Case studies – Dam failures
D. Kero
Luleå University of Technology, Luleå, Sweden
H. Silvernagel
Luleå University of Technology, Luleå, Sweden
J. Forsman
Luleå University of Technology, Luleå, Sweden
ABSTRACT: This paper deals with three case studies of famous dam failures, Teton dam (USA), St.
Francis dam (USA) and Vaiont dam (Italy). The cases represent different dam constructions and
failures, Teton dam was a rockfill dam, St. Francis and Vaiont dam was concrete gravity-arch dams.
The reasons of failures are quite different, Teton dam failed because of seepage through the dam
which expanded rapidly resulting in a collapse. Vaiont dam did not have a construction fault, instead a
huge landslide pushed enormous amounts of water over the crest. St. Francis dam was built upon a
weak layer of rock and had been built to high, this resulted in a possible overturn failure in
combination with a landslide. These dam failures killed hundreds of people and caused devastating
destruction to the surroundings. Dam construction is one of the most demanding areas of expertise
because failure often leads to enormous casualties.
1
ST. FRANCIS DAM
1.1
Construction
The dam was built between 1924 and 1926 and was located 64 km northwest of Los Angeles,
California, and was designed as a reservoir to support Los Angeles with water for a year if the Los
Angeles Aqueduct should be damaged or sabotaged. The chief engineer for the project was William
Mulholland, a civil engineer that worked for Los Angeles Department of Water and Power.
The dam was planned to be 53 meters (175 feets) high and 185 meters (600 feets) long. When the
construction began, see figure 1, in 1924 Mulholland decided to raise the height of the dam three
meters (10 feets) to increase the capacity of the reservoir. Later when the dam was half finished in
1925 he made another decision to raise the dam 3 more meters. These decisions increased the capacity
of the dam from 37 million cubic meters to more than 47 million cubic meters of water. The final
height of the St. Francis dam where 59 meters. This change in construction was made without an
increase of the base of the dam. The city of Los Angeles was growing rapidly and the size of the
reservoir had to be this large to be able to support the city if needed.
Figure 1. Constuction of St. Francis dam. (1.)
1.2
The failure
In 1926 to 1927 several cracks appeared in the construction, some of those were even leaking water.
These cracks where inspected by Mulholland, who concluded that they were normal concrete cracks
for a dam the size of the St.Francis due to natural settlements.
The damkeeper of St.Francis dam was a man named Tony Harnischfeger who lived in a cottage 400
meters downstream of the dam. He discovered new cracks and leaks when the reservoir was filled to
its capacity for the first time on March 7th, 1928, see figure 2. He reported this to Mulholland who
dismissed them as normal a second time. On March 12th Harnischfeger located new leaks and alerted
Mulholland who once again pronounced the dam safe.
Figure 2. St. Francis dam filled with water. (1.)
Figure 3. “The tombstone” and the landslide. (1.)
Less than twelve hours after the inspection the dam collapsed, this happened approximately at 23:57
on March 12, 1928. The dam broke into several large pieces, some of which was carried several
hundred meters downstream, while the center section of the dam, called “The Tombstone”, remained
standing as can be seen in figure 3. (1)
The collapse released 45 billion liters of water in a powerful wave that destroyed everything in its
path. The damkeepers cabin was hit by a wave that’s been estimated to be 42 meter high. (4) The
water continued to flow south though the San Francisquito Canyon and then turned left into the Santa
Clara River bed, flooding the towns of Fillmore, Bardsdale and Castaic Junction. When the flood
finally reached the Pacific Ocean it had travelled 87 km from the reservoir, figure 4. Bodies was found
as far away as the Mexican border. (1)
Figure 4. The floods way to the Pacific Ocean, 87 km. (6.)
The exact number of victims is unknown but the official death toll is 495. No one knows how many
undocumented farm laborers died that night. The city of Los Angeles paid several million dollars in
recompense to families and landowners. (2)
1.3
The cause of failure
One of the main factors for the collapse is the heightening of the dam without widening the base of the
construction, according to Mulholland the factor of safety against overturning “was in excess of 4,”
but the dams new height would have reduced the factor to as low as 0.77. The massive force from the
water could have lifted the dam from its foundation causing a large tension crack in the upstream heal
of the dam. (3)
In the 1920s the geological investigation showed no problems with the dam being built on the
existing type of rock. This has later been proved to be an area that had been exposed to multiple
landslides throughout history.
