Bearing Capacity of Soil MCQ with answer and solution

Concept

Punching shear failure happens in very loose sand with relative density below about 35%.

Formula

I_D = (e_max − e)/(e_max − e_min) × 100

Step-by-step solution

1. The failure mode depends on the relative density (I_D) of the sand. 2. I_D > 70% (dense sand): general shear failure. 3. I_D between 35% and 70% (medium sand): local shear failure. 4. I_D < 35% (loose sand): punching shear failure. 5. So the answer is 35%, option (C).

Explanation

In very loose sand, the footing sinks straight down and the soil around it does not bulge up. This is called punching shear. It occurs when the relative density is less than about 35%.

Why the other options are wrong

A, B and D: 45%, 55% and 65% lie in the 35–70% range, which gives local shear failure, not punching shear.

Shortcut

Remember 35–70: below 35% punching, 35–70% local, above 70% general shear.

Common mistake

Mixing up the 35% and 70% limits, or confusing dry density with relative density.