Dr. D. V Thareja

1PLANNING, DESIGN AND FOUNDATION PROBLEMS OF

CONCRETE GRAVITY AND EARTH & ROCKFILL DAMS

Dr D.V.Thareja

Director,Technical

2

GENERAL

3Planning of a Dam

Dam for :

-Water supply

-Hydro-power

-Storage of water

-Multipurpose

Identification of stretch of river

-Water supply (Delhi ,Shillong water supply)

-Hydro-power (Arunachal,Himachal,Bhutan)

-Storage of water (Tributories of Chenab)

-Multipurpose (Sankosh, Dibang)

4Considerations for Extent of Stretch

Minimum reach –with desilter:-That can accommodate dam of height which can cater to:

-Volume for peaking + sediment encroachment of live capacity (defines MDDL & height between FRL &MDDL)

- Water seal for intake (defines height between MDDL & invert of intake)

-Needed level difference between invert of intake& crest of spillway, when spillway is assigned role of

sediment flushing (defines gate’s thrust)

-Needed height between spillway crest & river bed for efficent flipping etc.

5Considerations for Extent of Stretch

Minimum reach – no Desilter:-That can accommodate dam of height which can cater to:

-Volume for peaking + sediment encroachment of live capacity (defines MDDL & height between FRL &MDDL)

- Water seal for intake (defines height between MDDL & invert of intake)

-Needed level difference between invert of intake&crest of spillway,when reservoir is required to serve as desilting basin to perform the role of sediment management (defines gate’s thrust)

-Needed height between spillway crest & river bed for efficent flipping etc.

6Considerations for Extent of Stretch –with Desilter

Needed level difference between invert of intake &crest of spillway ,when spillway is assigned the role of bed load transport &sediment flushing ,whereas desilter removes suspended sediment depends on :

volume of incoming coarser &medium sediment vs.

space &location (wrt. Intake ) to park this sediment in

the reservoir i.e depends on fetch & volume of res. above spillway crest

(Lesser the EL difference ,more frequent is the

requirement of flushing ; more taxed is the desilter ;

eg. 5m level difference in Nathpa Jhakri, 20m level

difference in Tala)

7Considerations for Extent of Stretch-no Desilter

Needed level difference between invert of intake &crest of spillway

,when spillway is assigned the role of transporting bed load

&suspended and sediment flushing ;with the reservoir serving as

desilting basin also ,depends on :

volume of incoming sediment vs. space &location to park the coarse

&medium sediment in the head reaches of reservoir ;and the

suspended sediment that is moving towards intake, in the further part

of the reservoir . The sediment is made to moves out through spillway

by the process of flushing & by under sluicing ensuring that its entry

into the intake is minimal.

Thus a much bigger reservoir volume with longer fetch ,&significant level difference between invert of intake &spillway crest can only cater to the desired function

8

smaller reservoir volume &length ,lesser EL difference

between intake invert &spillway crest ;will not only require

more frequent flushing but will result in more sediment entry

into the intake .

Reservoir volume retrivable after flushing shall preferably be

two to three times the annual average sediment volume .Also,

level difference between intake invert & spillway crest shall

preferably be over 30m (For the case of Baglihar Project

though the level difference is 10m but the reservoir volume

above spillway crest is about 200 Mcum & the fetch is also

very long). To have confidence, mathematical &physical

modelling is essential. Provision for adequate no. of spare

runners shall also be made.

Considerations for Extent of Stretch-no Desilter

9Location of Dam

Examine various alternatives of locating dam beyond this minimum reach of river taking into account :

Topography that caters to:

-waterway for spillway

-positioning of intake ,feeder tunnel/channel ,desilter &silt flushing arrangement

-placement of energy dissipator

-location of preformed plung pool(if planned)

-construction stage requirements

-accommodation of diversion works

10Location of Dam

Geology that caters to:

-availability of acceptable foundation grade rock at reasoable depth for :

-dam &slopes above

-spillway &related structures

-intake &feeding tunnels/channel

-desilter &silt flushing arrangement

-temporary diversion dam & related structures

11

Hydro Power development projects in Himalayan Region require

innovations in:

• Managing heavy sediment laden flows that result in loss of

reservoir capacity and damage to turbines

• Managing high flood flows that pose a problem in

accommodating large capacity spillways and energy dissipation

structures

• Meeting the criteria of stress vs. strength (weak formation with

high superimposed load)

Demonstration through case histories

INNOVATIVE APPROACHES IN PLANNING & DESIGN

12

With the best of sites for dam construction getting exhausted, most

of the dams have to be built on complex foundations requiring

special treatments

The cascade hydro-power development as is being planned on

many rivers gives limited choice in selecting dam sites.

The Himalayas, which have the bulk of hydro-power potential, have

fragile geology. The presence of weak features in any dam site is a

distinct possibility.

SITE CONSTRAINTS

13GEOLOGICAL FEATURES POSING CHALLENGES

The various types of geological challenging features encountered in dam

Construction are:

Dam Foundation

(a) Faults

(b) Shear Zones (Karbi Langpi,Thoubal, Bansagar)

(c) Shear Seams (Horizontal or Vertical) (Rana Pratap Project)

(d) Shattered/Highly jointed rocks

(e) Foundations with more than one type of rock with different

properties/characteristics

(f) Folds

(g) Buried Channels (Punatsangchu-I)

(h) Jointing Pattern of the rock mass.

(i) Caverns / cavities

(j) Springs etc.

