Soil Bearing Capacity Calculator
Calculate the ultimate and allowable bearing capacity of shallow foundations using Terzaghi's General Bearing Capacity Equation. Supports strip, square, and circular footings.
Foundation Geometry
Soil Properties
Design Parameters
Results will appear here.
Formula — Terzaghi's General Bearing Capacity Equation
Ultimate Bearing Capacity:
qu = c · Nc · sc + q · Nq · sq + 0.5 · γ · B · Nγ · sγ
Where q = γ · Df (overburden pressure)
Bearing Capacity Factors (Meyerhof):
- Nq = eπ·tan φ · tan²(45° + φ/2)
- Nc = (Nq − 1) · cot φ [= 5.14 when φ = 0°]
- Nγ = 2(Nq + 1) · tan φ
Terzaghi Shape Factors:
| Footing | sc | sq | sγ |
|---|---|---|---|
| Strip | 1.00 | 1.00 | 1.00 |
| Square | 1.30 | 1.00 | 0.80 |
| Circular | 1.30 | 1.00 | 0.60 |
Water Table Corrections:
- Deep: No correction — use γ throughout.
- At foundation base: Overburden uses γ; base term uses γ' = γsat − γw.
- At ground surface: Both terms use γ' = γsat − γw.
Allowable Bearing Capacity:
qa = qu / FOS
qu,net = qu − q | qa,net = qu,net / FOS
Assumptions & References
- Based on Terzaghi's (1943) general bearing capacity theory for shallow foundations (Df ≤ B).
- Bearing capacity factors Nc, Nq, Nγ follow Meyerhof (1963) formulations, which are widely adopted in modern practice.
- Shape factors follow Terzaghi's original values for strip, square, and circular footings.
- Soil is assumed to be homogeneous, isotropic, and the failure mode is general shear failure.
- No inclination factors (load assumed vertical and centric) or depth factors are applied — conservative for preliminary design.
- Water table correction uses the effective stress approach with γw = 9.81 kN/m³.
- A Factor of Safety of 3.0 is typical for permanent structures (Das, 2016).
- References: Das, B.M. (2016). Principles of Foundation Engineering, 8th Ed. Cengage Learning. | Terzaghi, K. (1943). Theoretical Soil Mechanics. Wiley.