4. DAMS
Classifications based on type and materials of construction
Criteria for selection of best dam type:
1. Feasibility
-topography, geology, and climate (& its effect on materials)
2. Cost
-availability of construction materials near the site; accessibility of
transportation facilities
Types Materials of Construction
A. Gravity Concrete, rubble masonry
B. Arch Concrete
C. Buttress Concrete, also timber & steel
D. Embankment Earth or rock
5. Foundation Requirements
Strong foundation
Minimal differential settlement
No bearing capacity shear failure
Sand/Gravel or rock
Low hydraulic conductivity
Silt and/or Clay, non-fractured rock
5
6. GRAVITY DAMS
Gravity dams are dams which resist the horizontal thrust of the water
entirely by their own weight.
They use their weight to hold back the water in the reservoir.
Can be made of earth or rock fill or concrete.
DAMS
7. DAMS
Gravity
-Depends on its own weight for stability
-Usually straight in plan although slightly curved
Forces on Gravity Dam
1. Gravity (weight of dam)
W = V x γ = (volume)(specific weight of material)
(lb) = (ft3)(lb/ft3)
2. Hydrostatic pressure
Hh = γ h2 / 2 (horizontal component)
(lb/ft) = (lb/ft3) (ft)2 /2
where, h = depth of water at that section
γ = specific weight of water
Hv = γ V / h (vertical component)
(lb/ft) = (lb/ft3) (ft3) / ft
Where, V = volume of the dam at that point
8. DAMS
Gravity
Forces on Gravity Dam
3. Uplift
the water under pressure that comes b/t dam and foundation and results
in upward (uplift) forces against the dam
h1 = depth of water @ upstream face, aka “heel” (higher)
h2 = depth of water@ downstream face, aka “toe” (lower)
γ = specific weight of water
t = base thickness of dam.
4. Ice pressure
pressure created by thermal expansion exerts thrust against upstream
face of the dam
5. Earthquake forces
results in inertial forces that include vertical motion, oscillatory
increase, or decrease in hydrostatic pressure (all put force against dam)
9. GRAVITY DAMS
Causes of Failure:
1. Sliding along horizontal plane (shear failure)
net force > shear resistance at that level
2. Rotation about the toe
3. Failure of material
DAMS
12. DAMS
ARCH DAMS
Curved dam which is dependent upon arch action for its strength.
Transmits most of horizontal water thrust behind them to the abutments by
the arch action.
Thinner and requires less material than any other type of dam.
Used only in narrow canyons.
13. Arch dams includes:
*series of horizontal arches
*series of vertical cantilevers
Load distribution Most of load carried by
Near bottom of dam cantilevers (Known as Trial Load
Near top of dam arches Method)
I. Constant-center (Constant radius) best for U shaped canyons
II. Variable-center (Variable radius, constant-angle) best for V shaped canyons
DAMS
ARCH DAMS
16. DAMS
BUTTRESS DAMS
Buttress dams are dams in which the face is held up by a series of supports.
Buttress dams can take many forms -- the face may be flat or curved.
Usually, buttress dams are made of concrete and may be reinforced with steel
bars.
17. DAMS
BUTTRESS DAMS
sloping membrane that transmits the water load to a series of
buttresses @ right angles to axis of dam
-Increased formwork & reinforced steel compared w/gravity dam
-Less massive than gravity dam (requires 1/3 to 1/2 as much concrete)
-Use on weaker foundation
-Same forces as gravity and arch dams, however, ice pressures not as
prevalent; gaps b/t buttresses relieve majority of uplift forces
Types Water Supporting Membrane
1. Flat-slab flat, concrete-reinforced slabs
2. Multiple-arch series of arches
20. Embankment dams are massive dams made of earth or rock.
They rely on their weight to resist the flow of water, just like concrete gravity
dams.
DAMS
EMBANKMENT DAMS
22. DAMS
EMBANKMENT DAMS
Generally have some sort of water proof insides (called the core), which is covered
with earth or rock fill. Water will seep in through the earth or rock fill, but should
not seep into the core. The water will seep into the core material and should
stop at the seepage line.
Forces on Embankment Dams:
1. Force of the water (main force)
2. Uplift force
24. DAMS
COFFER DAMS
temporary structures (sheet-pile, water-tight) that allow
construction operations
diverts flow from construction areas until work completed
25. Hoover Dam
• 726.4 feet high .. • 1,244 feet across at the top ..
• 660 feet thick at the base .. • 45 feet thick at the top ..
• weighs 6.6 millions ton ... • 17 generators giving it the capacity to
produce over 2,000 megawatts
• can store up 2 years 'average' flow from the Colorado River ...
• total storage capacity can be measured in 30,500,000 acre feet ...
