Pile Foundations MCQ with answer and solution

Concept

Under-reamed piles are cast-in-situ concrete piles having one or more bulbs (enlargements) formed in their base to increase the bearing and uplift capacity, particularly in expansive soils such as black cotton soils.

Formula

D_b = 2.5 × d

Step-by-step solution

1. Identify the type of pile: Bored cast-in-situ under-reamed pile. 2. Recall the standard specifications as per IS 2911 (Part III) for under-reamed piles. 3. The standard ratio of bulb diameter (D_b) to stem diameter (d) is normally 2.5.

Explanation

According to IS 2911 (Part 3) for under-reamed piles, the diameter of the bulb (under-ream) is normally kept as 2.5 times the stem diameter for single and multi-under-reamed piles in soils like expansive clays.

Why the other options are wrong

A: 1.5 is too small and not standard for under-reamed pile bulbs. C: 3.25 is not a standard code specification for bulb diameter ratio. D: 3.5 is generally the maximum limit or used in special cases, whereas 2.5 is the normal standard value.

Shortcut

Remember the standard 2.5 ratio for under-reamed pile bulbs in Indian Standard codes.

Common mistake

Confusing the bulb diameter ratio with spacing or length parameters of piles.