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土石坝(earth and rock dam)

(2011-03-09 16:44:07)
标签:

饱和区

土石坝

坝体

坝坡

土料

分类: 工程学习

第一章 概述summary

 

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

Earth 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, and exploded rocks.

 

一、土石坝的特点features of earth and rock dam)

优点strong points

1、筑坝材料就地取材。可节省大量钢材、水泥、木材等建筑材料。With convenient supply of materials, many building materials such as steel, cement, and timbers can be saved.

2、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,对地基的要求比混凝土坝低。With granular structure more suitable to foundation deformation, it demands less on the foundation.

3、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。Very flexible from simple artificial filling to highly mechanized construction, the procedure become simple, the construction become efficient, and the quality guarantee become easy.

4、结构简单。造价低廉、运行管理方便、工作可靠,便于维修加高。Simply structured, the cost is low, the operation is convenient, works is reliable, and maintenance and height adding is convient.

缺点weak points

1、坝顶不能溢流,常须另开溢洪道Overflow not allowed, spillway has to be built.

2、施工导流不如混凝土坝方便,因而相应增加了工程造价Diversion less convenient, cost increases

3、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 increase

 

二、土石坝的工作条件Working conditions

1、梯形剖面Trapeziform section 

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。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。

Earth-rock dam is a water retaining structure built with loose granules of earth and rocks filled and roller compacted. With weaker strength between these granules, both upsteam and downsteam slopes have to be kept at a certain degree to avoid landslide. So the dam section is usually trapeziform. It can be destablized in two ways, simple slope sliding and sametime sliding of slope and foundation caused by shear damage. It's a difference from other structures.

2、渗流影响seepage effects

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。With a large section, the dam is generally kept from entire sliding unless caused by weak interlayers.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。effected by water levels at the upsteam and downsteam, seepage is easy to happen with streams passing the  faying surfaces between the dam and foundation, and between dam earth and concrete buildings.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。The seeping streams form 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 effect. And its angle of internal friction is narrowed, and  cohesive force weakened.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。With the hydrodynamic pressure from the seeping steams, more sliding of dam slopes is possible.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。When seeping steams move in soil, the dam body and foundation will be deformed from too steep hydraulic gradient.  Sometimes the dam even crashes.

3、冲刷影响 scour effect

由于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。

Its 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 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.

4、沉陷影响sinking effect

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。

The dam body and foundation will sink under 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 the dam at risk.

5、其它影响other effects

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。

In 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 will 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.

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。

Earthquakes have to be taken into account. They can make landslide more possible. If the foundation is made of silty sand, liquidified damage is more possible.

 

三、设计和建造土石坝的原则要求Principals for earth and rock dam designing and building

(一)不允许水流漫顶Avoid overtopping

设计时由于对洪水估计偏低,坝顶高程不足,溢洪道尺寸偏小,或水库控制运用不当等,都会造成土石坝漫顶溃坝的严重事故。Flood underevaluation at design phase will result in lower elevated level of the dam crest,  smaller-size spillway, or improper reservoir control. All these may cause the serious accident of overtopping failure.因此在土石坝枢纽中应设置容量足够大的泄水建筑物,绝对不允许洪水漫顶。So a discharge structure of sufficient size must be built for an earth and rock dam in order to absolutely avoid overtopping failure.设计中,要充分估计水库风浪及坝的沉陷值,预留足够的超高。Scale of wind waves and degree of dam sinking have to be fully evaluated for design. Enough extra height has to be built. 库区滑坡要查勘清楚,滑坡体在水库内坍滑产生的涌浪对土石坝极为不利。Surges in the reservoir caused by sliding slopes extremely go evil for the earth and rock dam, so relevant survey have to be very careful. 除了对设计标准洪水有足够的泄洪建筑物外,对于可能发生的特殊洪水,也应有应急的泄洪保坝措施。Beside emergency protection measures must be made for special floods possible to happen.

