The decision of construction of a deep foundation is taken when the load has to be distributed to an area either with soft weak compressible soils or to reach strata that have strong soil or rock or any other special concerns. One such generally used a type of deep foundation is called as Hollow box foundations or buoyancy rafts foundation.
These types of foundations are designed such a way that they behave as buoyant (floating) substructures for the net loading over it. Hence reducing the load intensity over the soil.
The buoyancy raft foundations are also known as compensated foundations or deep cellular rafts. Whatever be the name they are known for , they come under the category of floating foundations.
These are known as fully compensated foundations as during their construction the soil underneath the foundation is removed , whose weight is equal to the weight of the whole superstructure. Hence the weight removed from the soil is compensated by the weight of the building.
The buoyancy rafts are adopted under cases that The soil bearing capacity is very low or The estimated building settlement is more than the safe limit.
Those areas with soft soil , layer in a huge depth is observed , it is economical to go for floating foundation. No other foundation like pile foundation cannot be an efficient replacement for these.
Occupants in low-altitude areas face the problem of high floods resulting in the collapse of houses. The construction of buoyant foundation would help in increasing the elevation of the house.
This arrangement is a flexible method , as the building would remain on the ground under the normal conditions. When flood approaches , the building would rise to a necessary height.
Now the floating foundation can be of two types: The basement rafts , and The buoyant raft.
The buoyant rafts differ from the basement rafts and both should not be confused. The basement rafts , unlike buoyant raft foundation , involve only excavation of soil whose weight equals to a part of the weight of the building. The whole building weight is not taken and hence called as a partially compensated foundation.