VE 471 WATER RESOURCES ENGINEERING

VE 471
WATER RESOURCES ENGINEERING
DAMS
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3. DAMS
Overview

Classification of Dams
Parts of Dams
Planning of Dams
Construction of Dams
Concrete Gravity Dams
Arch Dams
Cross-sectional Layout Design of Dams
Local Scour at the Downstream of Dams
Dam Safety and Rehabilitation
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3. DAMS
Overview

Classification of Dams
Parts of Dams
Planning of Dams
Construction of Dams
Concrete Gravity Dams
Arch Dams
Buttress Dams
Embankment (Fill Dams)
Cross-sectional Layout Design of Dams
Local Scour at the Downstream of Dams
Dam Safety and Rehabilitation
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3. DAMS
Classification of Dams

A dam is an impervious barrier built across a watercourse to
store water for several purposes:

There are disadvantages of dams as well:

water supply,
creating head (energy generation),
forming a lake,
sediment control,
flood control,
recharging of groundwater, etc.
imbalance of ecosystem,
decrease amount of downstream water,
reduction in the fertility of farmlands, etc.
Therefore, detailed survey should be carried out to ensure that
the relative weights of advantages over disadvantages are
higher.
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3. DAMS
Classification of Dams

Dams can be classified into a number of different categories
depending upon the purpose of classifications.
A classification based on the type and materials of construction:

Gravity Dams

Arch Dams

Constant-angle arch dams
Constant-center arch dams
Variable-angel, variable-cemter arch dams
Buttress Dams

Concrete gravity dams
Prestressed concrete gravity dams
Roller compacted concrete (RCC) gravity dams
Flat-slab buttress dams
Multiple-arch buttress dams
Embankment (Fill) Dams
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3. DAMS
Classification of Dams

Gravity Dams

Concrete gravity dams
Pre-stressed concrete gravity
dams
Roller compacted concrete
(RCC) gravity dams
Karun Dam, Iran
http://en.wikipedia.org/wiki/Dam
Shasta Dam, California, USA
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3. DAMS
Classification of Dams

Arch Dams

Constant-angle arch dams
Constant-center arch dams
Variable-angel arch dams
Variable-center arch dams
Monticello Dam, California, USA
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Gordon Dam, Tasmania
http://en.wikipedia.org/wiki/Dam
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3. DAMS
Classification of Dams

Buttress Dams
Used mainly in wide valleys, it
consists of an impermeable wall,
which is shored up by a series of
buttresses to transmit the thrust of
the water to the foundation.
Flat-slab buttress dams
Multiple-arch buttress dams
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3. DAMS
Classification of Dams

Buttress Dams

Flat-slab buttress dams
Lake Tahoe Dam, California, USA
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3. DAMS
Classification of Dams

Buttress Dams

Multiple-arch buttress dams
Bartlett Dam , Phoenix, Arizona, USA
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3. DAMS
Classification of Dams

Embankment (Fill) Dams

Earth-fill dams

Simple embankment
Zoned embankment
Diaphragm type embankment
Upstream of Ataturk Dam, Turkey

Embankment (Fill) Dams

Downstream of Ataturk Dam, Turkey
Rock-fill dams

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Impermeable-face
Impermeable-earth core
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3. DAMS
Classification of Dams

A classifications based on
purpose, such as

storage
diversion
flood control
hydropower generation
A classification based on
hydraulic design such as

overflow dams,
non-overflow dams
Gilboa Dam, New York State, USA
http://en.wikipedia.org/wiki/Dam
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3. DAMS
Classification of Dams

A classification based on dam height:
According to the International Commission on Large Dams (ICOLD):

Large Dam Æ if height > 15 m
Large Dam Æ if 10 m < height < 15 m
reservoir storage > 106 m3
crest length > 500 m
High Dam Æ height > 50 m
Small Dam Æ height < 10 m
Distribution of dam heights in Turkey as of 2002.
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3. DAMS
Overview

