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Department Of Civil Engineering

Roorkee Institute of Technology, Roorkee

Certificate

This is to certify that Mr. Vikas badoni, B.Tech – 4thyear, CIVIL

ENGNEERING student delivered a Report on “TEHRE DAM”, at

THDC INDIA LIMITED.

His performance in the seminar was excellent/ very good/ good/

satisfactory

Mr. Vikas Badoni Mr. Ajay singh

Seminar Co-ordinator HOD(CE Deptt.)

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ACKNOWLEDGEMENT This report has been made possible through the direct and indirect cooperation of various persons for whom I wish to express my sincere thanks & gratitude.

I would especially like to thank Mr. ATUL JAIN, Mr. KUSHAL SINGH & Mr. K.S. RANA for his significant help during this visit.

I would be lagging behind in my duty if I fail to express my heartiest gratitude to respected Dr. S. K. Saini (Director, RIT) and Dr. A.K. MATHUR (Director General, RIT) for giving me their guidance.

I am beholder to my beloved FATHER AND MOTHER and friends who have helped me in crafting this report.

I hope that I have done enough work which will live up to the expectations of people of ‘THDC INDIA LIMITED’ and all the concerned people.

VIKAS BADONI

B.Tech 4th year

Civil Engineering

Rool no.- 110240107056

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CONTENTS

INTRODUCTION……………………………………………………….6

HISTORY……………………………………………………………………7

TECHNICAL SPECIFICATION…………………………………….9

FEATURES OF TEHRI PROJECT……………………………….10

Tehri HPP features…………………………………………………………11

Uniqe Features Of Tehri Project……………………………………13

In World/Asia…………………………………………………………….13

In India………………………………………………………………………13

BENEFITS FROM TEHRI DAM PROJECT………………….14

ENVIRONMENTAL ISSUES………………………………………15

GENERAL LAYOUT PLAN………………………………………….16

TYPICAL SECTION OF TEHRI DAM………………………….17

Impervious Core……………………………………………………………..18

Upstream Shell……………………………………………………………….18

Downstream Shell…………………………………………………………..19

Processed Shell……………………………………………………………….19

Processed Shell……………………………………………………………….20

Fine Filter………………………………………………………………………..20

Coarse Filter…………………………………………………………………….21

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Riprap……………………………………………………………………………..21

Inspection Gallery at EI. 725 m…………………………………….21

Inspection Gallery at EI.>835 m…………………………………..22

Consolidation Grouting……………………………………………………22

Grout Curtain………………………………………………………………….22

Underground Grouting Gallery……………………………………….22

SISMIC ASPECTS OF DAM………………………………………23

Geology Of Dam Site………………………………………………………23

Seismo-Tectonic Feature Of Project……………………………….23

Seismic Safety Analysis………………………………………………….25

CONCLUSION…………………………………………………………..26

BIBLIOGRAPHY………………………………………………………..27

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INTRODUCTION:-

The Tehri Dam is the highest dam in India and one of the

tallest in the world. It is a multi-purpose rock and earth-

fill embankment dam on the Bhagirathi

River near Tehri in Uttarakhand, India. It is the primary

dam of the THDC India Ltd. and the Tehri hydroelectric

complex. Phase 1 was completed in 2006, the Tehri Dam

withholds a reservoir for irrigation, municipal water

supply and the generation of 1,000 MW of

hydroelectricity. The dam's 1,000 MW pumped-

storage scheme is currently under construction.

Tehri Hydro Power Complex (2400 MW), comprises the following components:

1. Tehri Dam & Hydro Power Plant (1000 MW)

2. Koteshwar Hydro Electric Project (400 MW)

3. Tehri Pumped Storage Plant (PSP) (1000 MW)

Govt. of India approved the implementation of Tehri Dam & HPP (1000 MW) in

March, 1994 along with committed works of Koteshwar HEP and essential works of Tehri

PSP, as Stage-I of Tehri Hydro Power Complex. All the four units of Tehri Power Station

were commissioned in the year 2006-07. This project has become the landmark and pride

of the Nation as a whole.

