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Dam and Intake |
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Background Detailed project engineering was carried out between 1990 and 1994 by the Mahab Ghodds – Acres General Partnership (MGA). This work included a program of field studies consisting of detailed geological investigations, a regional assessment of earthquake hazards and hydrology studies of the Karun River basin. Design work, technical specifications and tender documents were produced by combined Iranian and Canadian engineering teams in Tehran and Niagara Falls. MGA produced final designs, complete with technical specifications, for all aspects of the project. Iranian contractors carried out all construction work beginning in 1996 under MGA’s supervision.
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The advanced “thin-arch” design transmits loads from the reservoir pressure directly to the limestone bedrock foundation. This results in a structure that is much thinner and requires significantly less concrete than a conventional concrete dam. Since arch-dam design is very sensitive to the geological conditions of the underlying bedrock foundation, special geological studies and testing were needed throughout both the design and construction processes. Concrete shear keys were constructed in surface and underground excavations to reinforce the adjacent rock mass. Generation Facilities
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 Powerhouse |
Three large underground caverns (powerhouse, transformer and inlet valve gallery) were designed and constructed to house the 2000-MW power generation plant. The powerhouse cavern is 250 m long, 25 m wide and over 60 m high. It contains eight 250-MW vertical-shaft Francis turbines connected to enclosed conventional air-cooled generators. Each unit is protected on the upstream side by a butterfly valve and from downstream by draft tube gates. Each of the two tailrace tunnels is connected to four units and can be isolated from the river by bulkhead gates. The electricity generated at 15.75 kV will be transformed by three single-phase transformers per unit to 400 kV. These transformers are located in a separate underground transformer cavern which is located parallel and downstream of the main powerhouse cavern, an SF-6 bus duct conducts the output to the outdoor Take Off Yard which connects the 400-kV overhead lines to the nearby Dezhir substation.
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| Peripheral Design The electrical power generation facilities and water control works are located in a complex maze of tunnels and excavated caverns located deep inside the mountain on the river’s north side. Water is delivered to the eight powerhouse units through penstock tunnels with an average length of about 700 m each. Two huge intake tunnels connect the first phase penstocks to the reservoir lake which is 55 km long with a capacity of approximately three million cubic meters of water.
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 Underground complex with 3000 MW capacity: 1st Phase: 8 units x 250 MW = 2000 MW 2nd Phase: 4 units x 250 MW = 1000 MW |
 Power Tunnnel |
The intake tunnels have excavated diameters of 14 m to 17 m each. The natural pillars between these tunnels consisted of weak, poor-quality marlstone bedrock which required special treatment to ensure adequate stability during construction. In order to cope with unfavorable rock conditions in the portal area, a pre-support concrete arch was constructed within a series of interconnecting tunnels that were excavated around the perimeters of the tunnel crowns before final tunnel construction was carried out. Water flows from the turbines are conveyed back to the river from the powerhouse through two tailrace tunnels with maximum diameters of 14 m each. |
The transformer cavern and inlet valve gallery are 234 m and 244 m long and have widths of 21 m and 10 m respectively. Difficult rock conditions, including unusually high ground stresses in areas of the powerhouse, were encountered during the construction of the major caverns. Continuous monitoring of rock conditions and on-site rock engineering designs were carried out in order to ensure safe and stable working conditions.
Latest Achievements
The past year has seen much significant progress. The concreting and grout curtain installation of the dam has been completed except for the concreting associated with the crest spillway chutes. This is a major achievement in itself, although somewhat overshadowed by the fact that almost all the concrete lining of the 400-m long plunge pool was placed within the last year and a half. During this time the installation of the flow-compensation outlets and control valves, as well as the orifice spillways and their radial gates, were completed within the dam body. The headworks and concreting of the chute spillways were also all completed during this past year. Installation of the chute spillway radial gates is in progress and is scheduled to be completed by midsummer 2005. In the meantime, the reservoir will be held below 35 meters – its full supply until these gates are fully operational.
The power intakes have been completed together with the lining and grouting of the power tunnels. The inlet valves to Units 5 to 8 have been installed, as have the turbines and generators. All the transformers are installed as well as the erection of the SF-6 bus ducts. The mechanical and electrical auxiliaries to Units 7 and 8 have been installed and pre-commissioning of these units has taken place. The erection of the gantry cranes for the power intakes, flow-compensation-outlet (FCO) emergency gates and draft tubes has been completed and dry tested.Trash racks and bulkhead gates have been dry tested in all three power intakes, trash racks installed in power intake #2 and #3, and bulkhead gates installed in power intake #1. Intake gates have been installed and tested in intake gate shafts #4 and #3, serving Units 8 to 5.The FCOs and orifice spillways were dry tested and put into operation.
During the last dry season, the river was diverted from the second diversion tunnel and a permanent concrete plug was installed. On November 8, 2004, the gates at the intake of the remaining diversion tunnel were closed and the impounding of the reservoir commenced, thus achieving the first major milestone of this megaproject. During January and February of this year, the first wet tests were successfully completed on Unit No. 8 culminating in this unit running smoothly at full discharge on February 8, 2005. This was Karun’s second significant milestone. The facilities will be fully operational by 2006 and will be a critical component in supplying the long-term power requirements of Iran. |
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Mike Boase |
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John Young |