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A buttress dam or hollow dam is a dam with a solid, water-tight upstream side that is supported at intervals on the downstream side by a series of buttresses or supports.〔(【引用サイトリンク】title= Glossary )〕 The dam wall may be straight or curved. Most buttress dams are made of reinforced concrete and are heavy, pushing the dam into the ground. Water pushes against the dam, but the buttresses are inflexible and prevent the dam from falling over.〔(【引用サイトリンク】title=Buttress dam forces )〕 Buttress or hollow gravity dams were originally built to retain water for irrigation or mining in areas of scarce or expensive resources but cheap labour. A buttress dam is a good choice in wide valleys where solid rock is rare.〔(【引用サイトリンク】title=Introduction to Buttress Dams )〕 As designs have become more sophisticated, the virtues and weaknesses of the buttress type dams have become apparent. The Romans were the first to use buttresses to increase the stability of a dam wall. Buttress dams of slab concrete construction became popular in the United States in the early 20th Century with the patented process of Norwegian-American civil engineer Nils F. Ambursen.〔http://www.loc.gov/pictures/collection/hh/item/pa3237/〕〔http://pdfhost.focus.nps.gov/docs/NRHP/Text/01000497.pdf〕〔Edward Wegmann, Masonry dams; a historical, theoretical and practical review and discussion, (p.33 ), American Society of Engineering Contractors, Paper No. 34, New York, 1912〕 ==See also== *Clywedog reservoir *Coolidge Dam *Mountain Dell Dam 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Buttress dam」の詳細全文を読む スポンサード リンク
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