土木專業(yè)外文翻譯3

1、<p><b>　　Dam</b></p><p>　　A dam is a structure built across, river, or estuary to retain water. Its purposes are to meet demands for water for human consumption, irrigation, or industry; to

2、reduce peak discharge of flood water; to increase available water stored for generating hydroelectric power; or to increase the depth of water in a river so as to improve navigation. An incidental purpose can be to propo

3、se can be to provide a lake for recreation.</p><p>　　Auxiliary works at a dam may include spillways, gates, or valves to control the discharge of surplus water downstream form the dam; an intake structure co

4、nducting water to power station or to canals, tunnels, or pipelines for more distant use; provision for evacuating silt carried into the reservoir; and means for permitting ships or fish to pass the dam. A dam therefore

5、is the central structure in a multipurpose scheme aiming at the conservation of water resources. The multipurpose dam holds sp</p><p>　　Dams fall into several distinct classes, by profile and by building mat

6、erial. The decision as to which type of dam be build depends largely on the foundation conditions in the valley and the construction materials available. Basically, the choice of materials now lies between concrete, soil

7、s, 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 </p>

8、<p>　　Basic Problems in Dam Design</p><p>　　Most modern dams continue to be of two basic types: masonry (concrete) and embankment (earthfill). Masonry dams are typically used to block streams running t

9、hrough narrow gorges, as in mountainous terrain; though such dams may be very high, the total amount of material required is limited. Embankment dams sre preferred to control broad streams, where only a very large barrie

10、r, requiring a great volume of material, will suffice. The choice of masonry or embankment and the precise design depend on</p><p>　　Site investigation and testing. Investigation of a site for a dam includes

11、 sinking trial borings to determine the strata. The borings are supplemented by shafts and tunnels which, because of their cost, must be used as sparingly as possible. In the shafts and tunnels, tests can be made to meas

12、ure strength, elasticity, permeability, and prevailing stresses in strata, with particular attention given to the properties of thin partings, or walls, between the more massive beds, The presence in ground</p>&l

13、t;p>　　Models are particularly useful in analysis of arch dams and in verifying analytical stress calculations. Various materials have been used for model tests; on some early tests for Hoover Dam, rubber was employed.

14、 The need for accurate reproduction of stress patterns in complex models is met by using material of low elasticity. In a sense, dams themselves are models for future design. The instruments built into them to record mov

15、ements under load, strains within materials after construction, tempe</p><p>　　The digital computer has permitted considerable advance in analytical methods of design. Its ability to handle a great volume of

16、 data and to solve large sets of simultaneous equations containing many variables ha made practicable the method of Finite Element Analysis. In this method, a complicated structure is divided into a number of separate eq

17、uilibrium conditions, and strains are rendered compatible, thus leading to a complete analysis of stress and strain distribution throughout the structur</p><p>　　Problems of materials. Each of the two basic

18、dam materials, concrete and earth or rock fill, has a weakness that must be overcome by the proper design of the dam.</p><p>　　Weaknesses of concrete.. Concrete is weak in tensile strength; that is, it can b

19、e pulled apart easily. Concrete dams must therefore be designed to place minimum tensile strain on the dam and to make use of concrete’s great compressive strength, or ability to support vertical loads. The chief constit

20、uent of concrete, cement, shrinks as it sets and hardens, due to water absorption in the crystalline structure, to evaporation of water to the atmosphere, and to cooling form the higher temperatures r</p><p>

21、;　　Various expedients are used to overcome the problem. Concrete is usually cast in separate blocks of limited height. Gaps may be left to permit heat losses and filled in later. Low-heat cements may be used; these are s

22、pecially 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 im

23、portant. The cement content, and therefore the heat caused by h</p><p>　　Weaknesses of earth and rock fill. Soils and rock fragments lack the strength of concrete, are much more permeable, and possess less r

24、esistance to deterioration and disturbance by flowing water. These disadvantages are compensated for by a much lower cost and by the ability of earth fill to adapt to deformation caused by movements in the dam foundation

25、. 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</p><p>　　Soil consists of solid particles with water and air

26、 in between. When the soil is compressed by loading, as occurs in dam construction, some drainage of air and water takes place, causing an increase in pressures between the solid particles. When there is a high rate of s

