ce- 451 design of hydraulic structures -...

CE-451 Design of Hydraulic Structures, by Prof. A. S.

Alghamdi ١ Spring, 2014

Textbook: Hydraulic Structures, by Novak et. al, 2007 References: Handouts

CE- 451 Design of Hydraulic Structures Spring 2014 (1434/1435H) Prof. Abdullah S. Alghamdi

Spring, 2014

CE-٤٥١ Design of Hydraulic Structures, by Prof. A. S.

Alghamdi ٢

Chapter 1 Elements of Dam Engineering

A purpose of a dam is To provide a safe retention and storage of

water. • Every dam must represent a design

solution specific to its site circumstances. • The design represents an optimum

balance of local technical and economical consideration at the time of construction.

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Purposes of Reservoirs

• Irrigation • Water supply • Hydroelectric power generation • River regulation • Flood control • Recreation • etc

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Dams Types

1. Embankemnt dams: constructed of earthfill and/or rockfill.

– Upstream and down stream slopes are similar and of moderate angle.

– Wide sections. – high construction volume relative to height.

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2. Concrete dams- constructed of mass concrete

– Face slopes are dissimilar (usually steep d/s and near vertical upstream

– Slender profile depending on type. Total large dams (1988) = 36235 dams

– Embankment = 82.9% – Concrete -gravity 11.3% – Concrete -Arch 4.4% – Concrete- Buttress 1% – Concrete -multiple arch 0.4%

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• Large dams are defined by ICOLD as – dams exceeding 15 m in height or – storage volume exceeds 1 million m3, or – discharge capacity over 2000 m3/s 1998 World Registry of dams shows that total dams

worldwide is more than 300,000: Country Large dams Total dams UK 535 >5500 USA 6375 75000 China(>30m) 4434 >86000

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• Table 1.3 shows highest dams worldwide • Table 1.4 shows largest volume dams

worldwide • Table 1.5 shows dams with largest

capacity reservoir worldwide

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Historical Prospective

• The oldest dam is Sad El-Kafara in Egypt 2600 BC

• Numerous dams were built in the middle east in early civilizations, notably in Iraq, Iran, Saudi Arabia & Yemen.

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Dams Focus points Unlike major civil engineering structures, dams have

important regards: • Every dam is unique: foundation geology, material

characteristics, catchments flood hydrology...etc, are all site specific.

• Dams are required to function at or close to their design loads for extended periods.

• Dams do not have structural lifespan • Most dams are earthfill, constructed from natural soils

which are mostly inconsistent materials. • Dam engineering needs many disciplines; structural &

fluid mechanics, geology & geotechnical, hydrology and hydraulics.

• Dam engineering depends upon application of informed engineering judgment

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Embankment Dams Types & Characteristics

• The embankment dam can be defined as – A dam constructed from natural materials excavated

or obtained close by

• Natural fill materials are placed and compacted without the addition of any binding agent, using high capacity mechanical plant.

• Embankment is plant intensive rather than labor intensive

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Earthfill embankment: at least 50 % of the materials is compacted soils. – Is constructed primarily of selected engineering soils

compacted uniformly and intensively in thin layers at a controlled moisture contents.

Rockfill embankment: at least 50% of the material may be classified as rockfill, i.e. coarse grained frictional materials

Saving in fill quantity when using rockfill for a given hight is considerable due to high frictional nature of rocks

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Concrete Dam Types & Characteristics

• Gravity dams • Buttress dams • Arch dams

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Gravity Concrete Dam

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Buttress Dams

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Arch Dam

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Hover Dam USA

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Advantages of Concrete Dams

1. Concrete dams are suitable to the site topography of wide and narrow valley alike (except arch dams), provided that a competent rock foundation is accessible at moderate depth (< 5 m).

2. Concrete dams are not sensitive to overtopping under extreme flood conditions.

3. All concrete dams can accommodate a crest spillway over the entire length (if necessary).

4. Outlet pipework, valves and other ancillary works are readily and safely housed in chambers or galleries within the dam.

5. High ability to with stand seismic loads. 6. Arch dams are extremely strong and efficient structures,

given a narrow valley and competent abutments.

