What is caisson construction?
Caisson construction is a construction method that uses a watertight structure that is sunk through ground or water to exclude water and semi-fluid materials during the excavation process and subsequently becomes an integral part of the structure.
This watertight structure is often referred to as a “caisson foundation”. The caisson construction method can be used for a wide variety of applications including, but not limited to:
- Deep foundation construction where the foundation will be extended up to or below the river bed to ensure proper stability.
- Constructing piers and abutments in rivers and lakes, bridges, breakwater dock structures, etc.
- When a good foundation is to be constructed underwater.
- Building a foundation for bridge piers, and abutments in rivers, seas, lakes, breakwaters, and other similar shore construction work.
- Pumphouse construction in which is subjected to huge vertical as well as horizontal forces.
Caisson foundation construction is also occasionally used to build large and multi-story buildings and other structures.
Material, shapes, types
There are a variety of different types of caisson foundations made with different materials and in different shapes:
- Materials: Caisson foundations are made of either wood, steel, or reinforced concrete.
- Shapes: Caisson foundations can be everything from circular and square to rectangular and octagonal.
- Types: There are three main types of caisson foundations, the open caisson, the box caisson, and the pneumatic caisson.
The caisson foundation construction process
Here’s how the process of caisson foundation construction works:
- After some initial formwork and concrete pour, the cutting edge is floated to the breakwater by a towboat and fastened to the caisson guide. Concrete is placed into forms built up along the perimeter of the caisson. With every concrete placement, the caisson becomes heavier and sinks into the water along the caisson guide.
- Forms are also built inside the caisson around the air domes and concrete is placed in between them. This results in open tubes above the air domes that are called “dredge wells”.
- When the caisson touches the river bottom, the air domes are removed and the soil is excavated through long dredge well tubes. The caisson sinks to the bottom of the water body. Excavation continues until the caisson sinks to its predetermined depth.
- As a final step, concrete is placed into the bottom of the hollow dredge wells and the tops are sealed.
There are a number of requirements to be able to perform caisson construction. The most crucial factors include the height of the concrete lifts and the length of the reinforcement bars. As is the case with any type of construction method, caisson construction needs to be carried out with great precision and accuracy for successful results.
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