27、eepage, the soil tends to develop differential pressures and reach a condition called quick, in which it behaves as a fluid. Even if it does not reach this condition, there is often some weakening of its structure, and s

28、teps must</p><p>　　The earthquake problem. Many large dams have been built in the seismically active regions of the world, including Japan, the western United States, New Zealand, the Himalayas, and the Midd

29、le East. In 1968, the Tokachi earthquake damaged 93 dams in Honshu, the main Japanese Island; all were embankment dams of relatively small height.</p><p>　　Despite a great deal of work on the distribution of

30、 seismic activity, the measurement of strong ground motions, and the response of dams to such motions, earthquake design of dams remains imprecise. The characteristics of strong ground motions at a given site cannot be p

31、redicted, and all types of dams possess some degree of freedom, imperfect elasticity, and imprecise damping. Nevertheless, the digital computer and model testing have given promise of considerable progress. It is now pos

32、sible cal</p><p>　　There has also been considerable advance in the theoretical estimation of the effects of ground motion on embankment dams.</p><p><b>　　壩</b></p><p>　　

33、大壩是橫跨在溪流，河流或河口之間用于儲水的建筑物。他的目的是為了提供人民用水，灌溉和工業(yè)用水；削減洪峰，而且能增加蓄水和發(fā)電能力；還可以增加河道深度以有利于航運。還有一個附帶效果就是能提供玩樂的湖泊。</p><p>　　大壩的某些輔助功能包括溢洪道、水閘，或利用自身閥門來控制從大壩中排出多余的水到下游；吸水結(jié)構(gòu)引水到發(fā)電站或運河、隧道，或渠道用于更遠距離的使用。還可以提供從蓄水池中抽出的泥沙；同時還要允許船和魚

34、類通過大壩。大壩因此在控制蓄水量的體系中成了中心建筑。在不發(fā)達國家中大壩更具特殊重要性，在一個小國家可以從一個簡單的大壩中獲得巨大的農(nóng)業(yè)和工業(yè)利益。</p><p>　　大壩從外觀和建筑材料可以分成幾個不同的級別，建哪一類的大壩的結(jié)論很大程度要根據(jù)山地的基礎條件和方便就地使用的建材?；镜乃x的材料是混泥土，泥和碎石。大部分大壩在過去建設中采用有接縫的石木術(shù)，但是這種做法已完全被摒棄了?；炷嗤链髩蔚恼w形式在側(cè)面

35、上分為很多種類。根據(jù)水壓程度利用結(jié)構(gòu)自重或采用橫跨山谷由倆邊峽谷支撐的水平橫拱來抵抗側(cè)向位移。</p><p>　　大壩設計的基本問題被分為兩個基本類型： M壩和E壩，M壩是用來在峽谷的峽谷中橫跨河流，如在群山中這類壩可能非常高，但所需的總體材料受到限制。E壩用于寬的河流上建一座大壩需要足夠多的材料。選擇M或E壩和精確地設計都可依靠這一位置的地質(zhì)情況和構(gòu)造，大壩的基礎和成本因素。</p><p

36、>　　地質(zhì)研究和試驗，壩址研究包括沉降試驗和地層鉆孔測試。用豎井和坑道代替鉆孔試驗，因為盡可能地節(jié)約試驗的成本。</p><p>　　通過豎井的坑道試驗可以測出強度、彈力，滲透系數(shù)和地層的壓力分布情況，還必須重視那些更結(jié)實的基礎中的薄的分離或間隔地區(qū)的特性。存在的地下水對大壩的建筑材料有害的化學溶解必須評定。建筑原料需要經(jīng)過反復的試驗。如果連續(xù)增加高度，基礎條件的研究也變得更加重要。</p>

37、<p>　　模型試驗在大壩的結(jié)構(gòu)抗震和水力設計中扮演重要的角色。結(jié)構(gòu)模型在分析拱形大壩和檢驗分析壓力計算有特殊的用途。各類建筑材料都將用于模型試驗之中，在Hoover大壩的一些早期試驗重，科學家常利用橡膠來作為試驗材料模型，這需要在復雜模型中準確復制應力樣本，模型要符合使用低彈型材料的特性。</p><p>　　主觀上來看，大壩模型本身就是未來的設計，說明了建成模型用來記錄在荷載下的活動，建筑材料所受的

