Description & Background

Bulging of dam crest east of spillway observed in January 1910. The uplift pressures caused layers of the foundation rock to slide on each other, resulting in the dam bulge (Courtesy of the Potter County Historical Society).

Bulging of dam crest east of spillway observed at Austin (Bayless) Dam in January 1910. The uplift pressures caused layers of the foundation rock to slide on each other, resulting in the bulge and ultimately the failure of the dam (Courtesy of the Potter County Historical Society).

Foundation defects cause approximately 30% of all documented dam failures in the United States.¹ Because of inherent uncertainty associated with the properties of the foundation it is essential that the regional geology and dam foundation geologic conditions be thoroughly investigated and characterized in order to reduce the risk of failure.

Prior to the design phase, reconnaissance and feasibility studies should be performed at the proposed dam site to understand the regional geology and properly characterize the site conditions as they relate to stability. Such studies should be conducted by an experienced engineering geologist with training in dam stability. A complete understanding of the geologic conditions is critical to the evaluation of dam site selection, feasibility, and stability as well as selection of the dam type and configuration. In addition, constructability and costs are directly related to the geologic conditions, particularly the potential need for mitigation of seepage and/or stability concerns.

During the construction phase of the dam, additional geotechnical investigations and pilot tests may be conducted in order to finalize the foundation preparation specifications and foundation treatment methods most compatible with the geologic conditions and dam design. Consideration of geologic features through comprehensive geotechnical investigations conducted throughout several phases of dam design will ensure the most appropriate means of foundation preparation and treatment at the site.

Foundation treatment may include surficial measures such as excavation of low quality rock, application of dental concrete, or contact grouting; deeper treatments such as the installation of a cutoff wall, foundation grouting or a combination of the two, and the use of drains and filters at the base of concrete dams or within an embankment. In seismically active regions, the construction of a berm or buttress on the upstream or downstream slope may be required to increase the factor of safety against seismically induced stability failures, sliding, and settlement due to strength reductions from shaking and liquefaction.

Improper foundation preparation resulting from a lack of geologic consideration can lead to dam failure by a variety of modes including differential settlement, slope instability, sliding, uplift pressures, uncontrolled foundation seepage, internal erosion, shearing, and faulting.


References:

(1) ASDSO. (2014).  Dam Failures and Incidents.  Association of State Dam Safety Officials. 

(2) USACE. (2001).  Geotechnical Investigations, EM 1110-1-1804.  Washington D.C.:  U.S. Army Corps of Engineers. 

 

Summary

Photos

Videos

Case Studies

Austin (Bayless) Dam (Pennsylvania, 1911)

Austin Dam (also known as Bayless Dam) was constructed between May and November of 1909 just outside Austin, Pennsylvania, a town of approximately 2,500 people in Potter County.

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Baldwin Hills Dam (California, 1963)

The Baldwin Hills Reservoir was constructed in 1951 to provide water to the south and southwest portions of the city of Los Angeles, California. Sitting atop one of the tallest hills in the region, the reservoir was confined on three sides by compacted earth dikes...

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Fontenelle Dam (Wyoming, 1965)

Fontenelle Dam is located on the Green River near La Barge, Wyoming and was originally built in 1964 to provide irrigation water and hydropower for a region of southwest Wyoming. The earthfill embankment structure...

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Malpasset Dam (France, 1959)

Malpasset Dam was a concrete arch dam located on the Riveria in the Cannes District near Fréjus, in Southern France. Exhibiting curvature in both the plan and section directions, the double-curvature arch structure spanned the Reyran River. At the time of completion in 1954, it was reported...

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St. Francis Dam (California, 1928)

Located approximately forty miles northwest of Los Angeles, California, St. Francis Dam was a curved concrete gravity dam constructed between 1924 and 1926 in order to provide a storage reservoir for the Los Angeles Aqueduct system...

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Teton Dam (Idaho, 1976)

Teton Dam was located in southeastern Idaho about 15 miles from Rexburg in the valley of the Teton River. The dam and its reservoir were the principal elements of the Teton Basin Project designed by the Bureau of Reclamation to control flooding as well as provide a source of...

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Additional Case Studies (Not Yet Developed)

  1. Alla Sella Zerbino Dam (Italy, 1935)
  2. Shi Kang Dam (Taiwan, 1999)
  3. Vajont Dam (Italy, 1963)

Best Practices

Federal Guidelines for Dam Safety: Earthquake Analyses and Design of Dams

Author: Federal Emergency Management Agency
Date Published: 2005

Training Aids for Dam Safety: Evaluation of Embankment Dam Stability and Deformation

Author: Interagency Committee on Dam Safety
Date Published: Unknown

Training Aids for Dam Safety: Evaluation of Concrete Dam Stability

Author: Interagency Committee on Dam Safety
Date Published: Unknown

Other Resources

Field Investigations for New and Existing Dams

Author: R. Martin

Webinar published by Association of State Dam Safety Officials

Bearing Capacity of Soils, EM 1110-1-1905

Author: U.S. Army Corps of Engineers

Engineering Manual for USACE

Design of Pile Foundations, EM 1110-2-2906

Author: U.S. Army Corps of Engineers

Engineering Manual for USACE

Geotechnical Investigations, EM 1110-1-1804

Author: U.S. Army Corps of Engineers

Engineering Manual for USACE

Rock Foundations, EM 1110-1-2908

Author: U.S. Army Corps of Engineers

Engineering Manual for USACE

Rock Reinforcement, EM 1110-1-2907

Author: U.S. Army Corps of Engineers

Engineering Manual for USACE

Settlement Analysis, EM 1110-1-1904

Author: U.S. Army Corps of Engineers

Engineering Manual for USACE

Slope Stability, EM 1110-2-1902

Author: U.S. Army Corps of Engineers

Engineering Manual for USACE