Settlement Of Foundations

Through settlement we mean the vertical downward movements of the foundation. The effect of settlement on the structure depends on its magnitude, both absolute as well as associative along with respect to the various parts of the foundation. Settlement might be caused through:

(a)        The weight of the structure and the superimposed loads,

(b)       Subsidence because of mining,

(c)        Shrinkage because of change in moisture content, and

(d)       General earth movement.

Settlements, which take place when the static load is inside the range of the safe bearing capacity of the soil, consist of the subsequent elements:

(1)        Elastic deformation that takes place immediately on application of load,

(2)        Primary consolidation of foundation soil resulting from expulsion of pore water,

(3)        Secondary compression of foundation soil, and

(4)        Creep of the foundation soil.

It the structure settles uniformly, there will be no harm but if the settlement is excessive the underground service lines might be affected. In fact practice, as the soil is not a purely homogeneous material and superimposed loadings are not equivalent, settlements are non-uniform, inducing corresponding stress within the structure. Depending upon the extent of these stresses, a settlement has to be limited through appropriate designs.

Based on the loading pattern and the soil features the settlements could be computed and if it exceeds the desirable limits, the foundation has to be redesigned.

The permissible values of settlement for various categories of structure are given in IS : 1904-1986. The similar can be referred for additional details.