Allowable Bearing Pressure for a Settlement Limit
The inverse of the elastic-settlement tile: the largest net contact pressure that keeps immediate settlement within a limit, q = Se Es / (B (1 - nu^2) Is). A 6 ft footing on Es = 250 ksf soil holds ~4.65 ksf at a 1 in limit; a 12 ft footing only ~2.33 ksf, since a wider footing settles more. A settlement (serviceability) pressure, not the bearing-capacity strength limit. A design aid, not the geotechnical engineer's report.
Formula and source
q = Se Es / (B (1 - nu^2) Is), the theory-of-elasticity immediate settlement Se = q B (1 - nu^2) Is / Es solved for the pressure (Se in feet = limit_in / 12).
The theory-of-elasticity immediate (elastic) settlement of a shallow foundation solved for the allowable pressure, with the shape-and-rigidity influence factor Is (Bowles, Foundation Analysis and Design), by name.
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