Topic : Dams
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DAMS
Types of dam
Dams are separated into two main types by the choice of material used for their construction: (1) embankment; and (2) concrete dams.
(1) Embankment dams are made from nonorganic particulate material excavated from the Earth's surface local to the dam site and used more or less as excavated. They are subdivided into earthfill and rockfill dams, although many embankment dams contain both types of fill. Further subdivisions can be made, according to the material used, to make the waterproof element, e.g. central clay core, sloping clay core or upstream membrane of asphalt or reinforced concrete.
(2) Concrete dams are made from a carefully selected and processed harder fraction of this material, bound together and strengthened by an hydraulic cement. They are subdivided according to their mechanism for remaining stable. (a) gravity dams: these are the simplest because
they rely on gravitational force to oppose the overturning moment caused by the pressure of the reservoir water on their upstream faces.
(b) hollow gravity dams: these require less concrete and therefore cost less to construct. Foundation requirements are more critical.
(c) buttress dams: these also require less concrete than gravity dams. The buttresses support the upstream face of a buttress dam. The upstream edges of the buttresses are commonly widened so that they join, forming the contiguous buttress dam. As an alternative, the upstream face may consist of small arches between buttresses, forming a multi-arch dam.
(d) arch dams: these may be constructed as a whole in one large arch, spanning the valley sides and relying on them to carry the very large thrusts caused by reservoir water pressure. This type is the most sophisticated of the concrete dams and may be subdivided into singlecurvature and double-curvature, according to
whether the vertical section is straight, or is curved to further reduce bending moments in the concrete.
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