Types, Advantages, And Disavantages Of Dam By Ibnu Abi 6x5l1

Task 1... Arch DAM , Gravity DAM, Embankment DAM : Its Types, Advantages, and Disavantages by Ibnu Abi Laila 1515011011 Civil Engineering University of Lampung

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In this article, i want to share information about Arch dam, Gravity dam, and Embankment dam. So Let’s Move on.

Arch DAM An arch dam is a dam curved in plan and carries at major part of its water load horizontally to the abutments by arch action. This part of water load depends primarily upon the amount of curvature. The balance of the water load is transferred to the foundation by cantilever action. The thrust developed by the water load carried by arch action essentially requires strong side walls of the canyon to resist the arch forces.

Civil Engineering Universty of Lampung Ibnu Abi L. 1515011011

The weight of arch dams is not counted on to assist materially in the resistance of external loads. For this reason, uplift on the base is not an important design factor. Many early arch dams were built of rubble, ashlar masonry, etc. However, practically all arch dams constructed during recent years have been built of concrete. The famous Hoover dam of U.S.A., constructed in 1936, is an an arch dam of constant radius type having the following dimensions: Height Length Top width and Base thickness

: 222 m(726 ft); : 380 m (1244 ft); : 13.7 m (45 ft) : 201 m (660 ft).

Advantages of Arch Dam. 1. Arch dams are particularly adapted to the gorges where the length is small in proportion to the height. 2. For a given height, the section of an arch dam is much lesser than a corresponding gravity dam. Hence, an arch dam requires less material and is, therefore, cheaper. 3. Because of much less base width, the problems of uplift pressure are minor. 4. Since only a small part of water load is transferred to the foundation by cantilever action, an arch dam can be constructed in moderate foundations where gravity dam requiring sound foundation rock may be unsuitable.

Civil Engineering Universty of Lampung Ibnu Abi L. 1515011011

Disadvantages of Arch Dam. 1. It requires skilled labor and sophisticated form work. The design of an arch dams are also quite specialized 2. The speed of construction is normally slow. 3. It requires very strong abutments of solid rock capable of resisting arch thrust. Hence, it is not suitable in the locations where strong abutments are not available. Unfortunately, only fey sites are suitable for this type of dam.

Types of Arch Dams. The arch dams may he divided into the following three types: 1. Constant radius dam. 2. Variable radius dam, and 3. Constant angle dam. 1. Constant radius arch dam. A constant radius arch dam is the one in which the radius to some prominent feature (such as upstream face, or the downstream face, or the arch axis) is constant. In most cases, however, the constant radius refers to the upstream side. In a constant radius arch dams, the arch centers for upstream face, downstream face and the center line of the horizontal arch rings at various elevations lie on a straight vertical line that es through the center of the horizontal arch ring of the upstream face at the crest. Hence this type of arch dam is also sometimes known as the constant center arch dam.

Civil Engineering Universty of Lampung Ibnu Abi L. 1515011011

In most of the simple arch types, the upstream face is vertical (i.e., its radius is constant at all elevations), and the thickness is proportional to the height. This makes the central angles of the arch rings of the introdos vary at various elevations, the maximum being at the top of the dam and a certain minimum at the bottom of the dam. A constant radius arch dam is particularly adopted to U-shaped canyons as cantilever action will carry a large proportion of the load at lower levels. The constant radius arch dams are less economical than the constant angle arch dams, and the latter is constructed in preference to constant radius arch darn. However, the form work for the constant radius arch dam is much simpler to construct. 2. Variable radius arch dam. A variable radius arch dam is the one in which the radii of the extrodos curves (i.e., arch rings corresponding to upstream face) and introdos curves (i.e., arch rings corresponding to downstream face) vary at various elevations being maximum at the top and certain minimum at its bottom.

Civil Engineering Universty of Lampung Ibnu Abi L. 1515011011

This makes the central angle as large as possible so that maximum arch efficiency may be obtained at all elevations. The variable radius arch dams have often vertical or even overhanging laces at the upstream side near the abutments and the downstream side near the crown. The centers of the horizontal arch rings at various elevation do not lie on the single vertical line. Hence it is also known as variable center arch dam. A variable radius arch dams are often adapted to narrow V-shaped canyons since arch action can be depended upon at the lower levels. A variable radius arch dam has greater arch efficiency, resulting in saving of concrete. Hence it is preferred in comparison to the constant radius arch dam.

Civil Engineering Universty of Lampung Ibnu Abi L. 1515011011

3. Constant angle arch dams. The constant angle arch dam is a special type of variable radius arch dam in which the central angle of the horizontal arch rings is of the same magnitude at all elevations.

It has been shown that the volume of concrete is minimum when the central angle is 133° 34′. A variable radius arch uses about 58% of the concrete required in constant radius arch dams. A constant angle arch dams requires about 42.6% of the concrete required in constant radius arch dams. Hence a constant angle arch dam is the most economical.

Civil Engineering Universty of Lampung Ibnu Abi L. 1515011011

Gravity DAM A gravity dam is the one in which the external forces (such as water pressure, wave pressure, silt pressure, uplift pressure, etc.) are resisted by the weight of the dam itself. Thus the forces disturbing the stability of the dam are resisted by the gravity forces of the mass of the dam. A gravity dam may be constructed either of masonry or of concrete. Masonry gravity dams are now-a-days constructed of only small heights. All major and important gravity dams are now constructed of concrete only. A gravity dam may be either straight or curved in plan.

