Bearing Capacity Factor Nc
Worked example: Nc 46.12 with Nq 33.30 → φ = 35.005° — press Try an example to run it live, then adjust anything.
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Bearing Capacity Factor Nc explained
is not an independent result but a consequence: Prandtl's plasticity solution ties the cohesion term to the surcharge term through . With = 18.40 at φ = 30°, = 17.40 ÷ tan 30° = 30.14 — again the tabulated value. At φ = 35°, = 33.30 gives = 46.12.
The interesting case is φ = 0, where cot φ blows up and the formula is useless — but the limit is finite and famous: → π + 2 = 5.14. That is the undrained bearing capacity of saturated clay, for a strip footing and about for a square or circular one, and it is the single most-used number in shallow foundation design on clay. The trap is applying the φ = 0 analysis with a drained strength, or vice versa: undrained (total stress, , φ = 0) governs immediately after construction, drained (effective stress, c′, φ′) governs decades later, and a clay foundation must be checked for both. Skempton's 1951 paper set out that two-case discipline and it has not been improved on.
Bearing Capacity Factor Nc formula
- = Cohesion bearing capacity factor
- = Surcharge bearing capacity factor
- = Angle of internal friction (°)
Missing one of these? Work it out first, then come back
- Cohesion bearing capacity factor — Bearing Capacity Factor Nq, Terzaghi Ultimate Bearing Capacity (Strip Footing)
- Surcharge bearing capacity factor — Bearing Capacity Factor Nq, Terzaghi Ultimate Bearing Capacity (Strip Footing)
- Angle of internal friction — Rankine Active Earth Pressure Coefficient, Rankine Passive Earth Pressure Coefficient