The original Skytrain line – the Expo Line – was built for Expo 86 and re-used an abandoned CPR train tunnel under downtown Vancouver that was originally built in the 1930s to allow Trans-Continental trains to be moved from the CPR terminal on the harbour (todays Waterfront Centre) to the service/ maintenance yard on False Creek (todays BC Place and Yaletown) without crossing over the city streets downtown. The old CPR Tunnel had to be underpinned to lower the trackbed in order to have enough room for both Skytrain tracks to be built over/under each other in a single-track train tunnel – eastbound on the lower track, westbound on the upper track.

        The newest Skytrain line – Canada Line – was completed in time for the 2010 Olympics, and was constructed downtown by using a TBM to create new bores from the Cambie & 6th starter pit on the south side of False Creek to Yaletown on the north side of False Creek, then curve north under Granville St to the retrieval pit at Granville & Cordova. After the TBM finished the first tunnel, it was dismantled in the retrieval pit, trucked back to the starter pit where it was re-assembled and it drilled out the second parallel bore to the retrieval pit. The construction pits for the stations at Yaletown (Pacific & Davie) and City Centre (Granville & Georgia) were dug down to meet the completed TBM bores. The starter pit became the Olympic Station, and retrieval pit became the Waterfront Station for the Canada Line (which is part of the Waterfront complex where the SkyTrain Expo line, the West Coast Express commuter rail, and the Seabus converge).

        The rest of the new Canada Line in Vancouver was built under Cambie Street from False Creek to the Fraser River using the Cut and Cover method – universally hated by anyone who needed to drive along or across Cambie to get from one side of the city to the other, or who had the unfortunate need to visit friends, family or businesses that were within a mile of the ‘trench to hell’. There was such an outcry over this method of construction, the city council passed a bylaw which forbids any future subway construction using the Cut and Cover method. One business impacted by this construction on Cambie has successfully sued for damages & lost business (but this is currently under appeal), and the case may be turned into a class action for all businesses and residents along Cambie to sue for damages & lost business.

        The northern end of the Cut and Cover tunnel connects to the Olympic Station, so you will notice when standing on that platform that the train tunnels to the south are square (the Cut and Cover tunnels) and to the north are round (the TBM bores).

    2. They could have built the station under Broadway, but for various reasons decided to build the station under the block to the East. Brooklyn station is going to be built under the street rather than demolishing a block first.

      1. Although there will be various parts of the adjacent blocks that will be knocked down, pretty much all low-rise stuff (like the Chase Bank). You can’t build a super deep station like ours right under the street, you really need a lot of room for staging.
        And wow Ben that’s super interesting. I hadn’t heard that before.

  4. So, exactly how much greenhouse gas is being emitted from the construction of this new section of Link? All the hauling of dirt and equipment, and all this concrete (making concrete generates a lot of ghg) is obviously generating a lot of greenhouse gases. What is the estimated amount?

      1. Metro’s fleet carries close to 400,000 people per day over 100’s of miles of routes. What does U-Link have to do with that?

      1. U-Link is only about 3 miles and is only expected to average about 80,000 boardings per day. I-5 carries around 500,000 people per day over the boat canal.

        Why would you compare 3-mile U-Link to 15 miles of I-5? And exactly when do you think the I-5 bridge will need to be “rebuilt”? It’s already about 50 years old, and nobody is talking about “rebuilding” it, are they?

      2. I-5 needs repaving. The Interstates were built with an approximate 40yr lifespan in mind. They are well beyond that. When they re-grind the surface to make it smoother, they are also making it thinner. They can also align the concrete panels to extend the life of the heavily travelled right hand lanes (where the truck traffic is). Those are the concrete hash marks (or stitches, if you like) you see between the panels in some areas. You can piecemeal the repaving by working on segments that fail, but the WSDOT can perform that repaving at the same time they widen a given freeway.

        WSDOT knows I-5 needs to be repaved, but coming up with a project that only repaves the highway for billions of dollars is a hard sell, so no public proposals have been put forward.

        For some interesting cost comparisons, check this link out:

      3. Rails need to be replaced about every 30 years.

        They are not going to “rebuild” a highway tunnel or bridge any more often than they rebuild a rail tunnel or bridge.

      4. The cost to ‘replace’ the roadbed of an Interstate is roughly the same cost as building it in the first place. That means it’s cheaper in today’s dollars than it was to construct it in the first place, since 1) there are no ROW acquistions to add to the cost, 2) no need to ‘re-landscape’, i.e. build tunnels, make cuts into hills or fill low areas and build retaining walls, and 3) no need to redo the subgrade. It essentially means that they would only have to take the pavement down to the subgrade, and re-pour it.

        Bridges are another story, since deferred maintenance on elevated structures can cause serious problems such as the I-35W bridge collapse in Minneapolis, for example.

        In other words, and since I don’t have the figures at hand for a specific section of I-5 when it was built, I’ll just give an example.

        Let’s say it cost $1 Billion to originally build a segment of I-5 50 years ago. If we were to try to build that today (as if it never existed), it would cost $4 billion. However, given that it does exist, today, it would cost only $1 Billion to relay the roadbed.

        The current gas tax is not covering the areas where major rebuilds are needed, hence, the talk of tolls.

        If you were to exclude the portion of the projects such as I-405 and SR-520, that widen those freeways, then the funding gap is much smaller.

      1. This was a canard I think posited by David Brewster or the Seattle Weekly that the construction of Link was a significant contributor to Greenhouse Gases. Any infrastructure endeavor whether building a skyscraper, a large road system, or a railway will involve an expenditure of energy and use of fossil fuels (while we still use a fossil fuel driven system) to create the infrastructure. The key difference would be the end result. Does the system created reduce the amount of CO2 deposited in the air from its operation as compared to prior modes of transportation and does the system offer the possibility severing the dependence on fossil based fuel – the key factor in overall global warming?

    1. Norman
      First off your traffic count over ship canal bridge is way off. According to wsdots traffic counts for 2009 ship canal bridge at mile post 169.18 has a usage of 174000 vehicles per day this doesn’t include the reversible lanes. The closest count for the reversible lanes is mile post 168.31 which had a count of 45000. Total count 219000. I am not to sure if there are any ramps between mile post 169.18 and 168.31 but I would imagine that that 45000 number isn’t going to change all that much.

      Second there are many place near downtown that unless you tear out a whole bunch of buildings the only way to increase capcity on I-5 is to tunnel which reverts back to your original complaint.

  5. Norman, once again you are missing the point. There’s more to it than just be energy efficient. But, I guess you only read and listen to what you want to.

  6. While this is being built, Seattle must begin construction on at least a couple more light rail lines if this city wants to complete at a global level. The East Link should continue west along Seattle’s waterfront to Magnolia and terminate in Ballard. Another line needs to be built from West Seattle through downtown and run through Fremont, the Zoo, and cross the Central Link at Northgate and terminate in Woodinville passing through Lake City and Kenmore.

    If Seattle takes its time building one tiny segment at a time, light rail will not be finished for another hundred years.

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