(二)满足渗流控制要求Satisfy seepage control

土石坝蓄水后,一般都会在坝体和坝基中形成渗流,有时还会有绕坝渗漏,若不进行有效的控制,将会引起多方面的问题。渗流量过大,影响水库效益;坝体和坝基产生危害性渗透变形,导致大坝失事。浸润线高,也会降低坝的稳定性。为此,应特别注意土石坝防渗体的合理设计,并保证其施工质量。加强坝与地基、岸坡或其他建筑物的连接,合理布置排水及反滤设施,以避免事故的发生。Seepage will appear in dam body and foundation after water is retained. Without effective control, many problems will happen. If it's too much, the benefit from the reservoir will be less. If pernicious deformation occurs, dam failure will be caused. If the soakage line is too high, the dam will become less stable. So attention has to be paid to reseasonable design of anti-seepage and construction quality. Connection between dam, foundation, bank slopes and other structures has to be strengthened, and drainage and anti-filtering facilities have to be properly arranged to avoid accident mentioned above.   

(三)坝体坝基稳定可靠Stability and reliability of dam body and its foundation

土石坝为散粒体结构,局部范围内土体的抗剪强度不足时,土体开始滑动。因此应有足够的断面维持坝坡的稳定。With loose granule formed structures, the earth body of the dam will slide when its shear strength is not sufficient. So a section of sufficient size shall be built for stablize the slope.

边坡稳定是坝安全的基本保证。Stable side slopes are basic guarantee of the security of the dam.

据统计,过去失事的土石坝中1/4是由于滑坡破坏造成的。如何结合土石坝的类型、材料、构造、选择适宜的坝坡,使之既能保持稳定又最为经济,是土石坝设计的主要内容。

As reported by statistics, one fourth of the earth and rock dams crashed in the past were caused by damaged slopes. So it's a major part of the designing job for ensuring the stability and costeffectiveness while taking into account types, materials, structures, and slopes of dams.

(四)土石坝须能抵抗其它自然界的破坏作用Resisting other bad natural effects

库水风浪将淘刷坝坡;雨水冲刷坝体;冬季冰冻膨胀影响产生裂缝;夏季日晒龟裂;南方有些省份还有白蚁蛀空坝脚等等。对这些不利因素都应采取防护措施。

Waves in the reservoir will wash out slopes. Rain will scour the dam body. Cracks will appear due to winter expansion or summer solarization. In the south, white ants can hollow the dam heel. So precautions have to be taken to avoid these disadvantages.

 

四、土石坝的类型Earth & rock dam types

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。Based on constructing ways, earth and rock dams can be classified into rolled ones of earth & rock, thrown rock-filled ones, rock-filled ones with directional detonation, ones with earth thrown into the water, and ones filled by hydraulic forces. Among them, rolled ones are most popular.

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。Based on the earth proportion and the location of anti-seepage parts, there are homogeneous (even-granular) dams,  zoned earth dams, and dams with artificial anti-seepage materials.

均质坝优点: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

Strong points of homogeneous dams: one fold materials, simple process

weak points: flat gradient, large section, weather-limited, strong water pressure in holes.

分区坝分心墙坝、斜墙坝等,Zoned dams are classified into ones with core anti-seepage and ones with front anti-seepage

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。

Less amount of earth, less affect of season. interfering with the filling of the dam body.

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。

Less interference with the construction of the dam body. weaker anti-earthquake and uneven sinking

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。

The anti-seepage parts of dams with 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.

 

第二节 土石坝的剖面和构造Sections and structures of earth & rock-filled dams

 

土石坝的设计,首先是根据坝址附近土石料的分布情况(种类、数量、运距)及地形地质条件选定合适的坝型。其次拟定坝的基本尺寸,包括坝坡、坝顶高程、坝顶宽度以及防渗体及排水设备、护坡等的尺寸,使之满足土石坝的工作要求。然后进行必要的计算较核,并根据其结果进一步修正原设计尺寸与构造,使之达到既安全又经济的目的。

Before designing the dam, you have to consider the accessibility for earth and rocks materials, what kinds, how many, and how far, and topographical and geological conditions. Then, you can decide the basic sizes, including those of slope, crest el, crest width, anti-seepage, drainage, protecting slope, and etc. Finally, you have to make necessary calculations and checks after which further modifications have to be done for safety and economy.

