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篇篇学之5：Hydraulic tunnelsIn the above articls,we have described the types of dams.Here we will discribe the tunnels.A tunnel is an underground passage usually made without removing the overlying rock or soil.Although the tunnels are approximately horizontal.they must be built with sufficient gradient for proper drainage.tunnels may be ventilated by shafts leading to the surface or by exhaust fans at the ends.
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tanshengchu
沙发
大家共享！！不胜感激！！
2010-02-25 16:02:25
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hsinlingchen
板凳
因为想考咨询师,所以下载了解收藏,谢谢!
2009-08-25 08:00:25
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加载更多大家共享！！不胜感激！！
谢谢楼主
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