What are the Requirements for Caisson Construction?
Caisson construction, also known as caisson foundation, is a water retaining structure that is mainly used in construction projects that take place underwater. Caissons are prefabricated cylinders or hollow boxes that are sunk to the desired depths beneath oceans, rivers and other water bodies. They are then filled with concrete to create a solid foundation for the project, serving as an anchor. Structures such as concrete dams and bridge piers generally require a caisson as a base.
While somewhat similar to pile foundations, caissons are installed using a different method. Soil of adequate bearing strength is found below the surface and a deep foundation is sunk to the required level through material excavation. During caisson construction, steel reinforcement is sometimes used for a portion of its length.
A caisson is essential during construction for the purpose of providing stability to the structure. It helps to distribute the weight of structures evenly as the ground shifts under their weight. Depending on the type of caisson being constructed, the material used for building can vary from concrete to wood.
Requirements for Caisson Construction
There are a few key factors to consider during the construction and transfer of caissons. Depending upon the type of caisson construction, structural conditions and methods of installation used, there are some valid concerns held by the designers and engineers involved in the process. These include issues related to the construction, component design and installation of the caissons. Durability, stability, soil nature, scour depth, and the level of the water table are some of them.
Various requirements for caisson construction are involved for the purpose of sinking, filling and sealing. Important factors such as the length of the reinforcement bars and the height of the concrete lifts need to be decided in consultation with the construction contractors. In order to ensure the optimum facilitation of operations, the on-site supervisory staff must maintain the highest standards when it comes to the quality of materials used. Moreover, they must be specially trained to handle the challenging situations faced by the personnel during the sinking process of the caisson construction.
It is essential for contractors and engineers to keep the following requirements for caisson construction in mind. These involve the strength of the concrete mix design, the concrete shaft cover, and most importantly the quality of the formwork and concrete during caisson construction. Depending on the compliance and quality, the friction resistance to the soil can significantly increase or decrease during the sinking process.
Types of Caissons
There are different types of caisson foundations such as open, pneumatic, box, excavated and floating caissons. Open caissons are generally constructed to the depth of 50 metres and are open at both ends. Pneumatic caissons are open at the bottom but closed at the top for caisson construction at depths of over 100 metres. As the name suggests, excavated caissons are used at excavation sites, while floating caissons are prefabricated boxes with cylindrical cavities.
Advantages and Disadvantages of Caissons
There are some major benefits of using caisson construction for underwater projects. They are cost-effective to construct as compared to their alternatives, and also prove effective at deep depths of water bodies. They also have a high load capacity and can easily adapt to different environments and site conditions.
On the other hand, there are also a few disadvantages to caisson construction. They can be sensitive to gruelling construction procedures and are not considered good for use at contaminated sites. Moreover, only a few construction companies possess the requisite expertise and qualified inspectors needed for the supervision of caisson construction.
Caissons are considered to be essential building blocks during construction. Hence, it is necessary to maintain the highest standards during caisson construction, by ensuring that they are built and installed by a competent team of professionals.