 

一、土石坝剖面的基本尺寸Basic size of dam section

 

(一)坝顶高程(dam crest height)

坝顶高程由水库静水位加波浪爬高及安全超高决定。坝顶在静水位以上的超高按下式计算。

The dam crest height is determined based on static water level, wave run-up, and freeboard. The freeboard is calculated according to the following formula

水库静水位以上的超高(d)=波浪在坝坡上的爬高(hB)+坝前静水位因风浪引起的涌高(e)+安全超高(a,按坝的等级给值)

 

波浪要素涉及以下几个因素:风速,吹程,坝前水深,风向与坝轴线法线方向的夹角,波高,上游面坡角,坝坡护面粗糙系数。

wave factors can be considered through velocity, distance of wind stretch, water depth, normal-inclined angle between wind and axis, wave height, upstream slope, and roughness coefficient of slope surface 

 

坝顶高程要分别计算正常情况和非常情况,得出两个坝顶高程计算值后取大值。

There are two crest heights under normal and abnormal conditions. We choose the bigger one.

 

(二)坝顶宽度crest width

 

坝顶宽度与坝的稳定没有直接的关系,主要取决于构造、交通、施工及运行等要求。

Irrelvant to dam stability, crest width is determined as required by structure, traffic, construction, and operation.

一般坝高小于100米时,坝顶最小宽度采用下式Bmin=0.1H,坝高大于100米时,采用Bmin=H的开方

Minimum width of dam crest should be one tenth of the height below 100 meters, or evolution of the height above 100.

 

(三)坝坡dam slope

 

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1:2.0~1:4.0左右。当坝基较为软弱时还需适当放缓。

Influencing dam stability and construction directly, dam slope is determined by dam type, dam height, dam scale, material of dam body and foundation, load to bear, and 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. For dam foundation which is weaker, the gradient should be slow.

 

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。

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 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 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.  

 

一般坝的下游坡每隔10~30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1.5~2.0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。

generally, there is a road on downstream slope every 10 to 30 meters. When gradients changes, the road will be at the changing line. the road width is determined by its purposes, but never less than 1.5~2.0 meters. drainage ditches are built on road for collecting rainwater, resisting wash, observing, repairing, and traffic.

 

二、坝的防渗体antiseepage

 

 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。

seepage-proofing work for a dam must be based on structural and constructing requirements, reducing seepage gradient, down-stream saturation line, and seepage to an allowance extent.

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。

We can use terrene seepage-proofting materials and artificial materials including asphalt concrete and reinforced concrete. terrene materials are more used.

 

(一)土质防渗体terrene seepage-proofing materials

1、土质心墙terrene core wall

心墙顶部在静水位以上的超高,正常运用时为0.3~0.6米,非常运用时则不低于校核洪水位。

the height of core wall crest above the static water shall be normally 0.3~0.6 meters, and never lower than  the flood level determined.

心墙的顶宽考虑到机械施工的可能不应小于2.0米。心墙的两侧的边坡一般在1:0.15~1:0.30之间。

for mechanical works, the core wall should have a crest no less than 2 meters wide, and have two side slopes with gradients between 0.15~0.30.

防渗体底部的厚度,取决于土料的允许渗透起降,采用粘土,重壤土时,心墙底厚不应小于H/4,且不应小于3米,其中H为作用水头。

the thickness of seepage-proofing base is determined by soil-allowed gradient. For loam and heavy loam, the thickness should be no less than H/4 or 3 meters. H is effective waterhead.

心墙顶面必须设砂砾保护层,其厚度不小于当地冰冻和干燥厚度,且不小于1.0米。心墙与地基及岸坡必须有可靠的结合,防止结合面漏水和产生集中渗流。心墙与岸坡拼命处常需加大心墙剖面。

for crest surface of the core wall, there has to be a protecting layer made of sand gravel no thinner than local frozen and drying thickness or 1 meters. there has to be reliable combination between core wall and foundation and bank slopes to avoid leakage and concentrated seepage at faying surfaces. core wall sections have to be enlarged where core wall and bank slopes are joined.

 

2.土质斜墙terrene inclined wall

斜墙顶部在静水位以上的超高,正常运用情况时为0.6~0.8米,非常运用时不低于校核洪水位。

crest superelevation above the static level must normally be 0.6~0.8 meters, and never lower than flood level proved.

斜墙的顶厚(垂直于斜墙上游面的厚度)不小于2.0米。

crest vertical to upstream water surface shall be no thinner than 2 meters.

