WATER RESOURCE ENGINEERING

1. Swami Keshvanand Institute of Technology
Management & Gramothan Jaipur
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SUBJECT: WATER RESOURCE ENGINEERING (WRE)
SITARAM SAINI
ASSISTANT PROFESSOR
DEPARTMENT OF CIVIL ENGINEERING

2. Introduction
1. What is the gravity dam.
2. Need of gravity dam.
3. Forces acting on gravity dam.
4. Stability analysis of gravity dam.
5. Numerical problems on gravity dam.
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3. What is gravity dam:
 It is a solid structure made of concrete or masonry which is
generally constructed across a river to create a reservoir on it`s
upstream side.
The section of gravity dam is approximately triangular in shape
with larger bottom.
Gravity dam resist all the forces acting on it by it`s self weight (or
weight component).
Highest gravity dam in India is Bhakra dam. Which is constructed
at bhakra village district bilaspur state Himachal pradesh in India.
DAM is 226m high at Sutlej river.
Highest gravity dam in the world is Grand dixence dam in
Switzerland. DAM is 285m high.
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Google image

5. Need of Gravity dam.
 Drinking and domestic water supply
 Flood control
 Irrigation
 Industrial water supply
 Hydroelectric energy production
 Retention and control of sediments
 Inland navigation
 Improvement of water quality
 Fish Farming.
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6. Advantages of Gravity Dam:
1. Strong, Stable and Durable.
2. Suitable for moderately wide valleys having steep slopes.
3. Can be constructed to very great heights.
4. Suitable for an overflow spillway section.
5. Maintenance cost is very low.
6. Does not fail suddenly.
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7. Disadvantages of Gravity Dam:
1. Gravity dams of great height can be constructed only on
sound rock foundations.
2. Initial cost is more than earth dam.
3. Takes longer time in construction.
4. Require more skilled labour than earth dam.
5. Subsequent raise is not possible in a gravity dam.
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8. 1. Water pressure.
2. Weight of the dam.
3. Uplift pressure.
4. Earthquake pressure.
5. Ice pressure.
6. Wave pressure.
7. Silt pressure.
8. Wind pressure.
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Forces acting on gravity dam.

9. Water Pressure:
This is the major external force acting on dam Pressure
Components on both upstream and downstream are:
1. Vertical Component 2. Horizontal Component
Unit weight of water, γw=1000 kg/m3
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Google image

10. Weight of Dam:
This is the major resisting force
 Generally unit length of dam is
considered
 The cross section of dam may be
divided into several triangles and
rectangles and weights W1, W2,
W3 etc., may be computed
 The total weight W of the dam acts
at the C.G. of its section.
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Google image
Weight = Volume per unit length x
unit weight of material

11. Uplift Pressure:
Water enters the pores, cracks & fissures with in the body of the
dam, at the interface between the dam and with in the
foundation, because the water is under pressure ,it creates uplift
pressure on the dam.
Uplift pressure depends upon the character of foundation.
1. Area factor.
2. Intensity of uplift pressure.
3. Effects of drains on uplift pressure.
4. Effects of grout curtain(or cut-off).
5. Effects of tension crack.
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12. 1. Uplift Pressure (No Gallery).
2. Uplift Pressure (with Gallery).
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Uplift Pressure
(No Gallery)
Google image

13. Determination of uplift pressure for different conditions:
1. Uplift pressure without drainage gallery but tail water is there.
2. Uplift pressure with no drainage gallery and no tail water.
3. Uplift pressure with drainage gallery and tail water.
4. Uplift pressure with drainage gallery and no tail water.
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14. Pressure due to Earthquake:
Earthquake waves imparts accelerations to the foundations under
the dam and causes its movement ,This earthquake wave may travel
in any direction.
For design purpose, Horizontal and Vertical directions are
considered.
Seismic Force = Mass x Earthquake Acceleration
According to IS 1893-2002, India was divided into Four zones: zone
II, III, VI, and V.
EarthquakeAcceleration:
Earthquake Acceleration is usually designated as fraction of the
acceleration due to gravity
It is expressed as α.g where α is knownas Seismic Coefficient
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Google image

