# Irrigation Engineering Questions and Answers – Arch Dams – Types

This set of Irrigation Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Arch Dams – Types”.

1. An arch dam looks like a single arch in _________________
a) plan
b) front elevation
c) side elevation
d) both plan and front elevation

Explanation: A solid wall curved in plan standing across the entire width of the river valley in a single span is an arch dam. The dam body is usually made of cement concrete. When multiple or number of arches are used supported between intermediate piers, the dam is known as buttress dam.

2. A non-vertical arch dam is known as a _______________
a) buttress dam
b) double curvature arch dam
c) shell arch dam
d) both double curvature and shell arch dams

Explanation: The economy in dam thickness is further increased by making the dam body not only curved in the plan but also in section. This non-vertical dam is known as the double curvature arch dam or shell-arch dam. These dams are designed as shell structures which are quite complex.

3. Greater is the wall curvature in an arch dam, greater will be the economy in the dam thickness.
a) True
b) False

Explanation: The curved wall will structurally behave as a cantilever retaining wall standing up from its base and partly the load will be transferred to the two ends of the arch span. The load on the cantilever wall reduces as it is distributed to the side walls which in turn reduces the thickness.

4. Which of the following is the most economical type of arch dam?
c) Constant angle type
d) Variable angle type

Explanation: A special type of variable radius arch dam in which the central angles of the horizontal arch rings are of the same magnitude at all elevations is called a constant angle arch dam. Such a dam proves to be economical as the design can be made by adopting the best central angle of 133°-34′.

5. A constant angle arch dam when compared to constant radius arch dam utilizes concrete quality of about ______________
a) 43%
b) 130%
c) 230%
d) 113%

Explanation: The simplest in design as well as construction is a constant radius arch dam but uses the maximum concrete. An intermediate choice is a variable radius arch dam using around 58% of the concrete used by constant radius arch dam. A constant angle arch dam uses about 43% of the concrete used by a constant radius arch dam.

6. Which among the following type of dam section is expected to be the thinnest and the most economical?
a) Constant angle arch dam
b) Shell-arch dam
d) Concrete gravity dam

Explanation: Shell arch dams are much more economical than the constant angle arch dams as their sections are quite thin. The Idduki dam in India is only 45 m thick at its base even with 170.7 m height whereas the famous Hoover dam of the USA which is a constant radius arch dam is 201m thick at its base with only 222 m in height.

7. The most economical central angle of the arch rings of an arch dam can be adopted only at one place preferably at mid-height in an arch dam is of the type __________________
a) constant angle arch dam
c) both constant angle and constant radius arch dam

Explanation: The most economical central angle is equal to 1330-34’ and such an angle can be adopted only at one place in constant radius arch dam since as there is considerable variation with height due to narrow V-shape of the valley. It is therefore considered to keep the economical angle of 1330-34’ at about mid-height and the angle at the top will be more than this value due to topographical conditions.

8. In an arch dam, the extrados curve refer to the arch rings corresponding to the ____________________
a) the upstream face of the dam
b) downstream face of the dam
c) side face of the dam
d) either upstream or downstream face of the dam

Explanation: The arch rings corresponding to the upstream face is called the extrados curve. The arch rings corresponding to the downstream face are the intrados curve.

9. A V-shaped valley with stronger foundations can suggest the choice of an arch dam is of the type ___________________________
c) constant angle arch dam
d) variable angle arch dam

Explanation: The variable center arch dam is also preferred for V-shaped valleys as compared to constant radius arch dams. The constant radius arch dam may be preferred for comparatively wider U-shaped valleys.

10. A constant radius arch dam is also sometimes called as _______________
a) constant centre arch dam
b) constant angle arch dam
c) variable angle arch dam
d) variable centre arch dam

Explanation: In a constant radius arch dam, the centres of extrados, intrados as well as the centrelines of the horizontal arch rings lie on a straight vertical line at various elevations that passes through the centre of the horizontal arch ring at the crest. The centre of the arch rings is not at one point but lies along on vertical line at different heights where in variable centre arch dam the centres do not lie on the same vertical line.

11. The type of arch dam which generally requires overhangs at abutments is of ________________________
c) constant angle type
d) variable angle type

Explanation: The design of a constant angle dam usually involves providing overhangs at abutments which requires stronger foundations. Hence, they are not used if the foundations are weak. Such a dam proves to be most economical out of all other dams.

Sanfoundry Global Education & Learning Series – Irrigation Engineering.

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