斜墙底部的厚度应满足允许渗透坡降的要求,一般要求不小于水头的1/5.为防止斜墙断裂,其厚度常比按渗透稳定条件确定的数值大。

foundation shall be no thinner than H/5, satisfying demands for seepage gradient. the thickness always exceed the one determined based on stable conditions for preventing wall crashing.

斜墙上游应设置保护层以防止冰冻和机械破坏。保护层材料可为砂砾,卵石,块石,其厚度不得小于当地冰冻及干燥深度,且不小于1.0米,一般取1.5~2.5米。保护层应分层碾压填筑,达到坝体相同标准。其外坡坡度应按稳定计算确定,使保护层不致沿斜面或连同斜墙一起滑动。

protecting layers have to be built upstream for preventing damages caused by freezing and in mechanical terms. materials can be used such as sand gravel,cobble, and block stones. the layers shall be no thinner than local depth to be frozen and dried or 1 meters, generally 1.5~2.5 meters. the layers shall be rolled and filled one layer by one layer to the standards of the dam boday. outside slope's gradient shall be determined based on stability calculation avoiding sliding with inclined core along the inclined plane.

3.铺盖seepage control bedding

铺盖与斜墙相连,铺盖由粘土或壤土做成,一般要求地基与铺盖土料渗透系数之比至少在1000以上。铺盖应铺成不等厚的,由上游向下游逐渐加厚,具体数值由土料的允许渗透坡降而定。前端厚度由于构造要求应不小于0.5米,一般采用1.0米。末端与斜墙连接处的厚度不小于3~5米。两端通常做小槽嵌入地基中,铺盖长度一般为水头的4~6倍。填筑铺盖前必须清基,在砂卵石地基上应设置过渡层,以防渗透破坏,顶面应设保护层。

Bedding is made of clay or loam. It is joined to inclined core. The ratio of foundation soil permeability to that of bedding is no less than 1000 to 1. Thickness of bedding at different places is different. It is gradually thickening from upstream to downstream. Thickness values are determined by permeability gradient allowed by soil. Front end is no thinner than 0.5 meters as required by structure, normally 1.0 meters. Tail end is no thinner than 3~5 meters, where bedding is joined to inclined core. The two ends are embedded in foundation with small sinks. Bedding's length is normally 4 ~6 times of waterhead. foundation clearance is done before bedding filling. For cobble stone made foundation, a transition layer is built to avoid infiltation. The surface has a protecting layer.

4.斜心墙inclined soil core

它介于心墙与斜墙之间,即心墙略向上游倾斜.这种坝是为了克服心墙坝可能产生拱效应和斜墙坝对变形敏感等不足而发展起来的。它很适合于高土石坝。斜心墙倾斜度对心墙的应力影响很大。防渗体结构尺寸要求与心墙和斜墙类似。

Inclined soil core is between the place where core wall should be and the place where inclined wall should be. It is slightly closer to upstream. It's developed for overcoming core wall-caused arching effect and inclined wall's sensibility to deformation. It suits high earth-rock dam very much. Its inclination has a great influence upon its stress. As for the structure and size of the antiseepage, the requirements are similar to those by core walls and inclined walls.

 

(二)沥青混凝土防渗体asphalt concrete antiseepage

沥青混凝土有较好的柔性和塑性,渗透系数10~7-10~10cm/s。因此,防渗性及变形适应的能力均较好。当产生裂缝时,尚有自行愈合的性能,而且施工简单、造价低廉,因此得到广泛应用。沥青混凝土防渗体有心墙和斜墙两种基本的类型。这种防渗体在堆石坝中应用较广。

Asphalt concrete has good flexibility and plastic. Its permeability coefficient is between 10~7 and 10~10cm/s. So it's good both in anti-seepage and deformation suitability. When cracks appear, they are able to close up automatically. Besides, construction is simple, cost is low, so it's widely used. For asphalt concrete antiseepage, there are two basic types, one is core wall, and the other inclined wall. This kind of antiseepage is widely used in rockfill dam.

