April 12, 2016

Two-week viaduct shutdown is likely to be next month: WSDOT

Photo by Benjamin Minnick [enlarge]

Traffic will be allowed below the viaduct while it is closed between Battery and South Spokane streets.

In a presentation before Seattle City Council yesterday, WSDOT deputy program administrator Dave Sowers said the Alaskan Way Viaduct is likely to be shut down next month while the tunneling machine named Bertha digs below it.

Sowers said the shutdown will last about two weeks so Bertha can dig about 300 feet under the aging viaduct. He said the machine will travel at a high skew angle below the viaduct, not perpendicular to it.

The viaduct will be closed between Battery and South Spokane streets.

A project update posted yesterday by WSDOT said crews from Seattle Tunnel Partners have finished inspecting and replacing cutting tools on the machine's face. For about month, Bertha has been sitting at a planned maintenance stop near Yesler Way next to the viaduct.

STP crews have completed more than 100 shifts of hyperbaric work inside the tunneling machine. They replaced only 11 of the more than 700 tools because most of the tools were replaced during a two-year repair that necessitated construction of a 120-foot-deep rescue pit about 400 feet south of the maintenance stop. That operation removed Bertha's 2,000-ton cutterhead and brought it to the surface for repairs.

WSDOT program administrator Todd Trepanier said crews at the maintenance stop still need to work on sensor systems and inspect the ribbon screw assembly, as well as the polymer injection system used in the soil extraction process.

Once STP is done with its maintenance, the machine will have to wait two weeks to resume tunneling.

That time will be used to educate commuters about how the closure will affect them.

Trepanier said cars and pedestrians will be allowed to travel below the viaduct during the closure. He said WSDOT will have a 24-7 command center set up during the dig that will be staffed with a decision-maker if quick action is needed, including closing all traffic below the viaduct.

The command center will also be able to coordinate with King County Metro and Seattle Department of Transportation for quick responses.

An SDOT manager said the agency is doing a number of things to help reduce the impact of removing 60,000 cars and 30,000 transit commuters that use the viaduct daily. Measures will include police directing traffic during rush hours at about a dozen choke-point intersections, limiting road closures at construction sites, eliminating parking on Fourth Avenue South, adding water taxis to Vashon Island and changing traffic signal timing.

SDOT will also have a temporary transit-only lane on Lenora Street in the mornings and on Blanchard Street in the evenings.

Metro will detour 12 bus routes that use the viaduct onto Fourth Avenue, Airport Way, South Lander Street, the Fifth Avenue busway and other streets.

Trepanier said the viaduct's semi-annual inspection last month found no new cracking.

STP has reinforced the viaduct in spots and installed micro-piles. Crews will work in two 12-hour shifts while digging below the viaduct.

More on the closure can be found at www.99closure.org.