大坝设计外文翻译从非饱和土力学的角度,土石坝材料的特性

大坝设计外文翻译-从非饱和土力学的角度,土石坝材料的特性 附录2 Eduardo E. ALONSO, Rafaela CARDOSO Behavior of materials for earth and rockfill dams: Perspective from unsaturated soil mechanics ? Higher Education Press and Springer-VerlagBerlin Heidelberg 2010 Abstract ：The basis of the design of earth and rockfill dams is focused on ensuring the stability of the structure under a set of conditions expected to occur during its life. Combined mechanical and hydraulic conditions must be considered since pore pressures develop during construction, after impoundment and in drawdown. Other instabilityphenomena caused by transient flow and internalerosion must be considered. The prediction of the hydromechanicalbehavior of traditional and non-traditionalmaterials used in the construction of dams is thereforefundamental. The materials used for dams constructioncover a wide range from clayey materials to rockfill. In abroad sense they are compacted materials and thereforeunsaturated materials. A summary of the current level ofknowledge on the behavior of raditional materials used inthe construction of dams is presented in the paper. Regularcompacted materials (with a significant clay fraction),rockfilland ompacted soft rocks are studied with moredetail. The latter are non-traditional materials. They areanalysed because their use, as well as the use of mixtures ofsoil and rock, is becoming more necessary for sustainabilityreasons. Keywords：ams, unsaturated soil mechanics, suction,rockfill, clayey soil, mixture 1 Introduction The basis of the design of earth and rockfill dams is focused on ensuring the stability of the structure under a setof conditions expected to occur during its life. The stabilityof the upstream and downstream slopes must be guaranteed at the end of the construction but also during reservoir impoundment and the operational phase, including drawdown and long-term steady state conditions as a limiting case. A fundamental aspect of the analysis is the generation of pore pressures during the construction and during the first filling, reservoir impounding and cases of rapid drawdown. Other aspects are also of concern, such as the deformation of the structure during the construction andoperational stages, and also incidents caused by hydraulicfracture, internal erosion, long term effects and othercombined cases. Failures associated with hydraulic fracture and internal erosion is largely reported in the literature. Two recent cases of failure caused by collapse and internal erosion are presented in the first part of the paper. The hydromechanical behavior of the materials used in the construction of the earth structures are used to explain their failure. An additional source of complexity is the fact thatdifferent types of materials are used. For traditional dams,impervious clayey materials are used for the core, rockfillmaterials (any type of rock) are used for shells and granularmaterials are used for filters. However, for sustainabilityconstraints and environmental reasons, the use of marginalmaterials, i.e., materials that traditionally would not beused in the construction of dams, is becoming frequent.Such is the case of soft rocks or evolving rocks and soil orrock formations with some proportion of evaporites. Figure 1 is a photograph of Lechago Dam in Teruel,Spain. A very traditional design was adopted. Threedistinct zones can be distinguished: the core, built withregular compacted soils (low to medium plasticity sandyclays, clayey sands and clays), the shoulders built withindurated shale rockfill and the filter built with finegranular materials. Other solutions are also adopted in thedesign as a consequence of the available material for theconstruction. For