Bearing Capacity of Soil MCQ with answer and solution

Concept

Allowable bearing capacity is the net pressure that is safe against both shear failure and excess settlement.

Formula

q_na = smaller of (q_ns, q_settlement); q_ns = q_nu / FOS

Step-by-step solution

1. Net ultimate bearing capacity (q_nu) is the net pressure at which soil just fails in shear. 2. Net safe bearing capacity (q_ns) = q_nu / FOS. It checks only shear failure. 3. Safe bearing capacity (q_s) = q_ns + γDf. This is the gross value. 4. Allowable bearing capacity checks both shear failure and permissible settlement. 5. So the answer is option A.

Explanation

Allowable bearing capacity is the net loading intensity that the soil can carry safely. At this pressure there is no shear failure and the settlement stays within the permissible limit. It is the smaller of the net safe bearing capacity and the safe bearing pressure for settlement.

Why the other options are wrong

B: This is net safe bearing capacity. It checks only shear, not settlement. C: This is net ultimate bearing capacity, the value at actual shear failure. D: This is safe bearing capacity, a gross value that includes overburden γDf.

Shortcut

Allowable = Shear safe + Settlement safe (both checks).

Common mistake

Students often confuse allowable bearing capacity with net safe bearing capacity (q_nu/FOS), which ignores settlement.