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Buttress Dam

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Sugar Hollow Reservoir Dam - White Hall, VA
A buttress dam is basically a derivation of a gravity dam with the introduction of intermediate space. With a buttress dam, the face of the dam is held by a series of supports or buttresses that are placed at intervals on the downstream side.[1] The buttresses work to combat the force of reservoir water from trying to push the dam over.[2]

A buttress dam is also commonly known as a hollow dam because the buttresses do not join together to form an actual solid wall across the river valley. The shape of the actual buttress or support is mostly flat or curved with most buttress dams today being constructed out of concrete and reinforced steel.[3] Another common characteristic of the buttress dam is that the upstream face of the dam is inclined at about 45 degrees.[4]

Contents

[edit] History

Buttress dams were originally developed to help conserve water in areas where materials were either in scarce supply or expensive. They were used mostly for irrigation and in mining operations.

Some of the very first buttress type dams ever built actually date back to the Roman Empire. Some dams during that period were backed up with irregularly spaced buttresses to ensure stability. Approximately one third of all the dams built on the Iberian Peninsula were buttress dams. One flaw of these Roman-built buttress dams was that they were constructed too thin and failed to restrain water.[5]

Another version of a buttress type dam emerged throughout post-medieval Europe. The Castellar storage dam in Spain, for example, embodied a style of buttress dam that sprung up during the period that incorporated the end walls of a mill house as the actual buttresses that provided support to the dam.[6]

Eventually the design of buttress dams evolved into different variations that included large span multiple arch dams, flat slab buttress dams, and contiguous dams becoming increasingly sophisticated, exposing both the inherent strengths and weaknesses of the buttress design.[7]

[edit] How it Works

The forces or laws of physics working against a buttress dam are exactly the same as those that act on a gravity dam except the vertical load presented by the water on a buttress dam is greater. The advantage of a buttress dam is that it typically requires less concrete to construct than a gravity dam. The formwork and reinforced steel used in the building of buttresses is expensive, however, and will ultimately offset any costs saved.[8]

[edit] Types

[edit] Multiple Arch Dam

Multiple-arch buttress dams were the first type of buttress dam ever built. Their one advantage is that less reinforced steel is used in their construction. The design also permits the spanning of greater distances between buttresses.[9]

John S. Eastwood completed the first multiple-arch dam, made of reinforced concrete, in 1908. The dam impounded Hume Lake reservoir on Ten Mile Creek in California’s Sierra Nevada Mountain range. The design proved to be very economical, costing less and requiring less concrete than a gravity dam.[10]

[edit] Flat Slab Buttress Dam

The flat slab buttress dam was designed and patented by Nils F. Ambursen in 1903. As a result, this type of dam is also referred to as an Ambursen dam. Ambursen’s flat slab buttress dam design took advantage of the stabilizing effect of the vertical water load on the strongly inclined upstream face that required a minimal buttress thickness per unit of dam length.

Flat buttress slab dams caught on quickly in the early part of the 20th century, providing stiff competition to its predecessor, the multiple arch dam, another type of buttress dam. The end of the 1920s saw the construction over 200 buttress dams actually outnumbering multiple arch dams. The use of the flat slab buttress design also was rapidly adopted outside the U.S. after World War II in the construction of around 50 dams measuring 49 feet (15 m) in height in Norway, Ambursen’s native home.[11]

[edit] Contiguous Buttress Dam

Extending from the flat slab buttress and multiple arch buttress dam designs, the contiguous buttress design entailed a thickening or widening of the upstream edges or heads of the buttresses in effect joining them together, thereby making them contiguous.[12]

The first use of the design was by Noetzli in 1927 for the 115-foot (35-m) high spillway section of the V. Carranza irrigation dam in Mexico.[13]

[edit] References

  1. Dams. MSN.com. 2008-09-09.
  2. About Dams. The British Dam Society. 2008-09-09.
  3. Cracking Dams. Simscience.org. 2008-09-09.
  4. Elliott, Thomas C. and Chen, Kao, and Swanekamp, Robert C. Standard Hanbook of Powerplant Engineering. McGraw-Hill Professional: 1998.
  5. Cracking Dams. Simscience.org. 2008-09-09.
  6. Cracking Dams. Simscience.ort. 2008-09-09.
  7. Introduction to Buttress Dams. 2008-09-09.
  8. Elliott, Thomas C. and Chen, Kao, and Swanekamp, Robert C. Standard Hanbook of Powerplant Engineering. McGraw-Hill Professional: 1998.
  9. Elliott, Thomas C. and Chen, Kao, and Swanekamp, Robert C. Standard Hanbook of Powerplant Engineering. McGraw-Hill Professional: 1998.
  10. Cracking Dams. Simscience.org. 2008-09-09.
  11. Cracking Dams. Simscience.org. 2008-09-09.
  12. Dams. CE Web. 2008-09-09.
  13. Cracking Dams. Simscience.org. 2008-09-09.