Why is WSDOT taking these precautions with the viaduct but not with other buildings along the tunnel route?

Tags: 99closure, 99safety

Bertha and the top of the future SR 99 tunnel will come within 14 vertical feet of the bottom of one of the viaduct’s foundations. By contrast, the closest Bertha will travel to any other building foundation or structure is 40 feet. This proximity, combined with the sands and gravels of the soil in this area, make tunneling under the Alaskan Way Viaduct some of the most challenging mining conditions of the tunnel alignment.