pneumatic caisson

PNEUMATIC CAISSON
A pneumatic caisson is a large hollow structure used in civil engineering projects to create foundations for structures such as bridges, tunnels, and buildings. It is typically constructed from steel or concrete, and is open at the bottom to allow it to sink into the ground. During construction, the caisson is sunk into the ground by excavating the soil from within the structure and filling it with water. As the water pressure inside the caisson is equalized with the pressure outside, the caisson sinks further into the ground.

To prevent the caisson from sinking too deeply into the ground or from becoming unstable, compressed air is introduced into the caisson to create an air pocket. Workers then enter the caisson through a small chamber called a "man lock" and work inside the air pocket to excavate the soil beneath the caisson. The use of pneumatic caissons allows for deep foundations to be constructed in areas with difficult soil conditions or in waterlogged areas. They are commonly used in bridge and pier construction, as well as in the construction of tunnels and other underground structures.