Soil Bearing Capacity Calculator
Estimate the ultimate bearing capacity of shallow foundations using Terzaghi bearing capacity factors.
Ultimate Bearing Capacity
643.8 kPa
Ultimate Bearing Capacity vs Soil Cohesion (c)
Formule
## Terzaghi's Bearing Capacity Theory The bearing capacity of a shallow foundation depends on soil properties, foundation depth, and width. ### Formula (strip footing) **q_u = c Nc + gamma Df Nq + 0.5 gamma B Ngamma** The three terms represent cohesion resistance, surcharge (overburden) resistance, and self-weight resistance. Nc, Nq, and Ngamma are dimensionless bearing capacity factors that depend on the soil friction angle.
Exemple Résolu
A 2 m wide strip footing at 1.5 m depth, c=20 kPa, gamma=18 kN/m^3, phi=20 deg.
- 01Cohesion term: 20 x 17.7 = 354 kPa
- 02Surcharge term: 18 x 1.5 x 7.4 = 199.8 kPa
- 03Width term: 0.5 x 18 x 2 x 5.0 = 90 kPa
- 04q_u = 354 + 199.8 + 90 = 643.8 kPa
- 05q_a = 643.8 / 3 = 214.6 kPa (with FoS = 3)
Questions Fréquentes
How do I find bearing capacity factors?
Nc, Nq, and Ngamma are functions of the soil friction angle (phi). They are published in geotechnical reference tables. For phi=0 (pure clay): Nc=5.7, Nq=1, Ngamma=0. For phi=30: Nc=37.2, Nq=22.5, Ngamma=19.7.
What factor of safety is standard?
A factor of safety of 3 is common for dead + live loads. Some codes use FoS=2.5 for well-characterised sites. Allowable bearing capacity = ultimate / FoS.
When does settlement govern instead of bearing capacity?
On sandy soils and for large foundations, settlement often controls the design even when bearing capacity is adequate. Settlement calculations are separate from bearing capacity analysis.
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