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1、 Earth and rock damSummaryEarth and rock dam, with another name as local material dam,is mainly built with earth and rock materials near the site. It can be classified based on the materials it used, earth dam mainly with earth, sand, grit, and gravel, and rock dam mainly with rock ballast, gravel,
2、and exploded rocks.Features of earth and rock damStrong pointsWith convenient supply of materials, many building materials such as steel, cement, and timbers can be saved.With granular structure more suitable to foundation deformation, it demands less on the foundation.Very flexible from simple arti
3、ficial filling to highly mechanized construction, the procedure become simple, the construction become efficient, and the quality guarantee become easy.Simply structured, thecost is low, the operation is convenient, worksis reliable, and maintenance and height adding is convient. Weak pointsOverflow
4、 not allowed, spillway has to be built.Diversionless convenient, cost increases.Section larger, earth to be filled is easy to be affected by climate. This kind of difficult means possible extention of time limit and cost increaseEarth and rock dam typesBased on constructing ways, earth and rock dams
5、 can be classified into rolled ones of earth & rock, thrown rock-filled ones,rock-filled ones withdirectional detonation, ones with earth thrown into the water, and ones filled by hydraulic forces.Among them, rolled ones are most popular.Based on the earth proportion and the location of anti-seepage
6、parts, there are homogeneous (even-granular) dams, zoned earth dams, and dams with artificial anti-seepage materials. Strong points of homogeneous dams: one fold materials, simple process weak points: flat gradient, large section, weather-limited, strong water pressure in holes. Zoned dams are class
7、ified into ones with core anti-seepage and ones with front anti-seepage. Less amount of earth, less affect of season. interfering with the filling of the dam body. Less interference with the construction of the dam body. weaker anti-earthquake and uneven sinking. The anti-seepage parts of dams with
8、artificial anti-seepage materials use asphalt concrete, reinforced concrete or other artifical materials. Sometimes, the anti-seepage parts are in the dam front facing the upstream, sometimes, they are at the core of the dam. Working conditionsTrapeziform sectionEarth-rock dam is a water retaining s
9、tructure built with loose granules of earth and rocksfilled and roller compacted. With weaker strength between these granules, both upsteam and downsteam slopes have to be kept at acertain degree to avoid landslide. So the dam section is usuallytrapeziform.It can be destablized in two ways, simple s
10、lope sliding and sametime sliding of slope and foundation caused by shear damage.Its a difference from other structuresSeepage effectsWith a large section, the dam is generally kept from entire sliding unless caused by weak interlayers. Effected by water levels at the upsteam and downsteam, seepage
