As we move closer to the 2019 milestone of opening the new State Route 99 tunnel under downtown Seattle, officials can start making plans for removal of the aging Alaskan Way Viaduct, the entire reason the new 1.7-mile tunnel was conceived originally.
Since boring has wrapped on the tunnel and crews continue to build the double-decker roadway inside the structure, plans have started on removing the in-use viaduct. Built in the 1950s to carry roughly half the number of vehicles it handles today, the structure has showed its age, sped up by the 2001 Nisqually Earthquake which required repairs to the viaduct.
Demolition work on the viaduct is now scheduled for early 2019, following the opening of the tunnel to traffic. Demolition is expected to take up to nine months, with the viaduct getting demolished in sections to minimize localized disruptions. The contract will also involve other project elements, such as filling in the Battery Street Tunnel and reconnecting surface streets across Aurora Avenue North.
Several weeks before the new tunnel opens, WSDOT will shift Alaskan Way to the west of the viaduct, allowing traffic to move along the waterfront before and during viaduct demolition.
As part of the timetable for removal, WSDOT plans to send out a request for qualifications for contractors and develop a request for proposals this summer. Late in 2017, WSDOT expects to issue a RFP to the most qualified contractors, with proposals due in early 2018 and the contract awarded to the best-value contractor shortly thereafter.
The best-value approach incudes a design-build contracting method that WSDOT says encourages “innovative and cost-effective proposals.” By giving contractors greater flexibility, WSDOT hopes to lean on the expertise and experience of the contractors.
Over spring and summer 2018, the contractor must develop its demolition plan and be prepared for preparation and work in late 2018, with actual demolition of the concrete structure in early 2019. WSDOT plans for the viaduct demolition to wrap up in fall 2019 and the Battery Street Tunnel decommissioning and Aurora Avenue North connections to finish in mid-2020.
WSDOT has successfully completed one mile of viaduct demolition, but that, done in just eight days in 2011, is quite different from the section still standing, which sits much closer to buildings, businesses, homes and the busy Colman Dock ferry terminal.
Demolition will require shifting Alaskan Way west from beneath the viaduct, removing the viaduct from South Dearborn Street to the Battery Street Tunnel, removing the Columbia Street and Seneca Street ramp structures, removing a majority of the viaduct’s 397 foundations and footings to five feet below ground, decommissioning the Battery Street Tunnel and restoring Aurora Avenue North between Harrison Street and Denny Way and restoring roadways, sidewalks, street lighting and other elements to a temporary condition until the City of Seattle builds the new waterfront.
Follow Tim Newcomb on Twitter at @tdnewcomb.