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Define settlement of foundation and its types. Enlist various causes and suggest remedial measures for the same.
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Settlement of foundation: Due to the self-weight and the live load of the structure and due to compressibility of the soil supporting the foundation of the structure, settlement of the structure does occur. Settlement is the vertical downward movement to the loaded base. As a result of settlement, the original depth of soil mass decrease due to soil grains coming closer together. Uneven settlement leads to cracks. The amount of settlement is different for different type of soil or rock For example there is no or very less settlement for rocky strata whereas settlement is very large in case if marshy land. Settlement is time dependent process i.e in case of clayey soil settlement is very gradual, continuous for long time and is more. On the other hand for sandy soil settlement is quick and less.

Types of Settlement:

1. Differential foundation settlement: Settlement that occurs at differing rates between different portions of a building is termed differential settlement. Differential settlement occurs if there is difference in soils, loads, or structural systems between parts of a building. In this case, different parts of the building structure could settle by substantially different amounts.

2. Uniform foundation settlement: When foundation settlement occurs at nearly the same rate throughout all portions of a building, it is called uniform settlement. If all parts of a building rest on the same kind of soil, then uniform settlement the most probable type to take place. However, it influences utility of the building for example damaging sewer; water supply; and mains and jamming doors and windows.

Causes of settlement are :-

  1. Uneven bearing capacity of soil at foundation level.

  2. Different loads on different parts of foundation.

  3. Varying ground water table height.

  4. Compressible foundation soil.

  5. Earthquakes and floods.

  6. Expansive soil such as black cotton soil.

Various remedial measures:

  1. Compaction of soil over the complete area at foundation level.

  2. Proper designs so that large load difference does not exist on different parts of the foundation.

  3. Dewatering of foundation if ground water table interference with construction of foundation.

  4. Stabilization of soil of foundation level if it is compressible.

  5. Special type of foundation for expansive soils such as black cotton soil.

  6. Consideration of earthquake loads and other earthquake resisting methods during design and construction of buildings.

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