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Arch-gravity dam
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An arch-gravity dam, such as the Hoover Dam, is a dam with the characteristics of both an arch dam and a gravity dam. It is a dam that curves upstream in a narrowing curve that directs most of the water against the canyon rock walls, providing the force to compress the dam. It combines the strengths of two common dam forms and is considered a compromise between the two. A gravity dam requires a large volume of internal fill.
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Encyclopedia
An arch-gravity dam, such as the Hoover Dam, is a dam with the characteristics of both an arch dam and a gravity dam. It is a dam that curves upstream in a narrowing curve that directs most of the water against the canyon rock walls, providing the force to compress the dam. It combines the strengths of two common dam forms and is considered a compromise between the two. A gravity dam requires a large volume of internal fill. An arch-gravity dam can be thinner than the pure gravity dam and requires less internal fill.
Arch-gravity dams are massive dams of reinforced concrete that resist the thrust of water by their weight pushing down using the force of gravity. A gravity dam is constructed so that the dam's massive weight resists the pressure of the water against it.
At the same time an arch-gravity dam incorporates the arch's curved design that is so effective in deflecting the water in narrow, rocky locations where the gorge's side are of hard rock and the water is forced into a narrow channel. Therefore the span needed for the dam is narrow; the dam's curved design effectively holds back the water in the reservoir using a lesser amount of construction material.
When properly situated on an appropriate site, the arch-gravity dam, combining the load resisting qualities of both a gravity and arch type dam inspires the most confidence in the public at large because of its appearance of massive permanence. However, curving a gravity dam may make it look stronger, but some of this effect may be psychological factors in operation in making a choice of dam style.
Gravity dam
The gravity dam is massive, made of masonry and cement with earth and rock fill, uses its own weight to resist opposing forces. The gravity dam is the most commonly built dam in the United States. One of the reasons is the simplicity of its design. Unfortunately it requires great quantities of material to construct. Gravity dams are massive dams, requiring a hard bedrock foundation, and they depend on their heavy weight to resist the enormous force exerted on it by the water. It depends on its great weight and size for its stability.
Arch dam
An arch dam is a thin, curved concrete or masonry dam structure with the curve to curve upstream so that the force of the water against the canyon wall where the dam is constructed squeezes the arch, compressing and strengthening its structure and pushing it into the ground. An arch dam is a good dam type for a narrow gorge in a mountainous area with steep walls of rock. It generally has steel rods or prestressed steel cables reinforcements and therefore requires less concrete than does a gravity or arch-gravity dam. However, the bedrock in the foundation and abutments must be sound to withstand the pressure of the water.
Arch dams with more than one contiguous arch or plane are described as multiple arch dams. A double arch dam has two contiguous arches. A dam that is curved in both its horizontal and vertical planes may be called a dome dam.
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