A look at ongoing development of nine of the world’s tallest dams provides examples of design, excavation, and construction work occurring in Asia, Africa, Latin America, and the Middle East.
To highlight dam design and construction work occurring, HRW shares information about development of nine of the largest dams in the world. These dams — all over 150 meters in height — are prominent components of major hydroelectric projects being built in Asia, Africa, Latin America, and the Middle East. Table 1 on page 20 provides details about the nine projects.
These nine dams involve record-setting achievements. For example, Diamer Basha Dam in Pakistan, to be completed in 2019, will be the tallest roller-compacted-concrete (RCC) dam in the world at 270 meters. And, at 305 meters tall, the massive Jinping 1 Dam in China will be the tallest double-curvature thin arch dam in the world when it is complete in 2014. The 288-meter-high Dibang Dam in India will be the tallest concrete gravity dam in the world when completed in 2017.
Of the nine dams being featured, three are arch concrete, three are concrete-faced rockfill, two are roller-compacted concrete, and one is concrete gravity. They range in height from 166 meters to 305 meters. Common design and construction challenges include working at sites with complex geology, solving problems with seepage, and managing sediment-laden waters.
The hydroelectric facilities associated with these dams range in capacity from 160 MW to 4,500 MW. Together, they will provide 17,500 MW of new capacity and are expected to produce more than 58,100 gigawatt-hours (GWh) of electricity each year.
Development of these nine projects — to be completed between 2009 and 2019 — will cost an estimated US$27.4 billion.
Owner: Sarawak Hidro Sdn Bhd
River: Batang Balui
Type: Concrete-Faced Rockfill (CFRD)
Height: 205 meters
Volume: 16.8 million cubic meters
Power Generation Component: 2,400 MW, surface powerhouse 250 meters long by 56 meters wide by 20.5 meters high with eight units: vertical Francis turbines and synchronous 360 megavolt-ampere generators
Anticipated Date of Completion: 2012
Estimated Cost: $4.6 billion
Ahmad Zaki Resources Bhd, Alstom, Atlas Copco (Malaysia) Sdn Bhd, Caterpillar, China National Water Resources and Hydropower Engineering Corporation, Dong Ah Construction of Korea, Edward and Son Sdn Bhd, Ekran Corporation Bhd, Fong Mook Seong Sdn Bhd (FMS), Geonor SA, Global Upline Sdn Bhd, Intraxis Engineering, JacobsGIBB Ltd., Meritec Limited, M K Ting, MTD Capital Bhd, Overseas Tunneling and Construction, PB Power, Sime Engineering Sdn Bhd, Snowy Mountains Engineering Corp., Syarikat Ismail Ibrahim Sdn Bhd, Volvo Malaysia Construction Equipment, WCT Engineering Bhd, YTL Ranhill Theiss Consortium
The design and build contract for the dam and ancillary facilities was awarded in October 2002 to Malaysia-China Hydro Joint Venture, which includes China National Water Resources and Hydropower Engineering Corporation, Sime Engineering, WCT Engingineering, MTD Capital, Ahmad Zaki Resources, Syarikat Ismail Ibrahim, and Edward and Son. Considerable effort was made in the design of the dam — including extensive laboratory and trial embankment tests on materials — to optimize the use of excavated materials and reduce waste. Some material for construction of the dam was obtained from site excavation, and the remainder was obtained from quarries. The 205-meter-high dam has a crest length of 750 meters.
Fong Mook Seong (FMS) carried out the drilling and blasting for the lower spillway and powerhouse, as well as general rock clearance along the banks of the river downstream of the dam. Most of the work was completed using two ROC D7 drill rigs from Atlas Copco. These machines were used to drill 76- and 89-millimeter-diameter holes to various depths. During an eight-hour shift, each machine can be used to drill more than 300 meters. M K Ting did blasting work to prepare the dam foundations.
