The bearing capacity factors Nc, Nq and Nγ are functions of:
Try it first: pick an option, then read the explanation.
Correct answer: C. Internal friction angle
Asked in SSC JE 2015
Detailed Explanation
In Terzaghi's equation, qu = cNc + γDfNq + ½γBNγ, the soil's cohesion c and unit weight γ appear outside the factors. The factors themselves describe the shape of the failure surface, which is set by φ.
Why “Internal friction angle” Is Correct
The bearing capacity factors are dimensionless numbers that depend only on the angle of internal friction φ of the soil. Cohesion multiplies Nc but does not change it. So the answer is (c).
| φ | Nc | Nq | Nγ |
|---|---|---|---|
| 0° | 5.7 | 1.0 | 0 |
| 10° | 9.6 | 2.7 | 1.2 |
| 20° | 17.7 | 7.4 | 5.0 |
| 30° | 37.2 | 22.5 | 19.7 |
Terzaghi's bearing capacity factors (general shear). They depend only on the angle of internal friction φ.
Why the Other Options Are Wrong
- A. Cohesion of the soil: Cohesion is multiplied by Nc; it does not determine the factors.
- B. Friction angle: ‘Friction angle’ is vague — it could mean wall or base friction; the factors depend on the soil's internal friction angle.
- D. Both cohesion of the soil and friction angle: Cohesion does not enter the factors.
Key Point
Nc, Nq, Nγ = f(φ) only.
Key Concepts for Students
- All three factors increase rapidly with φ.
- φ = 0: Nc = 5.7, Nq = 1, Nγ = 0 (Terzaghi).
- Shape, depth and inclination factors are applied separately.
Practice more: this is question 38 in Shallow and Deep Foundation MCQs – Part 3. Try the whole set and check every answer instantly.