11、is easy to happen with streams passing the faying surfaces between the dam and foundation, and between dam earth and concrete buildings. The seeping streamsform a free water surface inside the dam. Under the surface, all the earth body is saturated. Dipped in the water, the earth become lighter in e
12、ffect. And its angle of internal friction is narrowed, and cohesive force weakened. With the hydrodynamic pressure from the seeping steams, more sliding of dam slopes is possible. When seeping steamsmove insoil,the dam body and foundation will be deformed from too steep hydraulic gradient.Sometimes
13、the dam even crashes.Scour effectIts anti-scour ability is weak because the cohesive force between earth granules is small. On the one hand, the rain water enters the dam and lower the stability of the dam, and on the other hand, the rain scour the dam surface along the slope. At the same time, the
14、waves inside the reservoir also wash out the dam surface, putting the surface in the risk of being damaged. Sometime,landslide even happens due to this.So effective protecting measures have to be taken for dam slopes both upstream and downstream.Sinking effectThe dam body and foundation will sink un
15、der their self weight and water load besides the space between earth granules. If it sinks too much, the elevation level will not be sufficient, and then the operation of the dam will be affected. And, too much uneven sinkage will cause fracture of the dam boday, and even a seepage passage, putting
16、the dam at risk.Other effectsIn freezing regions, an ice-covered layer will be formed over the reservoir when the temperature is below 0 degree. Then the bank slope and dam slope will be frozen together with the ice. When the ice expands, slopes will be pressed. In this way, the protecting slopes wi
17、ll be damaged. Besides, the clay above the water level will have holes and cracks effected by freezing and thawing. In summer, with water lost, the clay will cracked, making seepage much easier.Earthquakes have to be taken into account. They can make landslide more possible. If the foundation is mad
18、e of silty sand, liquidified damage is more possible.Materials for building earth and rock damObtaining raw material locally is a basic design principle. Generally speaking, familiar earth and rock materials can be used. exceptions include swampy soil, bentonite, surface soil, and other soil materia
19、ls containing organic matter not completely decomposed. therefore, dam type is often determined based on availability of earth and rock materials nearby the site. stockyard must be rich in storage and near in distance. As for the selection, technical and economic factors will be considered. The dam
20、bodyis mainly made up of dam shell, antiseepage, drainage, and protection slope. They work under different conditions, so they demand differently. Materials must be durable and suitable to their purpose.Antiseepage and structure of dam crestSeepage-proofing work for a dam must be based on structural
21、 and constructing requirements, reducing seepage gradient, down-stream saturation line, and seepage to an allowance extent. We can use terrene seepage-proofting materials andartificial materials including asphalt concrete and reinforced concrete. terrene materials are more used. Road is built on cre
