A casting plant in Dearborn, Michigan, needed to build a 122x46-foot holding pit for its mill scale. Unfortunately, the soil at the site was found to be extremely soft and silty clay. Since the soil wasn't stable, an unbraced excavation would be dangerous. An alternative method had to be found to excavate the site. Using a sinking caisson saved 9 weeks of construction time and 18 percent of the originally estimated construction costs. The sinking caisson works by using the drag force of the soil that acts against the exterior and interior caisson walls. Excavating the soil reduces the drag force along the interior walls, allowing the caisson to sink under its own dead weight. As the caisson slowly sinks, increasing its embedded length, the drag force increases because of more wall contact area.