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Disadvantages of Concrete Dams

1. Concrete dams are demanding with respect to foundation conditions

2. They need processed natural materials for suitable quantity and quality of aggregate.

3. Mass concrete construction is relatively slow, labor intensive and discontinuous, and required certain skills.

4. Unit cost (cost per cubic meter) is high compared to embankment. Usually total cost is higher than that of embankment dams.

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Spillways, outlets and ancillary works Spillways: The purpose of spillway is to pass flood water safely downstream when the reservoir is over flowing. Spillway components: 1. Spillweir: controlling the flow 2. spillway channel: to convey flood flow safely d/s. They

may incorporate energy-dissipation devices.

• Spillway capacity must safely accommodate the maximum design flood.

• Spillweir level dictates the normal maximum water level (NWL)

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• Outlet works: Outlet facilities are required to permit water to

be drawn off as is operationally necessary. They can be used to empty the reservoir as

needed. Outlet facilities may include: intake tower, valves,

gates, tunnels .. Etc. • River diversion This provision is necessary to permit

construction to proceed in dry conditions.

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• Cut-off wall Cut-off walls are constructed to control the

seepage under the dam. They may include: concrete wall, trench filled with

rolled clay, or grouting for fractured rocked.

Internal drainage: Internal drainage is used to control internal pressure

generated by seepage through the body of the dam.

Internal galleries and shafts: Used for internal inspection particularly in concrete

dams, they usually accommodate valves, gates and instrumentations for structural monitoring.

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Site Assessment and Selection of Dam Type

General site appraisal: • Catchments hydrology, geological,

geophysical and geotechnical characteristics.

• Available head and storage volume • Satisfactory site for the dam. • Availability of construction materials • Feasibility of the project.

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Geological, geophysical and Geotechnical Investigations

• To determine the geological structures, faulting, jointing, groundwater conditions.. Etc.

• The general objectives of the investigations are: – To determine the engineering parameters that can be

used to evaluate stability of dam foundations. – To determine seepage pattern. – To confirm the containment integrity of the reservoir. – Confirmation of the availability of construction

materials

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Wadi N

oman

Wadi Rahajan

ARAFAT

Wadi Magarish

Kabkab mountain

Wadi NomanKabkab mountain

Wadi Al-Hawa0 1500 meters

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Arafat

Strike-Slip Fault

Inferred Fault

Late-tectonic granites

Syn-tectonic granites (Diorites - tonalites- monzogranites)

Syn-tectonic metagabbros

Area shown in Figure (2)

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Wadi No'man

Wadi A

l-hawa

Strike-Slip Fault

Late-Tectonic granites

Syn-tectonic metagabbros

Area of geophysical survey

40 0.5 E 40 1.00 E

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0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5

19.3

19.4

19.5

19.6

19.7

19.8

m1 m2

m3

m4 m5 m6

m7

m8

m9

wb2

wb3

wb4

a1a2a3a4

a5a6

a7

a8

a9

a9-1

a9-2 a1-1

s1

s1-1

s1-2

33343536

37383940

41424344454647

48

4950515253

5455

3231 3029

2827 2625 24

20

A AA AAAAAA A AAAAAA (A AAAA AAA)A AAA A AA A'AA A AAA

A AAAA AA A AAAAAAAAA A AAAAA

SOL-1

SOL-2EOL-1

EOL-2

SL1

SL2

EAST40

SL3SOL-3

EOL-3

500 100 m

SL4

EOL-4

SOL-4

45Kharaza # 45

End of Seismic Line # 1EOL-1

Start of Seismic Line # 1SOL-1

Seismic Line # 1SL1

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-200-170-140-110-80-50-20104070100130160190220250280310340370400430460490