 

三、坝体排水设备drainage inside

排水设备是土石坝的一个重要组成部分。主要目的是:(1)防止渗流逸出处的渗透变形;(2)降低坝体浸润线及孔隙渗流方向,增加坝体稳定;(3)保护坝坡,防止冻胀破坏。坝体排水设备须保证充分的排水能力。能自由地向下游排出全部渗水,同时应按排水反滤原则设计,保证坝体及地基土不发生渗透破坏。坝体排水设备的型式与坝型、下游水位、材料及施工条件及筑坝地区的气候条件等因素有关,应通过技术经济比较确定。主要型式有棱体排水、贴坡排水、褥垫排水和综合式排水等。

As a critical component of the earth and rock dam, the drainage is aimed to (1)avoid seepage-caused deformation where seepage occurs; (2)stabilize the dam by lowering seepage line and between-hole seeping direction; (3) protect dam slope and avoid damages caused by freezing expansion. Drainage must possess sufficient capability. It must be able to freely drain  downstream all creepage. At the same time, it must be designed based on inverted filter principles, guaranteeing that dam and foundation are not damnaged by seepage. As for its type, dam type, downstream water level, material, construction conditions, climate and other factors have to be taken into account. Drainage type must be determined after technical and economic comparison. There are drainage prism, drain on embankment slope, blanket drainage and comprehensive drainage.

(一)棱体排水drainage prism

在坝脚处用块石堆筑而成。棱体排水设备适于下游有水的情况,能降低坝体浸润线、防止坝坡冻胀和渗透变形,保护下游坝脚,且有支持坝体增加稳定的作用,是一种可靠的排水型式。

It's built by piled block stones at dam heel. It's applied to those that have water downstream. It can lower the saturation line, avoid freezing expansion and seepage-caused deformation, protect downstream dam heel, help stablize dam. It's a reliable way of drainage.

棱体排水的顶部高程应超出下游最高水位,应大于波浪沿坡面的爬高,且不小于下列0.5米。

Its top elevated level must exceed the highest water level downstream, be higher than the wave runup along the slope, and be no less than 0.5 meters.

棱体顶部高程应保证坝体浸润线距坡面的距离大于该地区的冻结深度。顶部宽度应根据施工条件及检查观测需要确定,且不得小于1.0米。棱体排水一般不作道路用,以免排水堵塞。棱体内坡根据施工条件确定,约为1:1.0~1:1.5.外坡一般为1:1.5~1:2.0.在排水与坝体及坝基之间应设反滤层。

For the prism's top elevated length, the distance between the saturation line and the slope must be bigger than local freezing depth. The top must be no narrower than 1 meter and be determined based on construction conditions and inspection requirements. Generally speaking, the prism is not used as road to avoid stems. As determined by construction conditions, the inner slope's gradient is about 1:1.0~1:1.5, the outside slope's gradient is about 1:1.5~1:2.0. Between the drainage, dam body, and foundation, there must be anti-filter layers.

(二)贴坡排水(drainage on embankment slope)

贴坡排水又称表层排水。排水设在下游坝坡底部,由1~2层堆石或砌石筑成。在石块与坝坡间应设反滤层。这种排水结构简单、省料且便于检修,可防止渗透破坏,保护下游坝脚。但因未伸入坝体,不能降低浸润线,且防冻性较差,常用于中小型水库且下游无水的均质坝,以及有良好防渗体、坝体浸润线较低的中等高度的土石坝。

Also known as surface drainage, it is built at the bottom of dam slope downstream, and made of 1~2 layers of piled stones and stone masonry. Anti-filter layers are built by blocks and dam slopes. Drainage in this way has simple structure, saves materials, and provide conveniences for repairing. So it can prevent seepage-caused damages and protect dam heel downstream. However, it doesn't enter the dam body, the saturation line can't be lowered, and anti-freezing ability is poor. So it is often used in mdeium and small-sized reservoir, homegeneous dam without water downstream, and earth-rock dam of medium height with good antiseepage and low saturation line.

贴坡排水层的顶部应高于坝体浸润线的逸出点,超出的高度务使坝体浸润线位于该地区冻结深度以下,且不小于1.5米。

Its top must be higher than dam saturation line's exit point, and the extent exceeded must ensure the saturation line is no less than 1.5 meters below local freezing depth.

贴坡排水层的底脚处必须设置排水沟或排水体,其深度或厚度应使水面结冰后,排水沟(排水体)的下部仍有足够的排水断面。当下游有水时,应同时满足护坡稳定的要求。

At the foot of the drainage on embankment slope, there must be a drain, the depth and thickness of which must guarantee enough draining section when the surface is frozen. In event of water downstream, the protecting slope's stability must be guaranteed.

