AAAAAAAAAAAAAHydraulic structure one .ppt

Hydraulic structure I Compiled by Habtom M
Because of the different perception about hydraulic structures, different textbooks
defined hydraulic structures in different context.
In general hydraulic structures are those structures which are in contact with water.
Chapter One
Elements of dam engineering
Introduction
Hydraulic structures I
Prerequisite : Engineering Hydrology, Soil Mechanics II, & Open channel Hydraulics

Definition:- A dam may be defined as an obstruction or barrier built across a stream
or a river.
The lake of water which is formed upstream is often called reservoir.
The stored water can be used for ;
Recreation purpose;
Reservoir of drinking water;
For farm land irrigation;
Generation of electric power etc ..
Reservoir
Dam
Upstream
Downstream

Dam structures and reservoirs
Depending upon the purpose served by a given reservoir, the reservoir may
be broadly classified
1) Storage or conservation reservoir:- are those reservoirs which retain excess
supplies during period of peak flow and can release them gradually during low
flows or when the need arises.
2) Flood control reservoirs:- store a portion of flood flows in such a way to minimize
the flood peaks at the area to be protected downstream.
3) Multipurpose reservoirs:-are those reservoirs which are planned and constricted
to serve not only one purpose but various purpose together.

Storage Capacity of the dam
• Storage capacity is the most important physical characteristics of the reservoir that
store water and stabilize the flow.
•The capacity of reservoir on dam site, is determined from the contour maps of the area.
• After the topographical survey of the dam sites is carried out and contour map is
prepared, the area enclosed within each contour can be measured with a planimeter.
)
(
2
2
1
h
A
A
S 



 
3
2
1 4
6
A
A
A
h
S 




S

The incremental storage volume between two successive contour can be
found by
A1
A2
h

( Simple average method )
( Prismoidal method )

Storage Components
Dead storage
Minimum pool level
Normal pool level
Live storage
Maximum pool level
Spillway
Outlet
Spillway crest
River bed

Classification of dams
The classification of dam can be schematically descried as follows;

Embankment dam:
- are those dams constructed of naturally excavated materials placed without
addition of binding material other than those inherent in the natural material.
Embankment dams are also classified as usually
 Earth fill dam:- an embankment dam constructed primarily of compacted earth in either
homogeneous or zoned areas containing more than 50% of earth.
 Rock fill dam:-embankment type of dam dependent for its stability primarily on rock. As rock fill dams
must contain an impervious zone, usually of selected earth with filter zones comprising a substantial volume
of the dam
 Hydraulic fill dam:-an embankment dam constructed of earth, sand, gravel or rock generally from
dredged material conveyed to the site of placement by suspension in flowing water.
Concrete dam
Gravity dam: A type of dam constructed of mass concrete or stone masonry, or both, which relies on
its weight for stability.

Arch dam: a dam with upstream curvature which transmits the major portion of the load or pressure to the
abutments rather than to the bottom foundation.
Buttress dam: a dam consisting of a watertight upstream face supported at intervals on the downstream
side by a serious of intermittent supports termed buttress.
Factors governing the selection of a particular types of dam.
The various factors which must be consider thoroughly, before selecting a particular type are ;
 Geology:
i. Foundation requirement
ii. Topography
 Availability of Technical skills
 Cost effectiveness
 Availability of materials
 Hydrology

Assignment One
Describe the governing factors that
used for the selection of dam site
(not more than two pages)
References;
1- P.Novak et al. (Hydraulic structures)
2- USBR 1987. (Design Of small Dam)
3-Jansen, R.B.(1988) Advanced Dam
Engineering for design and
construction
4-Garg. S.K 1996 Irrigation engineering
and Hydraulic structure
Submission deadline - next class.