22、st. If traffic is necessary, road has to be built based on relevant standard. If traffic is not anticipated, single-layer masonry or gravels is sufficient for resisting rain scouring. anti-wave wall is built upstream, and railings are built downstream. the wall, usually 1 to 1.3 meters high, is buil
23、t with stone masonry or reinforcing concrete.its foundation must be firmly buried in the dam, protruding into anti-seepage. For the sake of rain, the road on the crest is usually built with slopes on one side or on both sides. When there is a anti-wave wall, the slope is towards downstream, and ther
24、e will be a lengthways drainage downstream the dam crest for gathering water. The water will go downstream through drainage.Dam slopeInfluencing dam stability and construction directly, dam slope is determined by dam type, dam height, dam scale, material of dam body and foundation, load tobear, and
25、conditions for construction and operation. Generally speaking, dam slope is initially designed according to projects completed. Then a proper section is decided after calculation in terms of stability. To slopes made of sand and soil in a rolled dam, their gradient is between 1:2 and 1:4. Fordam fou
26、ndation which is weaker, the gradient should be slow.For slope design, we have to consider the shearing strength which of earth will be reduced due to being soaked in up-stream water. So if the upstream and downstream slopes are made of same earth materials, the former one has to be slow. for earth
27、dams with inclined soil walls, their upstream slopes are slower than those of core dams, and their downstream slopes are steeper than those of core dams. for homogeneous dams of sandy loam and loam, their slopes are slower than those of dams made of sand and gravels. slopes of homogeneous dams made
28、of cohesive soil have something to do with dam height. The higher the dam is, the slower the slope is. however, gradients of dam slopes made of sand or gravel have little to do with dam height.Generally, there is a road on downstream slope every 10 to 30 meters. When gradients changes, the road will
29、 be at the changing line. the road width is determined by its purposes, but never less than 1.5 to 2.0 meters. drainage ditches are built on road for collecting rainwater, resisting wash, observing, repairing, and traffic.Slope protectionFor earth and rock dams, there must be protection upstream and
30、 downstream. For upstream, damages caused by wave scouring, damwisestream scouring,ice, and floater must be avoided. For downstream of homogeneous dams, damages caused by rain scouring, storm, ice,stream, animal, swelling, and mud crack must be avoided.If there are rocks, cobbles, and gravels downst
31、ream, no more protection is needed. Revetments must be sturdy and durable, able to resist damages caused by various factors. Their undercourse must not be scoured. Materials should be used as local as possible to lower the cost. Simple construction and convenient repairing should be guaranteed. Rock