A dam is composed of the following structural components

Body forms the main part of a dam as an impervious barrier.
Reservoir is the artificial lake behind a dam body.
Spillway is that part of a dam to evacuate the flood wave from the
reservoir.
Water intake is a facility to withdraw water from a reservoir.
Outlet facilities are those appurtenances to withdraw water from
the reservoir to meet the demands or to discharge the excess
water in the reservoir to the downstream during high flows.

sluiceways,
penstocks,
diversion tunnels,
bottom outlets, and
water intake structures
Others: Hydropower station, site installations, roads, ship locks,
fish passages, etc.
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3. DAMS
Overview

There are commonly three steps in the planning and design:

reconnaissance survey,
feasibility study, and
planning study.
In reconnaissance surveys, the alternatives, which seem
infeasible without performing intensive study, are eliminated.
Feasibility Study:

Estimation of water demand
Determination of water potential
Optimal plans
Determination of dam site

Topography
Geologic information
Foundation conditions
Flood hazard
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3. DAMS
Planning of Dams

Feasibility Study:

Determination of dam site (cont’d)

Spillway location and possibility
Climate
Diversion facilities
Sediment problem
Water quality
Transportation facilities
Right of way cost
Determination of type of dams
Project design

Hydrologic design
Hydraulic design
Structural design
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3. DAMS
Planning of Dams

Planning Study:

Topographic surveys
Foundation studies
Details on materials and constructional facilities
Hydrologic study
Reservoir operation study
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3. DAMS
Overview

Details of dam construction are beyond the scope of this
course.
The principal steps to be followed during the construction of any
type of dam briefly:

Evaluation of time schedule and required equipment.
Diversion of river flow
Foundation treatment
Evaluation of Time Schedule and Required Equipment.
Items to be considered:

the characteristics of dam site
the approximate quantities of work
the preservation of construction equipment and materials
diversion facilities and urgency of work
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3. DAMS
Construction of Dams
Diversion of River Flow
Diversion of the river flow is may be accomplished in one of the following
ways
1. Water is diverted through a side tunnel or channel.
(Applicable for low flow depths ~1.5 m)
Diversion by side tunnel or channel
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3. DAMS
Construction of Dams
Diversion of River Flow (cont’d)

Typical cross-section of earth cofferdams
f: free board f=0.2(1+h)

h: flow depth (meters)

G=z/5 + 3 (meters)
Cofferdams should be constructed during the low flow season.
For fill type dams, embankment cofferdam may be kept in place as part of the
embankment (e.g. Keban Dam and Ataturk Dam).
For concrete dams, embankment cofferdam should be demolished after the dam has
been constructed.

Earth cofferdam on impervious foundation
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Earth cofferdam on pervious foundation
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3. DAMS
Construction of Dams
Diversion of River Flow (cont’d)
Hoover Dam, USA
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3. DAMS
Construction of Dams
Diversion of River Flow (cont’d)
Hoover Dam Overflow Tunnels (spillways), USA
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3. DAMS
Construction of Dams
Diversion of River Flow (cont’d)
Hoover Dam Overflow Tunnels (spillways), USA
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3. DAMS
Diversion of River Flow (cont’d)
Construction of Dams
Hoover Dam Overflow Tunnels (spillways), USA
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3. DAMS
Construction of Dams
Diversion of River Flow (cont’d)
2. Water is discharged through the construction, which takes place in two
stages.
This type of diversion is normally practiced in wider valleys.
Two-stage diversion
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3. DAMS
Construction of Dams
Diversion of River Flow (cont’d)
Two-stage diversion
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3. DAMS
Construction of Dams
Diversion of River Flow (cont’d)
A cofferdam on the Ohio River, Illinois, USA, built for the purpose of constructing the lock and dam.
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3. DAMS
Construction of Dams
Diversion of River Flow (cont’d)

Selection of a proper diversion scheme is based on the joint
consideration of

hydrologic characteristics of river flow,
type of dam and its height,
availability of materials,
characteristics of spilling arrangements.
The optimum design is based on cost minimization.
The cost analysis is carried out for various sizes of diversion
tunnels or channels to determine the corresponding total costs.
The optimum tunnel diameter or bottom width of a lined
trapezoidal channel is then determined according to the
minimum total cost of the facility.
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3. DAMS
Construction of Dams
Foundation Treatment

