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In general, where settlements expected are small, individual strips and footings tend to be cheaper than rafts, which will require much more steel to carry increased shear and bending moments due to continuity.ĥ. In such situations, careful analysis should be made as to whether individual footings or rafts are more economical.
FLOATING FOUNDATION SLAB MAT FULL
In situations, where individual footings may touch or overlap each other, and it is advisable to excavate the full site instead of the ground under individual footings. Mat foundation is specified to bridge over pockets of weak spots in moderately weak soil.Ĥ.
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Whereas for footings only 25 mm is specified for the same allowable differential settlement of 18 mm (3/4 inches) for both cases.ģ. Thus, an allowable maximum settlement of 50 mm is usually specified for raft foundations. Where differential settlements in the structure are to be reduced.Īs observed by Terzaghi and Peck, the differential settlement in rafts is only one half that of footings of the same intensity of loading due to the random distribution of compressible zones.Īnd also due to the stiffening effect of the raft and building frame.ĭue to continuity and negative moments, the bending moments produced in rafts tend to be less. In structures like chimneys, silos, cooling towers, buildings with basements where continuous water proofing is needed Īnd in floating foundations where a rigid structure is needed to reduce settlement.Ģ. Raft foundation is used under the following conditions:ġ. Situations where Raft Foundation is Used.