Abutments

(a) Slope Stability (Tala)

(b) Buried Channels (Ranganadi)

14

POLAVARAM PROJECT

15INDRA SAGAR POLAVARAM PROJECT - LAYOUT

Main dam

Powerhouse

Spillway

Main dam

Powerhouse

16

17

18MAIN CHALLENGES

Project scope entails very large quantities

Temporary diversion for 80,000 cumecs

Spillway with 48 very large size gates, 16 m x 23 m

Excavation quantities in the spillway itself (including theapproach and spill channels) are more than 50 MCM of commonexcavation and more than 20 MCM of rock excavation

Quantities in dams are: Excavation >1 MCM; Fill >12 MCM

Planning the works in such a manner that material handling andschedule are optimized

19

Presence of deep alluvial foundation

Inadequate strength of foundation material

Would require

Densification over a large area – Vibrocompaction

Construction of a deep cut-off - up to 100 m deep

under main dam

OTHER CHALLENGES

20TWO POSSIBLE APPROACHES FOR SPILLWAY

PLANNING

Approach 1: Part constructed spillway to pass non-

monsoon floods through low level sluices; remaining

width excavated to pass design diversion flood with

spillway construction undertaken in lean seasons

Approach 2: Spillway fully constructed before

temporary diversion of the river; will still require low

level sluices to pass lean period discharge in the first

season when cofferdams are built

21MAIN DAM

22

PERIBONKA PROJECT

23PERIBONKA – AERIAL VIEW

24PERIBONKA – CONSTRUCTION OF CUT-OFF

25PERIBONKA PROJECT – 120 m DEEP CUTOFF

SNC Lavalin has recently designed

and managed construction of 120 m

deep cutoff – world‟s deepest - under

a 83 m high fill dam

26

ICOLD

27CLASSIFICATION OF DAMS (ICOLD)

LARGE DAMS

More than 15m high

Between 10-15m high if :

- Crest length more than 500m or

- Reservoir capacity more than 1mm3 or

- Flood discharge more than 2000m3/sec

SMALL DAMS

Other than above

28GLOBAL SCENARIO

LARGE DAMS

EMBANKMENT

DAMS

OTHER

DAMS

83%

17%

29INDIA

LARGE DAMSEMBANKMENT

DAMS

OTHER DAMS

5%

95%

30GLOBAL SCENARIO

DISTRIBUTION OF DAMS - HEIGHTWISE

TOTAL NUMBER OF DAMS - 36235 (1986)

28546

6031

1247321 64 26

0

5000

10000

15000

20000

25000

30000

35000N

UM

BE

R O

F D

AM

S

15-30 30-60 60-100 100-150 150-200 >200

HEIGHT IN METRES

31GLOBAL SCENARIO HEIGHTWISE DISTRIBUTION

OF GRAVITY DAMS

TOTAL NUMBER OF GRAVITY DAMS IN THE WORLD - 3953 (1982)

32GLOBAL

SPILLWAY VIS-a-VIS DAM FAILURES

40 %

23 %

12 %10 %

15 %

Foundation Problems

Inadequate

SpillwayPoor Construction

Others

Uneven

Settlement

33

SPILLWAY

34

OGEE

SPILLWAYS

CHUTE

SIDE CHANNEL/LABYRINTH

SHAFT/MORNING GLORY

SIPHON

OVERFALL

TUNNEL

SADDLE

FUSE PLUG

SLUICE

TYPES OF SPILLWAYS

35FACTORS AFFECTING SELECTION OF

SPILLWAY TYPE

Foundation conditions

Topography

Inflow hydrograph and reservoir capacity

Amount, type and use of excavated material

Possibility of combining spillway with outlet or

Diversion works

Overall economy,hydraulic efficiency and

Structural adequacy

36INDIA

DISCHARGE PER METRE WATERWAY

0

100

200

300C

um

ecs/

m

202 200

159

114 108

Sardar Sarovar

BhakraNagarjunaSagar

Sri Sailam Ichari

37

PLAN

SECTION

CHUTE SPILLWAY

38

Used mostly with earth / rockfill dams

Located either along a dam abutment or through a saddle

After the control structure water is conveyed through open channel

Can be constructed on any type of foundation

CHUTE SPILLWAY

39

DESIGN HEAD

RESERVOIR ELEVATION

OGEE SPILLWAY

CREST ELEVATION

BUCKET INVERT

TAIL WATER LEVEL

RIVER BED

END SILL

40OGEE SPILLWAY

Most commonly used with gravity dams

Surface profile conforms to lower nappe of a free falling jet

At bottom generally a reverse curve turns the f low into the energy

dissipator

Comparatively high discharge efficiency

41SIDE CHANNEL SPILLWAY

GROUT HOLE

PLAN

SECTION AA

CREST

CONTROL

STRUCTURE

TOP OF

DAM

C OF SPILLWAYLA

A

42

Control weir is placed along the side of discharge channel

Flow over the crest falls into a trough opposite the weir, turns at an

angle and then continues into the discharge channel

Adopted where a long overflow crest is desired

Useful when abutments are steep

SIDE CHANNEL SPILLWAY

43TUNNEL SPILLWAY

GROUND LINE

MWL

GOOSE NECK

PLUG

DIVERSION TUNNEL

44

Suitable for dams in narrow valleys

Diversion tunnels can be modified to work as tunnel spillways

Tunnel may be horizontal or inclined and may run full or partly full

Can have any type of control structure

TUNNEL SPILLWAY

45MORNING GLORY SPILLWAY

POOL LEVEL

BRIDGE

PLUG

DIVERSION TUNNEL

FILL DAM

TUNNEL

46

Consists of vertical or sloping shaft joining horizontal or near

horizontal tunnel

For morning glory inlet is funnel shaped

Spillway attains maximum discharge at low head

Used for narrow canyon dam sites

SHAFT/MORNING GLORY SPILLWAY

47SIPHON SPILLWAY

AIR VENT

POND LEVEL

FLOW

INLET

48

Can be used to have full capacity discharges at relatively low heads

Have automatic operation without any mechanical device

But cannot handle flows materially greater than designedcapacity,cannot pass debris and structure is subjected to heavyvibrations during operation

SIPHON SPILLWAY

49SLUICE SPILLWAY

FRL

GATE TRUNION

GIRDER

50

Helps flush the reservoir sediments

Being with a low level crest , entry of silt into intakes is reduced

Helps to pass floods during construction

Separate outlets for downstream releases may not be necessary

SLUICE SPILLWAY

51

Facilitates freedom of construction because it is independent of main dam

Can be used as an auxiliary or emergency spillway

SADDLE SPILLWAY

52

Is generally a dyke which gets overtopped and washed away saving

the main dam from being overtopped in the event of extra-ordinary

flood, or failure of main spillway

Located generally in a saddle away from main dam

FUSE PLUG

53

CHUTE SPILLWAYOGEE SPILLWAY

EMBANKMENT DAMS

Sankosh (265 m)

