teton dam failure edit by aisha

8/13/2019 Teton Dam Failure Edit by Aisha

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INTRODUCTIONThe Teton Dam was situated on theTeton River, three miles northeastof Newdale, Idaho, US.

It was designed to providerecreation, flood control, power

generation, and irrigation for over40,000 hectares (100,000 acres) offarmland.

The collapse of the dam resulted inthe deaths of 11 people and 13,000head of cattle.

The dam cost about $100 million tobuild, and the federal governmentpaid over $300 million in claimsrelated to the dam failure. Totaldamage estimates have ranged upto $2 billion. The dam was neverrebuilt.


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Incidents Prior To The Collapse OfThe Dam:

On June 3, 1976 several small seepages were noticed in the north abutmentwall. Pictures were taken and these leaks were reported to the Bureau ofReclamation.

This led to more frequent inspections of the dam. It was now to be inspecteddaily, and readings were to be taken twice weekly instead of once a week.

On June 4, 1976 wetness was noticed in the right abutment and small springswere beginning to appear.

On June 5, 1976 the first major leak was noticed between 7:30 and 8:00 a.m.The leak was flowing at about 500 to 800 liters per second from rock in theright abutment. By 9:00 a.m. the flow had increased to 1,100 to 1,400 litersper second and seepage had been observed about 40 meters (130 feet)below the crest of the dam.

At 11:00 a.m. a whirlpool was observed in the reservoir directly upstreamfrom the dam and four bulldozers were sent to try to push riprap into thesinkhole near the dam crest.Two of the bulldozers were swallowed up by therapidly expanding hole, and the operators were pulled to safety by ropes tied

around their waists.


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Between 11:15 and 11:30 a.m. a 6by 6 meter (20-foot by 20-foot)chunk of dam fell into the whirlpooland within minutes the entire damcollapsed.

At 10:30 a.m. dispatchers at theFremont and Madison CountySheriffs offices were notified thatthe dam was failing. An estimated300 million cubic meters of water(80 billion gallons) headed downthe Upper Snake River Valley. Thetowns in its path included Wilford,Sugar City, Rexburg, and Roberts.

More than 200 families were lefthomeless. The final toll was 11killed directly or indirectly and anestimated 400 million to one billiondollars in property damage.


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Flow increasing. Dozers sent to fill hole About 10.45 AM June 5, 1976.


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Approximately 11.30 AM June 5, 1976


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Second hole in face of dam . A fewminutes after 11.30 AM. June 5, 1976


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About 11.50 AM. June 5, 1976


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Dam crest breaching. 11.55 AM. June 5,1976


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Early afternoon June 5, 1976


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Late afternoon June 5, 1976


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Teton dam as it is today. The left side is where thebreach occurred. The damage to the face and right sidewas done by engineers and other inspection teamstrying to determine the cause of the failure. A memorialwas built on the site but there are no plans to eithercomplete the dam or to remove the remnants.


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What caused the dam failure??

Common causes of dam failure include: Spillway design error. Geological instability caused by changes to water levels

during filling or poor surveying.

Sliding of a mountain into the dam lake; filling thereservoir caused geological failure in valley wall leadingto 110 km/h landslide into the lake, water escaped in amega tsunami. Strictly this could not be classified as adam failure, since the dam structure didn't collapse at alland is still standing.

Poor maintenance, especially of outlet pipes. Extreme rainfall. Human, computer or design error


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How did they solve?No plans were made for rebuilding the TetonDam immediately after the disaster.However, asof July 2009, there was new about rebuilding inorder to provide water for irrigation, one of the

purposes of the original structure.

The Bureau of Reclamation has reportedly setaside $400,000 of the $800,000 needed to study

the feasibility of rebuilding. A local Idaho newsstation, "Local News Channel 8" ran a two partspecial on the process and reactions by localresidents.


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Ethical Concern

None of these investigations provided anyconcrete evidence as to why the dambreached when the reservoir level reachedEarth Level 5300.7 ft and only at aroundSta.14+00 on the right abutment.Therefore, a full understanding of the

mechanism of this key aspect of failuremay make an important contribution tothe state-of-the-art for dam construction.


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Lessons Learned

The lessons learned from this case may bedivided into two categories.In addition tothe technical aspects of the failure,professional and procedural factors alsoinfluenced the course of events.Thelessons learned also have implications forengineering education.


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Technical Aspects The failure of the Teton Dam could have been avoided. Early investigationsinto the geology of the site showed that the rocks in the area were almostcompletely of volcanic origin. These volcanic rocks consisted of basalt andrhyolite. In the footnotes to the geological survey of January 1971, therhyolite is defined as lightly to locally highly fractured and jointed,relatively light weight (pp. 4 -7, Independent Panel, 1976). This was alsothe condition for other possible sites located upstream of the site where thedam was constructed. These materials are usually avoided due to a historyof erosion and deposition. The reason for the extensive foundation was thepoor quality of the underlying material, including the grout curtain. Thegrout curtain failed to do its job of preventing these materials from beingeasily washed away.The panel noted that the design did not provide for downstream defenseagainst cracking or leakage, and did not ensure sealing of the upper part ofthe rock under the grout cap. The grout curtain was not constructed inthree rows, and the reliance on a single curtain was judged to be undulyoptimistic. The dam and foundation were not instrumented sufficiently towarn of changing conditions.


