Caisson foundations are characterized by being very different compared to standard concrete slab foundations. This type of specialized foundation is very often used to cement piers, bridges, dams, or other structures that need support underwater. In this article we are going to tell you what are the different types of Caisson foundations or also known as foundation pits and their main benefits.
The foundation or also known as Caisson by its name in French, is categorized within semi-deep foundations, the caisson foundations are used when the soils are soft and do not support a superficial foundation due to their qualities. The foundation pits are used with great frequency at the time of making the foundations of bridge pillars in the river bed when it is not convenient or when it cannot be partially or totally diverted.
What is a caisson?
The first thing you should know about the Caisson foundation is that it consists of a hollow and hermetic chamber that floats or is transported to the place where you are going to work. Then it sinks into the ground, and builds up inside. Despite this, Caisson himself often remains part of the foundation.
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There are different types of Caissons under construction that are used to create foundations, however the vast majority fit into a few broad categories. Next, we are going to explain what their different types are and the benefits they offer, this you should know before choosing any in your projects.
This type is characterized by closing at the bottom and opening at the top. For this reason, as its name indicates, in most cases it has a shape similar to that of a box, instead of being cylindrical. It is built on land, and floats to the site where it is to be installed. Then it is immersed in the place of installation adding materials such as gravel, concrete or sand.
The Caisson box is generally used in situations where foundations are in soft soils such as gravel, clay, crushed rock or silt, which has rock formations or bedrock. The advantage of this foundation system is that the bottom of the box that is closed will settle by supplying fill materials through its top that is open.
Like the Caisson box, this type is also open in its upper part, the difference between these two is that the open one, as its name indicates, is also open in its lower part, something that is not presented with the box. For this reason, open Caissons often have a cylindrical shape. The construction procedure of this caisson is frequently carried out by placing it in an excavated site, this means a hole that has the depth of meters that the project needs.
In several cases there is a need to build a cofferdam in advance to excavate and place the open caissons. However, these are put into the water and then pumped to add concrete or any other type of filling material.
Benefit of open Caissons
The main benefit of this type is that it can be controlled very easily. Although at the time of filling it, it can sink a bit, thanks to the fact that it is placed in a dug well, at the beginning of the process. This makes drift or tilt less likely.
This is characterized by being closed at the top and open at the bottom. Once they are placed, the compressed air is responsible for expelling the water, which creates a dry work environment in the water. Workers enter this place through air locks.
Advantages of the pneumatic Caisson
This type has several advantages, such as the ability to examine the soil bed and the ability to work under controlled conditions. Despite this, the process of using this type of Caisson is expensive and time consuming. These reasons mean that they are generally used in situations such as rapid soil flow, where other types of Caissons are not as practical.