 

(三)褥垫排水(mattress drainage)

将排水体平铺在坝下游的部分地基上,形似褥垫,故名。伸入坝体的长度一般不超过1/3~1/4坝底宽度,向下游做成0.005~0.01的坡度以利排水。

Drain tiled on downstream of a dam is like a mattress, so came the name. It enters the dam body less than 1/3~1/4 the width of the dam. Its slope gradient toward downstream is 0.005~0.01 for easier drainage.

这种排水体伸入坝体内部,降低浸润线效果显著,有利于坝基排水。但对地基不均匀沉陷的适应能力较差,易断裂。而且检修也比较困难,只适用于下游无水或下游水位很低的情况。

Entering the dam, the mattress lowers the soaking line obviously for the good of foundation drainage. Yet, it can't be well adapted to the uneven sinking of foundation, easy to be broken. What's more, repairing is a problem except when there is no water downstream or the water level downstream is very low.

 

(四)综合式排水(Drainage in a comprehensive way)

实际工程中常将几种排水型组合应用,兼有各种排水的优点。

In construction, those ways above are always combined.

 

四、护坡Slope protection

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。

For earth and rock dams, there must be protection upstream and downstream. For upstream, damages caused by wave scouring, damwise stream 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 downstream, no more protection is needed.

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。

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.

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。

rocks, stonework, concrete, reinforced concrete, and asphalt concrete are used for building revetments upstream, and stonework, rocks, gravels, and turfs are used for those downstream.

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。

Revetments protect the space from dam crest to the line a certain distance, normally 2.5m, under the minimum water level 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.

 

(一)砌石护坡(masonry protection)

砌石护坡由人工将块石铺砌而成,是土石坝中采用最多的一种。石块应力求紧密嵌紧,砌石所用石块要求质地坚硬、耐风化。石块的大小应根据风浪大小计算决定,单层厚约0.3~0.35米,双层厚约0.4~0.6米。砌石下设碎石或砾石垫层以防水流淘刷。垫层厚一般为0.15~0.25米,有时需铺2~3层。

This kind of protection is made by paving stones. It's most used in earth and rock dam. stones must be closely embedded. stones used must be hard  and effloresce-resisting. as for the size, it should be determined based on the result of calculating waves. For single layers, it should be about 0.3~0.35 meters thick, and for double layers, it should be 0.4 ~0.6 meters thick. Under the stone, there must be gravels for resisting scouring. the gravels layer is generally 0.15~0.25meters. sometimes, two to three layers are needed.

根据我国的经验,当水库波浪较大时(浪高大于2.0米),可在砌石护坡上用水泥砂浆或细骨料混凝土填缝,以形成整体提高抗冲能力,但要留一定的缝隙或排水孔,以便排水。

For better resisting scouring in case of strong waves, cement mortar or fine aggregate concrete can be used for caulking. Yet, some scuppers must be left for drainage.

 

(二)堆石护坡(protection with dumped stones)

将适当级配的石块直接倾倒在坝面垫层上而成,不加人工铺砌。因堆石抵抗风浪能力低于砌石,所以厚度要大于砌石护坡,堆石护坡的厚度一般约0.5~0.9米。下面设厚度约0.4~0.5米的砂砾石垫层。

This kind of protection is achieved by directly dumping stone of proper gradations on the cushion. No artificial paving is needed. Considering these stones are weaker than masonry in resisting waves, their thickness is bigger, normally 0.5 to 0.9 meters. Under them are a cushion of gravels 0.4 to 0.5 meters thick.

 

(三)其它型式的护坡(protection of other types)

当坝址缺少石料或风浪过大,块石护坡不足以抵御风浪时可以采用混凝土或钢筋混凝土护坡。既可以就地浇筑,也可以预制。混凝土板下应设厚度不小于0.15~0.20米的碎石或砾石垫层,粒径一般为2~8mm,也可采用沥青混凝土。

In case of lack in stones and strong waves, block stones are not enough for resist waves. Now, concrete or reinforcing concrete can be used. Both on-site mould and prefabrication are allowed. Under the concrete plate, there must be a layer of gravels no thinner than 0.15~0.20mm. the gravels' diameters are generally 2~8mm. asphalt concrete can also be used.