example, rockfill materials can be usedcombined with solutions adopting impervious materials, aswell as compacted soft rocks. Figure 2 shows the rockfillslopes of Caracoles Dam in San Juan, Argentina, acombined solution using rockfill, made of alluvial boulders, gravels and sands, and an upstream concretediaphragm. Compacted soft rocks are also used in the constructionof dams and Albags Dam, Lleida (Spain) is an example(Figure 3 shows an experimental embankment being builtduring the design of this dam). Compacted soft rocks(fragments of evolving rocks such as schist, marls andother clayey rocks) are different from rockfill (fragments ofhard rock) because of the geological nature of the rocksused. After compaction and hydration, the large fragmentsof soft rock degrade and result in a material intermediatebetween soil and rock, relatively impervious, but morecompressible and more sensitive to wetting and dryingcycles than traditional rockfill. Mixtures of rock and fine materials are other alternativematerials. The characterization of their hydraulic andmechanical properties is usually complex because itdepends on the nature of the materials, the proportionsused and many other factors. Figure 4 is a photograph ofthe material used to build Villaveta Dam in Navarra, Spain(a natural mixture of gravels with clayey soil). Each type of material has a unique behavior and its ownparticularities should be considered in dam design.Experience earned in the past decades is being used indesign when traditional materials are adopted. Because it isno longer feasible to select “the best” emplacement or toimport “good” materials, virtually any kind of soil or rockis expected to be used in the design of dams. Moreover, asnew projects are being commissioned in Africa, SouthAmerica and Asia, local soils and rocks outcropping intropical and volcanic areas must be used. These soils arenot understood as much as the “regular” sedimentary andalluvial formations found in temperate climates of thenorthern hemisphere. The use of non-traditional materialsis an important challenge for a soil engineer. Concepts ofunsaturated soil mechanics offer a sufficient degree ofdevelopment to provide theories and models of compactedsoil behavior, specialized testing and computational tools,which could improve the current state of the art on earthdam and rockfill engineering. 2 Two failures Two cases are presented where collapse deformations werefollowed by internal erosion. The first case concerns anuncontrolled and dangerous leak and the second therupture of a dam caused by localized collapse duringimpoundment. 2.1 Differential collapse of foundation during the first filling The La Molina pond was built for water storage in theCatalonian Pyrenees. As shown in the plan view in Fig. 5, a15m high rockfill dam covered by an imperviousmembrane was built taking advantage of the topographicconditions. A pipe system (see Fig. 5) was included fordrainage under the membrane. It was buried in a gravel andsand fill layer. No special attention was taken in thecompaction of this fill layer, which was done probably dryof optimum. whirlpools marked their position directly abovedrainage pipes (see sketch in Fig. 5). There were attemptsto plug the holes by means of cement bags thrown fromhelicopters. The desperate procedure was partly successfulbut it was eventually decided to empty the pond. Tunnel-shaped depressions were discovered at thewhirlpool positions. The membrane was ruptured inthose points. The granular base was excavated and thepipe drains were uncovered (see Fig. 6). They were foundbroken and filled, in relatively long distances, with agranular material. High speed water was capable ofdragging the