This set of Irrigation Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Types of Earthen Dams”.
1. Which of the following earth dam is suitable only on impervious foundation?
a) Zoned embankment type
b) Homogenous embankment type
c) Non-homogenous type
d) Diaphragm type
Explanation: Homogenous earth dam may be constructed of uniform and homogenous material when locally available. The percolation of water is not checked in such dams. It is suitable only on impervious foundations.
2. Which of the following zone in Zoned type embankment prevents piping through cracks?
a) Central core
b) Transition zone
c) Outer zone
d) Core wall
Explanation: The outer zone is made of fairly pervious material like grit, gravel, and murrum. The innermost zone is done with fairly impervious material. The central core is covered by comparatively pervious transition zone which prevents piping through the cracks which may develop in the core.
3. Which of the following soil material is most preferred for the central core material of zoned embankment type dam?
a) Highly impervious clay
b) Sands or silty clays
c) Coarse sands
Explanation: Clay shrinks and swells and is highly impervious is not suitable. It is sometimes mixed with fine sand or fine gravel so as to make it a suitable material for the impervious central core. Coarse sands and gravels are used in the outer shell.
4. Which embankment has the thickness of the diaphragm at an elevation less than 10 meters or the height of the embankment above the corresponding elevation?
a) Diaphragm type dam
b) Zoned type dam
c) Non-homogenous earth dam
d) Homogenous earth dam
Explanation: The thickness of the core differentiates the diaphragm embankment from the zoned type embankment.
Embankment type The thickness of core or diaphragm
|1. Diaphragm-type embankment||< 10 m or
< the height of embankment
|2. Zoned-type embankment||≥ 10 m|
5. The blanket in earth dam is provided ___________________
a) At the ground level on u/s side
b) At the ground level on the d/s side
c) At the ground level of the D/s side of the dam
d) On the D/s slope
Explanation: A blanket of relatively impervious material may be placed on the upstream face. Since homogenous earth dam poses the problems of seepage, a homogenous section is generally added with an internal drainage system. This keeps the seepage line well within the body of the dam.
6. Which of the following statement is correct with reference to earthen dams?
a) These dams are very costly as compared to other types
b) Gravity dams are less susceptible to failure as compared to rigid dams
c) These dams are suitable for construction on almost every type of foundation
d) Highly skilled labor is generally not required
Explanation: Earthen dams are suitable for any type of foundation but there has to be a separate provision for the spillway location. The mode of failure is sudden and requires high maintenance and the overall life is not so long. It requires low to moderately skilled labors and moderate capital cost.
7. During the construction of an earthen dam by hydraulic fill method, development of pore pressure becomes important in the __________________
a) Central impervious core
b) Pervious outer shell
c) Transition zone
d) Both central core and outer shell
Explanation: In this method, an embankment is created by water and earth slurry which is discharged inwards to form a central pool at site. When water is pumped to the site it spreads the coarser material drops out first and the finest at last. Thus the core material settles within the central pool forming a zoned embankment and high pore pressures develop in the core.
8. The process of laying and compacting earth in layers by power rollers under OMC for construction of earthen dams is known as ______________________
a) Rolled fill method
b) Hydraulic fill method
c) OMC method
Explanation: In the rolled-fill method, the embankment is constructed by placing suitable soil materials in thin layers and compacting the layers with rollers. Power-operated rollers are used for dams and ordinary road rollers can be used for low embankments. The best compaction can be obtained at the optimum moisture content (OMC).
9. The central core of the zoned embankment type earth dam ________________________
a) Checks the seepage
b) Prevents piping
c) Gives stability to the central impervious fill
d) Distribute the load over a large area
Explanation: The central core or hearting is done with fairly impervious material and it checks the seepage. The transition zone of mediocre permeability prevents piping through cracks. The outer zone gives stability to the central fill.
10. Which type of dam is suitable on shallow pervious foundations?
a) Zoned embankment type
a) Homogenous embankment type
c) Both Non-homogenous type and homogenous type
d) Diaphragm type
Explanation: Zoned earth dam is also called non-homogenous or heterogeneous earth dam and it is suitable on shallow pervious foundations. This dam is widely constructed and the materials of the zone are selected depending upon the availabilities.
Sanfoundry Global Education & Learning Series – Irrigation Engineering.
To practice all areas of Irrigation Engineering, here is complete set of 1000+ Multiple Choice Questions and Answers.