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The Failure of Teton Dam

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1 The Failure of Teton Dam
by Anthony Gilbert Reza Ghany Charlie Pearcy

2 Contents Introduction Dam construction Geology of the site
Failure of the dam Aftermath of the failure Geology behind the failure Engineering factors behind the failure The future of the Teton Dam site Conclusion

3 Introduction Earth dam located between Fremont and Madison Counties on the Teton River, Idaho, USA Dam dimensions – 940m long 93m high and 540m wide at the base Construction began in June 1972 and was completed in November 1975 Construction cost $49,000,000 Intended to create the Teton reservoir with a capacity of 228,954,000m3

4 Dam Construction Zone 1- Impervious centre core with clayey silts of aeolin origin Zone 2- higher compaction, filter layer that controls seepage through core and rock foundation. Zone 3- structural stability Zone 4- Random cofferdam fills (allowing construction of dam in dry) Zone 5- Rock-fill to protect outer embankment slopes Note: Only one grout curtain installed, higher than anticipated grout take (due to poor rock condition)

5 Geology of the Site Dam site Snake River Plain
Steep walled canyon on a broad tectonic depression The volcanic rock at the dam site Hard, welded, rhyolitic ash-flow tuff (compacted ash) Permeable, one side highly fissured, unstable Sedimentary rock below Bed Rock Open-jointed rhyolite Basalt

6 Failure On Thursday 3rd June 1976 water was observed seeping through the dam, it was inspected by engineers who dismissed that there was a problem. At 7.30am on Saturday 5th June 1976 a muddy leak appeared suggesting sediment was in the water seeping through the dam. Again, engineers dismissed suggestions of a problem Teams of workmen using mechanical equipment attempted to stem the flow through the dam ultimately unsuccessfully with 2 workmen having to be rescued when their bulldozers were swallowed up by the collapsing dam At 11.15am an order to evacuate downstream was given The dam was completely breached at 11.55am releasing 57000m3/s of water By 8pm the dam was empty

7 Failure Approx 11.20am Approx 11.40am Approx 11.50am

8 Failure Approx 12pm After 12pm

9 Aftermath Upon failure the water rushed down the Teton canyon destroying the entire ecosystem. Communities of Wilford, Sugar City, Hibbard & Rexburg were badly hit by flood water. Photograph taken in Rexburg 11 people died in resulting floods Danger of collapse of ‘America Falls Dam’, however increasing flow through the dams slipways ensured its integrity Estimated cost of damage & cleanup up to $2billion

10 Geology Behind the Failure
Volcanic fumaroles large voids Favored development of cracks Fill material – rhyolite, basalt Not suitable for foundations Permeable, one side highly fissured, unstable trenching abutment rock providing large core-rock contact and long flow path (for low seepage gradient) Arching (increase in stress in some areas and a reduction in others)

11 Engineering Factors Behind Failure
Following the failure, an investigative panel was selected to review the cause. The panel issued its report in December 1976. The report concluded that the main contributing factors to the dam failure were: Erosion/Piping The geology of the site The design of the dam The lack of instrumentation to warn of changing conditions

12 The Future of The Teton Site
In July 2009, there was new speculation about rebuilding in order to provide water for irrigation. The Bureau of Reclamation has reportedly set aside $400,000 of the $800,000 needed to study the feasibility of rebuilding.

13 Conclusion Collapse caused by a combination of bad engineering decisions related to the geology of the site. Warning signs ignored early on the day of collapse. Evacuation order could have come sooner perhaps saving more lives “As every dam engineer knows, water also has one job, and that is to get past anything in its way!!”

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