Rainier Square Tower’s Shoring System
The Rainier Square Tower is situated in downtown Seattle, spanning nearly an entire city block. This impressive skyscraper stands at 850 feet in height, boasting 58 stories of mixed-use spaces. At the time of its construction, it ranked as the second-tallest building in Seattle. Just next to the excavation site for this skyscraper, the Rainier Tower (constructed in 1977) towered over as the excavation extended 60 feet below the bottom of its foundation. The excavation reached a depth of 87 feet below grade and required 85,000 square feet of shoring, utilizing soldier beams, lagging, and 80-foot-long tie-backs.
The soil conditions comprised 15 feet of fill, followed by 30 feet of silty sand, and 50-60 feet of clay with slickenside characteristics due to the nearby Seattle fault zone, followed by Glacial Till. In the deepest excavation areas, a secant pile shoring wall with tie-backs was installed to address potential settlement concerns related to the nearby Rainier Tower.
