SR 520 Bridge Replacement Study
Washington State Department of Transportation (WSDOT)
Map of Montlake/University of Washington Area, showing Union Bay and the Montlake Cut. Any tunnel alignment would be constructed across either one of these bodies of water
Montlake Cut Tunnel Expert Review Panel:
The Washington State Department of Transportation is addressing the need to ease bridge traffic congestion by replacing the existing SR 520 Bridge with a 6-Lane bridge capable of withstanding earthquakes and severe storm events. An additional part of the plan involves the road interchange on the western side of the bridge, for which NATM tunneling options have been discussed.
Gall Zeidler Consultants were part of the Montlake Cut Tunnel Expert Review Panel. The purpose of this panel was to evaluate the feasibility and advantages and disadvantages of all tunneling options for the interchange connection from the SR 520 mainline just east of Montlake, to the University of Washington. The tunnel options included an immersed tunnel, a tunnel boring machine (TBM) tunnel, and a New Austrian Tunneling Method (NATM) tunnel.
- LOCATION:
- Seattle, Washington
- DATE:
- June 2008
- STRUCTURE:
- Two-lane tunnel
- Length:
- 800 – 1,000 feet (240 – 300 meters)
- CROSS-SECTION:
- 1575 square feet (146 square meters)
- GEOLOGY:
- Mix of hard to very dense clay, till, sand and gravels at the bottom of Union Bay and Montlake Cut.
- Cost:
- —
- CLIENT:
- HDR Inc.
- Owner:
- Washington State Department of Transportation