Irrigation Engineering Multiple Choice Questions 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
Answer: a
Clarification: 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
Answer: d
Clarification: 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
Answer: a
Clarification: 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?
a) Constant radius type
b) Variable radius type
c) Constant angle type
d) Variable angle type
Answer: c
Clarification: 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%
Answer: a
Clarification: 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
c) Constant radius arch dam
d) Concrete gravity dam
Answer: b
Clarification: 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
b) constant radius arch dam
c) both constant angle and constant radius arch dam
d) variable radius arch dam