Two Units of Koteshwar HEP were commissioned in Mar, 2011 and 3rd and 4th unit

were commissioned in Jan, 2012 and Mar, 2012 respectively.

The essential works of Tehri PSP have already been completed along with Tehri

Dam & HPP Stage-I. Major works of the Project are being executed through a single EPC

contract. Contract for EPC/Turnkey execution of the Project has been awarded to

consortium of M/S Alstom Hydro France and Hindustan Construction Company on 23rd

June-2011. Work on the project has commenced w.e.f. 27th Jul, 2011.

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HISTORY:-

A preliminary investigation for the Tehri Dam

Project was completed in 1961 and its design was

completed in 1972 with a 600 MW capacity power

plant based on the study. Construction began in

1978 after feasibility studies but was delayed due

to financial, environmental and social impacts. In

1986, technical and financial assistance was

provided by the USSR but this was interrupted

years later with political instability. India was

forced to take control of the project and at first it

was placed under the direction of the Irrigation

Department of Uttar Pradesh. However, in 1988

the Tehri Hydro Development Corporation was

formed to manage the dam and 75% of the funding would be provide by the federal

government, 25% by the state. Uttar Pradesh would finance the entire irrigation portion

of the project. In 1990, the project was reconsidered and the design changed to its current

multi-purpose. Construction of the Tehri Dam was complete in 2006 while the second

part of the project, the Koteshwar Dam was completed in 2012. The pumped storage

power plant is slated for commissioning in February 2016.

Tehri Dam Project was first conceived in the year 1949. Since then, many important events

have occurred in the history of the project. All such events in chronological order are

given below:

1949 A dam on river Bhagirathi conceived

1961 Investigations started for site selection

1969 Detailed project report (DPR) submitted by U.P. irrigation department envisaging construction of rockfill dam, having installed capacity of 600 MW

1972 Planning commission approved the project for execution by Govt. of U.P.

1976 Govt. of U.P. accorded the administrative approval

1978 The construction commenced at site

1979 The project design was reviewed and revised DPR envisaging install capacity of 1000 MW submitted

Dec.1979- august 1989

Working group constituted by department of science and technology concluded that dam as designed was safe. A separate report by chairman did not give any recommendation

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Jan. 1983 Techno-economic clearance accorded by central water commission (CWC) and central electricity authority (CEA)

1985 Planning commission accorded clearance for the power portion of the project

Nov. 1986 Central cabinet approved the execution of Tehri Hydro Complex as a joint venture of Govt. of India and Govt. Of U.P., seeking Soviet assistance

Nov. 1986 A bilateral agreement for Techno-economic cooperation was signed between India and erstwhile USSR

12th July 1988 Tehri Hydro Development Corporation Ltd. (THDC) was incorporated as a joint venture of Govt. of India and Govt. Of U.P. for implementation of Tehri Hydro power complex

June 1989 Project work transferred by Govt. of U.P. to THDC

March-April 1990

High level committee (HLC) of experts constituted by the committee of secretaries, unanimously concluded that the proposed dam section was safe even for the worst scenario of an earthquake of +8 magnitude occurring right under the dam at 15km depth

August-Sept. 1990

Reference by department of mines to an independent expert of international repute, Prof. Jai Krishna recommended that the proposed dam section of Tehri was safe from the point of view of the seismicity of the region

Oct. 1991 Uttarkashi Earthquake occurred on 20/10/1991. No damage to the dam foundation was noticed. Even surficial cracks were not observed anywhere in the dam area.

