Shallow Foundation Bearing Capacity (Vesic)

qu = c x Nc + q x Nq + 0.5 x gamma x B x Ngamma with the Vesic bearing-capacity factors from the friction angle, De Beer / Vesic shape factors for square and circular footings, and the customary factor of safety of 3. A 6 ft strip footing 4 ft deep on a phi = 32 medium-dense sand carries 22 ksf ultimate, 7.3 ksf allowable -- the number a footing-area calculation needs handed to it; a phi = 0 stiff clay pins the Prandtl Nc = 5.14 branch. General shear on a level, concentric footing with deep groundwater; settlement usually governs on sand and is separate. A design aid, not a substitute for a geotechnical engineer's report.

qu = c Nc sc + q Nq sq + 0.5 gamma B Ngamma sgamma; Nq = e^(pi tan phi) x tan^2(45 + phi/2); Nc = (Nq - 1) x cot phi (5.14 at phi = 0); Ngamma = 2 x (Nq + 1) x tan phi; q_all = qu / FS.

The general bearing-capacity equation with the Vesic (1973) factors and De Beer / Vesic shape factors, as compiled in Das, Principles of Foundation Engineering, and FHWA-NHI-16-009 (GEC 6, Shallow Foundations), by name.

FHWA GEC 6 (FHWA-NHI-16-009) is a free public FHWA publication; the Vesic factor arithmetic is public and printed in every foundation-engineering text.

Estimate. AHJ and licensed professional govern.

Field names used by the API: phi, gamma, b_ft, df_ft, shape, fs, nq, nc, ngamma, q_surch, qu, q_all

• General shear, level and concentric a level, concentrically loaded footing failing in general shear with level ground; eccentric / inclined loads, sloping ground, and local or punching shear are separate correctionsDas / FHWA GEC 6
• Groundwater below the failure zone the water table is at or below one footing width beneath the base; a higher water table requires buoyant unit weightsDas / FHWA GEC 6
• Settlement separate the allowable is a strength check only; settlement usually governs a footing on sand and is a separate analysisDas / FHWA GEC 6