This set of Irrigation Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Buttress Dam – Types”.
1. The load from the deck of a buttress dam is transmitted to the foundations through the ______
c) lateral braces
d) sloping deck
Explanation: Buttresses are solid walls of specified thickness and sections are constructed parallel to the flow at suitable intervals. They are used to support the vertical slab which holds the water. The stability of the dam against external forces is obtained by transferring the water pressure to the supporting buttresses.
2. Multiple arch dams are generally used for ______________
a) high heights
b) low heights
c) medium heights
d) any height
Explanation: Free slab type dams are generally preferred for smaller heights and multiple arch dams are used for higher dam heights. Manicougan-5 dam in Canada is the highest multiple arch dam of the world having a height of 210 m.
3. Which of the following dam requires no reinforcement?
a) Fixed deck buttress dam
b) Simple deck buttress dam
c) Cantilever deck buttress dam
d) Massive head buttress dam
Explanation: Massive head buttress dam does not use slabs or arches for the upstream face. The head of the buttresses are enlarged to meet each other to form a continuous water supporting surface. The bending, as well as diagonal tension in the upstream part of the dam, is absent, so the deck is not reinforced.
4. Which of the following dam is also known as the Amberson dam?
a) Multiple arch buttress dam
b) Mushroom head buttress dam
c) Massive head buttress dam
d) Free deck buttress dam
Explanation: Free deck slab type dam is generally preferred for smaller heights. Rodriguez dam in Mexico is the highest dam of such kind having a height of 73.2 m. They are virtually referred to as Amberson dams.
5. Which of the following component of a buttress dam is also called counterfort?
c) Lateral brace
d) Sloping deck
Explanation: A counterfort or a buttress is a structure built against the wall to prevent overturning or to increase its bending strength. This term is synonymous with the buttress and is often used when referring to the dam, retaining walls and other structures.
6. Which of the following type of dam requires very strong and stable foundations and is not in use as much as the other types?
a) Multiple dome-type dams
b) Massive head type dam
c) Columnar buttress type dam
d) Deck slab type dam
Explanation: Columnar buttress type dam is a modification of the ordinary slab type and the deck is supported on columns. It requires a very durable base and more skill is required in constructing the buttresses.
7. Which of the following is the earliest recorded multiple arch buttress dam?
a) Meer Alam dam in India
b) The Coolidge dam in Arizona
c) Rodriguez dam in Mexico
d) Idduki dam in Kerela, India
Explanation: The Coolidge dam on San Carlos River in Arizona is a multiple dome-type dam having a height of 76.2 m with buttresses @ 54.8 m apart. The Rodriguez dam in Mexico is the highest deck slab type dam having a height of 73.2 m. The Idduki dam is a concrete double curvature parabolic thin arch dam.
8. In a simple deck slab buttress dam of a given height, the buttress spacing can be increased by increasing the upstream slope.
Explanation: The economical spacing of buttresses is governed to a very large extent by the values of the upstream slope of the dam which is given by the master curve. The lower values of upstream slope lesser than 47° are not available on the master curve which shows that lower values will not prove economical for the project.
9. The buttresses of a free deck buttress dam are provided at ‘x’ m clear spacing and buttress thickness is proposed to be ‘t’ m. The buttress section can then be designed like the section of a concrete gravity dam by considering the effective unit weight of water = Surcharge factor (S) x actual unit weight of water. The value of this surcharge factor is given as _____________
a) S = (x + t)/x
b) S = (x + t)/t
c) S = (x + t)/(x + 1)
d) S = (x + t)/(t + 1)
Explanation: Surcharge factor (S) is the ratio of the dam length (x + t) to the buttress thickness (t).
S = (x + t)/t
The resultant impact can be considered by increasing the unit weight of water by multiplying the actual value by a surcharge factor.
10. What is the suggested economic buttress spacing for a mean dam height of greater than 45 m?
b) 4.5 to 7.5
c) 7.5 to 12
d) 12 to 15
Explanation: The suggested economic buttress spacing in m for a normal Φ value of 40° to 50° for different dam heights –
|S.No||Mean Dam Height in m||Economic buttress spacing|
|1.||Less than 15||4.5|
|2.||15 – 30||4.5 to 7.5|
|3.||30 – 45||7.5 to 12|
|4.||Above 45||12 to 15|
11. What is the suggested slenderness ratio for simply supported RCC decks?
a) 4.5 to 7.5
b) 7.5 to 12
c) 12 to 15
d) 15 to 18
Explanation: The height, thickness and spacing of buttresses can be controlled by Slenderness ratio. Slenderness ratio is the ratio of the height of the buttress to the thickness of the buttress. The value usually ranges from 12 to 15.
12. What is suggested massiveness factor for simply supported RCC Decks?
a) 2.5 to 3
b) 3 to 4.5
c) 4.5 to 7.5
d) 7.5 to 12
Explanation: Massiveness factor and slenderness ratio both controls the height, thickness and the spacing of the buttress. The suggested slenderness ratio usually ranges from 12 to 15 and the massiveness factor varies from 2.5 to 3.
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