Page Comparison

Timber Dams

• They were readily used in the earlier of the industrial revolution due to the ease and speed of construction

• It is not used at often in the modern days because it has a short life span, and it is limited to a certain height.

• This type of dam also needs to be constantly wet in order for it to retain its water retention properties and limit deterioration due to rotting

• This dam was mostly built in areas where there was a lot of timber, where cement is too costly or difficult to build, when a low head diversion dam is required or when the dam is needed for a short time

• There were a lot of them, especially in the west side of North America, but a lot of them have failed and they are either hidden by earth embankment dams or they are replaced by new structures

• The two most common types of timber dams are

  • Crib: They were constructed with heavy timbers or dressed logs in a log house manner and the inside was filled with earth or rubble

  • Plank: they were more elegant dams that used various types of construction methods where heavy timbers were utilized to support a water retaining arraignment of planks

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Embankment Dams

• This dam is made from compacted earth. There are two types of them, the rock-filled and earth-filled dam

  • Rock-filled

    • they are compacted free-draining granular earth material with a zone that does not allow for fluid to pass through it. This zone is called impervious zone
    • This zone can be on the upstream face and made of masonry, concrete, plastic membrane, steel sheets piles, timber, or other material
    • If this zone is within the embankment, then it is called a core
    • When suitable material is available then transportation is minimized, minimizing the money that is spend during the construction process
    • They are highly resistance to damage even when an earthquake occurs
    • But insufficient quality control can lead to excessive fines in the embankment leading to liquefaction of rock-fill during an earthquake. This can be eliminated by keeping the material dry.

  • Earth dams

    • Made from well compacted earth
    • A homogenous earth dam is constructed entirely form one type of material but may contain a dryer layer to collect the seep water
    • Zoned-earth dam contains distinct part or dissimilar material, usually a shell with clay core.
    • Modern earth dams employ filter and drainage zones that collect the seep water and keep the integrity of the shell zone

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Gravity Dams

• This dam becomes stable if the size and shape are constructed in a way that overturning, sliding and the crushing of the toe are taken into consideration and it can resist all these possible failures
• The wall will not overturn if at the moment of overturning, the water pressure is lower then the weight of the dam
• Since this dam relies on its weight, it tends to have more persistence, stability, and safety
• Due to its reliability, this dam is usually built in area were flooding is an issue and the constructors do not want to use an arch dam to reduce the cost due it its flooding since the arch dam could collapse with a flood
• One of the tallest gravity walls in the world is Grande Dixence Dam in Switzerland at 285m tall

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Arch Dams

• When it comes to the stability of this dam, it depends on the arch and gravity action
• The most desirable place for an arch dam is a narrow canyon with step side walls composted of sound rock
• The safety of the arch dam depends on the strength of the side wall abutments, that is why the arch dam should be seated well on the side walls and also the rock should be inspected very carefully
• The two types of arches that are used, the constant-angle and constant-radius dam
  • Constant-radius dam employs the same face radius at all elevations of the dam meaning that the channel grows narrow at the bottom and the central angle subtended by the face of the dam becomes smaller. This type of dam is less common then the other one
  • The constant-angle dam has a constant subtended angle and the different distances between the abutments at various levels are taken care of by varying the radii

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