A watertight enclosure from which water is pumped to expose the bed of a water body in order to permit the construction of a pier or other hydraulic work is called
- AWell foundation
- BCofferdamCorrect
- CPier foundation
- DPneumatic Caisson
Solution
Concept
A cofferdam is a temporary watertight enclosure. Water is pumped out of it to allow construction in the dry.
Step-by-step solution
1. The question describes a watertight enclosure from which water is pumped out. 2. It exposes the bed so a pier or hydraulic work can be built. 3. This is the definition of a cofferdam. 4. So the answer is (B).
Explanation
A cofferdam is a temporary structure built in water. Water inside it is pumped out so that work can be done in dry conditions. It is removed after the work is complete.
Why the other options are wrong
A: A well foundation is a permanent deep foundation that is sunk into the bed. C: A pier foundation is the foundation itself, not a temporary enclosure. D: A pneumatic caisson keeps water out using compressed air, not by pumping out an open enclosure.
Shortcut
Temporary + watertight + pumped dry = Cofferdam.
Common mistake
Confusing a cofferdam with a caisson; a caisson usually becomes part of the permanent foundation.
Correct answer: B) Cofferdam