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  • Aug. 22 project update: Bertha passes the 4,000-foot mark

    Seattle Tunnel Partners crews have now mined more than 4,000 feet as they continue their push toward the SR 99 tunnel’s future north portal. As of this morning, Bertha, the SR 99 tunneling machine, had traveled approximately 4,000 feet of the 9,270-foot-long tunnel route, and installed 607 of the concrete rings that form the tunnel’s exterior walls. 
    The top of the cutterhead is approximately 165 feet below the centerline of First Avenue, approaching Union Street. Crews will continue mining beneath First Avenue for several blocks. Then, at Stewart Street, where First Avenue veers to the west, tunneling crews will continue mining north en route to the spot near Seattle Center where Bertha will emerge
    As we’ve highlighted before (links to YouTube), the program has an extensive network of instruments in place to monitor ground movement. Crews continue to see little to no movement as they tunnel through a mixture of clay, sand and gravel beneath downtown.
    The entire tunnel route, including descriptions of each of the 10 zones through which Bertha is mining, can be found on our Follow Bertha page. Tunneling statistics are updated on that page on Mondays and Thursdays. You can also track Bertha’s progress on Twitter @BerthaDigsSR99.
    The SR 99 tunnel under First Avenue in Seattle
    A look at the SR 99 tunnel as it curves toward First Avenue. Other recent project photos can be seen here.
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  • Aug. 4 project update: New video highlights tunnel segments as Bertha nears First Avenue

    Bertha, the SR 99 tunneling machine, is approaching the intersection of First Avenue and University Street as crews with Seattle Tunnel Partners continue mining north beneath downtown.
    As of this morning, the tunneling machine had traveled a total of 3,518 feet and installed 533 concrete tunnel rings. The top of the machine is nearly 130 feet below street level. Earlier this week, crews successfully tunneled beneath the off-ramp that connects northbound SR 99 to Seneca Street. The machine passed approximately 90 feet below the the piles that support the ramp.
    Crews will continue tunneling north beneath First Avenue for several blocks. Their ultimate destination is a receiving pit near Seattle Center, where Bertha will end her 9,270-foot-long journey beneath downtown.
    The building blocks of the SR 99 tunnel
    Crews have now installed more than 5,000 curved concrete segments in the tunnel – each one weighing an average of 36,000 pounds. Bertha takes 10 of these segments and creates a five-story-tall tunnel ring, as shown below. 

    Steps of ring building

    A look at how each tunnel ring is pieced together by Bertha, the SR 99 tunneling machine.

    It will take 1,426 of these rings – or 14,260 concrete segments – to create the nearly two-mile-long tunnel. All the precast segments were built locally, at the Encon Washington plant in Pierce County. Segment production wrapped up in fall 2014. Every segment is checked multiple times for quality before being brought into the tunnel for installation. This video shows you exactly what the tunnel is made of – building blocks of steel and concrete.


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  • Crews break ground on new off-ramp at the tunnel’s south portal

    South-end travelers will soon see their future access point from northbound SR 99 to downtown Seattle and SODO take shape near the stadiums. 
    Crews from Interwest Construction broke ground this week on a new bridge that will connect northbound SR 99 to South Dearborn Street when the SR 99 tunnel opens to traffic. Construction of the $3.56 million ramp is expected to last approximately nine months. 
    This work won't significantly affect the public because it will take place inside the existing south portal work zone, although it will require a few overnight closures on SR 99. We will keep the public informed as work progresses.
    South Dearborn Street Off-ramp Bridge   
    The above rendering shows the future off-ramp from northbound SR 99 to South Dearborn Street, near the stadiums. Crews from Interwest Construction broke ground on the new ramp this week (below).
    Ramp construction begins
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  • #99closure feature: Drone footage inside the SR 99 tunnel

    Just a few days before the SR 99 tunneling machine started tunneling under the Alaskan Way Viaduct, the Washington State Department of Transportation flew a video-equipped drone through the SR 99 tunnel to show Seattle Tunnel Partners’ construction progress. There has been continued interest in seeing what has been built below ground and this video gives a glimpse of the tunnel as well as the nooks and crannies of the complex tunneling machine.

    On an average day, the tunnel is … more

  • The choreography of a concrete pour

    This week, at the south entrance to the bored tunnel, Seattle Tunnel Partners is pouring concrete for a section of the future southbound highway. On one hand, the pouring of concrete (also known as a "concrete placement”) is nothing extraordinary – it’s a common occurrence on a project that will use enough concrete to build nine football stadiums. But their frequency belies the complex choreography that goes into executing each pour successfully. Since concrete plays … more

  • Take a virtual tour of SR 99 tunnel construction

    Keeping the public informed about our work to replace the Alaskan Way Viaduct is an important part of what we do every day. Our goal is to give you as much access as possible to this amazing project, which is why we regularly post updates, photos and videos of our progress. We even offer walking tours from our information center, Milepost 31, to a viewing platform that overlooks the pit where tunneling began in summer 2013.

    Unfortunately, there’s one frequently received request … more

  • New narrated video explains Bertha repair work

    As reported elsewhere on our website, work to access and repair the SR 99 tunneling machine is coming along. We’ve heard from some people that Seattle Tunnel Partners’ repair plan is hard to picture. Enter STP’s Chris Dixon, who was nice enough to narrate a video that explains what crews are doing to resume tunneling by March 2015. Watch it on YouTube or download a WMV file.

    Other resources 

    Seattle Tunnel Partners repair work plan (pdf 4.8 Mb) … more

  • What we’re doing to keep traffic moving during the four-day SR 99 closure

    We’ve been asking you to do your part to reduce congestion when SR 99 closes for four days starting Friday night, Aug. 22. That includes things like changing your commute habits and choosing an alternate way to get around.

    But what are we, the agencies tasked with keeping traffic moving during this closure, doing to help? Quite a bit, actually. Here’s a roundup of some of the steps we’re taking to help you and your fellow commuters through the closure.

    Washington … more

  • Traffic shift underway on State Route 99 near the stadiums

    Less than three years ago, crews demolished the southern mile of the Alaskan Way Viaduct. When they did, they shifted traffic onto a new section of State Route 99 south of downtown Seattle.

    Much of that new section of SR 99 is permanent, but the piece west of the stadiums is temporary. This curving stretch of road takes drivers around the SR 99 tunnel construction site and connects to the remaining section of the viaduct near South King Street. It’s nothing fancy, but it’s … more

  • Celebrate Bike Month on our new path

    Just in time for Bike Month, we opened a new permanent connection between the on-street bike lanes south of South Atlantic Street and the shared-use path from South King Street. Here’s a map that shows the improvements, which include:

    A dedicated, 14-foot-wide shared-use path with improved paving.

    Improved lighting.

    A separate northbound and southbound path for more efficient navigation.

    Signs warning of vehicles crossing the intersection of … more