The drilling and blasting work was challenging because of the complex geology at the site. The site is predominantly conglomerate sandstone greywacke with inter-bedded shale and mudstone, mostly folded and with a dip of more than 45 degrees. Work in this type of rock requires recognition of changes in rock condition in order to change drilling techniques as needed.
To protect against seepage through the dam foundation, a grout curtain with a maximum depth of about 130 meters was installed at the upstream side of the dam beneath the plinth of the concrete-faced rockfill dam. The main civil work at the project has been completed, and work is proceeding on installation of the electrical and mechanical equipment.
Information Obtained From: Sarawak Hidro Sdn Bhd website; Kai Leong Gooi, Atlas Copco (Malaysia) Sdn Bhd
Diamer Basha (formerly called Basha)
Owner: Water and Power Development Authority (WAPDA)
Type: Roller-Compacted Concrete (RCC)
Height: 272 meters
Volume: 17 million cubic meters of concrete
Power Generation Component: 4,500 MW, 18,100 gigawatt-hours, two underground powerhouses that each contain six units: vertical Francis turbines and 416 megavolt-ampere generators
Anticipated Date of Completion: 2019
Estimated Cost: US$11.3 billion
AMEC, Associated Consulting Engineers (Pvt) Ltd. (ACE), BARQAB Consulting Services, Binnie Black & Veatch, Lahmeyer International, MWH, National Engineering Services Pakistan (Pvt) Ltd. (NESPAK), National Development Consultants (NDC), Pakistan Engineering Services
The project consists of the dam and related structures, including two diversion tunnels and a permanent access bridge. There will be two underground powerhouses, one on the left bank and one on the right bank. Each powerhouse will contain six 375-MW turbine-generator units. The reservoir will have a gross storage of 10 billion cubic meters of water and a live storage of 7.9 billion cubic meters. The design discharge of the spillway is 18,126 cubic meters per second. To pass sediment in the river, the dam will feature five low-level sediment flushing outlets in the dam body under the spillway. To keep the power intake clear of sediment, the dam will contain an outlet under the right bank intake (built by converting one of the diversion tunnels) and a tunnel under the left bank.
The location of the underground powerhouse and transformer caverns was chosen to avoid fault areas. The tunnels, shafts, and caverns will be excavated by drilling and controlled blasting. Where fault zones will be intersected, increased support through use of shotcrete or rock bolts will be provided. Large rock excavation for construction of a 90-meter-wide diversion canal, together with the right and left bank excavation for the dam foundation, will supply more than 60 percent of the aggregate needed for construction of the dam. The project also features two 15.4-meter-diameter diversion tunnels — one 887 meters long and one 1,016 meters long. These tunnels will penetrate through the right rock ridge that forms an abutment of the dam.
The upstream and downstream cofferdams required to isolate the site for construction will be rockfill embankments with a core of alluvial material. The foundation of the dam and the embankments will be sealed by a plastic concrete diaphragm wall constructed to a maximum depth of 50 to 70 meters. The main construction activities for the project will take place in five contract lots, with work to begin in 2009. The RCC dam will be built in 32 blocks and will proceed in zones, starting from the bedrock. RCC will be placed by the sloped layer method, in 3-meter lifts in 0.3-meter layers. Reservoir impounding will begin in 2017 and be complete in 2019.
Information Obtained From: Izhar ul Haq, Water and Power Development Authority
Owner: NHPC Limited (formerly National Hydroelectric Power Corporation)
Type: Concrete Gravity
Height: 288 meters
Volume: 16.5 million cubic meters
Power Generation Component: 3,000 MW, 11,330 gigawatt-hours, underground powerhouse 24.5 meters wide by 54.8 meters high by 382.8 meters long with 12 units: Francis turbines
Anticipated Date of Completion: 2017
Estimated Cost: US$3.34 billion
AF Colenco, National Institute of Rock Mechanics
The concrete gravity dam will be 288 meters high from the deepest foundation level. When completed, this will be the tallest dam of its kind in the world. The length of the top of the dam is 816 meters, including 154 meters of overflow section. The spillway is designed for a probable flood of 22,809 cubic meters per second. To investigate the site, NHPC performed detailed engineering geological mapping and laboratory testing of rock samples. NHPC also investigated three axes for placement of the dam at this site.
