The foundation of a structure is designed for:
Try it first: pick an option, then read the explanation.
Asked in SSC JE 10/10/2023 (Evening)
Detailed Explanation
Soil is a collection of particles. It cannot carry tension and it does not bend like a beam. When it is overloaded, the particles slide past one another along a surface — the soil fails in shear.
Why “shear failure of soils” Is Correct
Every bearing capacity theory (Terzaghi, Meyerhof, Hansen) assumes that the soil under the footing reaches failure along shear (slip) surfaces. So foundations are designed so that the pressure stays safely below the shear failure value, with a factor of safety, and so that settlement stays within limits.
Why the Other Options Are Wrong
- B. compression failure of soils: Soil grains do not crush under normal footing loads; the soil compresses (settles) but fails by sliding.
- C. bending failure of soils: Bending is a property of structural members, not of soil.
- D. tension failure of soils: Soil has practically no tensile strength, so it is never designed to carry tension.
Key Point
Two design checks for a foundation: shear failure and settlement.
Key Concepts for Students
- Shear strength: τ = c + σ′ tan φ.
- Factor of safety on shear is usually 2.5 to 3.
- Settlement often governs on clays and loose sands.
Practice more: this is question 11 in Shallow and Deep Foundation MCQs – Part 1. Try the whole set and check every answer instantly.