Shear Strength MCQ with answer and solution

Concept

Cohesionless soil (sand, gravel) has c = 0, so its strength comes only from friction between grains.

Formula

τ = σ' tan φ'

Step-by-step solution

1. Mohr-Coulomb law: τ = c + σ tan φ. 2. For cohesionless soil, c = 0. 3. So τ = σ tan φ, which comes only from friction. 4. This friction acts between soil grains, so it is called inter granular friction.

Explanation

Sand and gravel have no cohesion. Their shear strength comes from sliding friction and interlocking between grains, called inter granular friction. Many exam keys give this option as the answer.

Why the other options are wrong

A: Internal friction is a near-correct general term, but the exam expects the more specific 'inter granular friction'. B: Cohesionless soil has no cohesion. D: Inter particle (electrical) forces matter in clays, not sands.

Shortcut

Cohesionless soil: c = 0, so strength comes only from grain-to-grain friction.

Common mistake

Choosing cohesion, or confusing interparticle electrical forces (in clay) with friction.