土石坝外文翻译(共9页).doc

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1、精选优质文档-倾情为你奉上The Design of Earth-Rock Dam and SpillwaysPart 1 Embankment DamsSelection of embankment type：In general, there are two types of embankment dams: earth and rockfill. The selection is dependent upon the usable materials from the required excavation and available borrow. It should be noted

2、 that rockfills 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 earthfills. Rocks which are

3、hard and will not break down significantly are treated as rockfills. The selection and the design of earth embankment are based upon the judgment and experience of the designer and is to a large extent of an empirical nature. The various methods of stability and seepage analyses are used mainly to c

4、onfirm the engineers judgment. 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 freebo

5、ard, an allowance must be made for settlement of the embankment and the foundation which will occur upon completion of the embankment. 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, th

6、e 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.Alignment ：construction costs but such alignment should not be such as to

7、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

8、 of the embankment under pool load will put the embankment in compression thus minimizing transverse cracking,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 pervious soils

9、 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,

10、This can be treated by excavation of the abutment to reduce the slope, especially in the imperious 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-he

11、aling should transverse cracking occur. 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 th

12、e 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 cases it may construction to permit an increase in shear strength through consolidation of the fill. In some cases it may be nec

13、essary to provide additional drainage of the foundation or fill by means of sand drain wells or by means of horizontal pervious drainage blankets.Embankment soils ：Most soils are suitable for use for embankment construction, however, there are physical and chemical limitations, soils which contain e

14、xcessive salts or other soluble materials should not be used. Substantial organic content should not exist in 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 an

15、d should be avoided.Compaction requirements ：The strength of the impervious and semi-impervious soils depends upon he 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 f

16、ill or after placement 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 moiste

17、ned 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 Proter optimum water content. Pervious soils should be conpacted to

18、 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

19、. All overhangs should either be removed or filled with lean concrete prior to fill placement.Types of instruments ：The type of instrumentation depends upon the size and complexity of the project. The devices in common use are :piezometers; surface movements; settlement gages; inclinometers; interna

20、l movement and strain indicators; pressure cells; movement indicators at conduit joints and other concrete structures.Part 2 SpillwaysA spillway is the safety valve for a dam. It must be designed to discharge maximum flow while keeping the reservoir below a predetermined level. A safe spillway is ex

21、tremely important. Many failures of dams have resulted from improperly designed spillways or spillways of insufficient capacity. Spillway size and frequency of use depend on the runoff characteristics of the drainage basin and the nature of the project. The determination and selection of the reservo

22、ir inflow design flood must be based on an adequate study of the hydrologic factors of basin. The routing of the flow past the dam requires a reasonably conservative design to avoid loss of life and property damage.Space limitations do not permit an adequate hydrologic treatment of flood flows. Howe

23、ver, data are supplied for estimates of maximum flows for the initial project studies. A more detailed hydrologic analysis is necessary for the utilization of the annual and long-turn stream flow in a proper project formulation.The study of stream or river flows involves:the determination of the amo

24、unt of water available throughout a period of years；and the determination of the maximum volumes of water that must be handled for spillway design and dam safety.In the first aspect, the flow is studied for periods of drought and programmed into this study. A mass curve of the stream runoff over a p

25、eriod of years is developed to determine the available water. The mass curve is the accumulative total of the volume of flow past a given point on the stream over a period of time. Unfortunately, most of the small streams do not have sufficient records to develop the hydrologic information. The engi

26、neer usually develops synthetic curves from neighboring stream data and rainfall information. However, methods are available in various texts, journals, and reports to estimate stream flow. The second aspect involves estimating maximum flood flow to determine spillway requirement and dam safety. Stu

27、dies show that flood flows are associated with frequency of the event of the risk of floods causing damage by exceeding the estimated design flow.If failure of the dam would result in loss of life, the spillway must have sufficient capacity to prevent failure when the maximum probable flood is route

28、d through the reservoir. This is particularly important in rock and earthfill dam that may be overtopped during a flood. Concrete dams can generally withstand some overtopping without failure if the structural analysis adheres to the generally accepted safety factors.The case of dam failure that doe

29、s not endanger life may be justified if the organization involved fully realizes the risks and ensuing damages. This situation may exist on low, small reservoir-type dams.A quick estimates of maximum probable flow can be obtained from a figure. Discharge determined from these curves should be modifi

30、ed by application of hydrologic data pertinent to the area. The curves are based records of unusual flood discharges for unregulated streams. The engineer should not accept the flood peak established from these experience curves without first bringing the data up to date to show all recent flood eve

