The dam built in a broad valley covered with alluvial deposit is:
- AMasonry Dam
- BEarth DamCorrect
- CRock-fill dam
- DNone of the above
Solution
Concept
Suitable dam type for alluvial valleys
Formula
NONE
Step-by-step solution
1. Broad valleys with deep alluvial deposits lack solid rock foundations close to the surface required for heavy rigid dams. 2. Earth dams exert lower foundation bearing pressure and can accommodate moderate settlement on compressible alluvial soil. 3. Therefore, earth dams are best suited for construction across broad valleys covered with alluvial deposits. Answer: B
Explanation
Broad valleys with alluvial deposits consist of deep soil layers that lack solid bed rock near the surface to support heavy masonry structures. Earth dams distribute their structural load over a wide base, making them ideal for foundations with lower bearing capacity and potential settlement. Hence, an earth dam is the correct choice for such sites.
Why the other options are wrong
A) Masonry dams require unyielding rock foundations rather than alluvial deposits. C) Rock-fill dams require firm rock foundations to prevent differential settlement. D) Option B is correct because earth dams are suitable for alluvial deposits.
Shortcut
Alluvial/soft valley soil requires flexible Earth Dams rather than rigid masonry.
Common mistake
Selecting a rigid masonry dam instead of a flexible earth dam suitable for weak alluvial foundations.
Correct answer: B) Earth Dam