report on tehri dam pdf
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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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