Chapter two
Concrete Dam
The structural integrity of any the dam must be maintained under different
loading circumstances.
 the gravity dam is mainly subjected to the following main forces;
Water load
Self weight
Uplift load
Wave load
Silt load
Wind load
Earth quake load

Hydraulic structure I
As per the degree of relative importance loads on the dam can be classified as ;
 primary loads:- Major important loads irrespective of the dam type;
E.g. Self Wight load, water load and related seepage load
Secondary loads:- Universally applicable loads , even though there magnitude
is less;
E.g. Silt load
Exceptional loads:- loads which has limited applicability;
E.g. Tectonic load
Concrete dam cont’s

Loads and their centroidal location in gravity dams
Case -1 Non-over flow section
(i) Up stream vertical face
PH
H
w

2
2
1
H
P w
H 

H
@ 3
H
3
H
from the base of the dam.
B
H’
'
H
P
2
'
2
1
' H
P w
H 
 @
'
H
w

3
'
H from the base of the dam.
Ap
H
w

U
  B
H
H
U w
*
2
'



Through the centroid of
Trapezoidal, with out
drainage gallery)
[ i.e. ]
@
)
'
(
3
'
2
5
H
H
H
H
Z



w
p
c A
W 
 @ Through the centroid of
x-sectional area Ap
Ap’
v
P
'
*
2
1
H
b
P w
v 

b
@ from the toe of the dam.
3
b

(ii) Up stream face inclined
Pv1
Pv2
If the upstream face of the gravity dam is inclined
in addition to the previous loads ( loads in vertical
u/s face) , only vertical loads of water i.e. Pv will be
added at its centroidal point from the toe of the dam.
where
Pv = Pv1+ Pv2

Case-2 Over flow section
H2
H1
g
V
H a
a
2

 
a
w H
H 
1

 
a
w H
H 
2

PH
)
(
2
1
2
2
1
H
H
H
H
H
P a
H 












 

T.E.L
  











2
1
2
1
1
_
2
3
2
3
1
H
H
H
H
H
H
H
H
Z
a
a
a
Z
from the base of the dam
@

Uplift pressure with drainage gallery and tension cracks
 To reduce the uplift pressure , drains are formed trough the body of the dam, this
make the intensity of the uplift pressure to be differ from the full concrete dam.
Drainage gallery
H
H’
H

'
H








 )
'
(
3
1
' H
H
H

B B
B’
H
H’
'
H

'
H

H

B’=location of tension crack from the heel of the dam

Wave Pressure ( hydrodynamic wave load)
Waves are generated on the reservoir by the blowing winds.
hw
w/r
hw = height of the wave
U = wind velocity in km/hr
F = fetch length
UF
hw 032
.
0

4
271
.
0
763
.
0
032
.
0 F
UF
hw 


km
F
if 32


km
F
if 32


Pwave
w
w
wave h
P 
4
.
2
 @ w
h
375
.
0 above the stilled water level.
Reservoir surface area
Dam

Earthquake force
 Eartquake force may move in any direction, but for the sack of design purpose it
has to be resolved in to vertical and horizontal components.
 The values of these horizontal (αh) and vertical (αv) accelerations are generally
expressed as percentage of the acceleration due to gravity i.e. 0.1g or 0.2g, etc.
Vertical acceleration(αv)
Dam foundation
Upward vertical acceleration
The contact b/n the foundation and the dam
will increase, hence the effective Wight
of the dam will also be increase
The contact b/n the foundation and the dam
Will decrease, which is the worst case!!
Down ward vertical movement.
W
Effective weight of the dam v
g
W
W 
*



Horizontal acceleration(αh)
Hydro-dynamic pressure.
Horizontal Inertia force.
Fe
2
555
.
0 H
F w
h
e 



3
4H
acts @

3
4H
H
from the base of the dam.
Von – Karman formula
There is also a hydrodynamic formula developed by Zanger, but for average ordinary
purposes, the Von-Karman formula is sufficient.
Reading assignment,
Reference, P.Novak and S.K. Garg

Sediment load
hs
Psh
N.B! it is usual practice to assume the value of hs equals
to the height of dead storage.
2
2
'
s
s
a
sh
h
K
P