Nov. 1991 Seismic stability of Tehri Dam against actual accelerogram of Gazli Earthquake with vertical acceleration of 1.36g and horizontal acceleration of 0.72g checked by hydro project institute, Moscow and dam was found to be safe

March. 1994 Govt. of India approved the implementation of Stage-I of the project i.e. Tehri Dam and HPP (1000 MW), along with compulsory works of PSP and Koteshwar, at the estimated cost of Rs.2963.67 crore

July 2006 Unit No.4 successfully synchronized

Sep. 2006 Unit No.4 declared for commercial operation

Oct. 2006 Unit No.3 declared for commercial operation

Feb. 2007 Unit. No.2 declared for commercial operation

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TECHNICAL SPECIFICATION:-

The dam is a 260.5 metres (855 ft) high rock and earth-fill embankment dam. Its length is

575 metres (1,886 ft), crest width 20 metres (66 ft), and base width 1,128 metres (3,701 ft).

The dam creates a reservoir of 2.6 cubic kilometres (2,100,000 acre·ft) with a surface area

of 52 square kilometres (20 sq mi). The installed hydro capacity is 1,000 MW along with

an additional 1,000 MW of pumped storage hydroelectricity. The lower reservoir for the

pumped-storage plant is created by the Koteshwar Dam downstream.

The Tehri Dam and the Tehri Pumped Storage Hydroelectric Power Plant are part of the

Tehri Hydropower Complex which also includes the 400 MW Koteshwar Dam. The

complex will afford irrigation to an area of 270,000 hectares (670,000 acres), irrigation

stabilization to an area of 600,000 hectares (1,500,000 acres), and a supply of 270 million

imperial gallons (1.2×106 m3) of drinking water per day to the industrialized areas

of Delhi, Uttar Pradesh and Uttarakhand. The total expenditure for this project was 1

billion U.S. dollars.

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FEATURES OF TEHRI PROJECT:-

Tehri dam project was first conceived in 1949. The site was inspected by the ‘Geological

Survey of India’ and a preliminary project report was prepared. Tehri dam project is the

first storage scheme to have been taken up for implementation to provide power,

irrigation and drinking water benefits. Tehri dam is a 260.5 m high Earth and Rockfill dam constructed across mythic river

Bhagirathi at 1.5 km downstream of its confluence with river Bhilangana in district

Their Garhwal of Uttarakhand.

The project would be implemented by a new company to be jointly promoted by Govt.

of India and Govt. of Uttar Pradesh.

Tehri Hydro Development Corporation Ltd. (THDC Ltd.) was incorporated as a limited

company under the companies act, 1956 in July 1988 as a joint venture corporation of the

Govt. of India and Govt. of UP to develop, operate and maintain the Tehri hydro power

complex and other hydro projects. The project works were transferred to THDC w.e.f 1st

June 1989.

Then cabinet approved the execution of Tehri Hydro Complex (2400 MV) comprising of

Tehri Dam & HPP (1000 MW), Tehri PSP (1000 MW) and Koteshwar HEP (400 MW).

L-SECTION OF TEHRI HYDRO POWER COMPLEX

(UPPER AND LOWER RESERVOIRS)

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Tehri HPP features:

LOCATION HYDROLOGY

State Uttarakhand Normal annual rainfall 1016 to 2630 mm

District Tehri Garhwal Maximum recorded flood discharge

3800 cumecs

Nature of scheme Storage Scheme Adopted maximum flood for diversion during monsoon period

8120 cumecs

RESERVOIR Probable Maximum flood 15540 cumecs

Full Reservoir Lever (FRL) El 830 m Routed flood 13040 cumecs

Maximum Water Level (MWL)

