What Is a Caisson in Construction: An In-Depth Guide

May 22, 2024

In the realm of geotechnical engineering, caissons play a pivotal role in enabling underwater construction tasks such as building bridge foundations, constructing concrete dams, and repairing ships. Designed as watertight retaining structures, caissons allow water to be pumped out, maintaining a dry working environment below water.

Historical Usage

Caissons have been a fundamental component in engineering for centuries. During the 19th century, they were utilized in monumental structures like the Royal Albert Bridge, Eads Bridge, and Brooklyn Bridge.

Types of Caissons

Box Caisson

A prefabricated concrete box with a bottom, box caissons are typically set on prepared bases and filled with concrete to become part of the permanent structure. To prevent floating, they must be ballasted or anchored securely.

Open Caisson

Similar to a box caisson but without a bottom face, open caissons are suitable for soft clay environments but not ideal where large ground obstructions exist. These caissons may include additional loads from above to aid sinking, and piles might be driven to stabilize unstable soils.

"Construction of south anchor pier caissons, 17 January 1936" by Queensland State Archives is marked with Public Domain Mark 1.0. To view the terms, visit https://creativecommons.org/publicdomain/mark/1.0/.

Pneumatic Caisson

Featuring a bottomless box sealed at the top, pneumatic caissons use compressed air to keep water and mud out. Equipped with airlocks for worker access and a muck tube for soil removal, they have historical significance but pose health risks like decompression sickness and barotrauma.

Monolithic Caisson

Larger than other types and similar to open caissons, monolithic caissons are used in quay walls to provide impact resistance from ships.

Construction Techniques and Challenges

To maintain the stability of caissons, ballasting and anchoring are essential until they can be filled with concrete. Hydraulic jacks and bentonite slurry are often utilized to aid sinking and reduce friction. When dealing with high water tables, it is crucial to balance upthrust forces to prevent sinking, sometimes requiring piles as load-bearing walls or anchors. Decompression safety is also critical to avoid 'caisson disease' during construction.

"Site J - Caisson Construction" by MTA C&D - EAST SIDE ACCESS is licensed under CC BY 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by/2.0/.

Additional Uses and Meanings

Beyond their traditional uses, caissons are employed in various engineering applications. They are used in hydraulic elevators for installing below-ground rams, in Mulberry harbors during World War II for the Normandy invasion, and in boat lifts and structural contexts. In hazardous material facilities, caissons serve as airtight housings for ventilation filtration systems.

Related Concepts

Several related concepts include suction caissons, which are anchoring structures with open bottoms, air lock diving-bell plants for underwater work support systems, and cofferdams, which are temporary structures similar to open caissons used for water exclusion during construction.

Historical Innovators

Patent references highlight the long-standing significance of caisson technology in engineering. Notably, U.S. patent 123,002 details the construction of sub-aqueous foundations, showcasing the ingenuity and innovation in caisson application over the years.

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