Allowable Bearing Pressure for a Settlement Limit
The largest net contact pressure that keeps immediate settlement within a limit.
Example
You enter
- Settlement limit Se (in) 1
- Footing width B (ft) 6
- Soil elastic modulus Es (ksf) 250
- Poisson's ratio nu (0.3 sand) 0.3
- Influence factor Is (0.82 rigid square) 0.82
You get
- Allowable pressure (ksf) 4.65321
Details, formula, and sources
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.
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.
The elasticity-based settlement form and the influence-factor tables are public in the standard foundation-engineering references; the arithmetic is public.
Estimate. AHJ and licensed professional govern.
Field names used by the API: settlement_limit_in, b_ft, es_ksf, nu, is_f, allowable_pressure_ksf
- Elastic form inverted q = Se Es / (B (1 - nu^2) Is) on a deep uniform elastic layertheory of elasticity / Bowles
- Serviceability limit a settlement-controlled pressure, not the bearing-capacity strength limitcustomary geotechnical practice
- Scope immediate settlement only; consolidation, layering, and embedment are separatecustomary geotechnical practice