The dam will be located at the junction of two rock formations. The thrusted contact of the two formations passes through the tailrace tunnel outlet area and intersects the main access tunnel and diversion tunnel near the outlet end. Subsurface explorations at the dam site indicated the rock on the left bank of the dam is comparatively weaker than the rock on the right bank. The overall height of the open excavation for the dam will be 300 to 350 meters. The total quantity of rock excavation in the dam abutments and river bed is estimated at 5.58 million cubic meters.
Construction of the structures will require 19.3 million cubic meters of coarse aggregate, 9.65 million cubic meters of fine aggregate, 74,000 cubic meters of shell material, and 26,000 cubic meters of impervious soil. Civil work on the project is scheduled to begin in 2009.
Owner: DSI (Devlet Su Isleri) General Directorate of State Hydraulic Works
Type: Thin Arch Concrete
Height: 218 meters
Volume: 299,000 cubic meters of concrete
Power Generation Component: 300 MW, 1,014 gigawatt-hours, two units in a surface powerhouse: vertical Francis turbines and synchronous generators
Anticipated Date of Completion: 2011
Estimated Cost: US$797 million
Alpine Mayreder Bau GmbH, Alstom Power Austria, BM Mühendsilik ve Insaat A.S., Pöyry Energy Ltd., VA Tech Hydro GmbH & Co., Voith Siemens Hydro Power Generation
The design of the double-curved arch dam is based on ellipses in horizontal sections and was carried out using the finite element method. A three-dimensional model of the dam and the abutment — based on geodetic measurements — is being used for numerical calculations. The bearing behavior is straightforward, owing to the site's narrow, "V"-shaped valley. In addition, Pöyry carried out detailed investigations to assess for abutment stability. Owing to highly karstified rock at the site, design issues for the grout and drainage curtain play an important role. Grout takes and check holes are the basis for the curtain design and the connection of the curtain into impervious rock. A grout curtain of 682,000 square meters was specified.
Owing to the narrow and steep gorge and the good rock quality at the dam site, excavation could be kept to a minimum. To excavate the dam abutment in the vertical rock walls, step-wise smooth blasting in depths of about 5 to 6.5 meters, supervised by Austrian blasting expert Mr. Bubendorfer, was used. The upper part of the rock is supported by 103 pre-stressed anchors, each with a carrying capacity of 1,500 kilo Newtons (kN). To monitor rock movement during excavation, the contractor studied records from inclinometers, extensometers, anchor force uplift tests, and anchor load cell tests.
The dam is being constructed in blocks; post cooling is provided by pipes at every 3 meters in height and a horizontal distance of about 2 meters. Owing to the huge reservoir volume (4.6 billion cubic meters), block joint grouting is being carried out within an intermediate stage during construction. This intermediate block joint grouting is necessary to achieve the arch dam bearing behavior to impound the reservoir during construction. Impounding is scheduled to commence in February 2009.
Information Obtained From: Gerald Zenz, Graz University of Technology
Gibe III (formerly called Gilgel Gibe III)
Owner: Ethiopian Electric Power Corp.
Type: Roller-Compacted Concrete (RCC)
Height: 243 meters
Vol.: 6 million cubic meters of concrete
Power Generation Component: 1,870 MW, 6,500 gigawatt-hours, ten units in a surface powerhouse: Francis turbines
Anticipated Date of Completion: July 2013
Estimated Cost: US$1.95 billion
AG Consult, Coyne et Bellier, ElectroConsult, Mott MacDonald, Roctest Telemac, Salini Costruttori SpA, Sialitec Engineer, Sogreah, Studio Pietrangeli
A variety of technologies was used to carry out basic site investigations, including shuttle digital terrain modeling, laser scanning, satellite imagery, helicopter surveying, and surface terrain tomography. The dam will have a crest length of 610 meters. The spillway is located on the central blocks of the dam and will discharge up to 18,600 cubic meters per second via an overflow crest controlled by nine radial gates.