38、拉力，溫度和壓力改變和基本安裝的其他因素，在研究成果下，結(jié)構(gòu)可能出現(xiàn)的，但是它們的價值在于論證所設計的假設，這是非常重要的。數(shù)字電腦已經(jīng)允許考慮高級的分析方法設計，它處理大量的數(shù)據(jù)和解答多組包含許多變量的聯(lián)立方程的能力使得有限元分析是可行的。用這種方法，一個復雜結(jié)構(gòu)被分為許多單獨的平衡條件，而且所有拉力都具有兼容性，這樣可以對整個結(jié)構(gòu)的壓力的分布全面地來分析。</p><p>　　大壩設計的主要問題：</p

39、><p>　　關(guān)于大壩材料基本上有兩種材料：混凝土和泥域填石，但是它們在大壩的正確設計中都有一些弱點需要被克服。</p><p>　　混凝土的弱點，混凝土的弱點在于抗拉強度，因為它很容易被拉裂，混凝土大壩因此要被設計承受最小拉應力和利用混凝土大的壓應力或盡可能地承受垂直荷載。由于晶體結(jié)構(gòu)對水的吸收，水在空氣中的蒸發(fā)和從水泥水化過程中產(chǎn)生的高溫冷卻，混凝土的主要成分---水泥，在凝固和硬化時要收

40、縮。因為大量混凝土用于大壩上，收縮而出現(xiàn)嚴重裂縫的危險。</p><p>　　很多快捷的方法被用于解決這方面的問題，混凝土常被分層限厚澆筑，裂口被用來散發(fā)熱量而被最后澆筑。低熱水泥也被使用。還有混合特殊添加劑而使散熱變得遲緩。在大壩內(nèi)部混凝土中的水泥要做到安全而量少。也就是能滿足強度，其次能抵抗氣候和化學侵蝕。能滿足用于大石塊中的水泥可以減少用量。另外一個好的辦法是用級配好的材料，如粉煤灰（經(jīng)過研磨后的燃料）作為

41、填料可以減少混凝土的水泥用量。另外就是使用添加劑。表面活性劑和加氣劑都被允許用于低水灰比的混凝土，用冰代替水的技巧增加了冷卻速度?；旌匣蛴醚h(huán)水通過埋入混凝土中的導管 而用利用直空抽出其表面過剩的水。</p><p>　　土和巖塊的弱點：土和巖塊不具備混凝土的強度，可滲透性大，抗流水損壞和干擾的能力差，這些缺點可以由低成本和能用合適填入在大壩基礎因運動毀壞的地方。假如能得到足夠的土用于壩址的合攏在光山區(qū)域，它可能

42、比堤壩更需要采石場的巖石和構(gòu)造巖石。土填當然是最經(jīng)濟的，也常適合用于借土合攏壩址。</p><p>　　土由固體物質(zhì)，水和空氣構(gòu)成，土受荷而壓縮，如出現(xiàn)在大壩建筑，排出水和空氣導致增加固體物質(zhì)間的壓力，當有很高的滲透比時，土趨向于產(chǎn)生不同的壓力和達到臨界狀態(tài)，這時它的狀態(tài)如同液體。如果達不到這個條件，通常它的結(jié)構(gòu)會變?nèi)酰抑鸩竭M行計算結(jié)構(gòu)。</p><p>　　地震問題：大部分大壩都建在

43、世界上地震活動地帶，包括日本，美國西部，新西蘭，喜馬拉雅山和中東，在1968年，在HonShu的ToKachi大地震中毀壞了93座大壩，在日本主島，所有的堤壩高度都相對較小。</p><p>　　盡管針對地震活動分布，強地震運動的量測水壩對這種運動的反應做了大量工作，水壩的地震設計依然不夠精確，強的地質(zhì)運動特征給壩址帶來不少預料性。而且不完善的彈力分析和不嚴格的衰減分析使所有類型的大壩都具有一些自由度，不過，電腦