Soil Bearing Capacity Calculator
Estimate the ultimate and allowable bearing capacity of soil under a shallow foundation using Terzaghi's general bearing capacity equation.
Results
What is it?
Terzaghi's bearing capacity equation estimates the maximum pressure a shallow foundation can apply to soil without causing shear failure: qu = c·Nc·sc + γ·Df·Nq + 0.5·γ·B·Nγ·sγ where Nc, Nq, Nγ are dimensionless bearing capacity factors dependent on friction angle, and sc, sγ are shape factors.
How to use
Enter the soil properties (cohesion and friction angle from a geotechnical report or lab test), soil unit weight, foundation dimensions, and apply a factor of safety of 2.5 to 3.0 for structural foundations.
Example scenario
A square footing (1.5 m × 1.5 m, depth 1.5 m) on soil with c = 10 kPa, φ = 30°, γ = 18 kN/m³. Nc ≈ 30.1, Nq ≈ 18.4, Nγ ≈ 22.4. qu ≈ 10×30.1×1.3 + 18×1.5×18.4 + 0.5×18×1.5×22.4×0.8 ≈ 974 kPa. qa = 974/3 ≈ 325 kPa.
Pro tip
Always verify against field tests (SPT, CPT, plate load test). Terzaghi's formula assumes general shear failure — for loose sands or soft clays, use local or punching shear corrections. A FOS of 3 is standard for permanent structures.