土木專業(yè)外文翻譯3-建筑結(jié)構(gòu)-wenkub
2023-05-19 14:30:16 本頁面
【正文】 ls now lies between concrete, soils, and rockfill. Though a number of dams were built in the past of jointed masonry, this practice is now largely obsolete, The monolithic form of concrete dams permits greater variations in profile, according to the extent water pressure is resisted by the deadweight of the structure, is transferred laterally to buttresses, or is carried by horizontal arching across the valley to abutments formed by the sides of the valley. Basic Problems in Dam Design Most modern dams continue to be of two basic types: masonry (concrete) and embankment (earthfill). Masonry dams are typically used to block streams running through narrow gorges, as in mountainous terrain。 these are specially blended so that rates of heat evolution are retarded. Cement content can be safely reduced in the interior concrete in the dam, in which strength and resistance to climatic and chemical deterioration are less important. The cement content, and therefore the heat caused by hydrating, can also be reduced by using aggregate (the other major constituent of concrete) of larger stones. Another expedient is to use other finegrained materials, such as fly ash (pulverized fuel), as filler, reducing the total cement volume in the concrete. Another is to use certain additives, surfaceactive agents, and airentraining agents that permit using a lower watertocement ratio in mix by ice, circulating water through pipes laid in the concrete, and extracting excess water from surfaces by vacuum. Weaknesses of earth and rock fill. Soils and rock fragments lack the strength of concrete, are much more permeable, and possess less resistance to deterioration and disturbance by flowing water. These disadvantages are pensated for by a much lower cost and by the ability of earth fill to adapt to deformation caused by movements in the dam foundation. This assumes, of course, sufficient usable soil available close to the dam site. In bare mountain country it may be necessary to quarry rock and construct a rockfill rather than an rarthfill dam. Earth fill is of course more economical, and often a suitable borrow area can be found close to the site. Soil consists of so
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