水利水電工程畢業(yè)設計英文翻譯,混凝土重力壩.doc

Concrete Gravity DamThe type of dam selected for a site depends principally on topographic, geologic,hydrologic, and climatic conditions. Where more than one type can be built, alternative economic estimates are prepared and selection is based on economica considerations.Safety and performance are primary requirements, but construction time and materials often affect economic comparisons.Dam ClassificationDams are classified according to construction materials such as concrete or earth. Concrete dams are further classified as gravity, arch, buttress, or a combination of these. Earthfill dams are gravity dams built of either earth or rock materials, with particular provisions for spillways and seepage control.A concrete gravity dam depends on its own weight for structural stability. The dam may be straight or slightly curved, with the water load transmitted through the dam to the foundation material. Ordinarily, gravity dams have a base width of 0.7 to 0.9 the height of the dam. Solid rock provides the best foundation condition. However, many small concrete dams are built on previous or soft foundations and perform satisfactorily. A concrete gravity dam is well suited for use with an overflow spillway crest. Because of this advantage, it is often combined with an earthfill dam in wide flood plain sites.Arch dams are well suited to narrow V- or U-shaped canyons. Canyon walls must be of rock suitable for carrying the transmitted water load to the sides of the canyon by arch action. Arch sections carry the greatest part of the load; vertical elements carry sufficient load through cantilever action to produce cantilever deflections equal to arch deflections. Ordinarily, the crest length-to-height ratio should be less than 5, although greater ratios have been used. Generally, the base width of modern arch dams is 0.1 to 0.3 the height of the impounded water. A spillway may be designed into the crest of an arch dam.Multiple arches similarly transmit loads to the abutment or ends of the arch. This type of dam is suited to wider valleys. The main thrust and radial shears are transmitted to massive buttresses and then into the foundation material.Buttress dams include flat-slab, multiple-arch, roundhead-buttress, and multiple-dome types. The buttress dam adapts to all site locations. Downstream face slabs and aprons are used for overflow spillways similar to gravity dam spillways. Inclined sliding gates or light-weight low-head gates control the flow.The water loads are transmitted to the foundation by two systems of load-carrying members. The flat slabs, arches, or domes support the direct water load. The face slabs are supported by vertical buttresses. In most flat-slab buttress dams, steel reinforcement is used to carry the tension forces developed in the face slabs and buttress supports. Massive-head buttresses eliminate most tension forces and steel is not necessary.Combiantion designs may utilize one or more of the previously mentioned types of dams. For example, studies may indicate that an earthfill dam with a center concrete gravity overflow spillway section is the most economial in a wide, flat valley. Other design conditions may dictate a multiple-arch and buttress dam section or a buttress and gravity dam combination.Site ExplorationThe dam location is determined by the projects functions. The exact site within the general location must be determined by careful project consideration and systematic studies.In preliminary studies, two primary factors must be determined-the topography at the site and characteristics of the foundation materials. The first choice of the type of dam is based primarily on these two factors. However, the final choice will usually be controlled by construction cost if other site factors are also considered.Asite exploration requires the preparation of an accurate topographic map for each possible site in the general location. The scale of the maps should be large enough for layout. Exploration primarily determines the conditions that make sites usable or unusable.From the site explorations, tentative sketches can be made of the dam location and project features such as power plants. Physical features at the site must be ascertained in order to make a sketch of the dam and determine the position of materials and work plant during construction. Other factors that may affect dam selection are roadways,fishways, locks, and log passages.TopographyTopography often determines the type of dam. For example, a narrow V-shaped channel may dictate an arch dam. The topography indicates surface characteristics of the valley and the relation of the contours to the various requirements of the structure. Soundness of the rock surface must be included in the topographic study.In a location study, one should select the best position for the dam. An accurate sketch of the dam and how it fits into the topographic features of the valley are often sufficient to permit initial cost estimates. The tentative location of the other dam features should be included in this sketch since items such as spillways can influence the type and location of the dam.Topographic maps can be made from aerial surveys and subsequent contour plotting or they can be obtained from governmental agencies. The topographic survey should be correlated with the site exploration to ensure accuracy. Topographic maps give only