EL 835 m DAM

Dead storage level El 740 m Type Earth and Rock fill dam

Gross storage 3540 MCM Crest Level EL 839.5

Dead Storage 925 MCM Height 260.5 m

Live Storage 2615 MCM Width at river bed 1125 m

Water Spread at Full Reservoir Level

44 sq. km Width at top 25.5 m flared to 30.5 m at abutments

Water Spread at Dead Storage Level

18 sq. km Length at top 575 m

Diversion Flood Discharge 8120 cumecs SLOPE

Water Spread at Dead Storage Level

18 sq. km Upstream 1 : 2.5

Diversion Flood Discharge 8120 cumecs Downstream 1 : 2

SPILLWAYS

Chute Spillway Right Bank Shaft Spillway

Crest Level El 815.0 m Type & Nos. Ungated, 2 nos

Waterway 3 bays each of 10.5 m width

Crest Level El 830.2 m

Design Discharge 5500 cumecs Dia of shaft 12 m

Type & No. of gates Radial Gates, 3 nos

Design Discharge 3850 cumecs

Left Bank Shaft Spillway Intermediate Level Outlet

Type Gated, 2 nos No. and size 1 no., 8.5 m dia

Crest Level El 815.0 m Discharge Capacity (at FRL) 1100 cumecs

Dia of shaft 12 m INTAKE WORKS

Design Discharge 3650 cumecs Location Left bank of river Bhagirathi

Type of Gates Radial gates No. & type of structure 2 Nos. Submerged Structure

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HEAD RACE TUNNELS Invert of intake El 720 m

Number and size 2 Nos., 8.5 m dia PENSTOCKS

Total Length 1634 m Number and size 4 Nos., 5.75 m dia

POWER HOUSE Total Length 1040 m

Machine Hall Transformer Hall

Type Underground Type Underground

Location Left Bank Size 161 m long, 18.5 m wide, 29 m high

Number & Units 4 Nos., 250 MW each

Step-up Transformers

Size 197 m long, 18.5 m wide, 29 m high

Capacity 306 MVA

Head

Maximum 231.5 m, Minimum 127.5 m, Rated 188.0 m.

Number 4

Switchyard Voltage Ratio 15.75/400 KV

Location and Type Indoor SF-6 GIS TAIL RACE WORKS

Number and size of Tailrace Tunnels

2 Nos., 9 m dia

Length of Tunnels 862.5 m & 747.5 m

Invert Level of Outlet El 603 m

Installed Capacity 1000 MW (4 x 250 MW)

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Unique Features of Tehri Project:-

In World/Asia (a) 260.5 m high Earth and Rockfill dam – third highest dam in the world (4th Highest,

considering the Rogun Dam under Construction).

(b) Vertical Shaft spillways (230 m high) – highest in the World.

(c) Butterfly valve of 5 m diameter – largest in Asia.

In India (a) Chute spillway 220 m high – highest.

(b) Upstream Coffer dam – highest.

(c) Regulating Radial Gate under the head of 130 m – highest head operating gate.

(d) Sphearical valve of 4 m diameter – largest.

(e) Provision of the gallery in earth and rockfill dam body – first time in India.

(f) Provision of an inclined core in earth and rockfill dam – first time in India.

(g) Largest concrete monolithic block (80 m * 100 m) – largest.

(h) Cranes in machine hall – 2 nos each of 375 ton capacity – bigest in size.

(i) 62.5 m power house cavern – deepest.

(j) 670 m long, 400 kV, SF6 Gas insulated Bus Duct in underground switchyard

having capacity of 2000 MV ( for eight units ) for evacuation of power from

transformer to gantry – largest in India.

(k) Variation in operation head of 90m – maximum.

(l) 3 phase 306 MVA transformer (15.75 d/ 420 kV) – largest in hydropower station

in India.

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BENEFITS FROM TEHRI DAM PROJECT:-

Addition to the Installed Generating capacity in the Northen Region

2400 MW

Annual Energy Availability 6200 MU

Irrigation (additional) 2.70 lac ha

Stabilisation of Existing Irrigation (besides above)

6.04 lac ha

Additional Generation in Downstream Projects

200 MU

Drinking Water for Delhi (for about 40 lac people)

300 cusecs (162 million gallons per day)

Flood Moderation Flood of Bhagirathi river

Integrated development of Garhwal region, including construction of a new hill station town with provision of civic facilities; improved communication, education, health, tourism, development of horticulture, fisheries and afforestation of the region

Overall upliftment of Social Status of the people in region

Employment to the people (Direct or Indirect)

Approximate 2300 in THDC and around 10,000 through executing agencies during constuction. Substantial indirect Employment through commercial activities.