16. Seismic Coefficient:
Seismic coefficient is divided into
1. Horizontal Seismic coefficient, αh
2. Vertical Seismic Coefficient, αv = .75 αh
αh can be determined by one of the two methods
1. Seismic Coefficient Method < 100m height of the dam
2. Response Spectrum Method > 100m height of the dam
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17. Seismic Coefficient Method:
As per IS: 1893-1984,
Horizontal Seismic coefficient, αh = 2α0
Where α0 =Basic Seismic Coefficient
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Basic Seismic Coefficient as per IS 1893:1984
Seismic Zone II III IV V
Basic Seismic
Coefficient (α0)
0.02 0.04 0.05 0.08

18. Earthquake forces on the body of the dam:
(1) Due to the effects of horizontal acceleration.
(2) Due to the effects of vertical acceleration.
(1) Due to the effects of horizontal acceleration.
FH =
𝑤
𝑔
𝛼h 𝑔 = 𝛼h 𝑤
(2) Due to the effects of vertical acceleration.
FV =𝑤
𝑔
𝛼v 𝑔 = 𝛼v 𝑤
Where, 𝛼= seismic coefficient
𝛼v = 0.75 𝛼h
𝛼h = 2 𝛼o
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19. Ice Pressure:
1. The ice formed on water surface of the reservoir is subjected to
expansion and contraction due to temperature variations.
2. Coefficient of thermal expansion of ice is 5 times more than concrete.
3. The dam face has to resist the force due to expansion of ice.
4. This force acts linearly along the length of the dam, at reservoir level.
5. IS: 6512-1984 recommends 250 kN/m2 applied to the face of dam over
the anticipated area of contact of ice with the face of the dam.
The magnitude of the force due to ice pressure depends upon a number of
factors.
1.) Thickness of ice.
2.) Rate of temperature rise.
3.) Restraints of rim walls.
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20. Wave Pressure:
Waves are generated on the surface of the reservoir by the blowing
winds, which causes a pressure towards the downstream side. Wave
pressure depends upon the wave height.
Wave height may be given by the equation
Hw = 0.0322√V.F + 0.763 - 0.271 (F)1/4 for F < 32 Km
&
Hw = 0.032 √𝑉. 𝐹 for F > 32 Km
Where, F = Fetch of reservoir in Km.
V= Wind velocity in Km/ hour
Wave pressure distribution:
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PW = 2 𝛾 Hw
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21. Wave Pressure:
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Google image

22. Silt Pressure:
According to IS 6512:1972 the silt pressure and water pressure
exist together on submerged silt
Following are the values for horizontal and vertical direction for
silt force calculation.
Psh = 1360 kg/m3
Psv = 1925 kg/m3
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23. Silt Pressure:
It has been explained under `Reservoir Sedimentation' that it gets
deposited against the upstream face of the dam. If h is the height of
silt deposited, then the force exerted by this silt in addition to
external water pressure can be represented by
Rankine's formula as:
Where,
𝜑 = angle of internal friction of Soil, and cohesion is neglected.
𝛾sub = Submerged unit weight of silt material in KN/𝑚3
h = Height of silt deposited in m.
Ka = Coefficient of active earth pressure.
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𝑷𝑺𝒊𝒍𝒕 =
𝟏
𝟐
𝜸sub h2 Ka and it acts at (
𝟏
𝟑
) h from base.
Ka =
1−𝑠𝑖𝑛𝜑
1+𝑠𝑖𝑛 𝜑

24. Wind Pressure:
 It is a minor force acting on dam
 Acts on Superstructure of the dam
 Normally, wind pressure is taken as 1 to 1.5 kN/m2
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