0 50 100 meters

0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5

19.3

19.4

19.5

19.6

19.7

19.8

wb1

wb2

wb3

wb4

m1 m2

m3

m4 m5 m6

m7m8

m9

a1a2a3a4a5a6a7

a8a9

a9-1

a9-2 a1-1

e-p1-S

ep1-1

ep1-2

ep1-3

ep1-4ep1-5

ep1-6ep1-7

ep1-E

33343536

37383940

41424344454647

48

4950515253

5455

3231 3029

2827 2625 24

20

ep2-start

ep3-startep4-start

line-4-start

line-4-end

s1

s1-1

s1-2

line8-end

line8-start

mag-p-1-start

mag-p-1-end

b3-axis

P8

0.633552 to 6.13864 6.13864 to 8.03656 8.03656 to 10.1087 10.1087 to 10.9465 10.9465 to 12.0474 12.0474 to 13.1849 13.1849 to 14.7639 14.7639 to 16.7283 16.7283 to 19.4577 19.4577 to 27.18

Euler solution depthsnT

Possible location of dikes

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-200-170-140-110-80-50-20104070100130160190220250280310340370400430460490

0 50 100 meters

0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5

19.3

19.4

19.5

19.6

19.7

19.8

wb1

wb2

wb3

wb4

m1 m2

m3

m4 m5 m6

m7m8

m9

a1a2a3a4a5a6a7

a8a9

a9-1

a9-2 a1-1

e-p1-

ep1-1

ep1-2

ep1-3

ep1-4ep1-5

ep1-6ep1-7

ep1-E

33343536

37383940

41424344454647

48

4950515253

5455

3231 3029

2827 2625 24

20

ep2-start

ep3-startep4-start

line-4-s

line-4-end

s1

s1-1

s1-2

line8-end

lin

mag-p-1-start

mag-p-1-end

b3-axis

P1

P1

P8

1.77527 to 3.85796 3.85796 to 5.0524 5.0524 to 6.01133 6.01133 to 7.05926 7.05926 to 8.38745 8.38745 to 9.5679 9.5679 to 11.0366 11.0366 to 13.4413 13.4413 to 16.9767 16.9767 to 31.58

A

B

C

D

E F

G

H

Location of zones of magnetic contacts Euler solution depths

nT

Clustered solutions

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Easting from Long. 40

19.2

19.24

19.28

19.32

19.36

19.4

19.44

19.48

19.52

19.56

19.6

19.64

19.68

19.72

19.76or

ting

from

Lat

.21

1005 1042

1041 10041001

1011 1002

501

502

504

505

506

507

508

509

604

506603601 602

548549 505 550 551

552

W-prof. 4 W-prof.5

W-prof. 7

W-prof. 8

W-prof. 9W

-pro

f-2

W-p

rof-

3

W-p

rof-1

W-prof. 6

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19.32

19.34

19.36

19.38

19.4

19.42

19.44

19.46

19.48

19.5

19.52

19.54

19.56

19.58

19.6

19.62

19.64or

ting

from

Lat

.21

10051042

1041 1004

1001

10111002

501

502

504

505

506

507

508

509

604

506603

601602

548

549505

550551

552

VES-Profile S-N

VES-Profile 1000

VES-Profile 600

VES-Profile 500

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VES604 VES506 VES603 VES601 VES602

Log of Resistivity value in Ohm.m0 10 20 30 40 50 60

Distance in 5 m

-70

-60

-50

-40

-30

-20

-10

0

Dep

th in

m

1.9

2

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3

3.183388510071037819493

289

190

132

135

195

3637351197157216891266396

67

54

115

244

437682912900630

327

150

97

106

176

363

887102612521250837422

262

205

143

137

189

6519361025970797519

218

182

135

108

166

The center of geoelectric layer The the upper level of the geoelectric layer

W E

بر سقطاع كنتوري تحت سطحي للمقاومة النوعية على امتداد بروفيل ال (١٤-٣(شكل رقم منطقة مجري الوادي في ، الموازي لمضرب الوادي (600) الجيوكهربي العمودي

(٨-٣شكل (

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0 40 80 120 160 200 240 280 320 360 400 440 480 520Distance in m

-70

-60

-50

-40

-30

-20

-10

0

Dep

th in

m

VES 509 VES 508 VES 507 VES 506 VES 505 VES 504 VES 502 VES 501

Dray aluvium-1

Dray aluvium-2

Saturated aluvium

Basement surface

نموذج تحت سطحي للطبقات مستنبط من نتائج السبر الجيوكهربي العمودي على طول البروفيل ) ١٧-٣(شكل رقم )S-N (

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• Outcome of this stage: 1. Logging of all natural and excavated materials and

borehole records. 2. careful correlation between all exposures, boreholes

and other data, and 3. excavation of additional trial pits, boreholes, shafts

and as considered necessary.