Foundation treatment for dams is essential

to achieve less deformation under high loads,
to decrease permeability and seepage,
to increase shearing strength, and
to satisfy slope stability for the side hills.
Highly porous foundation material causes excessive seepage, uplift
and considerable settlement.
Such problems can be improved by a grouting operation.
In this operation, the grout mix is injected under pressure to
decrease the porosity, and hence to solidify the formations
underlying the dam and reservoir.
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3. DAMS
Overview

Gravity dams are satisfactorily adopted for narrow valleys having
stiff geological formations.
Their own weight resists the forces exerted upon them.
They must have sufficient weight against overturning tendency
about the toe.
The base width of gravity dams must be large enough to prevent
sliding.
These types of dams are susceptible to settlement, overturning,
sliding and severe earthquake shocks.
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3. DAMS
Gravity Dams
Concrete Gravity Dams

Concrete gravity dams area built of mainly plain concrete to
take compressive stresses.
Shasta Dam, California, USA
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3. DAMS
Gravity Dams
Concrete Gravity Dams (cont’d)

Concrete gravity dams have lower maintenance and operation costs
compared to the other types of dams.
In the design of these structures, the following criteria should be
satisfied:

Dimensions of the dam are chosen such that only compressive stresses
develop under all loading conditions.
The dam must be safe against overturning, shear and sliding.
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3. DAMS
Gravity Dams
Concrete Gravity Dams (cont’d)

In the construction of concrete gravity dams special care is
required for the problems due to shrinkage and expansion.
Formation of the body of the concrete gravity dam
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3. DAMS
Gravity Dams
Concrete Gravity Dams (cont’d)
Forces Acting on Gravity Dams
The weight:
Wc= dead load
Hydrostatic forces:
Uplift Force:
φ: uplift reduction coefficient
Moment arm of Fu=B(2h1+3h2) / 3(h1+h2)
Actual uplift pressures are determined by pressure
gauges installed at the bottom of the dam.
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Free body diagram. Forces acting on a concrete gravity dam
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3. DAMS
Gravity Dams
Concrete Gravity Dams (cont’d)
Forces Acting on Gravity Dams
Sediment Force:
γs: submerged specific weight of soil
Ka: active earth pressure coefficient according to the
Rankine theory.
Ka = (1-sinθ)/(1+sinθ)
Ice Load (Fi):
Free body diagram. Forces acting on a concrete gravity dam
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3. DAMS
Gravity Dams
Concrete Gravity Dams (cont’d)
Forces Acting on Gravity Dams
Earthquake Force:
Fd = kWc
k: earthquake coefficient
Dynamic Force in the reservoir induced by earthquake
Fw = 0.726Ckγh12
 θ′ 
C = 0.71 − 
 90 
Dynamic Force acting on a spillways
ΣF = ρQ∆u
obtained using momentum equation
Free body diagram. Forces acting on a concrete gravity dam
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3. DAMS
Gravity Dams
Concrete Gravity Dams (cont’d)
Forces Acting on Gravity Dams
Wave Force may be considered for wide and long
reservoirs.
Temperature Loads may be severe during
construction because of hydration reactions
Free body diagram. Forces acting on a concrete gravity dam
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3. DAMS
Gravity Dams
Concrete Gravity Dams (cont’d)
Stability Criteria

Stability analyses are performed for various loading conditions
The structure must prove its safety and stability under all loading conditions.
Since the probability of occurrence of extreme events is relatively small, the
joint probability of the independent extreme events is negligible.
In other word, the probability that two extreme events occur at the same time
is relatively very low.
Therefore, combination of extreme events are not considered in the stability
criteria.

