Gravity dams are rigid concrete dams that rely entirely on their weight to maintain stability. They are built with a triangular cross-section to transfer loads directly to strong rock foundations. Famous gravity dams discussed include the Bhakra Dam in India and Fontana Dam in the US. Advantages are that they are durable, allow heights over 700 feet, and have low maintenance costs. However, they require competent foundations and construction is complex. Forces like water pressure, uplift, and earthquakes must be addressed through design to prevent failures by overturning, sliding, tension, or crushing.

1. PRESENTATION ON
GRAVITY DAM

2. INTRODUCTION

3. GRAVITY DAM
 It is a masonry or concrete dam
which resists the forces acting on it
by its own weight.
 These dams are heavy and massive
wall-like structures of concrete in
which the whole weight acts
vertically downwards. Its c/s is
approximately triangular in shape.
 As the entire load is transmitted on
the small area of foundation, such
dams are constructed where rocks
are competent and stable.

4. Gravity dams are rigid concrete dams which ensure
stability against all loads by virtue of their weight alone.
They transfer all the loads to the foundation and hence
are built when the foundation is strong rock. A typical
section of a gravity dam is shown.

5. FAMOUS GRAVITY DAMS

6. BHAKRA DAM
HIMACHAL, INDIA
HEIGHT
741 feet
(226 m)

7. FONTANA DAM
NORTH CAROLINA, USA
HEIGHT
700 feet
(210 m)

8. LAKE VYRNWY DAM
LIVERPOOL, UK
HEIGHT
146 feet
(45 m)

9. NUREK DAM
TAJIKISTAN
HEIGHT
984 feet
(300 m)

10. SHASTA DAM
NORTH CALIFORNIA,USA
HEIGHT
602 feet
(183 m)

11. Heel
Gallery
Toe
Spillway
(inside dam)
Crest
NWL (Normal water level)
MWL (Max. water level)
Free board
Sluice way
Upstream Down stream

12. Purpose of Gravity dam

13. ADVANTAGES OF GRAVITY DAM
• Strong, Stable and Durable
• Suitable for moderately wide valleys having steep
slope
• Loss of water by seepage in gravity dams is less.
• Can be constructed to very great heights
• Suitable for an overflow spillway section
• Maintenance cost is very low
• Does not fail suddenly

14.  Gravity dams of great height can be constructed only on sound
rock foundations
 Initial cost is more than earth dam
 Takes longer time in construction
 Require more skilled labor than earth dam
 Subsequent raise is not possible in a gravity dam
 Design of gravity dams is very complicated
DISADVANTAGES OF GRAVITY DAM

15. Forces Acting On Gravity
Dam
 Water Pressure
 Weight of the Dam
 Uplift Pressure
 Silt Pressure
 Wave Pressure
 Wind pressure
 Ice pressure
 Earthquake Pressure

16. Water Pressure is the most major external force acting on a
gravity dam.
On upstream face pressure exerted by water is stored upto the ful
reservoir level. The upstream face may either be vertical or inclined.
On downstream face the pressure is exerted by tail water. The
downstream face is always inclined
Water Pressure

17. Weight of the Dam
The self weight of the gravity dam is the main stabilising
force which counter balances all the external forces
acting on it.

18. Uplift Pressure
 Uplift pressure is the
pressure exerted by water as
it seeps through the body of
the dam or its foundation.
 Seeping water exerts
pressure on the base of the
dam and it depends upon
water head.

19. Silt Pressure
 Sediment deposition in the reservoir results in a force
acting horizontally on the upstream face. This force is
assumed to have a hydrostatic distribution.

20. Wave Pressure
 Waves are generated on the surface of the reservoir by
the blowing winds, which exert a pressure on the
upstream side. Wave pressure depends upon wave
height

21. Wind pressure
• The top exposed portion on the dam is small & hence
the wind pressure on this portion of dam is negligible.

22.  The ice which may be formed on the water surface of
the reservoir in cold countries may sometimes melt and
expand. The dam face is subjected to the thrust exerted
by the expanding ice.
Ice pressure

23. Dams are subjected to vibration during earthquakes.
Vibration affects both the body of the dam as well as the water
in the reservoir behind the dam.
The most danger effect occurs when the vibration is
perpendicular to the face of the dam.
Earthquake Pressure

24. Sliding – It may take place on a horizontal joint above formation, on
the foundation. Sliding takes place when total horizontal forces are
greater than the combined shearing resistance of the joint and the
static friction induced by total vertical forces.
Causes of gravity dams Failure

25. Overturning – A dam fails in overturning when total horizontal
forces acting on the dam section are quite great in comparison with
total vertical forces. In such cases the resultant of two passes
outside the limits of the dam.
Causes of gravity dams Failure

26. Dam may fail when tension is produced in the concrete.
Dam may fail in crushing due to compression.
Causes of gravity dams Failure

27. To prevent overturning, the resultant of all forces acting on
the dam should remain within the middle-third of the base
width of the dam.
 In the dam, the sliding should be fully resisted when the
condition for no sliding exists in the dam section.
In the dam section, the compressive stresses of concrete or
masonry should not exceed the permissible working stress
to avoid failure due to crushing.
There should be no tension in the dam section to avoid the
formation of cracks.
The factor of safety should be maintained between 4 to 5
Precaution against dams Failure