Latest Program News

  • Stuffed to the grates: filling complete in Seattle’s Battery Street Tunnel

    Contractor crews working on Battery Street in Seattle completed a major milestone in the rebuilding of SR 99 through Seattle. And it’s possible nobody walking or driving nearby even noticed. In late September, crews completed the filling of the Battery Street Tunnel.

    The Battery Street Tunnel once carried SR 99 between Aurora Avenue North and the Alaskan Way Viaduct. After the SR 99 tunnel opened in February 2019, crews began methodically removing the old tunnel’s mechanical and electrical systems, installing new utilities, and filling the structure. Much of the Battery Street Tunnel was filled with recycled concrete from the demolished Alaskan Way Viaduct. The final seven feet was filled with lightweight concrete pumped through ventilation grates along Battery Street. You can see photos of this process on our Flickr page

    Two photos of of the same view of the Battery Street Tunnel entrance. In the top photo, traffic drives in and out. In the bottom photo, the space where the lanes had been is a dirt slope.

    Above: A before-and-after view of the Battery Street Tunnel's south portal.

    Through the rest of the year, contractor crews will continue their work along Battery Street, building ADA ramps at each intersection, removing and paving over the tunnel’s ventilation grates and fan boxes, and installing new lighting. The Battery Street Tunnel’s south portal will be also be turned into a slope and seeded with grass, then handed over to the City of Seattle.

    Seventh Avenue North work also wrapping up

    At the north end of the old Battery Street Tunnel, construction work is almost complete. The trench of highway lanes into and out of the tunnel that once prevented east-west travel between Denny Way and Mercer Street is now Seventh Avenue North. This new, three-block-long roadway offers bus lanes to help transit travel times, new signalized intersections for safe east-west crossings, and will support future bicycle and pedestrian corridor improvements along Thomas Street. The work has reconnected the South Lake Union and Uptown neighborhoods, as you can see in this video.

    Although the project is nearly done, construction barrels will remain visible along Seventh Avenue North into early next year when a signal pole for the Denny Way intersection is expected to be installed and turned on.

    What remains for the Alaskan Way Viaduct Replacement Program

    The program to replace the Alaskan Way Viaduct has involved 30 separate projects. When the North Surface Streets and Battery Street Tunnel work concludes, that previously long checklist will be down to just two: rebuilding Alaskan Way (the project overseen and managed by City of Seattle’s Office of the Waterfront), and the South Access Surface Streets Connections project near Seattle’s stadiums.

    The South Access project will complete roadway work between South Atlantic Street and South Dearborn Street in SODO. Sections of street and sidewalk that have been paved temporarily by asphalt will get longer-lasting concrete pavement. We will build a section of a new pedestrian plaza that will link Occidental Avenue to the new pedestrian amenities along Alaskan Way, connecting the waterfront to the stadiums. The project will also build a section of bicycle and pedestrian trail. Work on that project is scheduled to begin in spring 2021.

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  • Final filling begins for the Battery Street Tunnel

    The final ingredient in the layer cake that is filling up Seattle’s Battery Street Tunnel is being mixed starting this month. Crews have begun pouring a special type of concrete into the tunnel through ventilation grates and holes in the tunnel’s roof. This flowable material will fill in the remaining space within the old SR 99 highway tunnel.
     
    Crews working for the contractor, Kiewit, are starting the pouring at Denny Way, the tunnel’s north end. The low-density cellular concrete (LDCC) is mixed on-site with mobile equipment staged adjacent to Borealis Avenue. The mixing plant will stay there for several weeks, then move to the Battery Street Tunnel’s south portal, which is adjacent to First Avenue. Over the next several months, crews will pump LDCC from the south portal area using a series of  hoses placed along Battery Street.
     
    Trucks and construction equipment positioned on edge of Borealis Avenue
    Above: LDCC mixing equipment staged along Borealis Avenue, just south of Denny Way

     

    What is low-density cellular concrete (LDCC)?

    LDCC is produced by mixing water and slurry (a liquid form of concrete) and then injecting a foaming agent. This process produces a kind of concrete meringue that is lightweight and does not get as hard as typical concrete. The material’s lightweight property helps protect the utilities beneath it from excess weight, while its lower strength will allow future crews to dig through it when required to reach those utilities. A 5-gallon bucket of LDCC weighs about 20 pounds, versus 100 pounds for standard concrete.

    This final stage of filling will use approximately 40,000 cubic yards of LDCC to fill the roughly nine vertical feet left in the tunnel. This is a lot of material – by comparison, CenturyLink field reported using about 10,000 cubic yards of concrete in its construction.