Post-failure studies of the surrounding environment shows that a massive landslide occurred along the
dams left abutment. 500 000 cubic meters of schist could easily have torn the dams entire left
abutment from the rest of the construction. (4)
Two of the worlds greatest geologists at the time had found no fault with the rock. Following the
disaster Mr. Mulholland said “Don’t blame anyone else, you just fasten it on me. If there was an error
in human judgment, I was the human, and I won't try to fasten it on anyone else.” He was cleared of all
charges because no one could have known of the instable rock the dam was built upon. (1)
2
TETON DAM
2.1
Construction
The construction of the Teton dam started in February 1972 in Idaho, USA. It took almost four years
to finalize the dam and in October 1975 the dam began to store water in the reservoir. The contract for
the 93 meter high dam was won by the company of Morrison-Knudsen-Kiewit in December of 1971,
but the dam had been planned for many years ahead of the final decision to build it. The first site
investigations took place as early as in 1932. Many other alternative sites along the Teton River where
also investigated before the location of the dam was set. The intension of the dam was not only to
provide the area with hydropower but also to provide the irrigation in the area (40.000 hectares) with
water as well as flood control and recreation. (7)
Most of the dams in the world are embankment dams and so where the Teton dam. Because of the
bad rock in the area a genuine foundation work had to be done. A cut of trench was done down to the
rock and the rock under the abutments was excavated. Under the whole foundation a continuous
grouting curtain was injected. The embankment dam consisted of four zones of different material and
functions. Zone 1 was the core and this zone consisted of material with low permeability to prevent the
water from escaping the reservoir. Zone 2 was the filter that prevented the material in the core to be
filtrated out of the dam. Zone 3 was a layer that provided the dam with structural stability. Zone 5 was
the rockfill, the most outer layer of a rockfill embankment dam. The Zones are shown in figure 5
below. (8)
Figure 1. Cross-section of the dam construction. (7)
2.2
The failure
The first sign which indicated that something was wrong came on June 3 1976, when a small seepage
of water showed on the right abutment near downstream of the spillway. The day after a spring
showed closer to the embankment, the flow from the spring was about 80 liters per minute. (8) For the
rest of the day the dam was thoroughly investigated and no signs of seepage water was found
anywhere on the main dam construction. The flow in the spring remained constant until the morning
of June 7 when it increased rapidly. At 9.30 that morning the first sign of leakage in the actual
embankment started. At 10.30 the flow had gone from 2 cubic meters per second to 30 cubic meters
per second and a whirlpool had begun to show in the basin on the upstream side of the dam. The
police and media in the concerned areas had been notified when the first sign of leakage in the
embankment came but it was not until now they began to understand the real danger of the situation. A
few hours after the warnings had reached the people living in the risk area the dam failed and released
the whole reservoir containing around 370 million cubic meters of water into the surrounding
downstream area. (9)
Because of the basalt rock the dam was founded on the grout curtain was an essential part of the dam
construction; and the geologists at the Bureau of Reclamation had specified that in the deeds. The
curtain was injected in three rows of holes. It extended down to 100 meters under the foundation and
300 meters beyond the abutments. Even with such an extensive grouting program some people
consider a failure in the grout curtain to be the reason for the dam failure. Commissioner Gilbert
Stamm said that the water had either found its way around the grout curtain or went right through it.
In the catastrophe following the failure 11-14 (contrarious information) people died and some 2000
people where injured. The breach caused an area of more than 770 square kilometers to over flood.
The flooding caused damages costing several hundred million dollars; among the things ruined were
more than 7000 homes. (9)
The catastrophe got a lot of coverage in media because of the projects controversy. Before it got
built the dam project met a lot of resistance from environmentalists and various experts, it was placed
on a hit list for water constructions that were considered not cost effective or planed on to difficult
sites. Maybe it was because of the bad publicity the whole project had endured that the US
government did not put in more funds into dam inspection at this point. It took another 18 months and
another dam failure in Georgia to get them to act. (9)
2.3
The cause of failure
A panel of ten people where put together to investigate the incident and to find out what really caused
the breach of the dam. They got to the conclusion that piping occurred in the base of the core in the
keyway that was cut into the right abutment. They said the dam had been inadequately drained; that
was the reason water had burst through the face of the downstream embankment. The piping
phenomenon could have been due to the insufficient grouting. The committee completely freed the
contractor from having anything to do with the dam failure. They had followed the deeds and done
everything the Bureau of Reclamation had demanded; the responsibility according to the committee
lay instead in the bureau’s hands. The final report in the matter said that the reason of the breach was
poor embankment design and inadequate inspection of the Bureau of Reclamation. The poor
embankment design was primary a bad filter layer that did not protect the core from eroding due to
seepage water. The report also said that even if the conditions at the site of the dam where bad a safe
dam could have been constructed. If the core had been better drained and protected against internal
erosion their opinion was that it would still be standing there. (9)
References:
Internet:
1. http://en.wikipedia.org/wiki/St._Francis_Dam, 2007-12-14
2. http://www.scvhistory.com/scvhistory/sg031101.htm, 2007-12-14
3.
http://web.umr.edu/~rogersda/st_francis_dam/lessons_learned_from_the_st_francis_dam_failure(geost
rata_mar-apr_2006).pdf) , 2007-12-14
4. http://web.umr.edu/~rogersda/st_francis_dam/reassessment_of_st_francis_dam_failure.pdf, 200712-14
5.
http://web.umr.edu/~rogersda/st_francis_dam/Impacts%20of%20St.%20Francis%20Dam%20Failurecompressed.pdf, 2007-12-14
6. Google earth, 2007-12-14
7. http://www.eng.uab.edu/cee/faculty/ndelatte/case_studies_project/Teton%20Dam.htm
8. http://www.geol.ucsb.edu/faculty/sylvester/Teton%20Dam/narrative.html
Books:
9. Ross, Steven S. 1984. Construction Disasters. New York, USA. McGraw Hill Book Company.