Cofferdams MCQ with answer and solution

Concept

A cantilever sheet pile cofferdam has no bracing. It depends only on the embedment of the piles, so it is used for small heights of water or soil.

Step-by-step solution

1. A cantilever sheet pile wall is held only by passive soil pressure below dredge level. 2. Bending moment and deflection increase quickly as height increases. 3. So it is economical and safe only for small heights, about 3 to 4 m. 4. Braced, double wall and cellular types are used for larger heights. Answer is (A).

Explanation

A cantilever sheet pile cofferdam has no struts or ties, so its stability comes only from the pile depth inside the soil. This limits it to small heights. For greater heights we need bracing or double walls.

Why the other options are wrong

B: Braced cofferdams use struts, so they suit deeper excavations and greater heights. C: Embankment cofferdams need large space and plenty of material. They are used for wide, shallow sites, and the standard answer for small height is the cantilever sheet pile type. D: Double wall cofferdams are used for larger heights and greater water depth.

Shortcut

No support (cantilever) means small height only.

Common mistake

Choosing embankment type just because it is used in shallow water.