gravels inside the filter pipes. A possible explanation for the failure is described asfollows (see Fig. 7): Hydrostatic loading after impoundmentcaused probably some initial differential settlementsof the gravel and sand fill, poorly compacted. However, itis believed that the progressive saturation of this granularlayer, under the total stresses transmitted by the water levelin the pond, led to a soil collapse, which was nonhomogeneous.Then the differential collapse led to thebreakage of the pipes at some points. Sand and gravelentering the pipes created local subsidence troughs, whicheventually caused the breakage of the membrane under thewater head of the pond. Once the membrane broke, thelocal erosion of the granular layer could enlarge the initialrupture. Water had a free escape at those points. This case was not developed further but it illustrates theneed to ensure good compaction conditions of all thematerials. They must be adequate to minimize the penalizingeffects of their expected behavior in case of being fully saturated either in service conditions or by accident. 2.2 Fillcollapse during impoundment An artificial pond was created in an arid environment bybuilding a homogeneous dam covered upstream by animpervious HDPE membrane. The construction tookadvantage of the ground topography so that the dam wasnecessary only in part of the pond perimeter, as shown inFig. 8. The dam was built having a maximum height of20 m at the location of the creek, but progressivelydecreased in height in the rest of the dyke perimeter.Figure 8 shows a sketch of the small watershed areadrained by a small creek. Figure 9 shows the dam crosssection at the position of the original creek draining thearea later occupied by the pond. Low plasticity sandy clays and high plasticity clays werecompacted within short distances within the embankment.There are also indications that the achieved field densitieswere lower than the optimum Normal Proctor values.Wetting under load tests performed on some specimensindicated a high collapse potential. In two tests performed,collapse deformations reached values of 3.8% (for avertical load of 85 kPa) and 8.3% (for a vertical load of245 kPa). These two vertical loads are well within therange of vertical stresses expected within the maximumcross section given in Fig. 9. On first impoundment, when the water level reached 15mover the foundation, a section of the dam, located directlyabove the position of the creek, failed, causing a violentflood. Figures 10 and 11 show the failed section. Thedevelopment of the failure was not observed. When thephotographs in Figs. 10 and 11 were taken, the reservoirwas practically empty. Field observations (see Fig. 12) indicated that the fillcould have a significant collapse potential and, probably, asusceptibility to internal erosion. Troughs and sinkholeswere observed in the downstream slope of the dam a fewyears after the collapse. The compacted soils (they areobserved in the background of Fig. 12, where the almostvertical slope of the failed section remained stable a fewyears after the dam failure) were rather heterogeneous. It is acceptable to assume that any rain water falling intothe pond area during construction was eventually drainedout through the creek bed. This situation could only changein the final stage of the works, when the HDPE membranecovered the pond and the upstream slopes of the dam. A possible explanation for the failure is described as follows: Insufficient compaction of the fill, probably dry ofoptimum, builds a collapse potential into the fill. Thiscollapse potential develops when a given point within thefill experiences an increase in confining stress over theinitial yield stress