外文翻译---土石坝的特征及筑坝技术控制

附 录 英文论文 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 中文译文 土石坝的特征及筑坝技术控制 1、土石坝坝型的选择 一般来说，土石坝有两种类型：土坝和堆石坝。坝型的选择取决于能从需要开挖的地点和可用的料场处取得合用材料的情况。应当指出的是，根据岩石的物理特性，堆石可以逐渐变化为填土，因而不能对土石料作出严格而固定的分类。那些软弱的和在开挖填筑时容易破碎的岩石可被归入填土类。而坚硬和不会大量破碎的的岩石，则列为堆石类。 一座土坝的选定和设计都有赖于设计人员的判断和经验，而且在很大程度上是属于经验性的。各种稳定和渗透分析方法，主要是作为证实工程师的判断而使用的。 2、超高 所有的土坝都必须有一个足够的额外高度，称为超高，以防 止水库漫顶。超高的高度必须足以在波浪作用、风浪壅高和地震影响下，不会导致坝的漫顶。除了超高外，对于坝建成时发生的坝体和地基沉陷，还必须在高度上留有余地。 坝顶宽度 土坝的坝顶宽度一般用常规设备便于施工的填筑宽度来控制。通常，坝顶宽度应不小于 30 英尺。如果存在着大规模塌方进入水库，或者有因地震使岩块倒落而引起波浪漫顶的危险，则需要采用抗冲刷的材料填筑更宽的坝顶高度。 定线 土坝的坝轴线选定应尽量使建设费用降到最少，但是也不能因此引起坝体发生滑动或开裂。一般来说，一条横跨河谷的最短的直线，可能满足要求。但是，当 地的地形和地基条件可能要求采用另外的方案。对于峡谷的坝，常采用向上游拱出的坝轴线，以便在坝体受库水压力作用而发生变形时，能使坝体压紧，从而尽量减少其横向开裂。 5、两岸坝座 一般有三个问题与土坝坝座有关：渗透；不稳定；坝体的横向开裂。如果坝座是由透水的沉积土构成，就可能需要建造一道上游不透水的铺盖和下游排水设施，可尽量减少和控制坝座内的渗透。 在坝座岸坡很陡的地方，特别在边坡突变或有陡壁处，那里的坝体填土会产生横向裂缝的危险。这个问题可以用开挖坝座放缓边坡来处理，这样的处理在不透水区和过渡区特别需要。 过渡区，尤其是在上游侧的过渡区，必须用粘着力很小或无粘着力且颗粒级配良好的土料来填筑，这种土料如发生横向裂缝时能自行愈合。 6、分期施工