SR99 viaduct demolition next phase in Seattle 24 May 2018

TunnelTalk Reporting

As construction of the SR99 replacement highway tunnel in Seattle nears its completion, demolition of the existing aging and earthquake-damaged Alaskan Way viaduct is part of the next stage of the US$3.3 billion project that will transform the waterfront and upgrade traffic flow through the city.

Earthquake damaged viaduct to be demolished
Earthquake damaged viaduct to be demolished

Demolition of the viaduct and backfill of the existing Battery Street tunnel as part of the SR99 route through the city is awarded as a $93.7 million design-build contract by the Washington State Department of Transportation (WSDOT) Kiewit Infrastructure West. The contract also includes construction of street connections at the north end of the project that will redirect traffic off the existing SR99 route and into the new highway tunnel replacement.

Route of existing and new SR99 highway
Route of existing and new SR99 highway
Impression of revived Seattle waterfront
Impression of revived Seattle waterfront

The work is to be scheduled once the new tunnel is commissioned, which WSDOT estimates could be as soon as Fall this year (2018) once all the M&E equipment is installed and tested and based on the schedule by tunnel construction contractor STP (Seattle Tunnel Partnership). With traffic realigned into the new tunnel the viaduct and be closed permanently and work on its demolition can begin in late 2018 and continue through 2019.

In addition to the demolition of the viaduct, the equipment within the Battery Street tunnel will be removed and the underground roadway will be backfilled (Fig 1). The tunnel was constructed in the 1950s and while several ideas had been considered for alternative uses for the tunnel, its age and condition would require significant and costly structural and system upgrades to be safe for any ongoing use. As a result WSDOT has a legal obligation to decommission the tunnel. The work is part of the design-build contract with Kiewit and is expected to take up to two years to remove equipment, seal and backfill the structure and also carry out utility improvements along Battery Street.

Once the new tunnel route is opened and the viaduct is removed, the waterfront of Seattle will be transformed. The viaduct barrier between the city and its waterfront will be removed, the business and tourist activities and entertainment will be revitalised and the heavy through traffic of the SR99 route will be replaced underground through the new double-deck tunnel and replaced with just local traffic roads along the waterfront.

“We are excited to be so close to removing the seismically vulnerable viaduct and ushering in a new era on Seattle’s waterfront,” said Brian Nielsen, WSDOT’s Alaskan Way Viaduct Replacement Program Administrator. “It will be challenging to tear down a major highway in the heart of a booming city but we are looking forward to getting it done safely and as quickly as possible.”

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