Shallow placement caissons can be unsealed, and left open on the top and bottom faces while they are dug into place. These may look similar to a braced excavation from the surface, but differ in their ability to be gradually repositioned to lower elevations.
Dredging or digging soils from within the caissons are the most common methods of material removal. Dredge pipes can be positioned within the caisson’s perimeter at key locations to remove enough supporting soil for controlled placement. Dredge spoil pipes attached to a pump system carry the waste soils to the surface. Digging by hand or with construction equipment is another common method. In any case, the removal of material within the inside base perimeter of the caisson allows it to incrementally sink lower into the soil.
Common challenges of caisson operations include hitting obstructions or inconsistent sub-grade materials during their placement, either of which can cause tilting of the leading edge and cause delays and additional costs. Another concern arises when digging the caisson through very cohesive soils such as soft clays. It is possible for the caisson to generate enough skin friction moving through cohesive soils that it becomes stuck in place.
