Getting some concrete results at Three Gorges20 October 1999
The staggering task of placing more than 20 million m3 of concrete, enough to build a half dozen of the world's big dams, is currently well underway at the Three Gorges hydro project in China, where the workforce is expected to reach 25 000 at its peak. Adrian Greeman reports from the site.
The concreting operation means that this Gargantuan project is now well into Phase Two. Phase One, the five year long task of diverting the Yangtze, the world's third biggest river, was completed in November 1997 when thousands of pyramid shaped concrete blocks and granite boulders were tipped in to seal off the present construction site.
Following construction of a 26 million m3 upstream temporary dam and its smaller downstream sister, de-watering was able to begin in June last year, with the dry area for excavation of the riverbed and powerhouse areas ready three months later. The concreting has been going on in this area since January this year.
Phase Two comprises the major central section of the dam, the 483m long spillway section, and the fourteen-turbine powerhouse section on the left bank side, stretching 643.7m. Another 584m long section with 12 turbines will be built later in the current diversion channel. Side sections bring the total dam length to 2309.5m.
Construction of the first six powerhouses is now complete while excavation for the remainder is almost finished and concreting has started. This means that the turbine suppliers have been able to work on site for several months, and the shapes of the intakes and tailraces are already becoming apparent.
Western firms have contracts for all fourteen of the 710 MWe turbines and generators, eight with a European group of Alstom/ABB. Six more are with a transatlantic alliance of GE of Canada, and Germany's Voith and Siemens. The two sets of contracts were let in 1997, Alstom/ABB's for $400 million and Voith/GE Canada/Siemens' for $300 million.
Alstom's component, worth $212 million, includes design and installation of eight of these giants, which will utilize an 80.6 m fall, the water rotating a 10.6 m diameter turbine at 75 rpm. Each unit is 5.5 m high and weighs 440 t. Main components will not be delivered until between January 2002 and August 2004 but the Alstom team is settling in at site and initial works have begun well.
The plan is to bring the first 14 generators on stream in 2004-6. Another 12 machines will be installed in the third phase, which is scheduled to be finished in 2009. A further six underground units may be installed, bringing the total installed capacity of the plant to a colossal 22 720 MWe.
There have of course been concerns about the environmental impact of the project, the flooding of homes and the inundation of valuable archeological sites. The Chinese say they are spending 40 billion Yuan (just over 40 per cent of project cost) to create new infrastructure and towns and to create jobs in an area which was poorly developed previously. There have also been been concerns about shoddy workmanship and poor quality control, including widely publicized comments by Premier Zhu Rongji.
The State Council has a special commission on the project which has created the autonomous client body, the Three Gorges Project Development Corporation. The TGPDC has wide ranging powers and is charged with completing the whole scheme. It says it is aware of the crucial importance of concrete quality and has ongoing research with outside institutes. Senior engineer Li Jun Lin angrily rejects allegations that there have been problems with concrete quality to date declaring the stories to be the result of "journalistic simplification".
TGPDC has hired specialists from Atkinson Construction Co of the USA to help with concrete quality issues. Recently a further group of experts, from Harza Engineering Co, also of the USA, were hired in a supervisory role on the construction project.