Shallow Foundations MCQ with answer and solution

Concept

Raft Foundation Criteria

Formula

N/A

Step-by-step solution

1. Review the question regarding the selection criteria for a raft foundation. 2. Recall that raft foundations are used when the soil bearing capacity is low and total footing area exceeds 50% of the building area. 3. Select Option D as the correct choice.

Explanation

A raft (or mat) foundation is used when the soil is weak and has low bearing capacity. When individual footings would cover more than half of the total building footprint area, combining them into a single continuous concrete slab (a raft foundation) becomes more economical and structurally efficient to safely distribute heavy loads and prevent uneven settling.

Shortcut

To easily remember the selection criteria for a Raft Foundation, use the rule "RAFT = Weak Soil + >50% Area": - Low Bearing Capacity: Used when the soil is weak or soft - > 50% Footing Area: Chosen when individual footings cover more than 50% (half) of the total building footprint

Common mistake

A common mistake is selecting option A by confusing the conditions for a raft foundation with those for simple isolated footings, incorrectly assuming raft foundations are meant for light loads on strong soil. In reality, raft foundations are designed for soft soils with low bearing capacity to spread heavy structural loads across a large surface area. Another frequent error is overlooking the specific 50% area rule that makes a single continuous raft more economical than numerous closely spaced individual footings.