3
s
h
w
s
s 

 

'
@
above the base of the
dam.
The submerged unit weight and the active lateral pressure coefficient Ka
is given by
s
s
a
K


sin
1
sin
1



s

s

'
s

where
is the angle of shear resistance.
is sediment saturated unit weight.
Reading assignment
-Loading combinations in dams
Reference, Novak

Design and analysis of gravity dam
Gravity dam may fail in the following way
•By over turning rotation about the toe;
•By Crushing;
•By development of tension , causing ultimate failure by crushing;
•By shear failure called sliding
1- Over turning stability
To make the structure of the dam stable from rotational or overturning failure the
following governing criteria should be satisfied
F0 (factor of safety against over turning) should be greater than 1.5





ve
ve
o
M
M
F > 1.5……………(safe against overturning)

2-Siding Stability (Fs)
Sliding Factor (FSS)
Shear friction Factor(FSF)
Limit equilibrium factor (FLE)
i) Sliding factor can be defined by


tan
1
tan















V
H
V
H
Fss



V
H
Fss , for horizontal plane
, for foundations inclined at a small angle 
In order to be the dam stable against sliding Fss should be less than or equal
to 0.75 but for ELC up to 0.9 is acceptable.

ii) Shear friction factor (FSF) is defined as


H
S
FSF
m
kN
V
CA
S b
/
)
tan(
)
tan
tan
1
(
cos 








  




Where
S – total resistance to shear and defined by
Exercise
If there is a passive wedge resistance how does the shear friction factor modified?

Location of sliding plane Normal Unusual Extreme
Dam Concrete base interface
Recommended shear friction factor (USBR 1987)
Foundation rock
3.0 2.0 > 1.0
4.0 2.7 1.3

(ii) Limit Equilibrium Factor, FLE

 f
LE
F 


 tan
n
LE
c
F



f

n

= The shear stressed generated under the applied load
= Available shear strength and expressed by Mohr coulomb
failure criteria
= Streets acting normal to plain of sliding
FLE = 2.0 for normal operation
FLE = 1.3 for seismic activity

3- Stress analysis (compression or crushing)
If the compressive stress introduced in the dam is greater than its allowable stress ,the
dam may fail.
Reservoir full
condition
H
V









B
e
B
V
P
6
1
max









B
e
B
V
P
6
1
min
+ compression
B/2 B/2
Pmin
Pmax
+ compr.
-
Tension
Pmin
Resultant
force
Where;
e = Eccentricity of the resultant force
from the center of the base
Total vertical force
B= Base width
Normal pool level
 
V

 Because of the gravity dam materials can not sustain tensile stresses, it should be
designed for certain amount or no tension should develops anywhere in the body of
the dam.
The maximum permissible tensile stress for high concrete gravity dams, under worst
loadings, may be taken as 500 KN/m2 (5kg/cm2).
NB! A tension crack by itself does not fail the structure, but it leads to failure of the
structure by producing excessive compressive stresses.
 In order to ensure that no tension is developed anywhere, the amount of Pmin should
at most equal to zero.
0
6
1
min 









B
e
B
V
P
6
B
e 
_
x
The maximum value of eccentricity, that can be permitted on either side of the center is
equal to B/6 ------- “ the resultant must lie within the middle third”.
The resultant distance from the toe of the dam ( ) is given by




V
M
x

Principal stress
Pvmax
Pvmin
P
P’
A
B
c
c
B
A





 2
2
tan
'
sec p
pv 

For to be maximum, p’ should be
zero.


Example 2.1
For the following situation calculate;
•The maximum vertical stresses at the toe and heel of the dam.
•The major principal stresses at the toe of the dam.
•The intensity of shear stresses at the toe of the dam.
56m
8m
R.L. =205
R.L.=211
2
3
6m
•R.L.= 280
R.L.= 289
R.L.=285

Base width design for gravity dam for reservoir full condition
U
P W
H
B/2 B/2
e
B/3
H
C w

H
w

I) In order to no tension to be develop in the body of the dam the following should be satisfied
C
S
H
B
c 

II) In order the dam is to be safe from sliding the following should be satisfied
)
(
75
.
0 C
S
H
B
c 

Why and how ?