Wangchu (260 m)

Ramganga (128 m)

Beas (133 m)

Pandoh (76 m)

GRAVITY DAMS

Bhakra (225 m)

Nagarjuna Sagar (125 m)

Srisailam ( 145 m )

Narmada Sagar (92 m)

Sardar Sarovar (163 m)

IMPORTANT DAMS WITH SPILLWAY TYPE

54IMPORTANT DAMS WITH SPILLWAY TYPE

SLUICE

Ranga Nadi (68 m)

Chamera (141 m)

Tala ( 91m )

Singda (67 m)Tehri ( 261m )

Lakya ( 103m )

SIDE CHANNEL TUNNEL

55

IS :11223-1985

IS:6934-1973

IS:4997-1968

IS:5186-1969

IS:7365-1974

IS:11527-1985

IS:10137-1982

- Guidelines for fixing spillway capacity.

- Recommendations for hydraulic design of high

ogee overflow spillway.

- Criteria for design of hydraulic jump type stilling

basins with horizontal and sloping apron.

- Criteria for design of chute and side channel

spillways.

- Criteria for hydraulic design of bucket type energy

dissipaters

- Criteria for structural design of energy dissipaters

- Guidelines for selection of Spillway and

dissipaters.

INDIAN STANDARDS CONNECTED WITH

SPILLWAYS

56SPILLWAY DESIGN FLOOD

SIZE DESIGN FLOOD

Small 100 years

Intermediate SPF

Large PMF

Reference: IS 11223-1985-Guidelines for fixing spillway capacity

Flood of larger or smaller magnitude may be usedif the hazard involved in the eventuality of a failureis particularly high or low

57CLASSIFICATION OF DAM

CLASSIFICATION GROSS STORAGE HYDRAULIC HEAD (M cum) (m)

SMALL 0.5 TO 10 7.5 TO 12

INERMEDIATE 10 TO 60 12 TO 30

LARGE > 60 > 30

Reference: IS 11223-1985- Guidelines for fixing spillway capacity)

(EITHER OF THE TWO)

58INOPERATIVE SPILLWAY BAY

Reference : IS 11223-1985-Guidelines for fixing spillway capacity

For gated spillways, the contingency of atleast 10 percent of the

gates with a minimum of one gate being inoperative may be

considered as an emergency condition

59TYPES OF ENERGY DISSIPATERS

Bucket TypeStilling basin

60SELECTION OF TYPE OF ENERGY DISSIPATERS

Factors affecting

• Nature of foundations.

• Elevations of tail water.

• Rolling bed material.

• Safety of structures downstream.

61

STILLING BASIN FLIP BUCKET ROLLER BUCKET

IMPORTANT DAMS WITH ENERGY DISSIPATOR

TYPE

Bhadra

Bhakra

Sardar Sarovar

Ramganga

Pykara

Srisailam

Nagarjuna Sagar

Vaitarna

Ukai

Pandoh

Narmada Sagar *

Rihand *

Kadana * *

Ichari *

Jawahar Sagar *

* * Solid * Slotted

62

Tail water depth lower than sequent depth

Sound rock to withstand impact

Hydraulic jump type apron involves considerable excavation

TRAJECTORY BUCKET

Adopted When

63

TALA HE PROJECT - BHUTAN

64

2915m

2083m

1875m

2525m2214m

1650m

1728m

1728m2915m

FIG.1 GENERAL LAYOUT - TALA H.E.PROJECT

RD

34

56

RD

92

86

RD

17

98

3

RD

21

28

4

RD

0.0

0

1651

m15

95m

RD

13

24

4

RD

-22

87

9

65

m

TALA DAM - GEOLOGICAL SECTION

66TALA DAM - DPR STAGE – U/S ELEVATION

67

Experience of operating Chukha HE Project, the Tailrace of which

outfalls in the head reaches of Tala Reservoir - about 4 km long

• Chukha Project has desilting chambers but suffers from the

damage to turbines on account of sediment load

• Tala with head (≈ 850m) of almost double that of Chukha,

sediment related damages will be significantly higher

• Concluded that desilting Chambers needs supplementation with

reservoir as sediment management tool

• Being over 90m high dam, provides flexibility of locating spillway

crest significantly lower than invert of intake

TALA HE PROJECT - BHUTAN

68SCHEMATIC SEDIMENT PROFILE, SPILLWAY CREST,

INTAKE INVERT

69CHUKHA DAM-UPSTREAM ELEVATION

(in operation)

70TALA DAM - DPR STAGE U/S ELEVATION

71SEDIMENT MANAGEMENT THROUGH RESERVOIR

Shifting the crest of Spillway to a level lower than invert of intake –Intake will draw relatively clearer water from top when sediment ladenflow is discharged through spillway

Flood and sediment to be handled together, with reservoir and desiltingchambers acting as desanders; spillway and silt flushing tunnels actingas sediment discharge outlets

Various alternative sizes of gates at various crest elevations wereexamined

At tender stage ,decided to locate 8x12m sluice gate ,4 in nos. at el1330m which is 33m below FRL,10m below intake invert (NathpaJhakri was the drive)

At const. stage ,decided to locate 6.5x13m sluice gate, 5 in nos. atelevation which is 43m below FRL and 47m below dam top – ThreeGorges was the drive

Spillway Crest is 20m below the Invert of Intakes

72

73

TALA HYDRO ELECTRIC PROJECT, BHUTAN

WANGKHA DAM - UPSTREAM ELEVATION

74

EL.1275.50

EL.1339.014

EL.1333.15

EL.1320.00

EL.1356.50

MWL/FRL.1363.00EL.1366.00

AXIS OF DAM

ACCEPTABLE FOUNDATION GRADE

EL.1300.23 (LIP)

EL.1295.00(BUCKET INVERT)

TRAINING WALL

R=39

m

EL.1334.00

INSPECTION GALLERY

INSPECTION GALLERY

FOUNDATION GALLERY

(2x2.5m)

(2x2.5m)