Floods (spring and summer) ÅÆ Ice load (winter).
No need to consider these two forces at the same time.
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3. DAMS
Gravity Dams
Concrete Gravity Dams (cont’d)
Stability Criteria

Usual Loading

Unusual Loading

Hydrostatic force (normal operating level)
Uplift force
Temperature stress (normal temperature)
Dead loads
Ice loads
Silt load
Hydrostatic force (reservoir full)
Uplift force
Stress produced by minimum temperature at full level
Dead loads
Silt load
Extreme (severe) Loading

Forces in Usual Loading and earthquake forces
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3. DAMS
Gravity Dams
Concrete Gravity Dams (cont’d)
Stability Criteria

The ability of a dam to resist the applied loads is measured by some
safety factors.
To offset the uncertainties in the loads, safety criteria are chosen
sufficiently beyond the static equilibrium condition.
Recommended safety factors: (USBR, 1976 and 1987)
F.S0: Safety factor against overturning.
F.Ss: Safety factor against sliding.
F.Sss: Safety factor against shear and sliding.

However, since each dam site has unique features, different safety
factors may be derived considering the local condition.
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3. DAMS
Gravity Dams
Concrete Gravity Dams (cont’d)
Stability Criteria

The factor of safety against overturning:
F .S0 =

∑ Mr
∑ M0
where ΣMr: total resisting moment about the toe.
ΣM0: total overturning moment about the toe.
The factor of safety against sliding:
F .S s =
f ∑V
∑H
where f: coefficient of friction between any two planes
ΣV: vectorial summation of vertical forces.
ΣH: vectorial summation of horizontal forces.
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3. DAMS
Gravity Dams
Concrete Gravity Dams (cont’d)
Stability Criteria

The factor of safety against sliding and shear:
F .S ss =
f ∑ V + rAτ s
F .S ss =
∑H
f ∑ V + cA
∑H
(in the dam)
(at foundation level)
where A: Area of the shear plane,
τs: shear strength of concrete
r: factor to express max allowable average shear stress
r=0.33, 0.50, and 1.0 for usual, unusual, and extreme loading, respectively.
f: coefficient of friction between any two planes
ΣV: vectorial summation of vertical forces.
ΣH: vectorial summation of horizontal forces.
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3. DAMS
Gravity Dams
Concrete Gravity Dams (cont’d)
Stability Criteria

The contact stress between the foundation and the dam or the
internal stress in the dam body must be compressive:
σ=∑ ±
V
A
Normal stress
Mc
I
Bending or flexural stress
Base pressure distribution
where σ : vertical normal base pressure
A: Area of the shear plane,
M: net moment about the centerline of the base (M = ΣV.e)
e: eccentricity ( B / 2 − x )
c: B/2
I : Moment of inertia (B3/12)
ΣV: vectorial summation of vertical forces.
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3. DAMS
Gravity Dams
Concrete Gravity Dams (cont’d)
Stability Criteria

The contact stress between the foundation and the dam or the
internal stress in the dam body must be compressive:

In order to maintain compressive stresses in the dam or at the foundation
level, the minimum pressure σmin ≥ 0.
This can be achieved with a certain range of eccentricity.
σ=

ΣV Mc
±
A
I
for a unit width
σ min =
Σ V Σ V × e × B / 2 Σ V  6e 
−
=
1 −  ≥ 0
3
A
B
B

B / 12
σmin ≥ 0 can be achieved if e ≤ B/6
Full reservoir Æ σmax at the downstream face
Empty reservoir Æ σmax at the upstream face
Base pressure distribution
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3. DAMS
Gravity Dams
Concrete Gravity Dams (cont’d)
Stability Criteria

The contact stress between the foundation and the dam or the
internal stress in the dam body must be compressive:

Tension along the upstream face of a gravity dam is possible under
reservoir operating conditions.
z = 1.0 (if there is no drainage in the dam body)
z = 0.4 (if drains are used)
P: hydrostatic pressure at the level under consideration
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3. DAMS
Gravity Dams
Concrete Gravity Dams (cont’d)
Stability Criteria

Concrete gravity dams have varying thickness.
Hence the inclined compressive stresses parallel to the face of the
dam need to be computed.

