Pile Foundations MCQ with answer and solution

Concept

Spacing of piles in a pile group to avoid overlapping of stress bulbs and reduction in bearing capacity.

Formula

Spacing = 3 × D (where D is the diameter of the pile)

Step-by-step solution

1. Refer to IS 2911 provisions for pile foundations. 2. Identify the requirement for friction piles, where the load is transferred mainly through skin friction. 3. The minimum centre-to-centre spacing for friction piles is standardly recommended as 3D to ensure efficient load transfer and avoid group efficiency reduction.

Explanation

According to IS 2911 (Part 1/Sec 3), the minimum centre-to-centre spacing for friction piles is specified as 3 times the diameter of the pile. This ensures that the stress zones of adjacent piles do not overlap excessively, preventing a reduction in the group load-bearing capacity.

Why the other options are wrong

A: 2 times diameter is too close and causes severe stress overlap. B: 2.5 times diameter is generally used for point-bearing piles resting on rock. D: 6 times diameter is too conservative and uneconomical for standard friction piles.

Shortcut

Remember: Friction piles require a spacing of 3D, while point-bearing piles can sometimes be spaced at 2.5D if resting on a strong stratum.

Common mistake

Confusing friction piles (3D) with load-bearing end-bearing piles or under-reamed piles which may have different spacing criteria.