Construction methods · Caissons and marine foundations

Suction caissons

An open-bottomed steel cylinder lowered onto the seabed and sucked in by pumping water out of the top, so the pressure difference drives it into clay or sand without a hammer. Quiet, reversible, and quick in the right soils; used for anchors, offshore jackets and increasingly for temporary and light bridge foundations.

How bridges get built · Caissons and marine foundations · Suction caissons

Also called: suction buckets, suction anchors

How it is done

Lower the bucket to the bed; let self-weight penetrate the first metres.
Pump water out; the differential pressure pushes the bucket to full depth (typically one to two diameters).
Set the structure on top; reverse the pumping to remove it.

Where it fits

Soft clay and fine sand seabeds, temporary works platforms, anchors for floating cranes and moorings, small piers in calm water.

Where it does not

Gravel, boulders and layered soils with sand over clay (piping), high-scour sites.

Plant, pace and money

PlantBucket, pumps and control, crane vessel.

ProductivityHours per bucket.

CostLow installation cost; steel dominates.

Risks and controls

What goes wrong

Piping failure in sand, tilt during penetration, scour around the rim.

Quality assurance

Penetration versus pressure logs, tilt monitoring.

Examples

North Sea platforms, offshore wind jackets; marine trestle foundations on a few projects.