For a concrete gravity dam with slopes of 1V:mH at the upstream face and
1V:nH at the down stream face, the major principle compressive stresses,
σiu (parallel to the upstream face) and σid (parallel to the downstream face)
are obtained from the static equilibrium of forces in the vertical direction as:
(ΣFy=0)
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where σu and σd vertical normal compressive stresses and pu and pd hydrostatic pressures
at the upstream and downstream faces, respectively.
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3. DAMS
Gravity Dams
Concrete Gravity Dams (cont’d)
Stability Criteria

Internal horizontal and vertical shear stresses at the upstream and
downstream faces are obtained by equating the total moment to zero
as (ΣMA=0, ΣMB=0):
where τhu, τhd, τvu, and τvd are the horizontal and vertical internal shear stresses
at the upstream and downstream faces, respectively.
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3. DAMS
Gravity Dams
Concrete Gravity Dams (cont’d)
Stability Criteria

The maximum compressive stress, σmax ,must be smaller than a
certain fraction of the compressive strength of concrete, σc, and
foundation material, σf.
Safety criteria for concrete gravity dams
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Unconfined compressive strength, σf
for foundation materials
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3. DAMS
Gravity Dams
Concrete Gravity Dams (cont’d)
Stability Criteria

Excessive care must be taken during the filling of the reservoir.
Initially 1/3 of the dam height may be filled first.
After waiting for several weeks and assuring that the dam is safe,
further filling is performed.
Since safety levels change with respect to upstream water depth,
gravity dams must be analyzed for various operating levels and empty
reservoir cases, separately.
For the empty reservoir case, the overturning tendency must be
checked with respect to the toe and heel, separately.
The stability against sliding may be improved by providing a cut off
wall in the foundation at the upstream side.
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3. DAMS
Gravity Dams
Prestressed Concrete Gravity Dams

In a prestress concrete dam, forces are applied to the dam before
the reservoir is filled in order to counter undesirable stress that
would develop in the absence of the prestressing forces.
For prestressing, either small-diameter high-tensile wires or hightensile steel bars can be used.
Roller Compacted Concrete (RCC) Gravity Dams

RCC dam is constructed using cement, water, fine and course
aggregates, and fly ash which are mixed in certain proportions to
have a no-slump, rather dry composition.
Construction is based on the compaction of this mixture by heavy
static or vibrating rollers.
Construction period of RCC dams is shorter than that of
conventional concrete gravity dams.
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3. DAMS
Overview

Arch dams are thin concrete structures.

Gokcekaya, Oymapinar, Karakaya, Gezende, and Berke dams in Turkey.
Gokcekaya Dam
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Berke Dam
Karakaya Dam
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3. DAMS
Arch Dams

Arch dams: Oymapinar Dam, Turkey
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3. DAMS
Arch Dams
Hoover Dam, USA
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3. DAMS
Arch Dams

Arch dams are thin concrete structures.
Stability of an arch dam is based on its self weight and its ability to
transmit most of the imposed water loads into the valley walls.
At the sites of arch dams, the side formations and foundations should
be very stiff to resist the applied load.
For effective arching action, the radius of the arch should be as small
as possible.
They are formed by concrete blocks having base dimensions of
approximately 15 m by 15 m and height of 1.5 m
Reinforcement is not generally required in thick arch dams because it
increases the cost drastically.
Arch dams have normally higher structural safety than conventional
gravity dams.
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3. DAMS
Arch Dams
Types of Arch Dams

Arch dams are classified
according to geometric
characteristics of the valley where
they are adopted.
Arch dams are classified
according to the location of the
center and magnitude of the
central angle

Constant-center (variable
angle) arch dams are suitable for
medium-high dams in U-shape
valleys. They have single
curvature in plan with vertical
upstream face.
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3. DAMS
Arch Dams
Types of Arch Dams

Variable-center (constant angle)
arch dams are suitable for V-shape
valleys.

Radius of the arc reduces with respect
to depth.
So arching action is more pronounced
at low depths.
Since these types of dams are normally
thinner than constant-center dams,
they are more elastic and safer.
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Variable-center (constant angle) arch dams
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3. DAMS
Arch Dams
Types of Arch Dams

Variable-center (variable angle)
arch dams are composed of the
combination of two types described
above.

