Types of Caisson Foundation

Caisson Foundation is a watertight retaining structure which is used as a bridge pier or construction of dam. This foundation is used when the structures are above a river or similar water bodies. Caisson Foundation can be floated to the desired location and then sunk into place. It is a ready-made hollow cylinder kept into the soil and then it is filled with concrete which is mostly used as bridge piers. It is reasonable when the pile cap requirement is needed to be minimized, the noise and vibration is needed to be reduced and highly lateral loading capacity is required. It is constructed using various materials such as steel, timber, reinforced concrete and masonry.

We use caissons foundation when soil having sufficient bearing strength is located below surface layers of weak materials. It is built above the ground level and then drop down below the surface to the needed level by using digging material from within the caisson. 

There are various conditions for the need of the formation of caisson foundation. Caisson Foundation is needed to construct when the soil has large boulders that block the penetration of piles. It is built when a huge substructure is needed to provide resistance against the destructive forces caused by floating objects. If the foundation is kept through a huge lateral load then caisson foundation can be constructed. When the depth of the water level in the river and sea is high, it is suitable to prefer caissons. This type of foundation is also built when river forces are contained in the load compositions.

There are various types of caisson foundation which are listed below:

1.     Box Caissons
2.     Excavated Caissons
3.     Floating Caissons
4.     Open Caissons
5.     Pneumatic Caissons

Box Caisson Foundation

This type of caissons is a watertight box which contains timber or reinforced concrete and it is closed at bottom and open at top. It is sunk to the desired place after it is cast and cured on land. We use sand, concrete or gravel to sink the caisson and it is appropriate for the areas where the bearing strata is reasonably level.

Excavated Caissons Foundation

These types of caissons are filled with concrete which are used to excavate. Excavated Caissons are cylindrical in shape.

Open Caisson Foundation

These types of caissons are open from both sides at the top and at the bottom. It contains hollow chambers. There is a cutting edge at the bottom of the caisson. The soil inside of the chamber is removed till bearing stratum is reached and then the caissons are sunk into the needed place.

Pneumatic Caisson Foundation

This type of caissons is required when the soil enclosed in open caisson cannot dig satisfactorily through. Pneumatic caissons are closed at the top and open at the bottom. When a great rush of water and obstacle is predicted during sinking, we construct pneumatic caisson. It contains a working chamber at its bottom where compressed air is conserved at the needed pressure in order to prevent the water and mud from entering in the chamber. It has a similar construction method like open caissons but only the difference is the working chamber is kept airtight.

Floating Caisson Foundation

This type of caisson contains large hollow boxes which are open at the top and closed at the bottom. It is sunk to the destination by filling it with dry concrete, sand, gravel and ballast. These caissons are generally constructed with steel and its shape may be circular, rectangular, elliptical or square. It is designed as a ship when it is to be floated in rough waters.

Advantages of Caissons

1. We can excavate the bottom and pour concrete in dry conditions.
2. The obstruction like boulders or logs can be removed easily because there is entry to the bottom     of the caisson.
3. We get good and quality work as we can place dry concrete in it.
4. We can determine the soil bearing capacity by conducting in-situ tests in the working chamber.

Disadvantages of Caissons

1.     Caissons construction cost is high.
2.     It is not good to be constructed for polluted sites.
3.     There is a lack of construction expertise.
4.     There is a lack of qualified inspectors.

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