0.2m FORMED DRAIN

(2x2.5m)

WANGKHA DAM - SLUICE SPILLWAY

0.3m VENTILATION PIPE

TRUNION EL.1333.00

TALA HYDRO ELECTRIC PROJECT, BHUTAN

EL.1346.00

EL.1336.00

EL.1331.00

RADIAL GATE

EL.1340.50

EL.1306.50

EL.VARIES

75

DAM AXIS

N25°E

CONSTRUCTION ADIT 6 m D-ShapedHRT INLET ADIT

CONSTRUCTION ADIT

(TOP) 6 m D-Shaped

3.95m D-Shaped

SILT FLUSHING TUNNEL

6 m D-ShapedGATE CHAMBER ADIT

6m. D-Shaped

CONSTRUCTION ADIT (BOTTOM)

7m. D-Shaped

CONSTRUCTION ADIT

H.C.D. (E & NE) Dte.CENTRAL WATER COMMISSION

76

General Layout

THREE GORGES PROJECT - China (18200 MW)

77

Spillway Dam

Cross Section

THREE GORGES PROJECT

78

The operation of the Three Gorges Reservoir consists in keeping

the reservoir full during the dry season (EL. 175 m, from

November to April) and to bring it to the minimum operating level

(135 m) in the rainy season (June to September), in order to have

the reservoir ready to store and route the incoming floods.

RESERVOIR OPERATION SIMULATION AT THREE

GORGES

79THREE GORGES-SEDIMENT DEPOSITION PROFILE

80

The dam was modified by opening up several conduits under the dam to

allow for sediment flushing during the flood peak.

SANMENXIA DAM, CHINA - THE NEW OPENING UP

BEING CREATED FOR SEDIMENT FLUSHING

81SILT FLUSHING THROUGH SANMANXIA DAM

82

TALA CONSTRUCTION

83

84

85

86

87

BAGLIHAR HE PROJECT

88

For spillway design the Indus Waters Treaty stipulates that:

“If the conditions at the site of a Plant make a gated spillwaynecessary, the bottom level of the gates in normal closed positionshall be located at the highest level consistent with sound andeconomical design and satisfactory construction and operation of theworks.”

Sediment management outlets to be of smallest size at highest level

POINT OF DIFFERENCE

89SPILLWAY ARRANGEMENT ADOPTED BY INDIA

Sluice Spillway -

5 Bays 0f 10.0m X 10.5m at El 808.0m

Discharging Capacity = 10500 cumec

Chute Spillway -

3 Bays of 12.0m X 19.0m at El 821.0m

Discharging Capacity = 6000 cumec

Auxillary Spillway -

1 Bay of 6.0m X 3.0m at El 837.0m

Discharging Capacity = 53 cumec

90

91BAGLIHAR HYDRO ELECTRIC PROJECT

UPSTREAM ELEVATION OF DAM

92PAKISTAN’S POSITION

Design flood can be passed through free surface gated spillway,

hence orifice spillway is not required.

Discharging capacity of sluice spillways is excessive even if

designed for sediment management

Management of Sediment can be done through conventional means

such as sediment excluders, sluices, and desanders.

Sediment management must be limited to protection of power

intakes and not pondage.

Systems for sediment management must be compliant with the

Treaty provisions which stipulate – Sediment management outlets

to be of smallest size at highest elevation

Sluice spillway is ineffective in protecting the power intakes

93

To effectively control reservoir sedimentatio

require water to be lowered down beyond the Treaty provisions

Technology advancement cannot be the basis for design

Alternate design proposed by Pakistan is more effective in sediment

management

PAKISTAN’S POSITION (Contd..)

94

95

96

97

98

99SITE CONDITIONS

Narrow Gorge with fragile Himalayan geological set up

River taking a right turn just downstream of the dam toe

High flood discharge (PMF 16500 cumec)

High annual Sediment Load (4-119MT). There could be short

duration very high sediment concentration flows with ppm varying

between 100-200 thousand, generated by land slides etc.

High quantum of floating debris

100BAGLIHAR HYDRO ELECTRIC PROJECT (450 MW)

GEOLOGICAL SECTION AT DAM AXIS

101TECHNOLOGY AVAILABLE AT SPILLWAY DESIGN

STAGE

Advances in technology (gate anchorages, gate seals, concrete, etc)

have enabled sound and economical designs wherein spillways can

be reliably utilized for sediment management in addition to passing

floods.

The reservoir itself functions as a desilting basin and desilting

chambers can be dispensed with in projects having long gorge based

reservoirs, such as Baglihar resulting in not only a substantial savings

but evolving a sound design.

Today gate anchorages can be designed for a thrust of 6000t and the

spillway crest could be lower than El. 808.0m which would enable

much better sediment environment at the intake.

102

To utilize spillway effectively for sediment management in the vicinity

of intakes and maintaining pondage, the following design features

need to be incorporated

Technology Available at Spillway Design Stage

(Contd..)

• The crest elevation of the spillways should be at the

lowest

level possible with current technology.

• The intakes should be placed close to the spillway with

intake

axis at right angles to the spillway axis. The intake face

shall

be in line with the inner surface of the first sluice.

• The spillway crest elevation should be at a level so as to

enable a sediment bed profile below the Intake Invert.

103ELEVATION OF SLUICE SPILLWAY CREST

The crest level of the sluice spillway was taken at highest possible

El 808.0m.

This level, which is 10.0m below the power intake sill of El

818.0m, was decided on the basis of empirical approaches and

experiences of existing projects about the minimum level

difference needed between spillway crest and intake for

minimizing sediment entry into the Intake.

Ideally there should have been a buffer zone between the gate top

elevation and Intake invert to contain the turbulence effect

generated by the high velocity sluice spillway flows, the

technology available then did not permit further lowering of the

spillway crest.

104SLUICE SPILLWAY ARRANGEMENT – IF IT WERE

TO BE DESIGNED NOW

Present day technology available has provided much better

capability and the sluices of the same size can be provided even at

El. 780.0 metres.