• Evaluation of seismic risk for an important dam

requires identification of the regional geological structure, with particular attention being paid to fault complexes.

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Selection of type of dam • The optimum type of dam for a specific site is

determined by estimates of cost and construction program for all design solutions which are technically valid.

• Four considerations of cardinal importance are detailed below.

1. Hydraulic gradient: the nominal value of hydraulic gradient, i, for seepage under, around or through a dam varies by at least one order of magnitude according to type.

2. Foundation stress: nominal stresses transmitted to the foundation vary greatly with dam type.

.

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Table 1.6 Notional foundation stresses; dams 100m in height

Notional maximum stress (MNm−2)

Dam Type

1.8–2.1 Embankment

3.2–4.0 Gravity

5.5–7.5 Buttress

7.5–10.0 Arch

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3. Foundation deformability: certain types of dams are better able to accommodate appreciable foundation deformation and/or settlement without serious damage.

4. Foundation excavation: economic considerations dictate that the excavation volume and foundation preparation should be minimized

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Fig. 1.7 Illustrative examples of dam type in relation to valley profile

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Notes and characteristics Type Embankment

Suited to either rock or compressible soil foundation and wide valleys; can accept limited differential settlement given relatively broad and plastic core. Cut-off to sound, i.e. less permeable, horizons required. Low contact stresses.

Requires range of materials, e.g. for core, shoulder zones, internal filters etc.

Earthfill

Rock foundation preferable; can accept variable quality and limited weathering. Cut-off to sound horizons required. Rockfill suitable for all-weather placing.

Requires material for core, filters etc.

Rockfill

Concrete Suited to wide valleys, provided that excavation to rock is less than c.5m.

Limited weathering of rock acceptable. Check discontinuities in rock with regard to sliding. Moderate contact stress. Requires imported cement.

Gravity

As gravity dam, but higher contact stresses require sound rock. Concrete saved relative to gravity dam 30–60%.

Buttress

Suited to narrow gorges, subject to uniform sound rock of high strength and limited deformability in foundation and most particularly in abutments. High abutment loading. Concrete saving relative to gravity dam is 50–85%.

Arch and cupola

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1.7 Loads on dams 1. Primary loads are identified as universally applicable

and of prime importance to all dams, irrespective of type, e.g. water and related seepage loads, and self-weight loads.

2. Secondary loads are generally discretionary and of lesser magnitude (e.g. sediment load) or, alternatively, are of major importance only to certain types of dams (e.g. thermal effects within concrete dams).

3. Exceptional loads are so designated on the basis of

limited general applicability or having a low probability of occurrence (e.g. tectonic effects, or the inertia loads associated with seismic activity).

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Fig. 1.8 Schematic of principal loads: gravity dam profile

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(a) Primary loads : 1. Water load, P1: This is a hydrostatic

distribution of pressure with horizontal resultant force (may exist upstream and downstream)

2. Self-weight load, P2: operates at the centroid of the section.

3. Seepage loads: Internal P3, and External P4

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(b) Secondary Loads 1. Sediment load, P5: due to accumulated silt

which generates a horizontal thrust. 2. Hydrodynamic water load, P6: Load generated

by wave action on the dam 3. Ice load, P7: May develop in extreme climatic

conditions (usually in significant). 4. Thermal load (concrete dams): internal load

generated by temp. differentials associated with changes in ambient conditions.

5. Interactive loads: internal loads generated from deformation of dam and foundations.

6. Abutment hydrostatic load: this is internal seepage load in the abutment rock mass (arch and cupola dams)

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(c) Exceptional Loads 1. Seismic loads: Oscillatory horizontal and

vertical inertia loads with respect to dam and the retained water

2. Tectonic effects: Saturation or disturbance following deep excavation in rocks

ce- 451 design of hydraulic structures -...

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