Drilled Caissons

what are drilled caissons?

Drilled caissons are very high-capacity deep foundations typically installed when competent bedrock is encountered within about 150-ft from ground surface. Typical caisson diameters range from 9- to 36-inches with capacities achieved in excess 5,000-tons. A permanent steel casing, 0.5- to 0.75-inches thick is advanced through the overburden soils and seated into the bedrock. A roller bit or down the hole hammer is then used to drill a rock socket. The borehole is cleaned of cuttings and typically video inspected for bedrock quality. Steel reinforcing cages are then installed to the bottom of the rock socket and grout or a high slump concrete is tremied from the bottom of the rock socket to the top of the casing.

what are the advantages of drilled caissons?

Caissons can support substantial structural loads by transferring forces directly into competent rock, making them well suited for heavily loaded structures and high-rise construction. By extending into competent bedrock, caissons can provide a predictable foundation bearing condition even where weaker soils exist near the surface. Caissons are installed through drilling rather than pile driving, significantly reducing vibration and making them suitable for construction adjacent to existing buildings and sensitive infrastructure.