Embankment dam 1

Embankment dam

The Mica Dam in Canada.

Tataragi Dam in Asago, Hyōgo Pref., Japan.

Tarbela Dam in Pakistan

An embankment dam is a massive artificial water barrier. It istypically created by the emplacement and compaction of a complexsemi-plastic mound of various compositions of soil, sand, clay and/orrock. It has a semi-permanent waterproof natural covering for itssurface, and a dense, waterproof core. This makes such a damimpervious to surface or seepage erosion.[1] The force of theimpoundment 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 foundationof the dam, at the interface between the dam and its stream bed.[2] Sucha dam is composed of fragmented independent material particles. Thefriction and interaction of particles binds the particles together into astable mass rather than by the use of a cementing substance.[3]

Types

Embankment dams come in two types: the earth-filled dam (also calledan earthen dam or terrain dam) made of compacted earth, and therock-filled dam. A cross-section of an embankment dam shows a shapelike a bank, or hill. Most have a central section or core composed of animpermeable material to stop water from seeping through the dam. Thecore can be of clay, concrete or asphalt concrete. This dam type is agood choice for sites with wide valleys. Since they exert little pressureon their foundations, they can be built on hard rock or softer soils. Fora rock-fill dam, rock-fill is blasted using explosives to break the rock.Additionally, the rock pieces may need to be crushed into smallergrades to get the right range of size for use in an embankment dam.[4]

Safety

The building of a dam and the filling of the reservoir behind it places anew weight on the floor and sides of a valley. The stress of the waterincreases linearly with its depth. Water also pushes against theupstream face of the dam, a nonrigid structure that under stressbehaves semiplastically, and causes greater need for adjustment(flexibility) near the base of 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 isnot exceeded.[5]

Overtopping or overflow of an embankment dam beyond its spillways will cause its eventual failure. The erosion ofthe dam's material by an overtopping surface runoff will remove masses of material whose weight holds the dam inplace against the hydraulic forces acting to move the dam. Even a small sustained overtopping surface flow canremove thousands of tons of overburden soil from the mass of the dam within hours. The removal of this mass,

unbalances the forces that stabilize the dam against its impoundment. The mass of water still impounded behind the dam presses against the lightened mass of the embankment, (made lighter by surface erosion). As the mass of the

Embankment dam 2

dam erodes, the impoundment begins to move the entire structure. The embankment, having almost no elasticstrength, begins to break into separate pieces, allowing the impounded water to flow between them, eroding andremoving more material as it passes through. In the final stages of failure the remaining pieces of the embankmentoffer almost no resistance to the flow of the water as they continue to fracture into smaller and smaller sections ofearth and/or rock. The overtopped earth embankment dam disintegrates into a thick mud soup of earth, rocks andwater.Therefore safety requirements for the spillway are high, and require it to be capable of containing a maximum floodstage. It is common for its specifications to be written such that it can contain a five hundred year flood.[6] Recently anumber of embankment dam overtopping protection systems have been developed.[7] These techniques include theconcrete overtopping protection systems, timber cribs, sheet-piles, riprap and gabions, reinforced earth, minimumenergy loss weirs, embankment overflow stepped spillways and the precast concrete block protection systems.The earthen dam at Lake Elsman was damaged in the 1989 Loma Prieta earthquake.[8] The performance of AustrianDam during that earthquake has reinforced concerns about damage to the tops of earth dams by earthquakes.[8]

Notes[1] "Dam Basics" (http:/ / www. pbs. org/ wgbh/ buildingbig/ dam/ basics. html#emb). PBS. . Retrieved 2007-02-03.[2] "Embankment dam: forces" (http:/ / www. pbs. org/ wgbh/ buildingbig/ dam/ emb_forces. html). PBS. . Retrieved 2007-02-03.[3] "Introduction to rock filled dams" (http:/ / www. dur. ac. uk/ ~des0www4/ cal/ dams/ emba/ embaf17. htm). . Retrieved 2007-02-05.[4] "About Dams" (http:/ / www. britishdams. org/ about_dams/ embankment. htm). . Retrieved 2007-02-03.[5] "Pressures Associated with Dams and Reservoirs" (http:/ / www. dur. ac. uk/ ~des0www4/ cal/ dams/ foun/ founf5. htm). . Retrieved

2007-02-05.[6] "Dams – Appurtenant Features" (http:/ / www. dur. ac. uk/ ~des0www4/ cal/ dams/ intr/ intrf4. htm). . Retrieved 2007-02-05.[7] H. Chanson (2009). Embankment Overtopping Protections System and Earth Dam Spillways (http:/ / espace. library. uq. edu. au/ view/

UQ:185350). in "Dams: Impact, Stability and Design", Nova Science Publishers, Hauppauge NY, USA, Ed. W.P. Hayes and M.C. Barnes,Chapter 4, pp. 101-132. ISBN 978-1-60692-618-5. .

[8] Riverside County Integrated Project (http:/ / www. rcip. org/ Documents/ general_plan/ appendix_h/ pdf/ 03_06_04. pdf). Riverside CountyIntegrated Project. 2000. pp. Appendix H, 3–41. .

External links• Embankment dams Table of contents (http:/ / www. dur. ac. uk/ ~des0www4/ cal/ dams/ emba/ frame. htm)• An introduction to embankment dams (http:/ / simscience. org/ cracks/ advanced/ ebnk_char1. html)

Article Sources and Contributors 3

Article Sources and ContributorsEmbankment dam  Source: http://en.wikipedia.org/w/index.php?oldid=521550440  Contributors: 663highland, Argyriou, Art LaPella, Basar, Bento00, Chansonh, CommonsDelinker,Dreamyshade, FAAATTT, Gaius Cornelius, Howcheng, J.Gifford, Jeodesic, Jimmy Pitt, Lradrama, M.nelson, Magnus242, Mattisse, Mrt3366, Nomi887, NortyNort, Pigsonthewing,ProfessorXY, Qurren, Rehman, Tedickey, Toddst1, Tojo en, Wgfcrafty, Zedshort, Zuejay, 26 anonymous edits

Image Sources, Licenses and ContributorsImage:MicaDam.JPG  Source: http://en.wikipedia.org/w/index.php?title=File:MicaDam.JPG  License: Public Domain  Contributors: Original uploader was DAR56 at en.wikipediaImage:Tataragi Dam01n4272.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Tataragi_Dam01n4272.jpg  License: Creative Commons Attribution-ShareAlike 3.0 Unported Contributors: 663highlandImage:Tarbela.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Tarbela.jpg  License: unknown  Contributors: Badzil, Bantman, FSII, Howcheng, Mircea, Neon, Rehman, 1anonymous edits

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