What is the function of a 'caisson' foundation?

The function of a caisson foundation is to provide a stable and robust foundation for offshore structures, particularly in situations where the seabed soil is weak or unstable, or where significant scour (erosion) is expected. A caisson is a large, hollow, watertight box or cylinder that is sunk into the seabed to provide a foundation for a structure. Caissons can be made of steel or concrete and are typically prefabricated onshore and then towed to the offshore location. Once in place, the caisson is sunk by ballasting it with water or other heavy materials. The soil inside the caisson is then excavated, and the caisson is further sunk until it reaches a suitable bearing stratum. The bottom of the caisson is then sealed, and the interior is filled with concrete to provide a solid foundation. Caissons are particularly useful in areas where the seabed soil is too weak to support a traditional pile foundation or where scour is a concern. They provide a large bearing area and protect the soil beneath the structure from erosion. For example, caissons are used to support gravity-based platforms in areas with soft clay soils or to protect bridge piers from scour in riverbeds.