Arch-gravity dam

Arch-gravity Hoover Dam Architectural Plans

An arch-gravity dam, curved-gravity dam or arched 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. They are generally made of reinforced concrete which provides more strength compared to normal concrete. A typical example is the Hoover Dam. A gravity dam requires a large volume of internal fill.^[1] An arch-gravity dam can be thinner than the pure gravity dam and requires less internal fill.^[2]

Overview

Hoover Dam from the air

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.^[3]

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.^[4]

When properly situated on an appropriate site, the arch-gravity dam, combining the load resisting qualities of both a gravity dam and an arch dam, inspires the most confidence in the public at large because of its appearance of massive permanence.^[5] 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.^[6]

Gravity dam

Gravity dam - Dworshak Dam

The gravity dam is a massive structure made of masonry or concrete with earth and rock fill. Gravity dams use their own weight to resist opposing forces and as such require a hard bedrock foundation.^[4] They rely on their great weight and size for stability.^[7] The gravity dam is the most commonly built dam in the world. One of the reasons for this is the simplicity of design. Unfortunately it requires great quantities of material to construct.^[8]

Arch dam

Glen Canyon Dam

Mratinje Dam in Montenegro

An arch dam is a thin, curved concrete or masonry dam structure, with the concave side of the curve downstream. Therefore, the force of the water against the canyon wall squeezes the arch, compressing and strengthening its structure and pushing it into the ground.^[9] An arch dam is a good dam type for a narrow gorge in a mountainous area with steep walls of rock.^[10] It generally has steel rods or prestressed steel cable reinforcements and therefore requires less concrete than a gravity or arch-gravity dam. However, the bedrock in the foundation and abutments must be sound to withstand the pressure of the water.^[11]

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.^[11]

See also

• Masonry dam
• Arch dam
• Embankment dam

Footnotes

1. ^ Luis E. Plaza (1998). Dam Safety: Proceedings of the International Symposium on New Trends. Taylor and Francis. p. 425. ISBN 90-54109724. 
2. ^ "Arch Gravity dam". U.S. Bureau of Reclamation. http://www.usbr.gov/library/glossary/#archgravitydam. Retrieved 2007-12-27. 
3. ^ "Glossary onf Engineering Words - Gravity dam". pbs.org. http://www.pbs.org/wgbh/buildingbig/glossary_head.html. Retrieved 2007-12-28. 
4. ^ ^{a b} "Dam Basics". pbs.org. http://www.pbs.org/wgbh/buildingbig/dam/basics.html. Retrieved 2007-12-27. 
5. ^ "Dams - Types and Considerations". quest.arc.nasa.gov. http://google.com/search?q=cache:Pl4yHMFog5kJ:quest.arc.nasa.gov/projects/jason/xv1/docs/Unit3/HO-2Dam%27s-Type%26Considertions.doc+gravity%2Barch%2Bdam&hl=en&ct=clnk&cd=15&gl=us. Retrieved 2007-12-29. 
6. ^ Donald C. Jackson (1988). Great American Bridges and Dams. Wiley.com. p. 48. ISBN 978-0471143857. http://books.google.com/books?id=v3WWvdOUcFEC&pg=PA48&lpg=PA48&dq=gravity+arch+dam&source=web&ots=bqk8uN2GXq&sig=OAlZBQasGggHJDCrcSTtTWJ15f0. Retrieved 2007-12-29. 
7. ^ "Glossary - Gravity Dam". US Bureau of the Interior. http://www.usbr.gov/library/glossary/#gravitydam. Retrieved 2007-12-28. 
8. ^ "Gravity Dam - Characteristics". University of California - Davis. http://cee.engr.ucdavis.edu/faculty/lund/dams/Dam_History_Page/Diagrams.htm. Retrieved 2007-12-29. 
9. ^ "Managing Water - Glossary". US Bureau of the Interior. http://www.usbr.gov/library/glossary/#abutment. Retrieved 2007-12-28. 
10. ^ "Arch Dam Forces". http://www.pbs.org/wgbh/buildingbig/dam/arch_forces.html. Retrieved 2007-02-05. 
11. ^ ^{a b} "Introduction to Arch Dams". http://www.dur.ac.uk/~des0www4/cal/dams/conc/concf12.htm. Retrieved 2007-02-05.