The City of Grand Forks, North Dakota obtains drinking water from both the Red and Red Lake Rivers using a system of river intakes, shallow pipelines, and pump stations. However, during flood events, the City often loses access to the system, and persistent landslides along the riverbanks easily damage shallow components. As a result, the City decided to construct a gravity system with new pipelines leading to the base of a 65-foot deep pump station. Several construction techniques were evaluated for the pump station, including a self-sinking caisson, which was chosen for the project. Because the proposed 60-foot-diameter caisson was larger and would be sunk deeper than any previous caisson in the area, and would penetrate through a highly plastic, weak and brittle clay, FLAC soil-structure interaction analyses were completed using a strain-softening soil model. The paper discusses the results of the modeling and the subsequent design steps taken to avoid bottom instability. The paper also describes the construction process