在国外,有些土石坝采用水泥土护坡。这种护坡的材料由土、水和水泥混合而成。水泥占干土重的7~15%,用砂壤土或砾质土与水泥拌和。加水10%左右,分层压实。填筑后保持潮湿,养护1~2周。其防冲能力和柔性都较好。

In foreign countries, concrete is used for building protection of earth and rock dam. The material is a mixture of soil, water, and cement. cement is 7~15 percent the weight of dry materials mixed with sandy loam or gravel soil. water added is 10% or so. It is debulked layer by layer. After filled, it is kept humid, and is protected for 1~2 weeks. Its protection effect and flexibility is good.

 

土石坝的下游坡一般可用0.1~0.15米厚的碎石和砾石护坡。在气候适宜地区也可用草皮护坡。

Downstream can be protected with gravels no thinner than 0.1~0.15 meters. If weather allows, turf is used.

 

五、坝顶构造structure of dam crest

坝顶设路面,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。

Road is built on crest. 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.

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1~1.3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1~3%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,以便汇集雨水,经坡面排水沟排至下游。

anti-wave wall is built upstream, and railings are built downstream. the wall, usually 1~1.3 meters high, is built 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 there will be a lengthways drainage downstream the dam crest for gathering water. The water will go downstream through drainage.

 

第三节 土石坝的筑坝材料Materials for building earth and rock dam

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。

Obtaining 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 materials 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.

一、筑坝材料的选择Selection of materials

 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相适应的工程特性,并具有较好的长期稳定性。

The dam body is 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.

(一)防渗体土料soil material for antiseepage

防渗土料在压实后,应具有足够的防渗性能和一定的抗风化能力。高坝心墙土料还应具有低压缩性。一般用于填筑心墙、斜墙和铺盖的土料,其渗透系数k宜小于10-5cm/s,用作均质坝的土料k宜小于10-4cm/s。土料须具有足够的塑性,使之能适应坝体及坝基的变形而不致产生裂缝。土料中水溶盐含量(按重量计)不大于3%。有机质含量,对均质坝不大于5%。对心墙或斜墙不大小2%。土体浸水与失水时体积变化较小,以防止土体发生显著的膨胀与收缩。

After debulked, the material must be strong enough in antiseepage and resisting weathering. For core walls of high dams, its compressibility must be relative low. For core walls, inclined walls, and bedding, its seepage coefficient is normally 10-5cm/s.and for homogeneous dam, its coefficient is smaller than 10-4cm/s. The material must have enough plasticity for avoiding cracks while dam and its foundation become deformed. Water soluable salt must be no more than 3% in weight. Organic matters must be no more than 5% in weight. For core walls and inclined walls, organic matters must be no more than 2% in weight. After soaked or dehydrated, the soil's size must change little for avoiding obvious expansion and constriction.

 一般粘粒含量为15~30%或塑性指数为10~17的中壤土、重壤土及粘粒含量为30~40%或塑性指数为17~20的粘土较合适。塑性指数大于20和液限在于40%的冲积粘土,浸水后膨胀软化较大的粘土,难以压实的干硬性粘土应尽量不用。

Generally speaking, medium loam and heavy loam containing 15~30% of cosmid or with a plasticity index between 10 and 17, or clay containing 30~40% of cosmid or with a plasticity index between 17 and 20 are suitable. alluvial clay with a plasticity index above 20 or a liquid limit above 40%, or clay to be largely expanded and softened after soaked, or dry and hard clay difficult to debulk are not used.

我国南方的残坡积红土或红土状土,具有稳固的团粒结构,虽然粘粒含量很高,天然容重很低、天然含水量高,压实性差,但在较低填筑容量和较高填筑含水量下,仍具有较高的强度、较低压缩性和较小渗透性,耐水性和抗冲刷能力也较好,可用于填筑均质坝和防渗体。但用于高坝时应作必要的技术论证。

Residual laterite or laterite-like soil in South China possess a stable structure of granules. It contains much cosmid, and is low in natural bulk density, high in natural water content, and bad in debulk, but with low filling capacity and high filling water, it is still strong in stength, low in compressibility, little in penetrability, and good in water resistance and scouring resistance, so it can be used in building honogeneous dam and antiseepage. But for high dam, it must be technically testified first.