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ENVIRONMENTAL ISSUES:-

The Tehri Dam has been the object of protests

by environmental organizations and local

people of the region. In addition to the human

rights concerns, the project has spurred

concerns about the environmental

consequences of locating a large dam in the

fragile ecosystem of the Himalayan foothills.

There are further concerns regarding the dam's

geological stability. The Tehri dam is located in

the Central Himalayan Seismic Gap, a major

geologic zone. This region was the site of a

6.8 magnitude earthquake in October 1991, with

an epicenter 53 kilometers (33 mi) from the

location of the dam. Dam proponents claim that

the complex is designed to withstand an

earthquake of 8.4 magnitude, but some

seismologists say that earthquakes with a magnitude of 8.5 or more could occur in this

region. Were such a catastrophe to occur, the potentially resulting dam-break would

submerge numerous towns downstream, whose populations total near half a million.

The relocation of more than 100,000 people from the area has led to protracted legal

battles over resettlement rights, and ultimately resulted in the project's delayed

completion.

Since 2005, filling of the reservoir has led to the reduced flow of Bhagirathi water from

the normal 1,000 cubic feet per second (28 m3/s) to a mere 200 cubic feet per second

(5.7 m3/s). This reduction has been central to local protest against the dam, since the

Bhagirathi is considered part of the sacred Ganges whose waters are crucial

to Hindu beliefs. At some points during the year, the tampering with Bhagirathi waters

means this tributary stops flowing. This has created resentment among many Hindus,

who claim that the sanctity of the Ganges has been compromised for the generation of

electricity. Though the officials say that when the reservoir is filled to its maximum

capacity the flow of the river will again become normal. In spite of concerns and

protestation, operation of the Tehri Dam continues.

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GENERAL LAYOUT PLAN:-

Tehri Dam Project, has a reservoir spread of 44 sq km at FSL with a live storage capacity

of 2615 Million Cum. The general layout plan of present scheem of Tehri Dam Project

is -

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TYPICAL SECTION OF TEHRI DAM:-

Tehri Dam is an Earth and Rockfill dam, with slightly inclined clay core was considered

appropriate for Tehri dam site, from consideration of topography, geology, seismicity,

availability of construction material, safety and project economy. Based on conventional

static and pseudo static stability analyses the details of zoned dame section are -

Tehri dam is a 260.5m high (above deepest rock level) structure with a crest at eln. 839.5m,

with a crest width of 25.5m, flared to 30.5m near the abutments. Dam section has an

upstream slope of 2.5 (H) : 1.0 (V), with 10m wide berm at eln. 681.0m and downstream

slope of 2.0 (H) : 1.0 (V), with 6m wide roadway going down the slop from dam crest eln.

839.50m.

So the typical cross-section of dam, as finally executed, is indicated in fig.:-

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(1) Impervious Core

Well graded impervious blended core material with maximum size up to 200 mm and 80

mm in the central and near abutment zone respectively. The clay core material available

at Koti was required to be processed by blending it with coarser material from Dobata

shell borrow are (<200 mm). The clay material was planned to be transported to one

intermediate point (New Dobata) by deploying 30T dumpers to be loaded by

shovels/backhoe in Koti for blending. The clay material was laid in a layer of specified

thickness followed by a layer of coarser material from shell material after removal of

fraction >200 mm in size. The material was continued to be laid in layer to form a

stockpile up to a height of +/- 4.0 m. Before loading the material from these stockpiles its

blending was ensured by the loading backhoe/shovel.

The material from these stockpiles was hauled to dam site by loading the material by

shovels/backhoe into dumpers of 30/32T capacity. A special care was taken to blend the

material by loading shovels before it is loaded into the dumpers for hauling.

