In civil engineering, caisson represents watertight structures, constructed in connection with the excavation of foundations in bridges, piers, river and lake dock structures, future conservation, and more. The caisson remains in its nostrils and thus eventually becomes an integral part i.e a permanent structure. It can be made of wood, steel or reinforced concrete, etc.

Caisson foundation

When caisson is required:

The following conditions are appropriate for the foundation:
  • When there are large boulders in the soil, which impedes the penetration of the pile.
  • When a large sub-construction is required to extend under or over the back bed to provide resistance against destructive forces caused by floating objects and scores, etc.
  • When the foundation is subjected to a large lateral load.
  • When the water level in the river and sea is high.
  • When there are river forces involved in load compositions.
  • When a load is required to carry at the end, the caisson is preferred.
  • Caissons are suitable when current groundwater levels are aggressive flows.

Mechanism of caisson:

Caisson is a box but there is no floor below it. Therefore, when we place it underwater instead of filling it with water, it becomes airtight, bubbles. Therefore, we have a dirt floor from which all the water is kept out. But the water is heavy, so the surface of the water is increasing the pressure on the caisson and tries to enter the caisson. So, to solve this, we make a platform in the top and a tube connecting the caisson to the platform that suppresses the pressure on the surface of the caisson. The front pressure and chamber pressure are equal, therefore. The workers climb into the compartment and they start digging dirt out of it. Now if the dirt is taken out manually, all the water will come in and submerge everything. To solve this, we construct a pipe filled with water. The air pressure from the atmosphere and the pressure inside the caisson retain the water in the pipe. Next, workers send a bucket through the pipe and fill it with dirt and then take it back up. Thus, the workers can dig their way down the river.

Types of caissons:

There are several types of Caisson foundations.

Box caissons
Box cases have boxes with four arms and a floor. The top of these boxes is open. The concrete box is fabricated on the ground. The prepared box caisson is placed at the foundation location and pre-prepared bases. Once placed in a suitable location, the entire void space is filled with concrete in such a way that it becomes an integrated part of the already prepared base.
Box caissons are used to construct bridge ghats.
Box caissons are less expensive. Caissons are required when this is not possible for building site types.

Excavated caisson
This type of caisson is used for digging. Cylindrical in shape, these caissons are filled with concrete.

Floating caisson
These are prefabricated boxes filled with concrete. It is also called a floating deck.

Open caisson
Open caissons are very much like box caissons. There are two types of open caissons. Both top and bottom open and open-top closed bottom. Soft soil is suitable for this type of caisson. Open signs are used in the construction of ferries, deep manholes, pump stations, micro-tunneling, etc.

Pneumatic caissons
Watertight or box caissons that are used in underwater construction are known as pneumatic caissons.

Compressed Air Case caissons
These types of caissons are suitable for padded working conditions where other methods may seem inconvenient.

Monotholic caisson
The large size of caisson compared to others.

Manufacturing process:

The following steps can be followed to create a caisson.

  • We should first determine the place for the establishment of the caisson.
  • This is followed by Caisson's first 3.7-meter pre-cast.
  • Subsequently, with the help of a towboat, the caisson is taken in its place and tied into the caisson guide.
  • After that, concrete is poured using slip forming and as the concrete goes, the box becomes heavy and is submerged in water with casein guides.
  • Mooring cables are used to hold caissons in place.
  • When the caisson finally touches the bottom of the river, the mooring cables are removed.
  • Finally, the cap is inserted.