Geoscience Reference
In-Depth Information
10.2.10.
Earthquakeperformanceoflargezoneddamswithrockfill
The Matahina Dam (1967) was shaken by the Edgecumbe earthquake (M = 6.3)
on May 2, 1987. The maximum ground acceleration PGA = 0.33g triggered a
sinkhole at the crest, revealing and boosting internal erosion.
Since 1975, the 60 m La Villita Zoned Dam with a thick core and the 148 m El
Infiernillo Dam with a thin core have been shaken by a series of close earthquakes:
five of them had a magnitude greater than 7.2 and one was 8.1. The damage can be
summarized as cracks and settlements. It is interesting to note a trend of increasing
settlements at La Villita, suggesting a progressive deterioration of the material
strength that does not exist at El Infiernillo.
In 1984, the 105 m Makio Dam experienced the Nagano-Ken-Seibu earthquake
(M = 6.8), being 5 km from the epicenter. Only 1.5 m deep cracks at the crest were
observed, despite the ground acceleration being estimated at between 0.5 and 1.0 g.
All the modern zoned dams performed well, as has been generally predicted in
prior evaluation studies.
10.2.11.
Earthquakeperformanceofconcretefacerockfilldams
The 85 m Cogoti Dam was built in Chile in 1939 using dumped rockfill. It was
shaken by several earthquakes, including that of Illapel in 1943, leading to the
creation of a 40 cm crest settlement. The new settlement curve over time seems to
have converged with the old one. It seems that the earthquake only accelerated the
long-term settlement. Cracking slabs caused leaks that have increased over time and
need repair.
The 146 m Zipingpu Dam, with a capacity of 1 billion m
3
, was shaken on May
12, 2008 by the Wenchuan earthquake (M = 7.9), whose epicenter was 17 km away.
A peak acceleration of 2.0 g was measured at the crest. Localized settlement could
be seen on the downstream face near the spillway. The maximum settlement reached
73 cm and the maximum displacement reached 18 cm. Despite the many splits and
cracks along the joints of the upstream slabs, the increase in leakage was very small.
The main problem caused by this earthquake is not the performance of dams built by
man, but the management of the 69 natural dams that formed after landslides in the
valleys (see Figure 10.3). Their failures occurred without causing casualties. Some
failures were deliberately initiated after evacuating the population.
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