Example 2.2
86 m
4 m
7 m
6 m
63 m
69 m
26 m
For the following section of gravity dam examine the stability, take the horizontal and vertical earth-
quake force as 0.1 g and 0.05 g respectively,
 assume area factor as 60%, and
3
/
24 m
kN
c 
 3
/
10 m
kN
w 

The satiability analysis should be carried out for both reservoir empty and reservoir full condition.
10 m

Buttress Dam
Buttress dams are those dams which have sloping u/s face and transmit the water
load to a series of buttress at right angle to the axis of the dam.
 The advantage of buttress dam is
manifested by reduction of uplift pressure
and by saving concrete.

N.B.!
 The loading and safety criteria for
buttress dams or buttresses, is the same as
that for gravity dam section, except that the
provided buttress thickness ‘t’.
 the Uplift pressure is considered to act only
under the buttress head,

Example 2.3
The profile of the major monolith of a buttress dam is shown bellow. The stability of a
dam is to be reviewed against overturning (Fo >1.5) and against shear friction factor
(Fo >2.4).
Assume the following concrete x-ics and
analyze the statistic stability of buttress w.r.t
plan X-X.
3 m
16 m
3 m
0.7
1
2 m
22 m
20 m
10 m
3 m
0
35

c

3
23 
 kNm
c

2
500 
 kNm
c
X X

Arch Dams
Arch dams are those dams which has a solid wall, curved in plan and standing across
the entire width of the river valley, in a single span.
Depending upon the shape consideration, simple arch dams can be divided as;
 Constant radius arch dams;
Constant angle arch dams; and
Cupola arch dams
Valley suited for arch dam
Those valleys with narrow gorges and top-width to dam height ratio less than 5 may
be feasible.
5

 H
B
r
S
B
H

Constant radius arch dams
:- is the simplest geometry, u/s face of the dam is of constant radii with a uniform radial d/s slope. It is apparent
that central angle, 2θ, reaches a max. @ Crest level.
The most economical angle for a constant arch dams is maintained when;
o
133
2 

r1
r2
r3
Vertical axis

Constant angle arch dams
Central angle of different arch have the same magnitude from top to bottom & uses up to 70% of concrete as
compared to constant radius arch dam. But it is more complex as demonstrated in the figure. It is best suited to
narrow & steep-sided V-shaped valleys.

Copula arch dams
Has a particularly complex geometry & profile, with constantly varying horizontal & vertical radii to
either face.
Design of arch dams
Arch dams can be designed on the basis of any one of the following methods;
i. Thin cylinder theory;
ii. The thick cylinder theory; and
iii. The elastic theory
 Loads on arch dams are essentially the same as loads on gravity dams, and uplift forces
are less important, if no cracking occurs the uplift can be neglected.
 Internal stresses caused by temperature change, ice pressure, and yielding of abutment are
very important.

h
dh
B/2
F
B/2
F
Ru
Ri
T
t
Thin cylinder theory
 The theory assumes the arch to be
simply supported @ the abutments
& that the stresses are approximately
the same as in a thin cylinder of equal
outside radius.
Where,
Ru (Outer radius)– Extrados.
Ri (internal radius)– Intrados.
Rc – Central radius.
T– Arch thickness.
Rc
h
hR
h
hR
T
w
i
w
w
c
w










5
.
0
How ????......




 h
K
KR
hR
T w
w


 ;
The most economical angle of arch with minimum volume is 133o34’.
2
2
2
/
sin
2