Excavation work began in June 2008. Excavation has been completed for the river diversion works and for the access road tunnels. Excavation work is progressing for the main dam and the powerhouse.
In December 2008, the river was diverted through two tunnels, one 13 meters in diameter and the other 7 meters in diameter. Site preparation work has begun. The first unit is expected to begin producing electricity in July 2012.
Information Obtained From: Henok Abebe, Ethiopian Electric Power Corp.
Owner: Ertan Hydropower Development Company Ltd.
Type: Double-Curvature Thin Arch Concrete
Height: 305 meters
Volume: 4.7 million cubic meters of concrete
Power Generation Component: 3,600 MW, 16,600 gigawatt-hours, six units in an underground powerhouse 277 meters long by 29.2 meters wide by 68.82 meters high: air-cooled vertical Francis turbines, three-phase synchronous generators
Anticipated Date of Completion: 2014
Estimated Cost: US$3.6 billion
Changjiang Water Resources Commission, Chengdu Hydropower Investigation and Design Institute, Dongfang Electric Machinery Company Ltd., Gezhouba Construction Company, Harbin Electric Machinery Company Ltd., North-west Hydropower Investigation and Design Institute, Sinohydro Bureau No. 4, Sinohydro Bureau No. 7, Sinohydro Bureau No. 11, Sinohydro Bureau 14
The double-curvature thin arch concrete dam will be 16 meters thick at the crest and 63 meters thick at the base. The crest will be 552 meters long. The spillway will have a discharge capacity of 12,109 cubic meters per second. Designing the dam was a challenge because design experience and technical specifications only exist for arch dams about 200 meters high.
High steep slopes of 500 meters and more have been encountered during excavation work for the project. Because of the combination of high steep natural slopes and development of faults, crushed zones, and deep-seated fractures, engineering geology of the site is complicated. As a result, excavation for the dam abutments has been difficult. The deep-seated open fractures, steeply dipping outward approximately parallel with the natural slope, create a major threat to slope stability.
Because of adverse geological conditions at the site, extensive foundation treatment work is necessary, particularly in the dam abutments. On the left bank, foundation treatment covers a height of 289 meters, from elevation 1596 meters to 1885 meters. More than 70 tunnels and galleries totaling 12 kilometers in length are arranged on the left bank at five different elevations for the purposes of drainage, curtain grouting, consolidation grouting, and replacement of materials in faults and weak zones. On the right bank, 47 tunnels and galleries are provided at four different elevations.
Information Obtained From: Zhang Jiansheng, Ertan Hydropower Development Company Ltd.; Liu Kai, Sinohydro SA (Pty) Limited
Owner: Iran Water and Power Resources Development Company
Type: Double Arch Concrete
Height: 230 meters
Volume: 1.67 million cubic meters of concrete
Power Generation Component: 1,000 MW, 2,107 gigawatt-hours, surface powerhouse 121 meters long by 55 meters wide by 65 meters high with four units: vertical Francis turbines and synchronous generators
Anticipated Date of Completion: End of 2009
Estimated Cost: US$562 million
Alstom, Behan Sad, C.E.B., Coyne et Bellier, Farab, Jahad Tose Manabe Ab, Lahmeyer International, Mahab Ghodss, M.GH. Consulting Engineers, Voith Siemens Hydro Power Generation
The dam crest is 440 meters long. The dam is 7 meters wide at the crest and 37 to 52 meters wide at the foundation. The dam has a gated spillway with three radial gates and a discharge capacity of 6,150 cubic meters per second. During design of the dam, it was proposed to change the elevation of the second right gallery from 974 meters to 998 meters. This reduced the total length of access and grouting galleries required from 822 meters to 275 meters. This reduction in length shortened excavation time required by seven months.
The volume of excavation work required was 1 million cubic meters for the powerhouse, 124,000 cubic meters for the water conveyance tunnels, and 590,000 cubic meters for the intake.