the surface profile at the site. Further geological and foundation analyses are necessary for a final determination of dam feasibility.Foundation and Geological InvestigationFoundation and geological conditions determine the factors that support the weight of the dam. The foundation materials limit the type of dam to a great extent, although such limitations can be compensated for in design.Initial exploration may consist of a few core holes drilled along the tentatively selected site location. Their analysis in relation to the general geology of the area often rules out certain sites as unfeasible, particularly as dam height increases. Once the number of possible site locations has been narrowed down, more detailed geological investiagtions should be considered.The location of all faults, contacts, zones of permeability, fissures, and other underground conditions must be accurately defined. The probable required excavation depth at all points should be derived from the core drill analysis. Extensive drilling into rock formations isnt necessary for small dams. However, as dam height and safety requirements increase, investigations should be increased in depth and number. If foundation materials are soft, extensive investigations should determine their depth,permeability, and bearing capacity. It is not always necessary or possible to put a concrete dam on solid rock.The different foundations commonly encountered for dam construction are: (1)solid rock foundations, (2) gravel foundations, (3) silt or fine sand foundations, (4) clay foundations, and (5) nonuniform foundation materials. Small dams on soft foundation ( item 2 through item 5 ) present some additonal design problems such as settlement, prevention of piping, excessive percolation, and protection of foundation from downstream toe erosion. These conditions are above the normal design forces of a concrete dam on a rock foundation. The same problems also exist for earth dams.Geological formations can often be pictured in cross-section by a qualified geologist if he has certain core drill holes upon which to base his overall concept of the geology. However, the plans and specifications should not contain this overall geological concept. Only the logs of the core drill holes should be included for the contractors estimates. However, the geological picture of the underlying formations is a great aid in evaluating the dam safety. The appendix consists of excerpts from a geologic report for the site used in the design examples.HydrologyHydrology studies are necessary to estimate diversion requirements during construction, to establish frequency of use of emergency spillways in conjunction with outlets or spillways, to determine peak discharge estimates for diversion dams, and to provide the basis for power generation. Hydrologic studies are complex; however, simplified procedures may be used for small dams if certain conservative estimates are made to ensure structural safety.Formulas are only a guide to preliminary plans and design computations. The empirical equations provide only peak discharge estimates. However, the designer is more interested in the runoff volume associated with discharge and the time distribution of the flow. With these data, the designer knows both the peak discharge and the total inflow into the reservoir area. This provides a basis for making reliable diversion estimates for irrigation projects, water supply, or power generation.A reliable study of hydrology enables the designer to select the proper spillway capacity to ensure safety. The importance of a safe spillway cannot be overemphasized. Insufficient spillways have caused failures of dams. Adequate spillway capacity is of paramount importance for earthfill and rockfill dams. Concrete dams may be able to withstand moderate overtopping. Spillways release excess water that cannot be retained in the storage space of the reservoir. In the preliminary site exploration, the designer must consider spillway size and location. Site conditions greatly influence the selection of location, type, and components of a spillway. The design flows that the spillway must carry without endangering the dam are equally important. Therefore, study of streamflow is just as critical as the foundation and geological studies of the site.附錄2外文翻譯混凝土重力壩一個壩址的壩型選擇，主要取決于地形、地質(zhì)、水文和氣候條件。對于那些有幾種壩型可建造的地方，則要進行經(jīng)濟比較估算，并根據(jù)經(jīng)濟條件來做選擇。安全和運行性能是基本的要求，但是施工時間和材料也常會影響到經(jīng)濟比較。壩的分類壩可按照建筑材料（像混凝土或土）來分類?；炷翂斡诌M一步分為重力壩、拱壩、支墩壩或這些類型的組合。土壩則是用土或巖石材料建造的重力式壩，并要設有溢洪道和控制滲漏的特殊設施?；炷林亓我揽勘旧淼闹亓縼砭S持結構穩(wěn)定。水荷載經(jīng)過壩傳遞到壩基，壩可以是直的或稍呈曲線型。通常，重力壩的底寬是高度的0.70.9。堅硬巖石是最好的地基條件，不過，許多小混凝土壩都建筑在透水或軟質(zhì)地基上，而且運行良好。混凝土重力壩最適合于在壩頂設置溢流式溢洪堰，由于這一優(yōu)點，它經(jīng)常和土壩結合使用在寬闊的洪泛平原壩址上。上述一種或幾種壩型可以組合使用。例如，方案研究可能表明，在寬闊而平坦的河谷內(nèi)，一種在中間段設置混凝土重力式溢洪道的土壩是最經(jīng)濟的。在其它設計情況下，也可能采用連拱和支墩壩段或支墩和重力壩的組合。壩址查勘壩的位置是由工程的任務決定。在大致選定的位置（即壩址段）范圍內(nèi)，正確的壩址則必須經(jīng)過仔細的規(guī)劃考慮和系統(tǒng)的研究后決定。在初步研究時，必須確定兩個基本因素：即壩址的地形和地基材料的特性。第一次選擇壩型主要是根據(jù)這兩個因素。但是，如果壩址的其它因素也都考慮之后，則最終的選擇常將由建設費用決定。壩址查勘需要對壩址段內(nèi)每個可能采用的壩址準備好一張準確的地形圖。圖的比例尺應大到滿足布置的需要。查勘任務主要是查明壩址適用或不適用的一些條件。通過壩址查勘，就能繪制壩的位置和工程附屬建筑物如發(fā)電廠房的示意圖。壩址處的自然條件必須查明，以便繪出壩的示意圖并確定料場和施工期輔助企業(yè)的位置。其它影響選壩的因素有道路、魚道、船閘和筏道等。地形地形常常決定壩型。例如，一個狹窄V形河槽可選用拱壩。地形顯示出河谷的表面特征以及等高線和結構各種要求之間的關系。巖石表面的堅固完整情況，必須包括在地形研究之類。在壩址研究中，應該為壩選擇最好的位置。一張精確的壩體輪廓圖，同時表示出壩如何與河谷地形特征相適應的情況，往往就足夠供基建費的估算使用。壩的其他附屬建筑物的設想位置，也要包括在輪廓圖內(nèi)，因為諸如溢洪道等項目會影響壩型和壩址的選擇。地形圖可以從航空測量和隨后描繪的等高線制作，或者可以從政府