Bearing Capacity of Soil MCQ with answer and solution

Concept

Soil fails under a foundation by shear. So a foundation is designed against shear failure of the soil, and also to keep settlement within limits.

Formula

q_safe = q_nu / FS + γ D_f

Step-by-step solution

1. Under foundation load, soil fails when shear stress on a slip surface exceeds its shear strength. 2. Bearing capacity theories (Terzaghi, Meyerhof) are all based on shear failure of soil. 3. So the foundation is designed to give safety against shear failure (general, local or punching). 4. So the answer is (D).

Explanation

Soil is a granular, frictional material and fails by sliding along failure surfaces, which is shear failure. Bearing capacity is found using the shear strength parameters c and φ. So foundations are designed against shear failure of soil.

Why the other options are wrong

A: Soil does not fail by crushing in compression; it compresses and settles. B: Soil has almost no tensile strength, and foundation soil is not loaded in tension. C: Soil does not fail by bending; bending is checked in the footing slab, not the soil.

Shortcut

Soil failure means shear failure. Bearing capacity is based on c and φ.

Common mistake

Choosing compression because the load on soil is compressive. The soil still fails by shear along slip planes.