105

NATHPA JHAKRI PROJECT

106

27.4

KM

. LO

NG

SATLUJ RIVER

HEAD RACE TUNNEL Ø10.15M

LAYOUT PLAN OF NATHPA JHAKRI PROJECT

NH-22

NH-22

107

108

1A 1B 2 3 4 5 7 8 9 10 11

6

TOP OF DAM

DAM - U/S VIEW

109

TEESTA H. E. PROJECT (Stage IV)

PLAN AND UPSTREAM ELEVATION

110TEESTA H. E. PROJECT (Stage IV)

DIVERSION ARRANGEMENT : SECTION

111TEESTA H. E. PROJECT (Stage IV)

DIVERSION ARRANGEMENT : PLAN

112

MYNTDU H.E. PROJECT, MEGHALAYA

U/S ELEVATION & RIVER SECTIONS

113

EL. 590.00

C.J

ACCEPTABLE FOUNDATION GRADE

7 8 9 10 11 12

5000

5000

EL. 559.00

EL. 567.00

EL. 578.00

EL. 569.30

EL. 579.00

CONSTRUCTION SLUICE(3000 X 3000)

EL. 565.00

EL. 570.00

EL. 580.00

3000

.1

1.0

R.D

. (

-)1

52.1

0

R.D

. (

-)1

67.1

0

R.D

. (

-)1

82.1

0

R.D

. (

-)1

88.4

0

R.D

. (

-)1

73.4

0

OPEN CHANNEL

15000

1.0

.1

R.D

. (

-)1

70.4

0

3000 3000

R.D

. (

-)1

63.6

0

R.D

. (

-)1

48.6

0

ROCK LINE

NSL

( SCALE 1:100 )

WATER LEVEL EL.575.50

15000

R.C.C. DIVIDE WALL

EL. 570.00

1000

3000

EL. 580.00

MYNTDU H.E. PROJECT, MEGHALAYA

114

15000

11

TOP OF DAM EL. 620.00

R.D

(-)9

5.60

590

570

580

15000

14

16

15

1500015000

1312

1500015000

R.D

(-)2

23.6

0

CONCRETE APRON

15000

108 9

128000

1500015000

7

590

580

5

6600

UPSTREAM TOE OF DAM

1500014000 15000

610

DO

WN

STR

EAM

TO

E O

F D

AM

4

14000

R.D

(-)1

88.4

0

R.D

(-)1

73.4

0R

.D (-

)170

.40

R.D

(-)1

67.1

0

R.D

(-)1

63.6

0

R.D

(-)1

48.6

0

MYNTDU H.E. PROJECT, MEGHALAYA

115

8910

1

SLUICE SECTION THROUGH CENTRE LINE OF CONSTRUCTION SLUICE.

0.25

15000

1000

1 1

0.25

1

C.J.

CONCRETE APRON

15000

30

00

1000

EL.589.655

GATE SILL BEAM

FRESH ROCK LEVEL

FOUNDATION GALLERY

(2000x2500)

EL.559.00 1000(MIN.)

500 6200

31

67

1

0.25

10.5

EL.586.00

EL.588.00

1

1

EL. 560.50

EL.580.50

15000

(BUCKET INVERT)

EL.586.826 (T.P.)

ACCEPTABLE FOUNDATION GRADE

61000

4550

GALLERY

( 2000 x 2500 )

13800

3200

EL.575.00 (T.P.)

3934

EL.587.58

101

0.2

EL.585.00

STOP LOG SILL

EL.590.00

ORIGIN

EL.567.91

1

2

X3 2

Y2

+

EL.570.00

DETAIL ENTRANCE PROFILEORIGIN OF TOP ENTRANCE OF SLUICE

CONSTRUCTION SLUICE OF SIZE 3000X3000

EL. 565.00

( NOT TO SCALE)

20

00

3000

EL. 568.00

EL. 570.00

DAM OF AXIS

INSPECTION

PIER TRAINING WALL

MYNTDU H.E. PROJECT, MEGHALAYA

116

SANKOSH M. P. PROJECT

117SANKOSH M. P. PROJECT : LAYOUT

118SANKOSH M. P. PROJECT (4000MW)

Installed capacity : 8 x 400 = 4000 mw

Reservoir capacity : 6.32 billion m3

Catchment area : 10,820 sq. Kms.

Maximum probable : 18,213 cumecs flood

Annual generation : 6542 million units

Firm power : 630.6 mw

Load factor : 15.76

Time of completion : 7 years

PMF : 18213 cumecs

Diversion discharge (500 years) : 8500 cumecs

Coffer dam height : 70.0 m

Diversion tunnel : 3 no., 13 m dia

119SANKOSH MULTIPURPOSE PROJECT,

BHUTAN- Diversion flood

The flood for the different return periods and the risk corresponding to

the various assumed construction periods are given below :

Sl.

No

Return Period

(Years)

Flood

Magnitude

(Cumec)

Risk in percent during

period of construction

5

years

8

years

10

years

1. 50 6481 9.60 % 14.90

%

18.30

%

2. 100 7073 4.90 % 7.70 % 9.60 %

3. 200 7662 2.50 % 3.90 % 4.90 %

4. 500 8440 1.00

%

1.60

%

2.00 %

5. 1000 9027 0.50 % 0.80 % 1.00 %

120SANKOSH M. P. PROJECT, BHUTAN

121XIAOLANGDI DAM-LAYOUT PLAN

122XIAOLANGDI – UPSTREAM ELEVATION OF SPILLWAY

CUM INTAKE

123

124

TIPAIMUKH H.E. PROJECT (1500MW)

125TIPAIMUKH H.E. PROJECT (1500MW)

Installed capacity : 6 x 250 = 1500 mw

Reservoir capacity : 15.9 billion m3

Catchment area : 12,758 Sq. Kms.

Maximum probable : 16,964 cumecs flood

Annual generation : 3805 million units

Firm power : 434.44 mw

Load factor : 28.96

Time of completion : 7 years & 3 months

PMF : 16964 cumecs

Diversion discharge (100 years) : 4931 cumecs

Coffer dam height : 60.0 m

Diversion tunnel : 2 no., 12.5 m Dia

Tipaimukh reservoir will be largest reservoir of India.