Load distribution in vertical direction
governs the cross-sectional shape of
the dam.
This type has a pronounced double
curvature
They utilized the concrete strength
more compared the other types
resulting in thinner and more efficient
structure.
However, tensile stresses may develop
in the dam body.
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Variable-center (variable angle) arch dams
Gokcekaya Dam
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3. DAMS
Arch Dams
Types of Arch Dams

Variable-center (variable angle)
arch dams
Gokcekaya Dam
Cross-section of Gokcekaya Dam
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3. DAMS
Arch Dams
Design of Arch Dams

Structural design of an arch dam requires the determination of load
distribution in the dam body using the trial load method and
applications of the theory of elasticity and the theory of shells.
Structural design is beyond the scope of this course.
Simplified design:

The determination of the thickness at any elevation of an arch dam
whose crest elevation has already been determined in the hydrologic
design step.
In the arch dams, the total load is shared by arch and cantilever
actions and transmitted to the sides and foundation, respectively.
Therefore, the base width of arch dams is usually much narrower
than that of concrete gravity dams having almost the same height.
Hence, the effect of uplift pressure can be ignored.
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3. DAMS
Arch Dams
Design of Arch Dams

However, effect of temperature stresses
should be checked to ensure that they are
smaller than tensile strength.
Near the crest of the dam, most of the
loads taken by arches and transmitted to
the side abutments.
Near the bottom of the dam, cantilevers
take most of the load and transmit to the
foundation.
Gokcekaya Dam
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3. DAMS
Arch Dams
Design of Arch Dams

In the following analysis, the
water thrust induced by
hydrostatic pressure is assumed
to be taken by arch action only
and transmitted to the sides.

The differential force acting on a
differential element having a
central angle of dΦ is
dFv= P r dΦ
The vertical component of this
force is
dF'v= P r dΦ sinΦ
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Free-body diagram for arch dam analysis
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3. DAMS
Arch Dams
Design of Arch Dams

Hh = 2
Integration of this force along the
arc length gives the total
horizontal force, Hh.
π 
 
2
 π 
θa
 π θa  


=
−
−
−
γ
φ
φ
γ
γ
sin
2
cos
cos
2
sin
hr
d
hr
=
hr






∫
 π θa 
 − 
2 2 

2
2
2 
2
Free-body diagram for arch dam analysis
where
h: the height of the arch rib relative to the reservoir surface
r: the radius of arch
θa: the central angle
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3. DAMS
Arch Dams
Design of Arch Dams

The equilibrium of forces in ydirection involves
H h = 2R y
θ 
R y = R sin  a 
 2 
Therefore
θ 
θ 
2γhr sin  a  = 2 R sin  a 
 2 
 2 
R = γhr
where
Free-body diagram for arch dam analysis
where
R: the reaction offered by the sides against the transmission of water thrust.
As observed from the R = γhr, the reaction at the sides is directly proportional to the arc radius at
a given height. Therefore, narrow valleys having stiff geological formations and small r-values are
suitable for arch dams.
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3. DAMS
Arch Dams
Design of Arch Dams

If the thickness of the arch rib, t, is relatively small as compared with
r, there is small difference between the average and maximum
compressive stresses in the rib and σ≈R/t.
The required thickness of the rib is then
t=
γhr
σ all
(the thickness varies linearly with depth.)
where
σall: the allowable working stress for concrete in compression.
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3. DAMS
Arch Dams
Design of Arch Dams

The volume of concrete per unit height of a single arch rib across a
canyon of width of Ba is
V=Lt
where L is the arch length which is equal to rθa (θa in radians).
Inserting the values of L and t into the equation above
V=
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γh 2
r θa
σ all
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3. DAMS
Arch Dams
Design of Arch Dams

The optimum central angle θa for a minimum volume of arch rib
can be determined as 133º34‘ by differentiating V with respect to
θa and equating the result to zero.
This is the reason why a constant-angle arch dam can be design
to require less concrete than a constant-center dam.
In practice, the central angles of arch dams vary from 100º to
140º.
However, the formwork of a constant-angle dam is more difficult.
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3. DAMS
Arch Dams
Design of Arch Dams

A buttress dam consists of a sloping
slab.
Depending on the orientation of slab,
a buttress dam may be classified as

flat-slab buttress dam
multiple-arch buttress dam
Elmali Dam construction, Istanbul, 1941
A typical buttress dam.
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Elmali Dam
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3. DAMS
Buttress Dams