(2A) Upstream Shell

Well graded terrace gravelly material, maximum size 600mm and 200mm in the central

and near abutment zone respectively, fines (<4.75mm) not more 5%, provided further

that 80% of the material should not have a laurite content exceeding 30%. The shell

material was to be borrowed area. No processing of this material was required and it was

directly to be hauled to site for its placement in dam body. It was proposed to deploy 5.2

cum bucked capacity electric shovel for loading and 30T dumpers for transporting the

material to dam site. The shovels were supported by D8/D9 dozers for feeding the

material to them. While selecting the capacity of dumpers, it was also considered that the

capacity of dumpers (30T) proposed for deployment is on lower side and higher capacity

of dumpers of the order of 50T should be used, otherwise this may result into high traffic

density on the haul roads. A critical analysis of traffic density of dumpers and other

vehicles which will move on the same road was carried out. A stretch of road envisaged

to have maximum traffic was selected for the purpose. It was found that the distance

between two dumpers moving on either side should be about 40m. This traffic density

was considered acceptable subjected to provision of wide roads and other traffic

regulations.

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(2B) Downstream Shell

Well graded terrace gravelly material, maximum size 600mm and 200mm in the central

portion and near abutment respectively, fines (<4.75mm) not more than 35% and silt

content (<0.075mm) not more than 5%. The shell material was to be borrowed area. No

processing of this material was required and it was directly to be hauled to site for its

placement in dam body. It was proposed to deploy 5.2 cum bucked capacity electric

shovel for loading and 30T dumpers for transporting the material to dam site. The shovels

were supported by D8/D9 dozers for feeding the material to them. While selecting the

capacity of dumpers, it was also considered that the capacity of dumpers (30T) proposed

for deployment is on lower side and higher capacity of dumpers of the order of 50T

should be used, otherwise this may result into high traffic density on the haul roads. A

critical analysis of traffic density of dumpers and other vehicles which will move on the

same road was carried out. A stretch of road envisaged to have maximum traffic was

selected for the purpose. It was found that the distance between two dumpers moving on

either side should be about 40m. This traffic density was considered acceptable subjected

to provision of wide roads and other traffic regulations.

(2C) Processed Shell

Well graded terrace gravelly material, maximum size 600mm and 200mm in central

portion and near abutment portion respectively, fines (<4.75mm) between 10 to 20%. The

shell material was to be borrowed area. No processing of this material was required and

it was directly to be hauled to site for its placement in dam body. It was proposed to

deploy 5.2 cum bucked capacity electric shovel for loading and 30T dumpers for

transporting the material to dam site. The shovels were supported by D8/D9 dozers for

feeding the material to them. While selecting the capacity of dumpers, it was also

considered that the capacity of dumpers (30T) proposed for deployment is on lower side

and higher capacity of dumpers of the order of 50T should be used, otherwise this may

result into high traffic density on the haul roads. A critical analysis of traffic density of

dumpers and other vehicles which will move on the same road was carried out. A stretch

of road envisaged to have maximum traffic was selected for the purpose. It was found

that the distance between two dumpers moving on either side should be about 40m. This

traffic density was considered acceptable subjected to provision of wide roads and other

traffic regulations.

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(2D) Processed Shell

Well graded terrace gravelly material, maximum size 600mm and 200mm in central

portion and near abutment portion respectively, fines (<4.75mm) between 10-18% and

silt content not more than 3%. The shell material was to be borrowed area. No processing

of this material was required and it was directly to be hauled to site for its placement in

dam body. It was proposed to deploy 5.2 cum bucked capacity electric shovel for loading

and 30T dumpers for transporting the material to dam site. The shovels were supported

by D8/D9 dozers for feeding the material to them. While selecting the capacity of

dumpers, it was also considered that the capacity of dumpers (30T) proposed for

deployment is on lower side and higher capacity of dumpers of the order of 50T should

be used, otherwise this may result into high traffic density on the haul roads. A critical

analysis of traffic density of dumpers and other vehicles which will move on the same

road was carried out. A stretch of road envisaged to have maximum traffic was selected

for the purpose. It was found that the distance between two dumpers moving on either

side should be about 40m. This traffic density was considered acceptable subjected to

provision of wide roads and other traffic regulations.