B
K
KR
V
V= A.R2θ = T*1*R2θ
T
1 unit
0


d
dV
Vertical axis

Thick cylinder theory
Ri
R
Ru
Pu
pi
T
Ru
Ri
T
analysis
For
R
R
R
Z
T
design
For
R
R
for
R
R
T
R
Z
elevation
any
at
uniform
is
R
R
T
face
s
d
is
stress
ring
R
R
R
R
R
R
p
d
u
u
w
r
d
d
u
r
u
w
h
d
u
d
u
d
u
u
w
)
(
2
)
(
)
(
2
.
/
@
max
/
2
1
2
1
max
2
2
2
2
2
2

























:- is improvement of thin cylinder theory
Reading assignment
Reference:- P.Novack
(fourth edition)
On Elastic Arch theory

Tekezea
arch
dam
in
Ethiopia

Example 2.4
Draw the profile of arch dam using thin cylinder theory, assume the sustained angel 90o
45o
100 m
140 m
50 m

Embankment Dams
Embankment Dam
Earth Dam Rockfill Dam Composite
Type
Accordint to design
According to method of
Constructuion
Homogenous Zoned Diaphriagm Rolled
fill type
Hydraulic
fill type
Semi Hydraulic
fill type
What is there
difference ?
Embankment dams are those dams which are built of naturally available materials.

Homogeneous Earth Dams:- are constructed entirely or almost entirely of one type of earth
material (exclusive of slope protection).
Build up one type of material
Phreatic line or seepage line
Horizontal blanket
Slope protection
Zoned Earth Dam;- however, contains materials of different kinds in different parts of the
embankment. The most common type of an earth dam usually adopted in the zoned earth dam
as it leads to an economic & more stable design of the dam.
Vertical
core
u/s
shell
d/s
shell
Transition filter
Impervious
zone
Eg.Clay + fine sand

Diaphragm Earthen Dams; this types of dam are the same as that of Zone dam but the
main difference is it has thins thickness of core.
Diaphragm
(core)
Rock Fill Dam
The designation ‘rock fill embankment’ is appropriate where over 50% of the fill material
may be classified as rock pieces. It is an embankment which uses large size rock pieces
to provide stability and impervious membrane to provide water tightness.

Causes of Failure of Earth Dams
The analysis of earth dam must ask a question:……
How does the earthen dams most probably expected to fail? And
what are the causes failures?
Generally, from the previous experiences, the failure of earth dam is grouped in to
Hydraulic failures
Seepage failure
Structural failure

Hydraulic Failures: Hydraulic failures include the following:
 Overtopping
 Erosion of U/S face
 Erosion of D/S face
 Erosion of D/S toe
Seepage failures: Seepage failures may be due to
 Piping through the body of the dam
 Piping through the foundation of the dam
 Conduit leakage
 Sloughing of downstream toe.

Structural Failures: Structural failures may be due to the following reasons:
 Upstream and Downstream slope failures due to pore pressures
 Upstream slope failure due to sudden draw down
 Down stream slope failure during full reservoir condition
 Foundation slide: Spontaneous liquefaction
 Failure by spreading
 Failure due to Earth quake
 Slope protection failures
 Failure due to damage caused by burrowing animals
 Damage caused by Water soluble materials

Criteria for Safe Design of Earth Dam
Free from Overtopping
Free from seepage failure
Free from structural failure
There must be proper slope
protection against wind & rain
drop erosion.
There must be proper drainage
Economic section
How can one
satisfy these
design
criteria????......
 appropriate design flood
 Adequate spillway
 Sufficient outlet works
 Sufficient free board
 Phreatic (seepage) line should
exit the dam body safely without
sloughing downstream face.
 Seepage through the body of the
dam, foundation and abutments
should be controlled by adapting
measures. suitable
 The dam and foundation should
be safe against piping failure.
 There should be no opportunity
for free passage of water from
U/S to D/S both through the dam
and foundation.
 Safe U/S & D/S slope during
construction
 Safe U/S slope during sudden
draw down condition.
 Safe D/S slope during steady
seepage condition
 Foundation shear stress within
the safe limits.
 Earth quake resistant dam

AAAAAAAAAAAAAHydraulic structure one .ppt

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