Flat-slab buttress dams
Lake Tahoe Dam, California, USA
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3. DAMS
Buttress Dams

Multiple-arch buttress dams
Bartlett Dam , Phoenix, Arizona, USA
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3. DAMS
Buttress Dams

Some advantages of buttress dams over conventional gravity dams:

Main disadvantage of buttress dams:

They can be constructed on foundations having smaller bearing
capacity then required for gravity dams.
Since they have thinner slabs, possibility of development of vertical
cracks is less.
Problems encountered during the setting of concrete are reduced.
Unless a mat foundation is used, uplift forces are negligibly small
because of hollow spaces provided between the buttresses.
Ice pressures are also small as the ice
sheet slides up the inclined slab.
May have comparable costs, because of
increased formwork and reinforcement .
There is only one buttress dam in
Turkey (Elmali 2 Dam).
Elmali 2 Dam
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3. DAMS
Overview

They composed of fill of suitable earth materials at the dam site.

Coarse-grained soils (gravel and coarse sand)

Clay is considered as a core material (impermeable)

relatively pervious,
easily compacted,
resistant to moisture,
unstable when saturated (expands due to wetting, hard to compact)
Therefore, clay mixed with sand and fine gravel is used as a core.
Core must be compacted in thinner layers with fairly accurate moisture
control.
Compacted asphalt may also be used as an economical core material
in case of loose foundations.
Asphalt can absorb earthquake shocks effectively.
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3. DAMS
Embankment (Fill) Dams

Embankment dams are usually safer against deformations and
settlements.
Embankment dams
Earth-fill dams
Rock-fill dams
(More than 50% of the
total material is of rock.)
Earth-fill dams in Turkey
Seyhan Dam
Demirkopru Dam
Cubuk 2 Dam
Bayindir Dam
Rock-fill dams in Turkey
Keban Dam
Ataturk Dam
Hasan Ugurlu Dam

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Hasan Ugurlu Dam
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3. DAMS
Embankment (Fill) Dams

Body volume of embankment
dams is relatively greater
than the other types of dams.
Normally cheaper than the
other types where there is
enough fill material in the
close vicinity.
Fill dams comprise more
than 70% of the dams in the
world and 90% in Turkey.
Keban Dam
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3. DAMS
Embankment (Fill) Dams
Earth-fill Dams

Construction:

Placement of selected material on layers of 50 cm thick and
compaction.
Non-organic and non-plastic soils are needed.
The embankment soil is usually irrigated at the borrow area.
Piezometers can be placed in the embankment at various depths
during the construction to measure the pore water pressure.
A typical earth-fill dam is constructed in a multi-layer formation.

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3. DAMS
Embankment (Fill) Dams
Earth-fill Dams

A typical earth-fill dam is
constructed in a multi-layer
formation.
Earth dam on pervious foundation
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3. DAMS
Embankment (Fill) Dams
Earth-fill Dams

Seepage through an earth-fill dam.
The flow rate, ∆q, between two flow lines can be expressed using the Darcy law as
 ∆h 
∆q = KAi = K∆D

∆
L


The total flow rate, q
 Kh 
q = N ′

N


CVE 471 Water Resources Engineering
K: the hydraulic conductivity
i : the hydraulic gradient
∆h: head loss (h/N)
N : number of equipotential drops
N’: the number of stream tubes
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3. DAMS
Embankment (Fill) Dams
Earth-fill Dams

Drainage systems in an earth-fill dam.
Chimney drains, in the embankment as well as enlarged toe drains
are effective in controlling the seepage through the dam.
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3. DAMS
Embankment (Fill) Dams
Rock-fill Dams

Having relatively high pore space
Can be adopted to weaker foundations where a gravity dam cannot be
constructed.
Cross-sections of typical rock-fill dams
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3. DAMS
Embankment (Fill) Dams
Rock-fill Dams (Ataturk Dam)