31、nts and those pertinent to the area of study. An advanced procedure to estimate the maximum flood is to transpose storm producing great floods in the region over the drainage basin. The resulting flood is analyzed to determine the peak flow and the hydrograph. The hydrograph is the relationship of d

32、ischarge and time for precipitation when combined with other flood-contributing of the basin (including melting snow)to produce the flood hydrograph.Flood less than maximum may be used for structures where loss of human life is not involved. In minor structures with insignificant storage, where it i

33、s permissible to anticipate failure within the useful life of the project, a 50-year or 100-year frequency flood may be used for the inflow design flood.Site conditions greatly influence the location, type, and components of the spillway. The type of dam construction is also influenced by the type o

34、f spillway and spillway requirements.There are six general categories of spillways: overflow ,through or chute, side channel, shaft or glory hole, siphon, gated. The designer may use one or a combination of types to fulfill the project needs.Some designs will use one type of spillway for normal oper

35、ation and for flood peaks up to a 50-year or 100-year frequency storm. An emergency spillway provides additional safety if emergencies arise that was not covered by normal design assumptions. Such situations could result from floods above a certain level, malfunctioning spillway gates, or enforced s

36、hutdown of outlet works. The emergency spillway prevents overtopping the main portion of the dam and is particularly needed for earth and rock embankments.The overflow spillway is well suited to concrete dams. It is commonly used where dams have sufficient crest length for the desired discharge capa

37、city and where the foundation material is solid or can be protected against scouring. Some dams use a free overflow or non-supported type; others incorporate a chute or through to carry the flow to the downstream channel.Chute spillways are often used for earth dams or where there are poor downstrea

38、m foundation materials. Slide channels and shaft spillways are readily adapted to narrow canyons where space is limited. Limitations on crest length or maintaining a constant headwater level fit the flow characteristics of a siphon spillway. Gated spillways are used when it is desirable to limit the

39、 effects of the dam during high flows and prevent excessive flooding.The spillway may be part of the dam or a separate structure. Its function must be integrated with the dam. The location, size, and other dam features influence the spillway location and arrangement. The final plan is governed by th

40、e overall economy and hydraulic sufficiency of the spillway.This literature is fromHydraulic Engineering Specialty English土石坝及溢洪道设计1 土石坝的设计坝型的选择：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。应该注意，根据岩石的物理性质，堆石能逐渐变化为填土，因而不能对堆石作出严格而固定的分类。那些脆弱和在开挖填筑时容易破裂的岩石可归入填土类。而坚硬和不易破裂的岩石则列入堆石类。一座土坝的选定和设计都有赖

41、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。超高的确定：所有的土石坝都必须有一个足够的额外高度，成为超高，以防止库水漫顶。超高的高度必须足以在波浪作用、风力雍高和地震影响下，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采用常规设备便于填筑的宽度来控制。通常，把顶宽度应不小于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宽度。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

42、能因此而引起坝体发生滑动或开裂。一般说来，一条横跨河谷的最短直线，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。位于峡谷的坝，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，从而尽量减小其横向开裂。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，就可能建造一道与上游不透水铺盖和下游排水设施，以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，那里的坝体填土会有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，尤其在上游

43、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可自行愈合。分期施工：土坝的分期施工往往是可能的，而且在一些情况下是必须的。要求这样施工程序的因素是：河谷宽阔，可以允许导流或泄水工程于一些部分坝体同时施工；地基软弱，要求坝体不要过快填筑，以防止地基中产生过大的应力；料场潮湿，要求放慢施工，以使土料能通过固结作用来增加抗剪强度。在某些情况下，可以需要增设基础排水设施或填筑排水砂井，或采用水平透水的排水铺盖。坝体的土料：大多数土料适用于坝体填筑。然而，在物理和化学性质上也有一定的限制。含有过多盐分获可溶性物质的土料，不可使用。在土料里，不应存在大量的有机质

44、成分。褐煤若能通过填筑而充分分散，无自然之虞，就不能妨碍使用。而具有高度流限的肥粘土，多半难以施工，必须避免使用。压实的要求：不透水和半透水的土料强度取决于压实的密度。压实密度又取决于土料的含水量和压实设备的质量。因此，料场土料的含水量和在堆筑前或堆筑后而未碾压前的填土实际含水量变化，都会影响坝体的设计。若果天然含水量太高，可以在料场用排水或将土料耙松的办法来减低。如果土料太干燥，则须在料场用洒水或泡水的办法把土料润湿，然后再让涂料在使用以前保持稳定的含水量。填筑时的含水量范围一般介于比标准普氏最优含水量低2%到高2%3%之间。透水性土料应压实到相对密度的80%。如果需要，应该变换填筑层的含水