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Professional/Procedural Aspects

At the first sign of a problem the people at the dam site informed the Bureau ofReclamation. The Bureau did not immediately inform the public due to fear of panicand because there were initially no signs of imminent danger, but the public waswarned about 45 minutes before the collapse (Arthur, 1977). It was determined thatthe people involved acted responsibly and were not punished for their involvement.However, the failure of the Teton Dam brought about changes in dam constructionand operation by the Federal Bureau of Reclamation to ensure safety.

On the 25th anniversary of the disaster, Ken Pedde, the Acting RegionalDirector of the Pacific Northwest Region of the USBR, reviewed the lessons that hadbeen learned. Some of the changes in the process of dam design and constructioninclude peer review of dams, special treatment for fractured rock foundations, andfrequent site visits during construction by the design engineer. Also, redundantmeasures began to be used to control seepage and prevent piping (The Failure ofTeton Dam @ 2001). Pedde's address can be foun d athttp://www.pn.usbr.gov/news/01new/dcoped.html

This failure also made each federal agency review their dam safety activities andCongress passed several acts that authorized a national Dam Safety Program. Thesereviews and programs brought about annual dam inspections and the installation ofinstruments to monitor dams. Also, the Reclamation Safety of Dams Act of 1978provided funds to analyze and modify existing structures that were determined to bepotentially unsafe (The Failure of Teton Dam @ 2001).
http://www.pn.usbr.gov/news/01new/dcoped.htmlhttp://www.pn.usbr.gov/news/01new/dcoped.htmlhttp://www.pn.usbr.gov/news/01new/dcoped.html


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Educational Aspects This case demonstrates the importance of engineering geology and geotechnical engineering forcivil engineering students. Engineering geology is important for evaluation of the suitability offoundation and borrow or fill materials. In this instance, both the rhyolite under the dam and thefine aeolian silt used as a fill material were deficient. Ironically, better borrow material wasavailable in the valley downstream from the dam site, but the USBR decided that using it wouldbe environmentally disruptive (Independent Panel, 1976). It is also important to compact fill materials to maximum density at or near the optimummoisture content. In this case, the material was too dry and was not sufficiently compacted(Independent Panel, 1976)..The static hydraulic pressure may also be determined using the height of the dam of 93 meters(305 ft.) and the height of the water of 86.1 meters (282.4 ft.). The pressure increasedcontinually as the dam was filled. Also, this case can be used to review aspects of professionalpractice such as the responsibility of reviewing designs, and using redundant measures to ensurethe safety of the public. From the failure of Teton Dam, many lessons were learned. One of these lessons is thata dam site must have solid foundation material. An effective grout curtain may be an effectiveway of dealing with this unsuitable material, but only if there is a way to check if the groutcurtain is an effective barrier once it is in place. Also, this failure showed that dams must bedesigned so that pressure can be decreased if necessary. This was especially important in thiscase since the dam was allowed to begin filling while other parts were still under construction.


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Ethically, the conclusion of thiscase would be;

The case may be best summarized in the words of the panel report the Panel concludes (1)that the dam failed by internal erosion (piping) of the core of the dam deep in the rightfoundation key trench, with the eroded soil particles finding exits through the channels in andalong the interface of the dam with the highly pervious abutment rock and talus, to point at theright groin of the dam, (2) that the exit avenues were destroyed and removed by the outrush ofreservoir water, (3) that openings existed through inadequately sealed rock joints, and may havedeveloped through cracks in the core zone of the key trench, (4) that, once started, pipingprogressed rapidly through the main body of the dam and quickly led to complete failure, (5) thatthe design of the dam did not adequately take into account the foundation conditions and thecharacteristics of the soil used for filling the key trench, and (6) that construction activitiesconformed to the actual design in all significant aspects except scheduling. (pp. iii -iv,Independent Panel, 1976).In the design and construction of earth dams, it is necessary to select proper materials that aresufficiently resistant to piping and to ensure that they are compacted to the proper density. If agrout curtain is used, methods must be available to ensure that it is continuous and forms a sealwith the underlying rock. The design should incorporated adequate defense against cracking andleakage. Finally, dams must have sufficient instrumentation to provide early warning of pipingand impending failure.

As a final comment, this case stands as a warning against overconfidence and hubris. As everydam engineer knows, water also has one job, and that is to get past anything in its way (p. 93,Macauley, 2000).


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teton dam failure edit by aisha

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