Located a few feet from the soon-to-be-demolished Alaskan Way Viaduct, 450 Alaskan posed structural and environmental challenges.

Crews drilled within a foot of the foundations of the 1949 double-decker elevated viaduct while Bertha, the world’s largest earth pressure balance tunnel boring machine, maneuvered underground to dig the replacement tunnel. The team not only faced settlement risks posed by building adjacent to the vulnerable structure, but were also concerned about tower crane swings and driver distraction on the busy viaduct.

The team built formwork along the viaduct to minimize distracted driving and developed “no fly zones” for the tower crane. Workers also monitored viaduct bent supports twice a day during drilling. During excavation, crews dug 17 ft below the intricate underpinning of an adjacent historic brick-and-timber theater, which required significant stabilization. Excavation also included removing 40,833 tons of contaminated soil and an undocumented underground storage tank. The team built a complex secant pile shoring system along the perimeter to cut off shallow contaminated groundwater and installed monitoring wells.

Three sides of 450 Alaskan present a modern take on brick buildings, while a curtain wall covers the western facade. Installing a 40-ft totem pole in the lobby required a change to the schedule, since the tenant buildout overlapped with core and shell construction. The 170,000-sq-ft building features eight stories of office space.