Construction of this project began in 2001. The drilling and grouting operation is estimated to be 680,000 cubic meters, 380,000 of which is for the grout curtain and 300,000 for consolidation of the spillway, abutments, and foundation. Concrete is being placed for the dam body using an air cable crane. The surface powerhouse has been built downstream of the dam. Four tunnels with a total length of 1,400 meters convey water from the intake to the turbines. Construction is expected to be complete at the end of 2009.
Information Obtained From: Davood Zare, Hooman Mashayekhi, Javad Amini, and Rahman Mamizadeh, Iran Water and Power Resources Development Company
Owner: Comision Federal de Electricidad
Type: Concrete-Faced Rockfill (CFRD)
Height: 205 meters
Volume: 12 million cubic meters
Power Generation Component: 750 MW, 1,210 gigawatt-hours, underground powerhouse 22 meters long by 103.5 meters wide by 50 meters high with two units: Francis turbines and vertical synchronous generators with 0.95 power factor
Anticipated Date of Completion: June 2012
Estimated Cost: US$910 million
Constructora de Proyectos Hidroeléctricos, Ingenieros Civiles Asociados (ICA), La Peninsular Compañía Constructora, Power Machines, Promotora e Inversora Adisa
The main structure will be a concrete-faced rockfill dam with external slopes of 1.4 to 1 and a maximum height of 205 meters. The river will be diverted through two tunnels on the left bank of the river with a design discharge of 5,730 cubic meters per second (cms). The spillway, also on the left bank, is 80 meters wide and will have a discharge capacity of 15,110 cms.
Excavation work for the project includes open pit excavation of more than 14 million cubic meters of material for the river diversion, construction of the dam and power station, spillway, and other works. Underground excavation work for the river diversion and construction of the dam and powerhouse will involve about 650,000 cubic meters of material.
Construction of the project began in September 2007. River diversion will take place by the end of March 2009. The project is expected to begin generating electricity in January 2012, with the final unit on line in June 2012.
Information Obtained From: Evert Hernandez, Comision Federal de Electricidad
Owner: Hidropaute SA
Type: Concrete-Faced Rockfill (CFRD)
Height: 166 meters
Volume: 5 million cubic meters of rockfill
Power Generation Component: 160 MW, 1,280 gigawatt-hours, underground power house 62 meters long by 21 meters wide by 41 meters high with two units: Francis turbines and vertical axis synchronous semi-umbrella 100 megavolt-ampere generators
Anticipated Date of Completion: December 2009
Estimated Cost: US$362 million
Alstom, Caminosca Ingenieria, Coyne et Bellier, Herdoiza Crespo, Impregilo, Leme Engenharia Ltd., MN Ingenieria, Santos CMI, Siemens, Voith Siemens Hydro Power Generation
Numerical analysis, by means of a three-dimensional model, was used to determine the stresses and deformation generated in the rockfill and the concrete face of the dam. To deal with these stresses and deformation, designers are using 7.5-meter-wide slabs in the vertical compression zone and 15-meter-wide slabs in the remainder of the dam. The vertical compression joints of the concrete face will have 3.2-centimeter-wide spaces to prevent development of high stresses on the concrete face.
Excavation work was performed to place the tunnels and the underground powerhouse. The diversion tunnel for the project has a diameter of 12.26 meters and is 1,202 meters long. The power tunnel is 6 meters in diameter and 433 meters long. Other tunnels (discharge, access, etc.) are about 5,000 meters long in total.
Construction work began in April 2005. The river was diverted in December 2006, and the 45-meter-high upstream cofferdam was completed in January 2007. Work on the rockfill portion of the dam was completed in September 2008. Placement of the concrete slabs was to be completed at the beginning of 2009. To achieve high quality and performance for the rockfill in the dam, Hidropaute adopted several advanced techniques, including numerical analysis of a three-dimensional model and curtain reinforcement of the concrete face slab in areas of stress.
Information Obtained From: Segundo Vanegas, Hidropaute SA