湿陷性黄土或黄土状土可用于填筑均质坝和防渗体,但需具有适当的填筑含水量与压实密度,使土料的原状结构得到破坏,防止浸水后的湿陷和软化。

Wet-collapsing loess or loess like soil can be used for building homogeneous dam and anti-seepage, but only when their water content and compressibility is proper, for which the soil's original structure will be damaged and wet-collapsing and softening can be avoided after soaked.

国内外有些工程采用砾质粘土或人工加砾粘土作防渗体,收到很好的效果。用作防渗体的砾质粘土应满足:抗渗性能好;大于5mm的粗粒含量不超过50%;其最大粒径一般不超过10~15cm或铺土厚度的2/3,且不得发生粗料集中架空现象。

Sometimes,gravel clay or artificial gravel-added clay are used for building antiseepage. The effect is good. this kind of material must be good in antiseepage. the content of coarse grains larer than 5mm must be no more than 50%. the biggest ones can't be bigger than 10~15cm or 2/3 of the soil layer. Blocks concentration resulting in hollows is not allowed.

必要时,可以采用由粘土和粒状材料(如砂砾石、碎石、凤化料)按一定比例混合的或按设计规定的级配拌和而成的人工掺合料作为防渗体材料。

If necessary, artificial admixture made of clay and particle-shaped materials such as sand gravels, detritus, and weathered material mixed in a certain proportion or of grades as stipulated by design standard.

国内已建成的许多土石坝,防渗体大多采用纯粘性土,由于修建高土石坝,施工时采用重型的压实和运输机具,对防渗体土料的要求有所放宽。

Many earth and rock dams completed mainland use pure clay for building antiseepage. With heavy-duty compacting and transporting machines, even for building high dams, requirments on soil are softened.

 

(二)坝壳土石料(material for dam shell)

土石坝的坝壳材料主要为了保持坝体的稳定性,一般要求有较高的强度。下游坝壳水下部位及上游坝壳水位变动区宜有较高的透水性,且具有抗渗和抗震稳定性。凡粒径级配良好的无粘性土(包括砂、砾石、卵石、漂石、碎石等)以及料场开采的石料和由枢纽建筑物中开挖的石渣料,均可根据其性质用于坝壳的不同部位。均匀的中、细砂及粉砂一般只能应用于坝壳的干燥区,因在地震荷载作用下,用于浸润线以下坝区时易产生震动液化。

Strength of materials is required for building dam shell for the sake of stability. Water permeability is required under water of downstream dam shell and where water level changes upstream dam shell. There antiseepage and anti-quake stabibility are also required. cohesionless soil of good grade in particle diameters including sand, gravel, pebble, boudler, and detritus, and stones mined in stockyard, and rock ballast excavated in complex, all can be used in different parts of dam shell. well-proportioned medium sand, bank sand, and mealy sand can only be used in dry area of dam shell. If used in areas under saturation line, they will be liquidified under quake.

应优先选用不均匀和连续级配的砂石料。一般认为不均匀系数在30~100时较易压实,在5~10以下则压实性能不好。

nonuniformed sandstones of continous grading are preferred. those of nonuniformity coefficient 30~100 are good for debulk, those below 5~10 are bad.

 

(三)排水设备、护坡石料(drainage, stone protection)

排水设备与砌石护坡所用的石料,应有足够的抗水性,不易溶蚀,其软化系数(饱和抗压强度与干抗压程度之比)不小于0.75~0.85.同时还要能抗冻融和风化。块石的饱和抗压程度不小于40~50Mpa,岩石孔隙率不大于3%,吸水率(按孔隙体积比计算)不大于0.8.容重应大于22kN/m3。除块石外,碎石,卵石也可应用,但不宜使用风化岩石。

stones used for drainage and stone protection resist water and chemical denudation well. their inteneration coefficient (ratio of saturated resistance to compression to dry resistance to compression) is no smaller than 0.75~0.85. at the same time, they must resist freeze-thaw and weathering. for block stones, saturated resistance to compresion is no smaller than 40~50Mpa, holes are less than 3%. water absorption is no bigger than 0.8 calculated on the ratio of holes to stone. bulk density is bigger than 22kN/m3. besides block stones, gravels and cobbles can also be used,but weathered rocks are not used.

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