Caisson foundation: Types, pros and cons

The Caisson foundation is a significant part of civil engineering used while constructing bridges, docks, etc. The word caisson came from capsa, which signifies box or box-like materials. The caisson foundation is also known as the pier foundation. It is a watertight water barrier structure used as a bridge pier. It is a pre-made hollow box or cylinder that sinks into the ground to a certain preferred depth and is then filled with concrete, thus forming a foundation.

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Caisson foundations are similar in shape to pile foundations but are installed differently. It is used when soils of proper bearing strength are found beneath layers of weak surface material such as backfill or peat. Below are mentioned various types and purposes of the caisson foundation and other significant information.

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See also: Pile foundation: Importance, application and types

Caisson foundation: Purpose

Caisson foundation is used in a few circumstances. Here are those.

When the ground contains large rocks that impede the penetration of the pile
Caisson foundation is used if you want a sturdy undercarriage that extends up to or below the rear deck to resist destructive forces from floats, cuts, etc.
When a sizeable lateral load is applied to the foundation
When the river or sea is deep
When the load configuration includes flow forces, caissons are preferred if luggage must be carried at the end.
Caissons are a good choice if the current groundwater table is actively inflowing.

know about: Piling foundation

Caisson foundation: Types

There are a few types of caisson foundations. These are as follows:

Box caissons: These are watertight boxes made of heavy wood and open at the top. They are typically floated to a suitable location and then dropped into place with a masonry pier.

Excavated caissons: These kinds of caisson foundations are set within an unearthed site. These are generally cylindrical and then backfilled with concrete.

Floating caissons: These are also known as floating docks and prefabricated boxes with cylindrical cavities.

Open caissons: Open caissons are very similar to box caissons. There are two types of open boxes: high and low, open and high open-low close. Soft ground is suitable for these types of caissons. Open caissons are used to form jetties, deep manholes, pumping stations, small tunnels, etc.

Pneumatic caissons: These are large watertight boxes or cylinders that are mainly used for underwater construction.

Compressed air caissons: This box type is suitable for dry working conditions where other methods will not work properly.

Monolithic caissons: This is a larger caisson foundation type than any other type.

Caisson foundation: Uses

Transfer loads on bridge piers and building columns to the hardest underground layer.
Caissons placed close together act as impenetrable core walls of earthen dams.
To make space for deep shafts or tunnels.
To erect any obstacles for placing machines, pumps, etc., in water.
To protect the foundation from lateral forces.

Caisson foundation: Advantages

Minimises the need for post caps.
It causes slightly less noise and less vibration.
Easily adaptable in any changing field conditions.
High axial and lateral load capacity.

Caisson foundation: Disadvantages

It is very sensitive to construction methods.
It is not suitable for legacy assets.
Only expert engineers can design the construction. There is a lack of qualified workers.
It creates a hazardous situation for workers; they may suffer from caisson disease.
There is a shortage of qualified inspectors.

FAQs

What is the difference between a pile foundation and a caisson foundation?

A pile is a type of deep foundation used to transfer the load of the superstructure to the ground. Caisson foundations are used to build underwater foundations. A box of steel or other material is set in an underwater bed to act as a water barrier. And when the foundation reaches the required depth, the box is filled with concrete.

What is the difference between a cofferdam and a caisson?

The cofferdam is a temporary foundation, and the caisson foundation is permanent.

Why is the caisson used?

Caisson is used as an anchor for any foundation and is fixed underwater. This foundation is used when a bridge of other construction needs underwater support for construction.

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