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| East Asia |
| Cracks appear in China’s giant dam |
| 2003-06-13 |
| Dam Watch continues, more details on the concrete pouring. EFL Eighty cracks have been revealed in China's colossal Three Gorges Dam, just days after engineers closed the dam's sluice gates and began filling a 640 kilometre long reservoir. Pan Jiazhong, head of the dam's inspection group, said: "If water enters these cracks there could be negative effects, so we are fixing them very carefully. However, he denied that the cracks, up to 10 metres long, mean that the dam is seriously damaged. Experts contacted by New Scientist agree, saying a catastrophic failure is unlikely. "It's a statistical fact that most dam failures occur on first filling. But the Chinese are very competent engineers, so I would not be overly concerned," says Richard Cox, a dam supervising engineer for the UK Environment Agency. Cracks in the dam were first revealed in March 2002. Engineers sealed these but some of the fissures have since re-opened. The cracks are almost certainly the result of uneven cooling in the concrete structure of the dam, says one expert who has visited the project. Rodney Bridle, an engineer on the governing committee of the British Dam Society, explains that when concrete sets, it generates significant amounts of heat. The surface then cools - and shrinks - faster than the core. "In effect the interior is bigger than exterior," he told New Scientist. "This generates long vertical cracks in the middle of the dam. They are normally just grouted up. The problems with the Three Gorges Dam sound normal to me." The project's engineers went to extraordinary lengths during the dam's construction to ensure even cooling. The cement component of concrete is responsible for generating the heat when it solidifies, so almost half of the cement in the concrete was replaced with fly ash. The concrete was blasted with air at -5°C during mixing and then cooled to 12°C prior to pouring. The dam was also criss-crossed with a network of cooling pipes. And finally, the engineers shrouded in the entire dam in artificial fog to shield it from sunlight. Hope they're right for everyone downstream. |
| Posted by:Steve |
| #8 How long is it supposed to take to fill the thing to capacity? |
| Posted by: Laurence of the Rats 2003-06-13 18:41:11 |
| #7 Expect the People's Republic of China to corner the market on super-glue in the next few days... |
| Posted by: Old Patriot 2003-06-13 18:14:41 |
| #6 You're right! Juche solves everything. If that won't do it, maybe they can stuff some grass in the cracks. |
| Posted by: Mike N. 2003-06-13 16:53:55 |
| #5 Get Kim Jong Il up there pronto! He'll fix it! He can do everything! |
| Posted by: tu3031 2003-06-13 16:28:00 |
| #4 Frank G: That's what I was going to say. It may set cooler, but it's going to be a hell of a lot weaker. I wonder if there is more information available so we could compute a strength: sacks of cement per cu yd, agregates used, water per cu yd. Cracks plus crappy concrete equals... |
| Posted by: 11A5S 2003-06-13 15:56:57 |
| #3 Frank---It sounds like the basic engineering may be good. It is not everyone that designs huge dams. It is like tramways, only a couple of them around make and design them (and they are Swiss). But messing with the concrete mix design is scary. Hell, I don't even live there and I worry. |
| Posted by: Alaska Paul 2003-06-13 15:54:28 |
| #2 For those Engineers out there - 50% replacement with Flyash is extreme. Caltrans specs (90-4 Admixtures) allow up to 15% max replacement of cementitious materials with flyash..... usually such a large substitution is due more to cutting costs (pocketing the difference) than trying to reduce the heat of hydration, since flyash is a cheap byproduct of blast furnace operations ... Can anyone say "massive corruption"? |
| Posted by: Frank G 2003-06-13 14:27:31 |
| #1 I wonder if, in a good Stalinesque way, the Reds wouldn't force the design team, contractors, and other senior members of the construction team along with their families to relocate downstream of the dam during--and for some time after--construction. If I were dictator in the classic spirit of Uncle Joe, I'd do it (along with mandating everyone call me "O Illustrious One"). |
| Posted by: Dar 2003-06-13 14:15:17 |