3

126TYPICAL SPILLWAY TUNNEL

127

DIVERSION FLOOD

ROLE IN TYPE OF DAM

128

Diversion Capacity for Concrete Dams and Barrages

• The capacity of the diversion flood for concrete dams and

barrages may be less because flood higher than the designed one

could be passed safely over the partly constructed dam. The

following criteria would help in deciding the capacity :

• The higher of the two should be taken as the capacity of the

design flood for diversion.

- Maximum non-monsoon flow observed at the dam site.

OR

- 25 years return period flow, calculated on the basis on non

monsoon yearly peaks.

129

Diversion Capacity for Embankment Dams

• Overtopping of a partly completed embankment dam would be

very serious and even disastrous.

• For small dams to be constructed in a single season, it would

be sufficiently conservative to provide for the largest flood likely

to occur in a 5 year period.

130

For Small and Intermediate Dams

• Usually a frequency of 5 to 20 years flood is taken to decide the

capacity of diversion works. In case the diversion arrangements

like tunnels are to be used subsequently as permanent structure

like tunnel spillway, the capacity may be equal to the discharging

capacity of the permanent structure.

131

For Large Dams

• The diversion capacity should be evaluated on the basis of risk

and cost factors. However, for large dams, it is desirable that

100 years flood should be adopted for diversion works.

• Suitable protection measure should be taken at the end of the

construction season for the top and downstream of the

embankment dam to pass surplus flow considering the

possibility of the flood exceeding the design diversion flood.

132

TEHRI M. P. PROJECT (2000 MW)

133TEHRI M. P. PROJECT (2000 MW)

134

Typical section of ECRD

(Tehri HE Project, Uttaranchal)

135TEHRI M. P. PROJECT (2000 MW)

PMF : 15540 cumecs

Diversion discharge (500 years) : 8120 cumecs

Coffer dam height : 85.0 m

Diversion Tunnel : 4 no., 11 m Dia

136

DESIGN OF CONCRETE DAM

137FORCES ACTING ON GRAVITY DAM

HORIZONTAL FORCES THAT MAY ACT ARE :

• Hydrostatic pressure on u/s face (H1)

• Silt pressure against u/s face (H2)

• Ice load against u/s face (H3)

• Impact of waves against u/s face (H4)

• Hydrostatic pressure of tail water against the d/s face (H5)

• Inertia force of water against the dam due to seismicity (H6)

• Inertia force of mass of dam due to seismicity (H7)

VERTICAL FORCES THAT MAY ACT ARE :

• Gravity acting on mass of water if u/s face is inclined (V2)

• Dead load (gravity acting on mass) of dam (V1)

• Uplift force on any hor. Plane (V3)

• Inertia force due to mass caused by seismicity invert. Direction (V4)

138FORCES ACTING ON GRAVITY DAM

139

Forces such as weight of dam, water pressure can be calculated

accurately

But forces such as uplift; earthquake load; silt pressure; can only be

assumed & thus require judgement, care & experience

Besides forces indicated earlier the dam may be subjected to:

FORCES ACTING ON GRAVITY DAM (Contd..)

• Heat generrated by hydration of cement, solar radiations

• Deformability of foundation (tilt etc.)

• Alkali - aggregate reactions

140NEED OF SPECIFIC COMBINATION OF FORCES

The designer can assure the safety of dam by designing for all

combinations of loads including those whose simultaneous

occurrence is highly improbable & by using unduly large safety

factors.

This may lead to overly conservative & uneconomical designs

To avoid this we need design standards & criteria so that forces,

their combinations & safety factors should be such that dam is safe

yet economical

141

• The reservoir level is decided by reservoir operation studies

based on operating criteria & hydrologic data such as:

- Reservoir capacity;

- Stream flow records;

- Flood hydrograph & reservoir releases

• Tail water level is decided by tail water rating curves associatedwith operating studies

HYDROSTATIC FORCE BECAUSE OF

RESERVOIR LOAD ON U/S & TAILWATER LOAD

ON D/S

Reservoir & tail water loads depend upon the water level in the

reservoir & in the stream d/s of the dam

142

Water pressure is considered to vary directly with depth & acts

normal to the contact surfaces. (In case of overflow dams the

vertical pressure component of flowing water is not considered

because most of head is changed to velocity head)

COMPUTATIONS OF RESERVOIR & TAIL WATER

LOADS

143

Weight of concrete plus other such appurtenances as gates &

bridges

It is assumed to be transmitted vertically to the foundation without

transfer of shear between adjacent blocks

DEAD LOAD

144

Not all dams will be subjected to silt pressure, it is for the designer

to refer hydrologic data to decide allowance for silt pressures

Horizontal pressure exerted by the saturated silt load is assumed to

be equivalent to that of a fluid weighing 1360 kg/m3

Vertical pressure exerted by silt is determined as if silt were a soil

having a wet density of 1925 kg/m3; the magnitude of pressure

varying directly with depth

SILT LOAD

145

Reservoir water & tail water cause internal pressure in pores, cracks

& seams within the body of dam, at the contact of dam & foundation

& within the foundation

The distribution of internal hydrostatic pressures along a horizontal

section through the dam is assumed to vary linearly from full

reservoir pressure at the u/s face to zero or tail water pressure at the

downstream face

When formed drains are included in the dam, the internal pressure

distribution should be modified to reflect the effect of size, location &

spacing of drains

UPLIFT FORCES (OR INTERNAL HYDROSTATIC

PRESSURE)

146UPLIFT PRESSURE DISTRIBUTION

Through the foundation depends on depth of drains, grout curtain,

rock porosity, jointing, faulting & any other feature which may

modify the flow.

Determination of such pressure distribution can be made from flow

nets computed by several methods;

- 2D & 3D physical models;

- 2D & 3D FE models &

- electric analogs

The effect of internal hydrostatic pressure acts to reduce the

vertical compressive stresses in the concrete on a horizontal

section through the dam or at its base & is referred as uplift.

147

Laboratory tests indicate pore pressures act over 100% area of any

section through the concrete

Location of line of drain at a distance from u/s face of 5% of max.