A gravity dam is mostly straight in plan and is known as ‘straight gravity dam’. However, it may also be slightly curved in plan. A curved gravity dam resists the external forces by its weight and not by arch action. The most ancient gravity dam on record was built in Egypt more than 400 years B.C. of uncemented masonry. Archaeological experts believe that this dam was kept in perfect condition for more than 45 centuries. Most of the gravity dams are solid, so that no bending stress is introduced at any point and hence, they are sometimes known as ‘solid gravity dams’.

Civil Engineering Universty of Lampung Ibnu Abi L. 1515011011

A gravity dam, however, can be hollow and is known as ‘hollow gravity dam’. Gravity dams are particularly suited across gorges with very steep side slopes where earth dams might slip. Where good foundations are available, gravity dams can be built up to any height. The highest dams in the world are of gravity type.

Advantages of gravity dams. There is no type of dam more permanent than one of the solid concrete, nor does any other type require less for maintenance. As compared to earth and rock-fill dams gravity dams have the following advantages : 1. Gravity dams are relatively more strong and stable than earth dams. They are particularly suited across gorges having very steep side slopes where earth dam, if constructed, might slip. 2. Gravity dams are well adapted for use as an overflow spillway crest. Earth dams cannot be used as overflow dams. Due to this, a gravity overflow dam is often used for the spillway feature of earth and rock-fill dams. 3. They can be constructed of any height, provided suitable foundations are available to bear the stresses. The height of an earth dam is usually limited by the stability of its slopes requiring a very wide base width. Highest dams in the world are made of gravity dams only. 4. Gravity dam is specially suited to such areas where there is likelihood of very heavy downpour. The slopes of earth dam might get washed away in such a situation. 5. They requires the least maintenance. 6. The failure of this dam, if any, is not sudden. It gives enough warning time before the area to downstream side is flooded due to the damage of the structure. On the contrary, an earth dam generally fails suddenly. 7. Deep-set sluices can be used in the gravity dams, to retard the sedimentation or silt deposit in the reservoir. The trap efficiency of a reservoir of an earth dam is more than that of a reservoir of gravity dam. 8. They are cheaper in the long run since it is more permanent than any other type. Thus the benefit-cost ratio of such a dam is always higher.

Civil Engineering Universty of Lampung Ibnu Abi L. 1515011011

Disadvantages of Gravity Dams. The disadvantages of gravity dam, as compared to an earth dam are as follows: 1. Gravity dams can be constructed only on sound rock foundations. They are unsuitable on weak foundations or on permeable foundations on which earth dams can be constructed with suitable foundation treatment. 2. The initial cost of a gravity dam is always higher than an earth dam. Hence, where funds are limited and where suitable materials are available for the construction of an earth dam, the earth dam may be preferred. 3. If mechanized plants, such as manufacturing and transporting mass concrete, curing of concrete etc. are not available, a gravity dam may take more time to construct. 4. They require skilled labor or mechanized plants for its construction. 5. It is very difficult to allow subsequent rise in the height of a gravity dam, unless specific provisions have been made in the initial design.

Civil Engineering Universty of Lampung Ibnu Abi L. 1515011011

Embankment DAM An embankment dam is a large artificial dam. It is typically created by the placement and compaction of a complex semi-plastic mound of various compositions of soil, sand, clay, or rock. It has a semi-pervious waterproof natural covering for its surface and a dense, impervious core. This makes such a dam impervious to surface or seepage erosion. 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 by the use of a cementing substance.

Types 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-section of an embankment dam shows a shape like a bank, or hill. Most have a central section or core composed 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 sites with wide valleys. They can be built on 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 grades to get the right range of size for use in an embankment dam.

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 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 is not exceeded. Overtopping or overflow of an embankment dam beyond its spillway capacity will cause its eventual failure. The erosion of the dam's material by overtopping runoff will remove masses of material whose weight holds the dam in place and against the hydraulic forces acting to move the dam. Even a small sustained overtopping flow can remove 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 reservoir as 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 dam erodes, the force exerted by the reservoir begins to move the entire structure. The embankment, having almost no elastic strength, would begin to break into separate pieces, allowing the impounded reservoir water to flow between them, eroding and removing even more material as it es through. In the final stages of failure the remaining pieces of the embankment would offer almost no resistance to the flow of the water and continue to fracture into smaller and smaller sections of earth or rock until these would disintegrates into a thick mud soup of earth, rocks and water. Therefore, safety requirements for the spillway are high, and require it to be capable of containing a maximum flood stage. It is common for its specifications to be written such that it can contain a five hundred year flood. Recently a number of embankment dam overtopping protection systems have been developed. These techniques include the concrete overtopping Civil Engineering Universty of Lampung Ibnu Abi L. 1515011011

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.

Embankments DAM Advantages 



Safer from flooding, the channel now has an increased carrying capacity so it is less likely to burst Earthen embankments provide habitats for riverbed animals e.g kingfishers, voles and otters

Disadvantages   

They deprive people of river access for fishing and boating They have a higher maintainance cost as they are prone to erosion If breached, water will stay on the embankments, destroying the animal habitats

Civil Engineering Universty of Lampung Ibnu Abi L. 1515011011