Largest dam in Turkey
Reservoir Volume: 48.7 x 109 m3
Installed capacity: 2400 MW
Annual energy production: 8.9 x 109kWh
Irrigated land: 874200 ha (with the completion of the project)
A cross-sections of the Ataturk Dam
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3. DAMS
Embankment (Fill) Dams
Rock-fill Dams (Ataturk Dam)
A cross-sections of the Ataturk Dam
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3. DAMS
Overview

A suitable dam cross-section should be provided such that both safety
and desired functionality concerning service requirement are attained.
Sufficient crest width, tc must be provided.
a width of two lane traffic may be selected.
For small embankment dams
up to Hf=15 m.
tc=0.2Hf+3
For large embankment dams
up to Hf=150 m.
tc=3.6 (Hf )1/3
where tc and Hf are in meter.

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3. DAMS
Cross-sectional Layout Design of Dams

By examining some existing muti-purpose concrete gravity dams
throughout the world, Yanmaz et al. (1999) proposed the following
regression equations to define the shape of a gravity dam.
H*=0.1075 Ht
tc=0.0475 Ht +2.392
where all variables are in meter
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3. DAMS
Cross-sectional Layout Design of Dams

United States Bureau of Reclamation (USBR) propose the following
formulas for cross-sectional layout of arch dams:
tc
= 0.01(H t + 1.2 Ba )
 H 
tb
= 3 0.0012 H t Ba B0.15  t 
 400 
t0.45 H t = 0.95tb
where
H t / 400
All the dimensions are in ft
Ba: the span width at the crest
B0.15: the span width at 15% of the dam height above the base
t0.45Ht: the dam thickness at 45% of the dam height above the base.
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3. DAMS
Cross-sectional Layout Design of Dams

The crest elevation of a dam is to be determined such that there is almost no
overtopping danger of the flood wave during the occurance of the design
flood.
Freeboards on flood levels for concrete and embankment dams

Greater freeboards are required for embankment dams since they are
susceptible to erosion at the downstream face due to overtopping from their
crest.
The required side slopes of concrete gravity dams are determined from
stability analyses.
The maximum downstream slope of gravity dams is 45°.
Side slopes of embankment dams are determined on the basis of seepage
and slope stability analyses.
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3. DAMS
Overview

Excessive kinetic energy of the flowing water at the downstream of
outlet works (spillways, sluiceways etc.) should be dissipated in order
to prevent the erosion of the streambed and the banks below the dam.
Local scour at the downstream of the dam and sluice gates

Excessive scours at the downstream of Keban Dam have resulted in serious
foundation stability problems (depth of approx 30 m).
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3. DAMS
Local Scour at the Downstream of Dams

Some of the scour prediction equations are given in the table.
Scour prediction equations for the downstream of dams.
ds: the maximum depth of scour hole in m.
b: the thickness of the jet in m.
Φ: the side inclination for the scour hole,
Fr: Jet Froude number.
U: the velocity of the jet in m/s
∆=(γs- γ)/γ,
γs: : specific weight of sediment in kN/m3
γ : specific weight of water in kN/m3.
Wf: Fall velocity in m/s
q: unit discharge in m3/s/m
Hg: gross head in m
h: tailwater depth in m
D50: median size of bed material in m.
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3. DAMS
Overview

Excessive care must be taken in planning, design, and construction
stages of a dam.
Major causes for a dam break:

Inadequate spillway capacity,
Improper construction of any type of dam,
Insufficient compaction of embankment dams or compaction with
undesirable water content,
Improper protective measures,
Excessive settlements, etc
Continuous inspection and monitoring are required to assess the
safety level of the dam throughout the lifetime.
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3. DAMS
Dam Safety and Rehabilitation

Upon periodic inspection, the following deficiencies may be observed
that are indicators of problems:

Large horizontal and vertical movements of crest,
Tilting of the roadway along the crest,
Deformation of embankment slope,
Higher than usual pore water pressure in embankment dams,
Unusual seepage at the toe or edges of an embankment dam,
Seepage flows with not decreasing with low flow conditions,
Turbit outflow through the embankment,
Tilting of the spillway crest
Increased leakage into inspection galleries in concrete dams, etc.
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VE 471 WATER RESOURCES ENGINEERING

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