Correct Answer - Option 4 : Pneumatic caissons
Concepts:
Drilled piers are deep foundations which are constructed by excavating cylindrical shafts into the ground and filling them with concrete in order to resist very high axial and lateral loads. They are also called caissons or bored cast – in- situ piles.
An open caisson is a hollow structure with top and bottom both is opened that is designed to keep water out of a construction zone. They are used in trenchless operations, such as in the excavation of entrance or exit pits. They are often suitable in soft soil.
A pneumatic caisson is a watertight box or cylinder-like structure that is closed at the top and opens at the bottom, resting on the bed of the water body. They are used for underwater construction of foundations for bridge piers, abutments in rivers, and foundations for large multi-story buildings.
Floating caissons are boxes with large holes open at the top and closed at the bottom. A floating caisson does not penetrate in the soil like the open and pneumatic caisson & remains on the flat bearing surface.
