The Rainier Square Tower is located in downtown Seattle and encompasses almost an entire city block. It is an 850-foot tall, 58-story mixed-use skyscraper and at the time it was constructed, it was the second-tallest building in Seattle. Immediately adjacent to the excavation for this skyscraper, Rainier Tower (built in 1977) loomed above as the excavation advanced 60 feet below the bottom of its foundation. The excavation stopped at 87 feet below grade with 85,000 square feet of shoring using soldier beams, lagging, and 80-foot long tiebacks.
Soil conditions consisted of 15 feet of fill over 30 feet of silty sand and 50-60 feet of clay with slickenside characteristic due to the nearby Seattle fault zone followed by Glacial Till. Where the excavation was deepest, a secant pile shoring wall with tiebacks was installed to mitigate any settlement issues of the nearby Rainier Tower.