TUNNELING IN SEATTLE - THE LONG AND SHORT OF IT

This article offers a historical overview of tunneling in Seattle, Washington. The diverse and complex geology of the region has had major impacts on the selection of construction methods as well as the success or failure of tunnel projects. The article mentions the geological difficulties that were encountered in the construction of the original Mt. Baker Ridge Twin Highway Tunnels built in the early 1940s. The new Mt. Baker Ridge Tunnel which was built between 1983 and 1986 is the largest diameter soil tunnel in the world. The single bore design was mandated by a group of property owners who feared the settlement problems associated with the original twin tunnels and thought that a single bore would limit the width of the settlement trough. The article briefly describes the process involved in the construction of this triple-deck, five lane highway tunnel. The article concludes with a look at the challenges that lie ahead for tunnel projects in the Seattle over the next ten years and how state-of-the-art technologies will be used meet the requirements of deeper and longer tunnels.