Reservoir depth at the dam is desireable

A lateral spacing of twice the above distance will reduce the

average pore pressure at the line of drains to tail water pressure

plus 1/3 of differential between the tail water & head water

pressures

Uplift pressures are assumed to be unaffected by eq acceleration

because of their transitory nature

UPLIFT PRESSURE DISTRIBUTION (CONTD..)

148

Earthquake causes random motion of ground & this motion causes

the structure to vibrate. Thus two steps are necessary to obtain

loadings on a gravity dam :

i) To estimate magnitude and locations of EQ to which the dam

may be subjected & determine the resulting rock motion at the

dam site (we need : Mag. of EQ; depth of focus, distance from

epicentre; foundation strata)

ii) To determine the response of the dam to the ground vibration

which is a function of :

- nature of foundation strata

- material, size & mode of construction of structure

- duration & intensity of ground motion

EARTHQUAKE FORCES

149

Earthquake engineering is applied to determine a design eq which

represents an operating basis event called the maximum credible

eq in terms of richter magnitudes & distances to the site

Records of seismological activity in the area need to be studied to

determine magnitude & location of any recorded eq:

based on these data hypothetical eq usually having magnitude

greater than the historical events are estimated for any active faults

in the area. (Richter‟s magnitude is a number which is a measure of

energy released)

EARTHQUAKE FORCES (Contd..)

150

The IS : 1893-2002 specifies design seismic coefficent based on

design practice conventionally followed & performance of structures

in past earthquakes

For determining the seismic forces the country is classified into five

zones

SEISMIC COEFFICIENT METHOD OF DESIGN

151

The eq Force depends on the dynamic characteristics of structure &

those of ground motion.

Response spectrum method takes into account these characteristics

& is recommended for use in case where it is desired to take such

effects otherwise an equivalent static approach employing use of

seismic coefficent may be adopted.

Response spectrum : the representation of the maximum response

of idealised single degree freedom systems having certain period &

damping, during that eq. The max. Response is plotted against

undamped natural period, for various damping values. The response

can be in terms of max acceleration, velocity or displacement.

RESPONSE SPECTRUM METHOD OF DESIGN

152

Cracking in dams is undesirable as it destroys the monolithic

nature of structure

Joints are essentially designed cracks, located where one wants

them

Three principal types of joints used in concrete dams are:

• Contraction joints

• Expansion joints

• Construction joint

JOINTS IN DAMS

CONTRACTION & EXPANSION JOINTS

Provided to accommodate volumetric changes which occurs after

placement

Longitudinal & transverse joints

LONGITUDINAL JOINTS

20 to 30 m

Being avoided utilising pre & post cooling options

TRANSVERSE JOINTS

15 to 25 m

usually adopted

153JOINTS IN DAMS (CONTD..)

CONSTRUCTION JOINTS

Lifts 0.75 to 2.5 m

Provided to facilitate construction

Permit metal embedments

Allow for subsequent placement for second stage

154

OPENING WITHIN THE DAM

To have access

May run longitudinally or transversely

Either horizontally or on slope

PURPOSE

Drainage way

space for drilling and grouting

Access to observe health of dam

for operation of gates/outlets

carry control cables/power cables

GALLERIES & ADITS

155

FOUNDATION GALLERY

Provided when dam height > 10 m

Min.Size 1.5 x 2.25 m but 2.0 x 2.5 m provided to accommodate

drilling equip.

Min. 2.0 m cover of conc. Above foundation

3.0 m away from u/s face or 5% of head

INSPECTION GALLERY

Provided above the foundation gallery

kept 7 m below overflow crest

Spacing between galleries 20 to 30 m

1.5 x 2.25 m size

FOUNDATION GALLERY & INSPECTION

GALLERY

156

157

158

INSTRUMENTATION GALLERY

Generally perpendicular to dam axis

1.5 x 2.25 m size

SUMP WELL

Provided in the deepest location

No. & Size depends on amount of seepage water

PUMP CHAMBER

Provided above the sump well to pump the water out of the dam

INSTRUMENTATION GALLERY SUMP WELL &

PUMP CHAMBER

159SUMP WELL & PUMP CHAMBER

160

ELEVATOR TOWER

Provide in nof blocks

3 m x 3 m is the normal size

Provides access to various galleries

If necessary stair well is also provided around lift well

VENTILATION SHAFT/PIPES

1m ø ventilation shaft when no adits

Otherwise 300 mm ø ventilation pipe

Provided one in each/alternate block

ELEVATOR TOWER & VENTILATION

SHAFT/PIPES

161ELEVATOR SHAFT

162

Provided to intercept seepage water in the dam

Helps to minimise hydrostatic pressure developing in the dam body

Size 200 mm ø spaced 3 m c/c along (parallel) to the axis and is

connected to galleries

In overflow dams - 1 m below crest

In nof dams – top is at road level

FORMED DRAINS

163

164

165

166

167

168

169

NATHPA SPILLWAY

170

171

BUNKKHA DAM

PLAN & SECTION

172

173

SPILLWAY

SIZE AND DISCHARGE

174

GAMBHIR PROJECT

175

176PROBLEM

WHILE EXCAVATION OF BLOCK 1&2 AND 10 & 11 SAND LAYERS FOUND AT EL 459.0 M TO 466.0 M

BORING WAS CARRIED OUT ALL ALONG THE EARTH DAM (LEFT & RIGHT) AND IN THE DOWNSTREAM SIDE.

177

178

179

180

SUBANSIRI

SPILLWAY

181

OVERFLOW BLOCK

182SUBANSIRI BASIN PROJECT

Single High Dam Cascade Development

Description Unit Subansiri Lower H.E.

Project

Subansiri Middle

Project

Subansiri Upper

Project

Type of Dam Rockfill Concrete Concrete Concrete

Dam height m 265 133* 202* 237*

FRL m 334 205 450 460

MRL (in June – July) m 190 418 435

Storage upto FRL M. cum. 13400 1365 1688 1743

Flood storage (FRL-MRL) M. cum. 442 689 499

Dedicated flood cushion above

FRL

M. cum. -- 258 236

Total flood storage capacity M. cum. 2700 442 947 735

M. cum. 2700 2124

*from deepest foundation level

SUBANSIRI BASIN PROJECT

183

DESIGN OF

EMBANKMENT DAMS

184ADVANTAGES OF EMBANKMENT DAMS

OVER CONCRETE DAMS

Suitable for any type of foundation

(Rock not necessary).