(3) Fine Filter

Fine filter for main down, silt content less than 3% maximum size < 20 mm. Filter material

was planned to be manufactured by installing cursing and screening plant of 250 MT

capacity. Fractions of different sizes of filter material were planned to be transported to

New Dobata stock pile area by deploying dumpers. The stockpile of about 2-3 m height

was created by laying the different sized material in layer to obtain well graded filter

material of required gradation. The well graded material was hauled to dam site by

dumpers of 30T capacity, which were loaded by deploying shovel/backhoe. Proper

blending of all size of material was ensured while loading the material into dumper.

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(4) Coarse Filter

Course Filter-sand and gravel mixture-maximum size < 60 mm, silt content less than3%.

Filter material was planned to be manufactured by installing cursing and screening plant

of 250 MT capacity. Fractions of different sizes of filter material were planned to be

transported to New Dobata stock pile area by deploying dumpers. The stockpile of about

2-3 m height was created by laying the different sized material in layer to obtain well

graded filter material of required gradation. The well graded material was hauled to dam

site by dumpers of 30T capacity, which were loaded by deploying shovel/backhoe.

Proper blending of all size of material was ensured while loading the material into

dumper.

(5) Riprap

Well graded hard blaster rock, with maximum up to 1200mm. The conventional haulage

scheme was planned for rip-rap material haulage. A combination of 20T dumpers with

backhoe of capacity of 3.00/1.70 cum was considered adequate. The capacity of dumpers

was restricted to 20T in view of haulage distance of 25 km and plying of these dumpers

on narrow public road. The road was proposed to be widened and have adequate

crossing zone. In view of longer lead and requirement of Rip-Rap material being more in

last two seasons and keeping the production rate of Rip-Rap constant, a buffer stock was

proposed to be maintained near dam site. The stoked material was planned to be used

during the peak demand of Rip-Rap material.

(6) Inspection Gallery at EI. 725 m

The gallery at EI. 725 m has been provided along the center line of core. Finished size of

the gallery is 2.2 m circular. Profile of the gallery has been kept according to the maximum

expected construction and operation period settlement. The primary purpose of the

inspection gallery eln. 725m in the dam core is to make long-term direct visual inspection

and monitoring of horizontal and vertical deformations which take place in the body of

clay core during construction and operation period. This gallery is to house junction

boxes and cables, coming from all the instruments installed in the core below the level of

inspection gallery.

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(7) Inspection Gallery at EI> 835 m

The top inspection gallery is provided along the Centre line of core. A total difference of

2.5 m has been kept between central portion of the gallery and both ends near abutments.

The finished internal shape of the gallery is 2.5m (W) * 2.4m (H).

The top gallery at eln. 838m is meant to enable direct continuous visual examination of

core surface at the top of dam with a view to identifying possible transverse cracks,

especially in the reaches close to abutments, at the dam top, due to tensile stresses

induced by differential settlement.

(8) Consolidation Grouting

Consolidation grouting below dam core seat was initially proposed through

underground galleries except in small portion above EL. 800 m on the left abutment,

where it was from surface. This scheme was adopted as per advice of consultant, in view

of the requirement to rise the dam in minimum time.

(9) Grout Curtain

The grout curtain at all levels was initially proposed through underground galleries

except above eln. 800 m, on left abutment. With the proposed arrangement of galleries,

grouting at the ends of galleries was proposed through deep inclined holes drilled in a

fanning pattern.

(10) Underground Grouting Gallery

A network of underground galleries-gallery below river bed at eln. 573.0 m, with cross

drifts, three tiers of galleries at eln. 640.0 m, 700.0 m and 760.0 m, along both left and right

dam abutments has been provided for curtain grouting of dam core seat below eln. 700

cm. The access to these galleries is through the approach cum drainage galleries on either

bank from downstream.

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SISMIC ASPECTS OF DAM:-

The Tehri dam falls in a high seismic zone (zone-IV). Hence, a detailed seismic design of

the dam was carried out with the involvement of National and internationally reputed

institute of this field. The project being located in the seismically active environment, lot

of resistance has been expressed by the anti-dam activists against its construction from

time to time on account of safety concerns. In view of the above, design of the dam has

also been reviewed by various high level committees set up by the Govt. of India from

time to time and vetted by the international experts.

