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What is a Floating Foundation?A floating foundation is a type of foundation constructed by excavating the soil 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 foundation is also called balancing raft and causes zero settlement to the structure.
Principle of Floating FoundationThe main principle of floating foundation is to balance the weight of removed soil by a structure of same weight which causes zero settlement to the structure. So, this foundation is also called as balancing raft foundation. Let’s consider a ground with water table at the top as shown in the above picture. The ground is excavated up to certain depth which is below water table. Now in the next step, a building is constructed which is as same weight as of the removed soil and water. Even the depth of excavation is below the table the total vertical pressure in the soil below the foundation is unchanged because of its balancing weight. But here one point is to be noted that we cannot build a structure immediately after the excavation. During the time of construction, the effective vertical pressure under the depth of excavation may slightly increase because of unbalancing weight. So, this type of foundations can also be called as partly compensated foundations instead of fully floating or compensated foundations.
Suitability of Floating FoundationsFloating foundations are desirable for the following types of soils:
- Soils which are having good shear strength but having a problem of large settlements and differential settlements under heavy loads. In which case, floating foundation can reduce the settlement values to greater extent.
- Soils which are having low shear strength and there is no hard layer of soil at reasonable depth. Here also, floating foundation helps to reduce the shear stresses to satisfactory level and hence settlement is prevented.
Difficulties in Construction of Floating FoundationDuring the construction of floating foundation some problems may arise which can be prevented by taking proper care. The problems will arise during
- Critical depth
- Bottom heave