8/7/2019 Embankment dam

http://slidepdf.com/reader/full/embankment-dam 1/3

Embankment dam

From Wikipedia, the free encyclopedia

Jump to: navigation, search

San Luis Dam - Embankment dam

Tarbela Dam, the world's largest embankment dam, in Pakistan

An embankment dam is a massive artificial water barrier . It is typically created by the

emplacement and compaction of a complex semi-plastic mound of various compositions

of soil, sand, clay and/or rock. It has a semi-permanent waterproof natural covering for itssurface, and a dense, waterproof core. This makes such a dam impervious to surface or 

seepage erosion.[1] The force of the impoundment creates a downward thrust upon the

mass of the dam, greatly increasing the weight of the dam on its foundation. This addedforce effectively seals and makes waterproof the underlying foundation of the dam, at the

interface between the dam and its stream bed.[2] Such a dam is composed of fragmented

independent material particles. The friction and interaction of particles binds the particles

together into a stable mass rather than the use of a cementing substance .[3]

Contents

8/7/2019 Embankment dam

http://slidepdf.com/reader/full/embankment-dam 2/3

[hide]

• 1 Types 

• 2 Safety 

• 3 See also 

•

4 Notes 

• 5 External links 

[edit] Types

Pothundi Dam, India

Embankment dams come in two types: the earth-filled dam (also called an earthen dam or 

terrain dam) made of compacted earth, and the rock-filled dam. A cross-sectio of an

embankment dam shows a shape like a bank, or hill. Most have a central section or corecomposed of an impermeable material to stop water from seeping through the dam. The

core can be of clay, concrete or asphalt concrete. This dam type is a good choice for siteswith wide valleys. Since they exert little pressure on their foundations, they can be builton hard rock or softer soils. For a rock-fill dam, rock-fill is blasted using explosives to

break the rock. Additionally, the rock pieces may need to be crushed into smaller chunks

to get the right range of size for use in an embankment dam.[4]

[edit] Safety

The building of a dam and the filling of the reservoir behind it places a new weight on the

floor and sides of a valley. The stress of the water increases linearly with its depth. Water 

also pushes against the upstream face of the dam, a nonrigid structure that under stress

behaves semiplastically, and causes greater need for adjustment (flexibility) near the baseof the dam than at shallower water levels. Thus the stress level of the dam must be

calculated in advance of building to ensure that its break level threshold is not exceeded.[5]

Overtopping or overflow of an embankment dam outside of its spillways will cause

disastrous flooding through the eventual failure of the dam. In the failure process the

sustained hydraulic force and pressure caused by an overtopping surface runoff;

8/7/2019 Embankment dam

http://slidepdf.com/reader/full/embankment-dam 3/3

immediately erodes the dam's material structure as it flows over the top of the dam. Even

a small sustained overtopping surface flow can remove thousands of tons of overburden

soil from the mass of the dam within hours. The removal of this mass unbalances theforces that stabilize the dam against its impoundment. The mass of water still impounded

behind the dam presses against the lighter mass of the embankment, (made lighter by

surface erosion). As the mass of the dam gets lighter, the impoundment begins to movethe whole structure. The embankment, having almost no elastic strength, begins to break 

into separate pieces, naturally allowing the impounded water to flow between them

eroding and removing more material as it goes. In the final stages of failure the remainingpieces of the embankment offer almost no resistance to the flow of the water; as they

continue to fracture into smaller and smaller sections of earth and/or rock. The

overtopped earth embankment dam literally dissolves into a thick mud soup of earth,

rocks and water.

Therefore safety requirements for the spillway are high, requiring the spillway to be

capable of containing a maximum flood stage. Specifying a spillway able to contain a

five hundred year flood is common.

[6]

Recently a number of embankment damovertopping protection systems were developed.[7] These techniques include the concreteovertopping protection systems, timber cribs, sheet-piles, riprap and gabions, reinforced

earth, Minimum Energy Loss weirs, embankment overflow stepped spillways and the

precast concrete block protection systems developed in Russia.