Caisson sinking is a construction technique in which a prefabricated hollow structure (the caisson) is built at ground level or above water and then gradually sunk into position by excavating material from underneath it. The weight of the structure, sometimes assisted by additional ballast, causes it to descend as soil or sediment is removed from its interior.
How it works
The process begins with constructing the caisson — typically a reinforced concrete box or cylinder — on the ground surface or on a temporary platform. The lower edges are fitted with a cutting shoe, a hardened steel or concrete edge designed to slice through soil. Workers or machinery excavate the material inside the caisson, allowing gravity to pull the structure downward. As it sinks, additional sections of wall may be added to the top to increase height and weight. Once the caisson reaches the desired depth, the interior is filled with concrete to create a solid foundation.
Application
Caisson sinking is used in a variety of demanding construction scenarios:
- Bridge foundations — Caissons provide deep, stable foundations for bridge piers, especially in riverbeds where conventional excavation is impractical.
- Underground structures — Pump stations, intake shafts, and underground reservoirs are often built using this technique.
- Basement construction — In residential and commercial building, caisson cellars (afzinkkelders) are sunk into position to create underground living or storage space.
- Port and harbour works — Quay walls and dock structures frequently rely on sunken caissons.
Advantages
- Minimal disturbance to surrounding soil and structures
- Effective in areas with high groundwater levels
- Suitable for reaching deep, stable soil layers
- Construction of the structure can begin before excavation starts
Related terms
- Caisson cellar
- Sheet piling
- Deep foundation
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