    The LDCC is the third type of fill material crews have used in the Battery Street Tunnel. First, crews poured crushed rubble produced from viaduct rubble into the tunnel with trucks from the surface. This spring and summer, crews have been filling the tunnel with Controlled Density Fill concrete (CDF) around the new utilities to protect them from heat and impact. The LDCC is the final layer in the cake, filling in the headroom between those utilities and the tunnel’s roof.

    What should I expect during construction?

    People traveling in the area should expect single-lane closures on Battery Street and cross streets between First and Sixth avenues, and along Borealis Avenue between Sixth Avenue and Denny Way. The batch machinery and idling trucks will also produce an increase in noise and possible vibration.

    Construction equipment staged adjacent to a gravel patch with Seattle skyline in background

    Above: The mobile LDCC mixing plant staged along Borealis Avenue.

    More work to come

    Fully filling the Battery Street Tunnel is not the end of the job. Once the LDCC is poured, crews will be able to turn to improving the surface of Battery Street. This work has already begun on some blocks, and includes patching over the tunnel’s ventilation grates, building new sidewalk and ADA-compliant ramps, and installing new street lighting. The tunnel’s south portal has been the construction staging yard for the job and will be turned into a slope and then handed over to the City of Seattle. All work on the project is expected to conclude in 2021.

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  • Limited construction resuming on Seventh Avenue North and in Battery Street Tunnel

    Last week crews working for Kiewit Infrastructure West Co. resumed limited work on the North Surface Streets and Battery Street Tunnel projects. Work in these two areas had been suspended since March due to the COVID-19 pandemic. This low-risk work is occurring in accordance with guidance from Governor Inslee and adhering to the state’s required safety plans required of all contractors.


    Work on Seventh Avenue North

    Orange construction barrels run down the middle of Seventh Avenue North

    Above: View looking north along Seventh Avenue North at Thomas Street. The barrels mark where center median construction will resume.

    Before work was suspended, crews had begun building the permanent center medians on Seventh Avenue North. Crews will soon begin breaking out asphalt in the middle of the street where the permanent, planted medians will be built. Forming the concrete curbs and landscaping will come later, when additional types of work are approved. Some turn restrictions remain in place between Denny Way and Harrison Street.


    Work on Battery Street

    Construction equipment sitting on dirt slope with buildings in background

    Above: Construction equipment staged at the south portal of the Battery Street Tunnel, just west of First Avenue. Restoring this area is one of the elements of the project still to be completed.

    There is a substantial amount of work remaining to decommission and fill the Battery Street Tunnel, with construction scheduled to extend into 2021. This includes utility work as well as filling the final (top) seven feet with a low-density concrete. Above ground, on Battery Street, crews still have street restoration activities to complete, such as building ADA-compliant curb ramps and removing and patching over the tunnel’s ventilation grates.

    This month crews are beginning limited work inside the tunnel, preparing for the time when tunnel filling can safely resume. When additional construction activities are cleared to resume, crews will begin pouring and forming ADA-compliant ramps along Battery Street at its intersection with First, Second, and Fourth avenues.

     

    Looking ahead

    “Phase Two” of Governor Inslee’s restart plan will allow a wider range of construction activities. On our project, that will include much of the construction that remains. In addition to the work activities noted above, work will resume at the intersection of Seneca Street and First Avenue. There, crews will rebuild the sidewalk on the west side of First Avenue and do other restoration activities associated with the viaduct off-ramp that used to terminate at the intersection. We encourage our neighbors to subscribe to our construction emails for updates on when that work will resume.

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  • Status of project construction work

    In March, the Washington State Department of Transportation suspended work on nearly all of its construction projects statewide. This included most Alaskan Way Viaduct Replacement Program construction on the Battery Street Tunnel and the North Surface Streets projects.
     
    Last Friday, Governor Inslee issued new guidance on the conditions under which low-risk construction may resume. WSDOT is requiring all contractors to develop plans that adhere to the safety protocols outlined in the Governor’s direction. WSDOT and our contractor Kiewit will work closely to identify which project elements may be resumed, and the safety plans and protocols that must first be in place to protect the safety of crews and the public at large.
     
    Certain types of work deemed critical were exempted from the March work-suspension order. On this project, that work entails:
    • Installing a water line at South King Street. That work began in early April and continues, with crews working daytime hours and completing work in accordance with CDC guidelines to ensure the safety of crews and the public.
    • Upcoming weekend work at First Avenue and Seneca Street. This work, at the abutment of the old viaduct off-ramp, requires deactivating the overhead bus trolley wires. This weather-dependent work is planned for May 9-10. Crews plan to work extended daytime weekend hours (6 a.m. - 8 p.m.), and the work will reduce First Avenue to one lane in each direction from 6 a.m. Saturday, May 9 to 6 a.m. Monday, May 11. 

    Work on the Battery Street Tunnel and Seventh Avenue North remains temporarily suspended. Once plans are in place to address safety protocols, crews will begin working on both projects.

     
     
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