32、s, stonework, concrete, reinforced concrete, and asphalt concrete are used for building revetments upstream, and stonework, rocks, gravels, and turfs are used for those downstream. Revetments protect the space from dam crest to the line a certain distance, normally2.5m, under the minimum water level
33、 of the dam upstream. For those downstream, they protect the space from dam crest to draining prism or to dam heel in event of no prism.概述土石坝又称“当地材料坝”，主要由坝址附近的土石料填筑而成，根据坝体所用材料不同又可分为土坝和堆石坝。坝体材料以当地土料和砂、砂砾、卵砾为主的称土坝，以石渣、卵石、爆破石料为主的称堆石坝。 土石坝的特点优点筑坝材料就地取材。可节省大量钢材、水泥、木材等建筑材料。适应地基变形能力强。土石坝散粒体结构具有适应地基变形的良好条件，
34、对地基的要求比混凝土坝低。施工方法选择灵活性大。能适应不同的施工方法，从简单的人工填筑到高度机械化施工都可以；且工序简单、施工速度快，质量也易保证。结构简单。造价低廉、运行管理方便、工作可靠，便于维修加高。缺点坝顶不能溢流，常须另开溢洪道施工。导流不如混凝土坝方便，因而相应增加了工程造价坝体断面大，土料填筑的质量易受气候影响。这给施工带来困难，甚至延长工期、增加造价。土石坝的类型土石坝按施工方法的不同可分为：碾压式土石坝，抛填式堆石坝，定向爆破堆石坝，水中倒土坝和水力冲填坝等。其中尤以碾压式土石坝应用最广。按土料在坝体中配置和防渗体的位置不同，又可分为均质坝，分区坝，人工防渗材料坝。均质坝优点
35、：材料单一、工序简单；缺点：坝坡较缓、剖面大，受气候限制，坝体孔隙水压力大，高坝很少采用。分区坝分心墙坝、斜墙坝等，前者优点：土料占总方量比重不大，施工受季节影响小。缺点：心墙与坝体大体要同时填筑，相互干扰。后者优点：与坝体施工干扰小。缺点：抗震性能和适应不均匀沉陷的能力不如前者。人工防渗材料坝的防渗体由沥青混凝土、钢筋混凝土或其他人工材料组成，其余部分由土石料筑成。其中防渗体在上游的称为斜墙坝（面板坝），在坝体中央的称为心墙坝。工作条件梯形剖面土石坝是由松散颗粒土石料填筑碾压而成的挡水建筑物。由于土粒间的抗剪强度小，上下游坡如不维持一定的坡度，就可能发生坍塌现象。所以，土石坝的剖面一般呈梯形
36、。失稳的形式则是坝坡滑动或坝坡连同地基一起滑动的剪切破坏，这是与其他建筑物的不同之处.渗流影响土坝挡水后，由于坝体断面较大，除坝基有水平软弱夹层外，产生整体滑动的可能性较小。但在上下游水位的作用下，水流经过坝身及坝基（包括两岸）的结合面和坝体土与混凝土等建筑物的结合面易产生渗漏。渗流在坝体内形成自由水面，浸润线以下的土体全部处于饱和状态。饱和区的土体受水的浸泡而使土的有效重量减轻，并使土的内摩擦角和粘结力减小。同时，渗透水流对土体还有动水压力的作用，这些力增加了坝坡滑动的可能性。渗透水流在土壤中运动时，如渗透坡降超过允许渗透坡降，还会引起坝体和坝基的渗透变形，严重时会导致坝的失事。冲刷影响由于
37、土料颗粒间的粘结力很小，因此土石坝抗冲能力较低。雨水一方面侵入坝内降低坝的稳定性，另一方面将沿坝坡面下流而冲刷坝面；库内风浪对坝面也将产生冲击和淘刷作用，使坝面容易受到破坏，甚至滑坡。因此，上下游坝坡均需采取有效的保护措施。沉陷影响待添加的隐藏文字内容1由于土料间存在孔隙，在坝体自重和水荷载作用下，坝体和地基（土基）都会由于压缩而产生沉陷。沉陷量过大会造成坝顶高程不足而影响坝的正常工作；过大的不均匀沉陷量还会引起坝体开裂，甚至造成渗水通道而威胁大坝安全。其它影响在严寒地区，当气温低于零度时，库水面结冰形成冰盖层。当岸坡及坝坡冻结在一起，冰层的膨胀，对坝坡产生很大冰压力，易导致护坡的破坏。位于水
38、位以上的坝体粘土，在冻融作用下会造成孔穴、裂缝。在夏季，由于含水量的损失，上述土壤也可能干裂引起集中渗流。在地震区筑坝，还应考虑地震影响。地震的作用增加坝坡坍滑的可能性。粉沙地基在强烈振动作用下还容易引起液化破坏。土石坝的筑坝材料就地取材是土石坝设计的基本原则。一般而言，常见的土石料（沼泽土、斑脱土、地表土及含有未完全分解有机质的土料除外）均可用作筑坝材料。因此，应根据坝址附近土石料的具体条件选择坝型。土石料场的选择宜储量充足，以近为原则，具体选用须通过技术经济比较而定。土石坝坝体主要由坝壳、防渗体、排水设备、护坡等组成。由于他们工作条件不同，因而对材料的要求也不同。筑坝材料应具有与其使用目的
39、相适应的工程特性，并具有较好的长期稳定性。坝的防渗体和坝顶构造坝的防渗体必须满足将渗透坡降、下游坝体浸润线及渗流量降低到允许范围内，还要满足结构上和施工上的要求。作为坝的防渗体的材料有土质防渗体，人工材料（沥青混凝土，钢筋混凝土），其中用的最多的是土质防渗体。在坝顶应该设路面，如坝顶有交通要求，则应按道路要求设计，如没有交通要求，则可用单层砌石或砾石护面以防雨水冲蚀。坝顶上游侧通常设防浪墙，下游侧设拦杆。防浪墙高度通常为11.3米。用浆砌石或钢筋混凝土筑成。墙的基础应牢固地埋入坝内，伸入防渗体内。为排除雨水坝顶路面通常向两侧或一侧做13%的斜坡。有防浪墙时坡向下游，并在坝顶下游侧设纵向排水沟，
40、以便汇集雨水，经坡面排水沟排至下游。坝坡土石坝坝坡对坝的稳定和工程有着直接的影响，主要取决于坝型、坝高、坝的等级、坝体及坝基的材料性质、所承受的荷载、施工和运用条件等因素。一般先参照已建工程的实践经验或用近似方法初步拟定坝坡，然后进行稳定计算、确定合理的坝体断面。对碾压式土坝砂、壤土类坝坡，其平均坡度一般在1：2.01：4.0左右。当坝基较为软弱时还需适当放缓。在拟定坝坡时，应考虑到上游坝坡长期浸泡于水中，土的抗剪强度降低。所以当采用相同土料时坝的上游坡比下流坡要缓；在一般情况下土质斜墙坝的上游坡比心墙坝缓，而下游坡则可比心墙坝陡些；砂壤土、壤土的均质坝坡比砂或砂砾料的坝坡缓些；粘性土均质坝的
41、坝坡与坝高有一定关系，其高度越大，坝坡越缓。砂或砂料坝体的坝坡与坝高的关系则很小。一般坝的下游坡每隔10至30米设置一条马道。当坝的坡度自上到下有变化时，马道则设在变坡处。马道的宽度视其用途而定，但其最小宽度不得小于1.5到2.0米。马道上设置排水沟以汇集雨水防止冲刷，还可用于观测、检修和交通。护坡土石坝的上、下游坝面一般都要设置护坡。上游护坡的作用是为防止波浪淘刷、冰层和漂浮物的损害、顺坝水流冲刷等危害；均质坝下游护坡的作用是防止雨水冲刷，风浪、冰层和水流作用，动物、冻胀干裂等对坝坡的破坏。如下游坡由堆石、卵石、碎石砌成，可不设护坡。对上下游护坡的要求是坚固耐久，能抵抗各种因素的破坏作用，并保证底层不受淘刷。尽可能就地取材，以降低造价。施工简单，维修方便。上游护坡的型式有：堆石护坡、砌石护坡、混凝土或钢筋混凝土护坡、沥青混凝土护坡；下游护坡的型式有：砌石、堆石、碎石和草皮护坡。护坡覆盖的范围，上游由坝顶护至水库最低水位以下一定距离，一般在最低水位以下2.5米。下游面则由坝顶护至排水棱体，无排水棱体时则护至坝脚。