This paper provides an overview of seismic aspect of Tehri dam.

Geology of Dam Site

The rocks in the area have been classified into 3 grades, namely Phyllites Grade-I

(PQM & PQT), Phyllites Grade-II (QP), and Phyllites Grade-III or Sheared Phyllite

(SP). These bedrock units laterally merge with one another and constitute nearly 45%,

25% and 30% respectively of the rock exposed in Tehri gorge. The thickness of

overburden is of the order of 10 to 15 m below the riverbed level at the proposed dam

site. There is no active fault below the dam.

Seismo-Tectonic Features of Project Area

The project area is in high seismic zone and falls in Zone-IV of the seismic zoning map

of India which corresponds to intensity VIII on MM scale (fig). Evaluation of the past

seismic data revealed that most of these earthquakes occurring in the region have a

magnitude of 5-7 on Richter scale.

Dam site is located in the Lesser Himalayas, which lies tectonically between the Main

Central Thrust (MCT) in the north and the Main Boundary Fault (MBF) in the south.

The MCT & MBF are recognized as the major northeasterly dipping thrusts in this

tectonically complex belt of Himalayas. There are some other tectonic features in the

vicinity of dam site. The important among them is Srinagar Thrust which has a strike

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continuation of over 100 km and lies at a distance of about 5 km towards North from

the dam site.

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Seismic Safety Analysis

The dam designs followed the usual practice of a pseudo-static analysis. It was later

analyzed for various levels of shaking as per different earthquake strong motions that

were evolved by experts under worst-case scenarios. The methods of estimating potential

earthquake parameters for a dam site are specified in various code of practice (ICOLD).

Seismic analysis was carried out initially by two independent agencies,

(I) In 1989, the Department of Earthquake Engineering; University of Roorkee analyzed

the dam for 7.0 Magnitude earthquake with 0.25g EPGA. In 1990, the Hydro Project

Institute (HIP), Moscow checked the dam for magnitude 8 earthquake with PGA of 0.5g

on a non-existent 2D plan cross-section. In November 1990, Hydro Project Institute,

Moscow, again analyzed the dam, for real 1976 Gazi earthquake (M=7, D=3.5 km, USSR)

having vertical acceleration of 0.72g, both acting simultaneously, and found safe.

Subsequently, the dam was analyses by HPI, by applying the Gazli earthquake three

times consecutively resulting in total duration of 42 sec, and found the dam safe.

(II) The dam was further tested as a result of studies carried out for another Expert Group

constituted by Government of India in June 1996. The site dependent response spectra

compatible acceleration time history of ground motion was generated corresponding to

0.5g PGA under MCE condition.

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CONCLUSION:-

My traning report was based on giving an overall detail on the design, layout and features

of the Tehri Dam project and it’s all the other aspects. The study was mainly focused on

the Tehri Dam & HPP (1000 MW).

The project covers a description of the Tehri Dam project. It also covers the various

layouts and features of the Tehri Dam.

Tehri dam is a 260.5 m high Earth and Rockfill dam constructed across mythic river

Bhagirathi at 1.5 km downstream of its confluence with river Bhilangana in district Their

Garhwal of Uttarakhand.

The project would be implemented by a new company to be jointly promoted by Govt.

of India and Govt. of Uttar Pradesh. Then cabinet approved the execution of Tehri Hydro

Complex (2400 MV) comprising of Tehri Dam & HPP (1000 MW), Tehri PSP (1000 MW)

and Koteshwar HEP (400 MW).

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BIBLIOGRAPHY:-

Handbook Of Tehri Dam Project

http://thdc.gov.in/Projects/english/Scripts/Prj_Introduction.aspx?Vid=132

http://en.wikipedia.org/wiki/Tehri_Dam

https://www.google.co.in/search?ie=tehri_dam

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