外文翻譯---土石壩的特征及筑壩技術(shù)控制

附 錄 英文論文 The characteristics of earth-rock DAMS and technical control 1. selection of embankment type In general, there are two types of embankment dams: earth （ earth fill dam） and rock fill（ rock fill dam） . The selection is dependent upon the usable materials from the required excavation and available borrow. It should be noted that rock fills can shade into soil fills depending upon the physical character of the rock and that no hard and fast system of classification can be made. Rocks which are soft and will easily break down under the action of excavation and placement can be classified with earth fills. Rocks which are hard and will not break down significantly are treated as rock fills. The selection and the design of an earth embankment are based upon the judge ment and experience of the designer and is to a large extent of an empirical nature. The various methods of stability and seepage analysis are used mainly to confirm the engineers judge ment 2. freeboard All earth dams must have sufficient extra height known as freeboard to prevent overtopping by the pool. The freeboard must be of such height that wave action, wind setup, and earthquake effects will not result in overtopping of the dam. In addition to freeboard, an allowance must be made for settlement of the embankment and the foundation which will occur upon completion of the embankment. 3. top width The width of the earth dam top is generally controlled by the required width of fill for ease of construction using conventional equipment. In general, the top width should not be less than 30 ft. if a danger exists of an overtopping wave caused either by massive landslides in the pool or by seismic block tipping, then extra top width of erosion resistive fill will be required. 4.alignment The alignment of an earth fill dam should be such as to minimize construction costs but such alignment should not be such as to encourage sliding or cracking of the embankment. Normally the shortest straight line across the valley will be satisfactory, but local topographic and foundation conditions may dictate otherwise. Dams located in narrow valleys often are given an alignment which is arched upstream so that deflections of the embankment under pool load will put the embankment in compression thus minimizing transverse cracking. 5. Abutments Three problems are generally associated with the abutments of earth dams: seepage, instability, and transverse cracking of the embankment. If the abutment consists of deposits of pervious soils it may be necessary to construct an upstream impervious blanket and downstream drainage measures to minimize and control abutment seepage. Where steep abutments exist, especially with sudden changes of slopes or with steep bluff, there exists a danger of transverse cracking of the embankment fills. This can be treated by excavation of the abutment to reduce the slope, especially in the impervious and transition zones. The transition zones, especially the upstream, should be constructed of fills which have little or no cohesion and a well-distributed gradation of soils which will promote self-healing should transverse cracking occur. 6. stage construction It is often possible, and in some cases necessary, to construct the dam embankment in stages. Factors dictating such a procedure are: a wide valley permitting the construction of the diversion or outlet works and part of the embankment at the same time; a weak foundation requiring that the embankment not be built too rapidly to prevent overstressing the foundation soils ; a wet borrow area which requires a slow construction to permit an increase in shear strength through consolidation of the fill. In some cases it may be necessary to provide additional drainage of the foundation or fill by means of sand drain wells or by means of horizontal pervious drainage blanket. 7. Embankment soils Most soils are suitable for use for embankment construction, however, there are physical and chemical limitations, soils which contain excessive salts or other soluble materials should not be used. Substantial organic content should not exist in the soils. Lignite sufficiently scattered through the fill to prevent the danger of spontaneous combustion, is not objectionable. Fat clays with high liquid limits may prove difficult to work and should be avoided. 8. Compaction requirements The strength of the impervious and semi-impervious soils depends upon the compacted densities. These depend in turn upon the water content and weight of the compacting equipment. The design of the embankment is thus influenced by the water content of the borrow soils and by the practicable alternations to the water content either prior to placement of the fill or after placement but prior to rolling. If the natural water content is too high, then it may be reduced in borrow area by drainage, or by harrowing. If the soil is too dry it should be moistened in the borrow area either by sprinkling or by ponding and then permitted to stabilize the moisture content before use. The range of placement water content is generally between 2 percent dry to 2 or 3 percent wet of the standard Porter optimum water content. Pervious soils should be compacted to at least 80 percent of relative density. If necessary, test fills should be constructed with variations in placement water content, lift thickness, number of roller passes and type of rollers. For cases of steep abutment, the fill must be placed in thin lifts and compacted by mechanical hand tampers. All overhangs should either be removed or filled with lean concrete prior to fill placement. 9. types of instruments The type of instrumentation depends upon the size and complexity of the project. The devices in common use are: piezometers ; surface movement monuments ; settlement gadges ; inclinometers ; internal movement and strain indicators ; pressure cells ; seismic acceleration meter ； movement indicators at conduit joints and other concrete structures 中文譯文 土石壩的特征及筑壩技術(shù)控制 1、土石壩壩型的選擇 一般來說，土石壩有兩種類型：土壩和堆石壩。壩型的選擇取決于能從需要開挖的地點和可用的料場處取得合用材料的情況。應當指出的是，根據(jù)巖石的物理特性，堆石可以逐漸變化為填土，因而不能對土石料作出嚴格而固定的分類。那些軟弱的和在開挖填筑時容易破碎的巖石可被歸入填土類。而堅硬和不會大量破碎的的巖石，則列為堆石類。 一座土壩的選定和設計都有賴于設計人員的判斷和經(jīng)驗，而且在很大程度上是屬于經(jīng)驗性的。各種穩(wěn)定和滲透分析方法，主要是作為證實工程師的判斷而使用的。 2、超高 所有的土壩都必須有一個足夠的額外高度，稱為超高，以防 止水庫漫頂。超高的高度必須足以在波浪作用、風浪壅高和地震影響下，不會導致壩的漫頂。除了超高外，對于壩建成時發(fā)生的壩體和地基沉陷，還必須在高度上留有余地。 壩頂寬度 土壩的壩頂寬度一般用常規(guī)設備便于施工的填筑寬度來控制。通常，壩頂寬度應不小于 30 英尺。如果存在著大規(guī)模塌方進入水庫，或者有因地震使巖塊倒落而引起波浪漫頂?shù)奈ｋU，則需要采用抗沖刷的材料填筑更寬的壩頂高度。 定線 土壩的壩軸線選定應盡量使建設費用降到最少，但是也不能因此引起壩體發(fā)生滑動或開裂。一般來說，一條橫跨河谷的最短的直線，可能滿足要求。但是，當 地的地形和地基條件可能要求采用另外的方案。對于峽谷的壩，常采用向上游拱出的壩軸線，以便在壩體受庫水壓力作用而發(fā)生變形時，能使壩體壓緊，從而盡量減少其橫向開裂。 5、兩岸壩座 一般有三個問題與土壩壩座有關(guān)：滲透；不穩(wěn)定；壩體的橫向開裂。如果壩座是由透水的沉積土構(gòu)成，就可能需要建造一道上游不透水的鋪蓋和下游排水設施，可盡量減少和控制壩座內(nèi)的滲透。 在壩座岸坡很陡的地方，特別在邊坡突變或有陡壁處，那里的壩體填土會產(chǎn)生橫向裂縫的危險。這個問題可以用開挖壩座放緩邊坡來處理，這樣的處理在不透水區(qū)和過渡區(qū)特別需要。 過渡區(qū)，尤其是在上游側(cè)的過渡區(qū)，必須用粘著力很小或無粘著力且顆粒級配良好的土料來填筑，這種土料如發(fā)生橫向裂縫時能自行愈合。 6、分期施工