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a poorly compacted sandy-clayey material (4 <N <17, 30%, <80 μm, IP = 13).
Located 26 km from the fault, it was shaken by a maximum site acceleration
estimated at 0.23 g. The water reservoir level was half its normal height. Major
sliding moved away the upstream face causing a step of 4 m, without overtopping
the dam. The safety factor decreased from 2.8 to 1.0 during the earthquake, due to
an increase in pore pressure of about 80%.
To ensure safety or to guarantee the availability of water, 245 small earth dams
damaged in the Bhuj earthquake in India on January 26, 2001 (M = 6.9) required
immediate repair [PAT 03]. The damage was mainly due to settlement of crests,
transverse and longitudinal cracks at the crest and upstream face, cracks and steps in
the upstream face of the highest section, openings of the contact with structures,
floor structures and sand boils. No spillway, however, suffered damage. The soils of
the Kachchh region are sandy and silty, poorly compacted, and vulnerable to
liquefaction. Saturated at the bottom of the valley, they caused significant
settlements and upstream landslides but, on account of the low water reservoir level,
only one failure. For instance, the 18 m Shivlakha Dam (1954), with a core of
masonry, was located 39 km from the epicenter. Traces of liquefaction of the
foundation were observed upstream and downstream, causing sliding of the
upstream slope and a ridge under the sliding of the downstream toe. The only
reported failure was the 17 m homogeneous Chang Dam, built with a masonry core
in 1959. This unusual design can barely sustain the probable seismic differential
settlements. The earthquake liquefied the foundation 16 km from the epicenter,
causing upstream and downstream sliding, accompanied by a collapse of the crest
and the shear of the core. The reservoir was deliberately emptied through a breach to
avoid damage following a probable high flood.
10.2.9. Earthquakeperformanceoflargeearthdams
Ono Dam, built in Japan in 1914, has a height of 37 m above the ground surface
and 40 m above its foundations. Shaken by the Kanto earthquake in 1923 (M = 8.3),
it is perhaps the first documented case of seismic damage. It did not fail, but it
settled nearly 30 cm, with longitudinal cracking on the upper third of the upstream
face and crest up to 60 m long, 10 m deep and 25 cm wide.
The 28 m Russian Nizhni Svirskaya Dam, built in 1934, broke in 1935 after a
mine fire [ICO 95], but this information has not been confirmed by ICOLD (2001).
The Hegben Dam, built in the USA in 1915, has a height of 34.5 m. Its reservoir
was full when it was shaken by the Yellowstone earthquake in 1959 with a
magnitude of 7.1. The earthquake caused a 5 m step along the active fault
crossing the reservoir, 500 m from the dam. Four landslides downstream released
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