Differential Settlement of Soil – Factors To Consider in Foundation Design

The substructure or foundation is the part of a structure that is usually placed below the surface of the ground and that transmits the load to the underlying soil or rock.

2 Important Factors in Foundation Design Regarding Settlement

The two essential requirements in the design of foundations are that the total settlement of the structure be limited to tolerably small amounts and that differential settlement of the various parts of the structure be eliminated as nearly as possible. With respect to possible structure damage, the elimination of different settlement, i. e. different amounts of settlement within the same structure, is even more important than limitation on uniform overall settlement.

differential settlement of soil - foundation crack
cracks due to different types of soil settlement

How To Limit The Differential Settlement

To limit or reduce the differential settlements, it is necessary –

  1. To transmit the load of the structure to a soil stratum of sufficient strength.
  2. To spread the total load over a sufficient large area of that stratum to minimize bearing pressure. If adequate soil is not found immediately below the structure, it becomes necessary  to use deep foundations such as piles or caissons to transmit the load to deeper, firmer layers. If satisfactory soil directly underlies the structure, it is merely necessary to spread the load, by footing or other means.

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