Abid Qasmi

How to decide a Raft or a Single Footing?

4 posts in this topic

Aoa dear S.Es

Wat is the criteria for selection of a particular type of a foundation especially with reference to an RCC building? e.g A RAFT or SINGLE FOOTING?

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1. P/A + My/I,xy

If area req for isolated footing is so large that it combines with other footings, provide raft.

 

2. Soil report recommendations including uplift and water table, soil type, liquification etc.

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17 minutes ago, Rana said:

1. P/A + My/I,xy

If area req for isolated footing is so large that it combines with other footings, provide raft.

 

2. Soil report recommendations including uplift and water table, soil type, liquification etc.

Kindly elaborate the second point sir,thnx

 

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1.The structural load are so high or soil conditions so poor that spread footings would be exceptionally large. As a general rule of thumb, if spread footing would cover more than 50 % of the building footprint area, a mat or some type of deep foundation will usually be more economical.
2.If the soil is very erratic and prone to excessive differential settlements (heaves). The structural continuity and flexural strength of a raft will bridge over these irregularities.
3.The uplift loads are larger than spread footings can accommodate. The greater weight and continuity of a mat may provide sufficient resistance.
4.The bottom of structure is located below the GWT, so water proofing is an important concern. Because mats are monolithic, they are much easier to waterproof. The weight of mat also helps resist hydrostatic uplift forces from the groundwater.

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