Locally available materials can be used.

Height of Dam can be raised easily.

Relatively safe in earthquake prone areas. (Especially Rockfill

dams)

Usually economical.

185HOMOGENEOUS V/S ZONED EARTH DAM

Homogeneous

Suitable where single type of material is available.

Convenient for construction.

Zoned

Suitable where different types of soils are available.

Composed of impervious core , transition zone and pervious or

semi-pervious shell.

Provides greater stability during rapid drawdown.

More suitable for large heights.

186SUITABILITY OF MATERIAL FOR CORE AND

SHELL

CORE

Impervious in nature.

Low plasticity.

Good shear strength.

BIS Code recommends GC , CL , CI soils.

SHELL

Semi pervious or pervious in nature.

Very good shear strength.

BIS Code recommends SW , GW , GM soils.

187BASIC DESIGN REQUIREMENTS

Safety against overtopping

Stability

Safety against internal erosion

Safety against piping through foundation

188SAFETY AGAINST OVERTOPPING

Sufficient spillway and outlet capacity during and after construction.

The freeboard should be sufficient to prevent overtopping by waves.

Extra freeboard if required to be provided as settlement allowance.

• For unyielding foundation, settlement should be 1 percent of the

height of dam.

• For compressible foundation, the settlement should be computed

based on laboratory test results and should be provided for by

increasing the height of dam corresponding.

189STABILITY

The slopes of the embankment shall be stable under all loading

conditions.

They should also be flat enough so as not to impose excessive

stress on foundation.

Embankment slopes shall be designed in accordance with the

provisions contained in IS: 7894.

The upstream slope shall be protected against erosion by wave

action and the crest and downstream slope shall be protected

against erosion due to wind and rain.

190SAFETY AGAINST INTERNAL EROSION

The seepage through the embankment and foundation should be

such as to control piping, erosion and sloughing and excessive

loss of water.

Seepage control measures are required to control seepage

through dam and seepage through foundation. Design for control

of seepage through dam shall be made in accordance with

provisions contained in „Indian Standard drainage systems for

earth and rockfill dams IS : 9429.

Design for control of seepage through foundation may be made in

accordance with provisions contained in IS : 8414.

191UPSTREAM SLOPE PROTECTION MEASURES

Hand placed riprap

Dumped riprap

Cement concrete facing

192DOWN STREAM SLOPE PROTECTION

MEASURES

Turfing

Stone pitching

Network of open paved drains

Geonet

193

194HIGHEST EARTH CORE ROCKFILL DAMS

S. No. Name of Project Height (m) Status

1. Rogun, CIS 335 Under construction

2. Nurek, CIS 300 Completed

3. Chicoasen, Mexico 262 Completed

4. Mica, Canada 262 Completed

5. Tehri, India 261 Under construction

6. Guavio, Colombia 240 Completed

7. Chivor, Colombia 237 Completed

8. Oroville, USA 236 Completed

195

Fig. 4.14 Typical calculations for downstream slope by analytical method (steady seepage)

196CONTACT WITH SPILLWAY

Adequate length of core wall or key wall should be provided

Foundation treatment similar to that of the Spillway should be provided

Foundation treatments of embankment and concrete dam should

provide a continuous impervious barrier

197JUNCTION OF EMBANKMENT DAM WITH

GRAVITY DAM

U/S ELEVATION

( CONVENTIONAL DESIGN )

NON-OVER FLOWEARTH DAM SPILLWAY

CORE WALL

PLAN

NON-OVER FLOW

BERM

BERM

ROAD

FLOW

EARTH DAM

CORE WALL

2.5 :1

3 :1

2 .5 :1

2.25 :1

198JUNCTION OF EMBANKMENT DAM WITH

GRAVITY DAM

NON-OVER FLOWEARTH DAM

BERM

BERM

ROAD

U/S ELEVATION

PLAN

FLOW

2.5 :1

3 :1

2 .5 :1

2.25 :1

NON-OVER FLOWEARTH DAM SPILLWAY

(MODERN TREND)

199

FOUNDATION

PROBLEM

200

USBR during the construction of Shasta Dam undertook extensive studies

for strengthening the weak rock seams in the dam foundation.

• Two dimensional analysis undertaken utilizing Airy’s function

showed that beyond a certain thickness of concrete plug, the rate of

decrease in deflection was exceedingly small

• Based on theoretical studies undertaken, the following formulae for

determining the depth of concrete plug were evolved:

d = 0.0066bh + 1.5 for H > 46m

d = 0.3b + 1.5 for H < 46m

where

d = Depth of plug(m)

b = Width of seam (m)

H = Height of dam above foundation level (m)

EMPIRICAL APPROACHES - USBR APPROACH

2014.4.1 Cut – off trench

A minimum width of 4 m recommended.

Bottom width of 0.1–0.3H to satisfy piping requirement.

Side slopes may be provided as:

1:1 in overburden

0.5:1 in soft rock

0.25:1 in hard rock

Should be taken at least 1 m into continuous impervious substratum.

2024.4.2 Consolidation grouting

Fractured and jointed rocks should be treated at contact of core and rock

foundation to:

Prevent piping of fines from core into rock

Seal near-surface rock against undue loss of curtain grout

Depth of hole 6-10 m; spacing 3-4.5 m.

Split spacing method; initial spacing 6 to 12 m.

Grout pressure 0.6-6 kg/cm2.

2034.4.3 Curtain grouting

Curtain would consist of one or more rows of holes.

Split spacing method.

If permeability can be brought down to 5 Lugeon with a final spacing of

1.5 m or larger, a single line curtain would be adequate.

If further drilling and grouting of holes at closer spacing is required, two

line curtain should be preferred.

2044.4.4 Depth of curtain

Should normally extend to relatively impervious rock of permeability 3

Lugeon or less.

When this cannot be realized due to deep pervious formations, curtain

should extend to a depth ranging from H/3 to H.