Photo courtesy of Lease Crutcher Lewis Lease Crutcher Lewis completed a 42-foot-deep garage excavation for Starbucks’ 505 First Avenue South building, digging 35 feet below the water table.

Lease Crutcher Lewis faced many challenges constructing a 292,000-square-foot, seven-story office building between two historic buildings and the Alaskan Way Viaduct, beginning with a garage excavation that extended 42 feet below grade.

The water table was only 7 feet below grade, so to keep the building from floating, 370 “hold down” anchors were installed below the 5-foot mat foundation.

For shoring, the Lewis team chose a cutter soil mix subterranean wall, an approach new to Seattle. It allowed for the drilling precision and vibration control necessary to protect the century-old sewers and structures around the site.

The shoring required 450 tiebacks coordinated using building-information modeling to avoid conflicts with soldier piles belonging to adjacent buildings. The fill material consisted of debris from old wharfs and piling, and the 1889 Great Seattle Fire. Artifacts from this period discovered during the excavation required an archeologist to be on site during much of the digging.