Deck 5: Dam Design and Spillways

Question 1

When the upstream face of a gravity dam is vertical, then the intensity of water pressure at the water surface and at the base respectively will be (where w is unit weight of water and H is the depth of water.)

A)0 and wH212
B)wH2/2and wH2/3
C)wH and 0
D)OandwII

Answer 1

OandwII

Question 2

The uplift pressure on a dam can be controlled by
i. constructing cutoff under upstream face
ii. constructing drainage channels bet-ween the dam and its foundation
iii. by pressure grouting in foundation
The corret answer is

A)only (i)
B)both (i) and (ii)
C)both (i) and (iii)
D)(i), (ii) and (iii)

Answer 2

(i), (ii) and (iii)

Question 3

The uplift pressure on the face of a drainage gallery in a dam is taken as

A)hydrostatic pressure at toe
B)average of hydrostatic pressure at toe and heel
C)two-third of hydrostatic pressure at toe plus one-third of hydrostatic pressure at heel
D)none of the above

Answer 3

two-third of hydrostatic pressure at toe plus one-third of hydrostatic pressure at heel

Question 4

Horizontal acceleration due to earthquake results in

A)hydrodynamic pressure
B)inertia force into the body of the dam
C)both (a) and (b)
D)none of the above

Question 5

Hydrodynamic pressure due to earthquake acts at a height of

A)3H/47I above the base
B)3H747t below the water surface
C)4H/371 above the base
D)4H737t below the water surface where H is the depth of water.

Question 6

The major resisting force in a gravity dam is

A)water pressure
B)wave pressure
C)self-weight of dam
D)uplift pressure

Question 7

When the reservoir is full, the maximum compressive force in a gravity dam is produced

A)at the toe
B)at the heel
C)within the middle third of base
D)at centre of base

Question 8

The maximum permissible eccentricity for no tension at the base of a gravity dam is

A)B/2
B)B/3
C)B/4
D)B/6

Question 9

Presence of tail water in a gravity dam
i. increases the principal stress
ii. decreases the principal stress
iii. increases the shear stressiv) decreases the shear stress
The correct answer is

A)(i) and (iii)
B)(i)and(iv)
C)(ii) and (iii)
D)(ii) and (iv)

Question 10

For wave action in dams, the maximum height of freeboard is generally taken to be equal to (where hw is height of wave.)

A)0.5 hw
B)0.75 hw
C)1.25 hw
D)1.50 hw

Question 11

As compared to gravity dams, earthen dams

A)are costlier
B)are less susceptible to failure
C)require sound rock foundations
D)require less skilled labour

Question 12

The most suitable material for the central impervious core of a zoned embankment type dam is

A)clay
B)coarse sand
C)silty clay
D)clay mixed with fine sand

Question 13

Seepage through embankments in an earthen dam is controlled by

A)drainage filters
B)relief wells
C)drain trenches
D)provision of downstream berms

Question 14

Seepage through foundation in an earthen dam is controlled by providing

A)rock toe
B)horizontal blanket
C)impervious cut off
D)chimney drain

Question 15

The flow of water after spilling over the weir crest in chute spillway and side channel spillway respectively are

A)at right angle and parallel to weir crest
B)parallel and at right angle to weir crest
C)parallel to weir crest in both
D)at right angle to weir crest in both

Question 16

The discharge passing over an ogee spillway is given by (where, L is effective length of spillway crest and H is the total head over the spillway crest including velocity head.)

A)CLH^3/2
B)CHL^3/2
C)CLH^5/2
D)CLH^1/2

Question 17

Coefficient of discharge of an ogee spillway

A)depends on depth of approach and upstream slope
B)depends on downstream apron interference and downstream submergence
C)remains constant
D)both (a) and (b)

Question 18

Which of the following spillways is least suitable for an earthen dam ?

A)ogee spillway
B)chute spillway
C)side channel spillway
D)shaft spillway

Question 19

In case of non-availability of space due to topography, the most suitable spillway is

A)straight drop spillway
B)shaft spillway
C)chute spillway
D)ogee spillway

Question 20

In a chute spillway, the flow is usually

A)uniform
B)subcritical
C)critical
D)super critical

Question 21

For the upstream face of an earthen dam, the most adverse condition for stability of slope is

A)sudden drawdown
B)steady seepage
C)during construction
D)sloughing of slope

Question 22

If there are two canals taking off from each flank of a river, then there will be

A)one divide wall and one undersluice
B)one divide wall and two undersluices
C)two divide walls and one undersluice
D)two divide walls and two undersluices

Question 23

Generally the weir is aligned at right angles to the direction of the main river current because

A)it ensures less length of the weir
B)it gives better discharging capacity
C)it is economical
D)all of the above

Question 24

The main function of a divide wall is to

A)control the silt entry in the canal
B)prevent river floods from entering the canal
C)separate the undersluices from weir proper
D)provide smooth flow at sufficiently low velocity

Question 25

A divide wall is provided

A)at right angle to the axis of weir
B)parallel to the axis of weir and up-stream of it
C)parallel to the axis of weir and down-stream of it
D)at an inclination to the axis of weir