What is a Floating Foundation?
​A floating foundation is a type of foundation constructed by excavating soils in such a way that the weight of structure built on the soil is nearly equal to the total weight of the soil excavated from the ground including the weight water in the soil before the construction of structure. Floating foundations are also called "balancing rafts" and cause zero settlement to the structure.
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The main principle of a floating foundation is to balance the weight of removed soil by a structure of same weight which causes zero settlement to the structure. This is why a floating foundation is also called a "balancing raft" foundation.
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​Floating foundations are desirable for the following types of soils:

• Soils which have a good shear strength but have a problem of large settlements and differential settlements under heavy loads. In this case, a floating foundation can reduce the settlement values to a greater extent.
• Soils which have a low shear strength where there is no hard layer of soil at a reasonable depth. Here, a floating foundation helps to reduce the shear stresses to a satisfactory level and settlement is prevented.

 

 

Floating foundations are necessary mainly in two cases:

• When the strength of the soil is sufficient to safeguard against shear failure, but the chances of differential settlement and subsequent cracking of building due to superstructure load are high.
• There is absence of a strong layer at a reasonable depth and shear strength of the soil is so low that failure in shear would occur if the building were to be founded at ground level.