All soils subjected to stress undergo strain. This will be taking place within the soil skeleton. This strain is caused by rolling, slipping, sliding and crushing at the particle contact points. The integration of the train (deformation per unit length) along the vertical direction (over the depth of influence) is Settlement. Settlement is not recoverable when the stress is removed. This is because, a permanent reduction in the void ratio has been produced. The effect of settlement depends on factors like, uniformity, type of structure and iQ magnitude. Therefore all foundations shall be checked for total and differential settlements. These settlements have to be within permissible limits as per IS codal provision.
The change in state of strain in soil layers will result in settlement. The construction of foundation structures will increase the stress level at various layers in the soil. The increase in stress will modify the strain field beneath the foundation structure. Hence, the various aspects to evaluate settlement are analysed in this unit. The chapter is concluded by stressing the need for usage of IS codes for settlement evaluation.