Caisson Foundation | Pneumatic Caisson | Drilled Caissons | Caisson Construction

Caisson Foundation

The caisson foundation is also called the deep foundation. Caisson means box, which is derived from the french word caisse. The caisson foundation is mainly done underwater. Caisson foundation is excavated before or after excavation.

The caisson foundation is mainly used of wood, RCC, and cast iron. There is a possibility of fire and erosion in the wooden caisson. So the caisson of wood is not especially used.

The caisson foundation is used as a foundation in the pier of the river bridge. Where dewatering is not possible caisson foundation should be done.

Use of Caisson Foundation

1. Doing caisson foundation gives a man a place to work.
2. Doing caisson foundation protects against bases and forces.
3. Dewatering is difficult; there is a useful caisson foundation.
4. The caisson foundation is economical when the depth is more than 12 mt.
5. The caisson foundation is useful where the river flow is high, and the water depth is high.
6. Caisson foundation can be embedded at any spot.

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Component Part of Open Caisson

1. Cutting Edge

The wall of the caisson is thick. So the cutting edge is placed at the bottom of the caisson. So that the soil is easily trimmed and the right level transferred. The cutting edge is made of iron.

2. Curb

1.0 mt to 1.5mt height of the cutting edge to the caisson wall, whose thickness gradually increases and becomes equal to the caisson wall.

The shape of the curb is triangular, which gives big space for excavation.

3. Staining

This wall starts from the curb to the height of the ground. It is made of masonry. Masonry walled caisson is used for the base in special circumstances.

The wall thickness is kept at 30 cm to 90 cm. The concrete wall is used more.

4. Bottom Plug

When the required depth is reached, the area is leveled and concreted.

When concrete is to be used in water, 10% more cement should be used in the bottom plug, making the foundation stronger.

5. Sand Filling

The sand filling is done in the middle of the caisson to increase the weight of the caisson.

6. Intermediate Plug and Top Plug

After sand filling, concrete is applied ON it. Its thickness is 30 cm to 45 cm. The base of the bridge is filled with sand up to the top. And concrete is made on it, which is called top PLUG.

7. Cap

Concrete is made in the same diameter as the caisson wall, which is called top cap.

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Type of Caisson Foundation

The type of caisson depends on things like size, shape, depth, and type of construction, etc. There are three types of caisson which are as follows,

• Open Caisson.
• Box Caisson.
• Pneumatic Caisson.

1. Open Caisson

This type of caisson is open from both the top and the bottom. The open caisson is a box-shaped structure. Open caisson is more used where shallow bases are to be made. This type of foundation should have dry soil conditions.

This type of caisson has vertical walls. This type of caisson has a cutting edge at the bottom so that the earth can be cut easily. The open caisson is divided into three parts.

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1.1. Single Wall Open Caisson

This type of caisson is used for shallow depths and is used where the soil is loose.

1.2. Cylindrical Open Caisson

This type of caisson is used for high depths and is used where the area of the caisson is large.

1.3. Open Caisson with Dredging Well

This type of caisson is used for greater depth. The foundations of this type of caisson are used to construct the foundations of the bridge’s pier. This caisson is used to prevent erosion of the base from flowing water flow.

2. Box Caisson

This type of caisson is similar to an open caisson. But the bottom of this caisson is closed.This type of caisson is made of R.C.C or steel.In this type of caisson, the ground should be level, and the space, where the foundation is laid, should have sufficient ground stability.

When a foundation is laid in a river, the sand is removed to a certain depth. The land is then leveled. After doing the above, the caisson is shuttered on the ground and concrete. Curing is then done on the site.

Where necessary, it is tied with a rope and dragged to the right place to sink. Dipping the caisson at the designated place increases the weight of sand or concrete in the space of the caisson.

A concrete cap is filled over the head of the caisson then the construction of a superstructure is started on it.

3. Pneumatic Caisson

The peculiarity of this type of caisson is the excavation that is done for its sinking. It occurs in the open, which is made possible by the special composition of the caisson.

It is not advisable to dig in the water and sink the caisson when uneven hard surfaces occur during excavation. If this is done, the caisson will sag. And it takes time, money, and special technique to straighten it out.

Pneumatic caisson is used when it is difficult to dispose of water. Pneumatic caisson is used when there is variation in soil levels.

Pneumatic caisson is used when layers with higher bearing capacity are located at greater depths. Pneumatic caisson is used when unable to use another type of caisson.

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Advantages of Caisson Foundation

Some of caisson Foundation’s Pros are:

1. Doing caisson foundation gives a man a place to work.
2. Doing caisson foundation protects against bases and forces.
3. Dewatering is difficult; there is a useful caisson foundation.
4. The caisson foundation is economical when the depth is more than 12 mt.
5. The caisson foundation is useful where the river flow is high, and the water depth is high.
6. Caisson foundation can be embedded at any spot.

Disadvantage of the Caisson Foundation

Some Caisson foundation Cons are:

1. In a shallow foundation, the caisson foundation costs more.
2. The caisson foundation is permanent,  so it cannot be used a second time.
3. In the caisson foundation, the air pressure has to increase as the depth increases.
4. Due to the high air pressure in the caisson foundation, the efficiency of man decreases.
5. High pressure of air in caisson foundation harms human health.
6. Caisson foundation is not used for depths greater than 35 mt
7. the caisson foundation needs specialists.
8. The caisson foundation needs a skilled carpenter.
9. The caisson foundation is very tedious and time-consuming.

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