Why do we have to place footings at least "B" distance from each other?

Why do we have to place footings at least "B" distance from each other?

Let me rephrase, isolated footings designed independently have to be placed in such a way that an adequate gap is ensured. That adequate gap is "B", which is the larger size width of the two footings under consideration.

Following Boussinesq stress distribution under a point load one can see that the stress from one footing extends B/2 distance from the face of the footing. Meaning if two footings with B width are placed in such way that the clear distance from the two is less than B, then the stress at B/2 from the footings is the sum of stress from the two.

Can we place footings such that the clear spacing between the two is less than B? Or do we have to go for combined footings?

The answer to this question is

to verify that the summation of the stress from the two is less than the allowable bearing capacity of the soil. If indeed the summation of stress from the two is less than the allowable no need to go for combined footings.

.....if the summation of stress between the two footings is greater than the allowable, then combined footings become inevitable.

The structural or geotechnical engineers out there, do u check the stress overlap between your closely spaced footings or u just go " as far as it is isolated and isn't overlapping"?

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