The main difference between the two is that cofferdams are temporary where as caissons are built to remain in place as a completed structure. Whatever project is being created will determine which structure is needed. Factors such as ground conditions and the depth of water come into play in deciding the appropriate format. Both are used when carrying out construction in areas submerged with water.
What is a cofferdam and a caisson?
Cofferdams are enclosures built across or within bodies of water to allow construction projects to take place. They can be built in many shapes and from a variety of materials. Water is pumped out of the cofferdam to allow workers to function in a clear, dry area.
A caisson is a box-like structure made of timber, steel, masonry, and reinforced concrete. The frame is floated to a required location then sunk into place. Remember, this design will remain in the area it is left permanently. After being fastened in place, it is used to access and undertake work.
What are they used for?
The goal of a cofferdam is to be as watertight as possible to create a dry environment for construction work to take place. For the caisson, it has virtually the same job. It is a structure built to help workers construct on top of water, such as building bridges.
Small amounts of water are allowed to get in as long as it can be pumped out safely throughout the job. Due to working in the water, sometimes it will leak in or breaks may occur causing flooding. However, cofferdams are designed to easily pump out any water inside the working space. After the job is done, workers dismantle the structure and the site is left clean.