Geotechnical Engineering
Bearing Capacity
Terzaghi bearing capacity calculator for shallow strip footings — ultimate and allowable bearing pressure.
Bearing Capacity
This calculator computes the ultimate and allowable bearing pressure of a shallow strip footing using Terzaghi's general shear failure equation. It combines three independent failure mechanisms — cohesion, surcharge from the overburden soil, and the weight of the soil wedge below the footing — each weighted by a bearing capacity factor that depends only on the soil's friction angle.
The bearing capacity factors Nc, Nq, and Nγ grow rapidly with friction angle, which is why a small change in assumed φ can shift the allowable pressure substantially. This calculator is a preliminary check using Terzaghi's original general shear factors; final geotechnical design should use the Meyerhof, Hansen, or Vesic refinements with shape, depth, and load-inclination factors, verified against an actual geotechnical report.
q_ult = c·Nc + q·Nq + 0.5·γ·B·Nγ [q = γ·D_f]
q_allow = q_ult / FS
A 4-ft-wide strip footing embedded 3 ft into cohesionless sand (φ = 30°, γ = 115 pcf) has a surcharge of q = 345 psf and bearing capacity factors Nc = 37.2, Nq = 22.5, Nγ = 19.7. The ultimate bearing capacity works out to q_ult = 345 × 22.5 + 0.5 × 115 × 4 × 19.7 ≈ 12,300 psf. Applying a factor of safety of 3 gives an allowable bearing pressure of roughly 4,100 psf — the value a structural engineer would use to size the footing for the applied column load.
Bearing Capacity Calculator
Terzaghi general shear · strip footing · imperial units