- Also called:
- hollow dam
buttress dam
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What is a buttress dam?
A buttress dam is a concrete dam that uses buttresses to support its upstream face on the downstream side. Unlike gravity dams, buttress dams don't rely on their weight to resist the water's thrust. The upstream face is angled 25° to 45° so the water's thrust inclines toward the foundation. The bracing action of the buttresses is where the dam’s stability comes from.
Several variations are possible in the design of buttress dams, with most modifications occurring at the junction between the buttresses at the water face. The Daniel-Johnson Dam in Quebec is an example of a multiple-arch buttress dam. The Latyan Dam in Iran is an example of a massive head buttress dam. Deck slab buttress dams feature a sloping deck supported by buttresses.
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How does a buttress dam work?
A buttress dam is a concrete dam that uses downstream buttresses to support its smooth upstream face. Unlike gravity dams, buttress dams don't rely on their weight to resist the water's thrust. The upstream face is angled, typically between 25° to 45°, so that the water's thrust against the face is directed towards the foundation. The buttresses brace and concentrate the load, providing stability. Buttress dams are suitable for both narrow and wide valleys but usually need solid bedrock for their foundation.
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What are the main parts of a buttress dam?
A buttress dam is a concrete dam with a smooth upstream face supported by buttresses on the downstream side. It does not rely on its weight to resist the water's thrust. Instead, the thrust of the water inclines toward the foundation, and the bracing action of the buttresses concentrates the load, providing stability.
The main parts of a buttress dam are:
* Upstream Face Inclines to direct the water's thrust toward the foundation.
* Buttresses Located on the downstream side to brace and support the upstream face.
* Foundation Transfers the load from the buttresses to the ground.2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How do buttress dams differ from gravity dams?
Buttress and gravity dams differ in their structure and how they resist water pressure. Buttress dams use a sloping upstream face supported by buttresses on the downstream side, which redirects the water's thrust toward the foundation. This design contrasts with gravity dams, which rely entirely on their own weight to withstand the water's horizontal pressure. The buttress dam's structure allows for smaller uplift forces compared to gravity dams, offering an advantage in certain foundation conditions.
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What materials are commonly used to build buttress dams?
Buttress dams are a type of concrete dam that uses buttresses to support the upstream face on the downstream side. These dams don't rely on their weight to resist the water's thrust.
Buttress dams often use reinforced concrete for the thin buttresses supporting the inclined upstream face. Modern designs aim to reduce the amount of formwork needed and avoid steel reinforcement. The Daniel-Johnson Dam in Quebec, Canada, is a multiple-arch buttress dam that uses 14 buttresses in its structure.
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What are the advantages and disadvantages of buttress dams in engineering projects?
Buttress dams utilize a solid bedrock foundation to support a smooth upstream face with buttresses on the downstream side. Unlike gravity dams, they don't rely on their weight to resist water thrust.
Advantages:
* Buttress dams can be used across narrow or wide valleys.
* They have smaller uplift forces compared to traditional gravity dams.Disadvantages:
* Buttress foundations might yield in seismically active areas, requiring designs that accommodate potential movement between the heads of the buttresses.
* Soils and rock fragments lack strength, are much more permeable, and possess less resistance to deterioration and disturbance by flowing water compared to concrete.2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
buttress dam, concrete dam in which the smooth upstream face is supported by buttresses on the downstream side. Unlike traditional gravity dams, buttress dams do not rely entirely upon their own weight to resist the thrust of the water. Their upstream face, therefore, is not vertical but inclines about 25° to 45°, so the thrust of the water on the upstream face inclines toward the foundation; the bracing action of the buttresses where the load is concentrated is the source of the dam’s stability. Buttress dams can be used across narrow or wide valleys but, like gravity dams, usually require a solid bedrock foundation at the site.
Embryonic buttresses existed in some Roman dams, among them the Proserpina Dam in southwestern Spain. The Proserpina Dam features a masonry-faced core wall of concrete backed by earth that is strengthened by buttresses on the downstream face. As technology advanced, dams with thin buttresses of reinforced concrete supporting an inclined upstream face were built. In many of today’s buttress dams, the trend is to reduce the area of costly formwork necessary and to avoid use of steel reinforcement. With greater heights, modern buttress dams are inevitably less slender.
Several variations are possible in the design of buttress dams, with most modifications occurring at the junction between the buttresses at the water face. Where no relative movement in the buttress foundations is anticipated, the design can link individual buttress heads rigidly, by means of arches, to form a multiple-arch buttress dam. A Canadian example of this type is the 214-metre- (703-foot-) high multiple-arch Daniel-Johnson Dam on the Manicouagan River in Quebec. The dam, which was completed in 1968, uses a total of 14 buttresses in its crest length of 1,314 metres (4,311 feet); two significantly larger buttresses support the structure over the original riverbed. The multiple-dome buttress dam is similar to multiple-arch buttress dams, but relies on domes instead of arches.
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Where buttress foundations might yield—as in seismically active areas—the design must accommodate some potential movement between the heads of the buttresses. This is normally achieved by enlarging the heads until they are almost in contact and then joining them with flexible seals. Thus joined, the heads present a solid face to the water. Such a design, known as a massive head buttress dam, was used in the construction of the Latyan Dam in Iran. Built for the Tehrān Regional Water Board in 1967, this dam has a maximum height of 107 metres (351 feet) and a crest length of nearly 360 metres (1,181 feet).
A comparison between the Daniel-Johnson multiple-arch buttress dam and the Latyan buttress dam shows that the arched buttresses of the former can be placed much farther apart than those of the latter. However, each buttress of the Latyan Dam is able to be more slender, and the design spreads the load more evenly over the foundation. The detailed design at the bottom of the Latyan buttresses was necessitated by weak foundation conditions at the site and by the need to limit the length of each buttress to reduce its response to seismic action. By contrast, the Daniel-Johnson buttresses could be founded individually, exploiting fully an important advantage of buttress dams over traditional gravity dams—that of smaller uplift forces.
Another type of buttress dam, the deck slab buttress dam, features a sloping deck (a reinforced concrete slab) that is supported by buttresses at an inclination between 40° and 55°. Such dams can be fixed deck slab, free deck slab, or cantilever slab and typically have lower deck heights than other buttress dam types. The first deck slab buttress dam was built by Nils F. Ambursen in New York in 1903.