Floating Foundation

ROLE OF SOIL’S EFFECTIVE STRESS IN THE FIELD OF CONSTRUCTION

(FLOATING FOUNDATION)

Abstract

Effective stresses at a point in soil mass are equal to the total stress at that point minus the pore water pressure at the location. Certain aspects of the engineering behavior of soil especially compression and shear strength are the functions of effective stress.

The concept is based on the fact that different depths below the ground surface the soil is subjected to different overburden pressures and therefore over a period of time it achieves different state of stresses.

Effective stress is based on *Depth *Shift of water table *Shift in ground surface *Permeability * Void ratio *Seepage *Compressibility.

Compressibility- a function of stress history

 Compressibility is defined as the volumetric strain that a soil undergoes on account of rearrangement of particles that is necessary to withstand the higher imposed stresses. When soil becomes denser the compressibility decreases and effective stress increases. When a soil is subjected to effective stress for the first time in its history exhibit greater compressibility than when it has in its past been subjected to effective stresses but then has been relieved of effective stresses. Soil are not elastic in their behavior once compressed do not spring back to their loose state upon being unloaded and also that upon reloading they do not compress as much as soil that have never been loaded before.

Floating Foundation

A floating foundation is defined as a foundation in which the weight of building is approximately equal to the full weight of soil and water removed from the site of the building. The principle of foundation is an exact balance of weight removed against weight imposed & the result is the zero
settlement of the building. This type of floating foundation is used in two main cases.

Type.1: Shear failure of the soil will not occur under the building load but the settlements and particularly differential settlements will be too large and will constitute failure of structure.

Type.2:  Shear strength of the soil is low that rupture of soil would occur if the building were to be founded at ground level.

The settlement problem can be solved by solving the problems like Excavation, Dewatering, Critical depth & Bottom heave.

Conclusion

Thus settlement problem of buildings is solved by using floating foundation and there is no risk of failure.