induced by compaction. The collapsestrains will develop if the water content increases. The fill located immediately above the creek holds themost critical situation: here, the dam reaches the maximumheight and the seeping waters through the creek bed couldeasily lead to a capillary rise affecting a certain thicknessabove the original ground level. Therefore, the fill volumehaving the highest collapse potential is viewed as anelongated mass of compacted soil lying directly above thecreek. A collapse of this volume will tend to create voidsand cracks, which could lead to a preferential pathconnecting the upstream and downstream slopes of the dam. 译文 爱德华五，阿隆索拉斐拉卡多佐 从非饱和土力学的角度，土石坝材料的特性 ?高等教育出版社与施普林格出版社2010年柏林海德堡 摘要 土石坝设计依据的重点是，在其生命中可能出现各种条件下的确保结构稳定。结合机械和水力条件，必须考虑孔隙压力的发展，因为空隙压力在施工期间发展，蓄水后下跌。另外，瞬变流和内部侵蚀造成的不稳定现象也必须加以考虑。因此作者在大坝建设中使用的传统和非传统材料的流体力学特性的预测成为根本。大坝的建设中使用的材料涵盖了从多种粘土材料到堆石。 从广义上讲，它们是碾压材料，所以是不饱和材料。作者在文件中，依据大坝建设采用传统的材料特性，对现有的知识水平进行总结。常规碾压材料（具有重大粘土含量），堆石和压实软岩研究更多细节。后者是非传统材料。他们分析，因为它们的使用，以及土壤和岩石混合使用，是可持续发展的所必须的。 关键词 坝，非饱和土力学，吸力，堆石，粘质土，混合物 1简介 土石坝设计的基础，重点确保发生在其预期生命中各种条件下的结构稳定性。不但在施工结束阶段而且在水库蓄水和运行阶段，上游和下游边坡的稳定性必须保证，包括下跌和长期稳定的状态作为一个限制条件。基本方面的分析是孔隙压力在施工，并在初次蓄水，水库蓄水及水位骤降的情况下产生。其他方面也是令人关注的，如在施工和运行阶段的结构变形，并通过水力压裂，内部侵蚀，长期影响和其他作用联合引起的事故。 与水力侵蚀和内部侵蚀的相关的失事主要是文献报道。最近两次倒塌和内部侵蚀造成的失事，在该文件的第一部分提出。土石坝结构的建筑材料流体力学特性来解释它们的失事。 另外一个复杂的原因是不同材料的使用。对于传统的坝，粘土防渗材料的用作心墙，堆石材料（任何岩型）用于壳状物和粒状物料的过滤层使用。然而，由于可持续发展制约因素和环境的原因，边际使用材料，即传统上不会在大坝建设使用的材料，已经变得越来越频繁使用。这就是一部分软岩或演变的岩石和土壤或岩石蒸发的比例情况。 图1是Lechago大坝在特鲁埃尔，西班牙的照片。一个非常传统的设计获得通过。三个不同的区域可以有所区别：心墙，常规（低到中等塑性粘土砂，粘土砂 和黏土）夯实土壤建成，建成与坝肩硬化页岩面板和细颗粒材料建成的过滤层。其它解决方案还通过了作为建筑用材料的设计结果。例如，堆材料可用于不透水材料解决方案，以及于压软岩相结合。图2显示了卡拉科莱斯大坝在圣胡安，阿根廷，联合解决方案，采用堆，冲积砾石，砾石和砂作出的，和上游混凝土防渗墙. 夯实软岩也用于坝和阿尔瓦赫斯大坝，莱里达建设（西班牙）就是一个例子（图3显示了一个正在建造的试验堤在此坝设计）。夯实软岩（如不断发展的岩石碎片片岩，如泥灰岩和，其他粘土岩）与堆石（坚硬的岩石碎片）不同，因为岩石地质性质。经过压实和水化，软岩大片段降解的材料造成土壤和岩石之间的中间，相对不透水，但比传统堆石，有更可压缩和更敏感干湿周期。 岩石混合物和细颗粒材料是其他替代材料。其液压和机械性能表征通常是复杂的，因为它由对材料的性质，使用的比例和许多其他因素而定的。图4是一个建立纳瓦拉，西班牙Villaveta大坝材料照片（一粘性土和砾石自然的混合物）。 每类材料具有独特的特性和自己的特殊性，应在大坝设计中考虑。当使用传统材料时，用过去数十年获得的经验设计。因为它不再是可行的选择“最好的”安置或导入“良好”的材料，几乎任何类型的土壤或岩石，预计将在大坝设计中的应用。此外，由于新项目正委托在非洲，南美和亚洲，当地热带和火山地区出露的土壤和岩石必须使用。这些是在北半球温带气候地层发现冲积和沉积土壤和常规的土壤的理解是不同的。对土壤工程师来说，非传统材料的使用是一个重要的挑战。非饱和土力学理论的发展在很大程度上程度，提供理论和压实土的特性，专门的测试和计算工具，它可以改善土石坝工程艺术的现况模型。 2 两次失事 两起案件的塌陷变形情况发生在内部侵蚀之后。第一个案件涉及失控和危险的泄漏，第二个是由局部坍塌造成大坝蓄水期间破裂。发生在初次蓄水不同基础的坍塌 在莫利纳建池的水储存在加泰罗尼亚比利牛斯山脉。正如图5中所示的计划的看法。一个15米高的墙堆石坝防渗膜覆盖利用地形条件的优势建造。管道系统（见图5）包括在膜下排水。这是埋在碎石和沙子填充层。不用特别注意在这个填充层的压缩，这样做是可能的最佳压实度。 少数灰岩坑进行全面蓄水后被发现。水漩涡标志着其正上方排水管位置（参见图草图5）。有人试图从直升飞机投掷水泥袋堵塞这些孔。这是一个绝望的过程，只有部分是成功的，但最终决定清空水池。 在漩涡点发现了隧道状凹陷。在这些漩涡点，该膜破裂。粒状地基开挖和管道显露出来（见图6）。在相当长的距离内发现颗粒材料填补和破碎。高速水有拖过滤管道内的砾石的能力。 对失事的描述一种可能的解释如下（见图7）：蓄水后静负荷可能引起的一些碎石和沙子填充，压实初步产生不均匀沉降差。然而，人们认为这个颗粒层逐渐饱和下，总应力转到池塘的水下，导致了土壤崩溃，这是非齐次。不同倒塌导致水管在一定程度的破裂。砂和砾石进入管道产生局部下陷，并最终导致在池塘的头部下水中的膜破损。一旦膜破裂，该颗粒层局部侵蚀可能扩大初始破裂。水已经在这些点自由逃脱。 这个事件没有进一步发展的需要，但它说明，需要确保所有材料具有压实良好条件。他们必须尽量减少他们在被预期的特性的惩罚，以防在不是在服务条件或意外条件下被完全饱和的影响。 2.2 蓄水期间填充物坍塌 在一个人造池塘干旱环境，建设一个覆盖均质坝上游防高密度聚乙烯膜防渗。利用地面地形的优势，使大坝必要在池塘周围部分，如图8所示. 大坝建成后在小溪位置，最大高度20米，但在堤坝周围其他部份高度逐渐下降。图8显示了小流域的一个小溪流排水区示意图。图9显示了大坝断面在原有的排水河的位置后来由池塘面积占用。 低塑性粘土和可塑性高砂质粘土在河堤的短距离内被压缩。也有迹象表明，所取得的实地密度均低于正常普罗克托最佳值。根据一些湿润标本进行负载测试图显示出高潜在倒塌。两个测试，测试坍塌变形达到了（垂直负载85千帕）和（245千帕一垂直荷载）.图9 这两个载荷在期望最大垂直应力范围内。 在首次蓄水，当水位达到了超过基础15米，一个大坝位于河正上方的位置，易发生失事，导致洪水泛滥。图10和11显示失事的部分。失事的发展并没有观察到。图10和图11的照片被采用，水库几乎空的。 野外观察（见图12）表示，填补可能有明显崩溃的可能，而且很可能是一个内部侵蚀。观察到在大坝下游槽和灰岩坑坡，数年后倒塌。土壤的压实（他们正在后台观察图12，大坝失事几年后，垂直边坡的破坏部分仍然保持稳定）都相当混杂。 这是可以接受的假设，任何施工期间落进池塘的任何雨水最终都通过河床排出来。改变这种局面只能在工程最后阶段，当高密度聚乙烯膜覆盖的池塘和水库上游山坡的最后阶段。 对失事一种可能的解释的描述如下： 填充材料压实不足，可能的最佳的压实度，构建成一个潜在倒塌的危险。这潜在倒塌的开始发展时，在给定的点在围填经历过的限制压力增加初始屈服应力的压实作用。水含量的增加使倒塌的压力将继续发展。 填充材料位于小溪正上方认为最关键的位置: 在这里，通过大坝河床到达的最高高度和渗出水很容易导致毛细血管上升影响高于原地面一定的厚度。因此，填充量最高潜在倒塌被看作是一个拉长的压实土直接躺在上面的小溪。这方面的体积崩溃往往会造成孔洞和裂缝，这可能导致一个完美连接大坝的上游和下游的斜坡的道路。