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•Owingtothefactthatelectricitycanbetransmittedfromwhereitisgeneratedtowhereitisneededbymeansofpowerlinesandtransformers,largepowerstationscanbebuiltinremoteplacesfarfromindustrialcentersorlargecities,asiscitedthecasewithhydroelectricpowerstationsthatareinseparablefromwatersources.•由于电力可以从发电的地方通过电线和变压器输送到需要用电的地方，因此大型电站可以建在远离工业中心或大城市的地方，离不开水源的水力发电站就常常是这样建立的。Ideallysuitedtonarrowcanyonscomposedofrock,thearchdamprovidesaneconomicalandefficientstructuretocontrolthestreamflow.Theload-carryingcapacityofanarchdamenablesthedesignertoconservematerialandstillmaintainanextremelysafestructure.•拱坝最适合于修建在岩石峡谷中，它是一种控制河道中水流经济而有效的建筑物。一座拱坝的承载能力足以使设计人员用较少的材料而仍能建成极为安全的结构。•Thegeneraltheoryofarchdamdesigniscomparativelynewandchangingrapidlyasmoreinformationisobtained.Engineershavecautiouslyappliedmathematicaltheory,thelawofmechanics,andtheoriesofelasticitytoreducethethicknessofarchdamsandgainsubstantialeconomies.•拱坝的一般设计理论比较新颖，同时在获得更多的资料之后，理论的变化也很迅速。工程师们曾慎重的应用数学理论、力学定律和弹性理论，以减小拱坝的厚度，并取得了很大的经济效果。•Historically,themethodofanalysisofarchdamsgrewfromthecylindertheorytoindependentarches,crowncantileveranalysis,andthenmultiplecantileveranalysis.Thecrowncantileverandarchactiontheoryhasprovedsatisfactoryforarchdamanalysis.•从历史发展来看，拱坝分析方法从圆筒理论开始，发展到多个独立拱圈分析、拱冠悬臂梁分析，以及多悬臂梁分析。拱冠悬臂梁和拱作用的理论已被证明能满足拱坝分析用。•Allearthdamsmusthavesufficientextraheightknownasfreeboardtopreventovertoppingbythepool.Thefreeboardmustbeofsuchheightthatwaveaction,windsetup,andearthquakeeffectswillnotresultinovertoppingofthedam.Inadditiontofreeboard,anallowancemustbemadeforsettlementoftheembankmentandthefoundationwhichwilloccuruponcompletionoftheembankment.•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。•Thewidthoftheearthdamtopisgenerallycontrolledbytherequiredwidthoffillforeaseofconstructionusingconventionalequipment.Ingeneral,thetopwidthshouldnotbelessthan30ft.ifadangerexistsofanovertoppingwavecausedeitherbymassivelandslidesinthepoolorbyseismicblocktipping,thenextratopwidthoferosionresistivefillwillberequired.•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。•Thealignmentofanearthfilldamshouldbesuchastominimizeconstructioncostsbutsuchalignmentshouldnotbesuchastoencourageslidingorcrackingoftheembankment.Normallytheshorteststraightlineacrossthevalleywillbesatisfactory,butlocaltopographicandfoundationconditionsmaydictateotherwise.Damslocatedinnarrowvalleysoftenaregivenanalignmentwhichisarchedupstreamsothatdeflectionsoftheembankmentunderpoolloadwillputtheembankmentincompressionthusminimizingtransversecracking.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。•Threeproblemsaregenerallyassociatedwiththeabutmentsofearthdams:①seepage,②instability,and③transversecrackingoftheembankment.Iftheabutmentconsistsofdepositsofpervioussoilsitmaybenecessarytoconstructanupstreamimperviousblanketanddownstreamdrainagemeasurestominimizeandcontrolabutmentseepage.•一般有三个问题与土坝坝座有关：①渗透；②不稳定；③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。•Wheresteepabutmentsexist,especiallywithsuddenchangesofslopesorwithsteepbluff,thereexistsadangeroftransversecrackingoftheembankmentfills.Thiscanbetreatedbyexcavationoftheabutmenttoreducetheslope,especiallyintheimperviousandtransitionzones.Thetransitionzones,especiallytheupstream,shouldbeconstructedoffillswhichhavelittleornocohesionandawell-distributedgradationofsoilswhichwillpromoteself-healingshouldtransversecrackingoccur.•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。•Itisoftenpossible,andinsomecasesnecessary,toconstructthedamembankmentinstages.Factorsdictatingsuchaprocedureare:①awidevalleypermittingtheconstructionofthediversionoroutletworksandpartoftheembankmentatthesametime;②aweakfoundationrequiringthattheembankmentnotbebuilttoorapidlytopreventoverstressingthefoundationsoils;③awetborrowareawhichrequiresaslowconstructiontopermitanincreaseinshearstrengththroughconsolidationofthefill.Insomecasesitmaybenecessarytoprovideadditionaldrainageofthefoundationorfillbymeansofsanddrainwellsorbymeansofhorizontalperviousdrainageblanket.•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：①河谷宽阔，可以允许导流或泄水工程与一部分坝体同时施工；②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；③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沙井，或采用水平透水的排水铺盖。•Mostsoilsaresuitableforuseforembankmentconstruction,however,therearephysicalandchemicallimitations,soilswhichcontainexcessivesaltsorothersolublematerialsshouldnotbeused.Substantialorganiccontentshouldnotexistinthesoils.Lignitesufficientlyscatteredthroughthefilltopreventthedangerofspontaneouscombustion,isnotobjectionable.Fatclayswithhighliquidlimitsmayprovedifficulttoworkandshouldbeavoided.•大多数土料适合于坝体填筑，然而，在物理和化学性质上也有一定的局限，含有过多盐和可溶性物质的土料，不可以使用。在土壤里不应存在大量的有机质成分。褐煤若能通过填筑而充分分散，无自燃危险，就不妨碍使用。而具有高度流限的肥粘土，多半难以施工，必须避免使用。•Thestrengthoftheimperviousandsemi-impervioussoilsdepend