45、量、铺层厚度、碾压遍数和碾压机的型式等，进行填筑试验。对于坡度很陡的坝座部位，必须用薄层填筑，并用手扶打夯机夯实。所有外悬突出部位，均应在填土填筑以前挖除或用贫混凝土填平。观测仪器的类型：观测仪器的类型取决于工程的规模或复杂性。通常的装置是：测压计；表面位移标志；沉陷量观测仪；测斜仪；内部位移和应变指示仪；压力盒（压力传感器或压应力计）；地震加速仪；在管道接头和其他混凝土结构上的位移标志。2溢洪道溢洪道相当于坝上的一个安全阀，它必须设计成能够泄放最大的流量，而同时能保持水库的水位在预定的水位以下。一个安全的溢洪道是极为重要的，许多坝的失事都是由溢洪道设计不当或者溢洪道容量不足造成的。溢洪道的尺

46、寸和使用频率取决于流域的径流特性和工程的性质。入库设计洪水的选择和确定，则必须在充分研究流域水文因素的基础上进行。对于过坝流水的调泄，需要有合理审慎的设计，以避免生命财产的损失。由于篇幅限制，这里不允许对洪水流量的水文分析做充分的讨论。但是提供了作工程初步研究的最大流量估算资料。至于在工程的正式规划中队河川水流作年或多年利用时，则需要进行更详细的水文分析。对江河流量的研究包括：确定经若干年一段时期内所能获得的水量；确定溢洪道的设计和大坝安全所必须宣泄的最大水量。第一方面，要联系工程开发中的用水情况，按枯水期和丰水期来研究流量。优先的用水权必须调查清楚，并纳入研究中，要做出若干年一段时期内河川径

47、流的累积曲线，以便确定可利用的水量。累积曲线表示一定时期内通过河道上某一地点的累积总量。遗憾的是，大部分小河流上都没有足够的记录可以用以编制水文资料。工程技术人员通常都从相邻的河流数据和雨量资料编制出综合曲线。从各种教材、杂志和报告中也可以得到各种估算河流流量的方法。第二方面包括最大洪水流量的估算，用以确定所需要的溢洪道容量和坝的安全。研究表明，洪水流量与不同时期中洪水的出现频率有关。这样，工程技术人员就能切实地估计洪水超过估算的设计流量所造成损失的危害性。如果坝的失事会造成生命伤亡，则溢洪道必须有充分的容量，以防止最大可能洪水通过水库是发生失事。这种情况对于发生洪水时可能漫顶的土坝和堆石坝，

48、尤为重要，混凝土坝如果在结构分析中遵守通用的安全系数，通常都能够经受一定程度的漫顶而不致失事。对于不致危及生命的失事情况，如果有关部门充分估计到所冒的风险以及随之而造成的损失，则也是允许的。这种情况可能存在于小水库的低坝上。用查图法可以快速估算出最大可能流量。由这些曲线定出的流量，应采用与该地区有关的水文资料加以修正。这些曲线系根据未经整治的河流的非常洪水流量记录作出的。工程技术人员首先要取得列有全部近期洪水过程的资料，以及与研究地区有关的资料，然后才能采用从这些经验曲线上得出的洪峰流量。估算最大洪水的一种先进方法是将地区内能产生大洪水的暴雨转换成流域的洪水，将所得出的洪水加以分析，就可以用来

49、确定洪峰流量和流量过程线。流量过程线是表示洪水产生特性的流量时间关系曲线。如果用综合流域内的其他洪水形成特性（包括融雪）来研究最大可能降水量，则也可以得到相似的方法求出洪水过程线。对于失事不会导致人员伤亡的的建筑物，也可以采用比最大流量洪水的洪水值。在蓄水量不多的较小结构上，容许在工程使用年限内发生预期的失事时，入库设计洪水可以采用50年或100年一遇的频率。坝址条件对于溢洪道的位置、型式和组成部分有很大影响。而溢洪道的型式和对泄洪的各种要求对坝的构造型式也有影响。溢洪道有六种常用类型：顶部溢流式；陡槽式；侧槽式；竖井或喇叭式；虹吸式；阀门式。设计人员可以采用一种或几种型式的组合以满足工程的要求。有些设计中，采用一个型式溢洪道供正常运行用，应付50年或100年一遇暴雨的洪峰。另一个非常溢洪道，则在发生正常设计假定没有考虑的非常情况时，提供附加安全度。这类情况可以发生在洪水超过某一水位、溢洪道阀门发生故障或泄水道强制关