When the depth of water is from 4.5 m to 6 m, the type of cofferdam used is
- AEarthen cofferdam
- BRockfill cofferdam
- CSingle-walled cofferdamCorrect
- DNone of the above
Solution
Concept
Selection of cofferdam based on depth
Formula
NONE
Step-by-step solution
1. Cofferdams are temporary structures constructed to enclose an area for dewatering and excavation. 2. Earthen cofferdams are used for water depths up to 3 m, and rockfill cofferdams are used for up to 3 m depth with strong currents. 3. Single-walled sheet pile cofferdams are suitable for moderate water depths ranging from 4.5 m to 6 m. Answer: C
Explanation
A single-walled sheet pile cofferdam is suitable for retaining water at moderate depths between 4.5 m and 6 m where working space is restricted. Shallow water depths under 3 m typically use earthen dams, while deeper waters require double-walled or cellular cofferdams.
Why the other options are wrong
A) Earthen cofferdams are used for small water depths up to 3 m. B) Rockfill cofferdams are typically used for depths up to 3 m when rock is available. D) Option C is correct as single-walled cofferdams are used for depths between 4.5 m and 6 m.
Shortcut
Cofferdam depth guidelines: Earthen (<3m), Rockfill (3–4.5m), Single-walled (4.5–6m).
Common mistake
Misremembering water depth applicability limits for different cofferdam types.
Correct answer: C) Single-walled cofferdam