Evaluating Seismic Stability of Embankment Dams - Multiscale Geomechanics: From Soil to Engineering Projects - page 334

and M = 6.7 (1990). Numerous longitudinal cracks appear, and sand boils indicate
the presence of liquefaction, but the levees do not break. An interesting case of
liquefaction has been reported [POP 93]. This is one of the embankments of the
Draganesti hydropower plant on the most important river in Romania, the Olt. The
length of the embankment is 28 km and its maximum height is 20 m. The typical
section is a homogeneous gravelly embankment based on a drainage layer with
upstream concrete slabs. The upper layer of the foundation is a 1.2 to 7.0 m thick
continuous layer of silty sand resting on the alluvial gravel deposit (used for the
body of the embankment). The silty sand was compacted by stone columns
increasing the relative density from 10% to about 60% over the first 4 m and along
80% of the length. The earthquake of May 30, 1990, with an estimated maximum
acceleration of 0.12 g, liquefied 60 m of the uncompacted foundation (silty sand
with a relative density of 10%) in a leaking zone. The level of the reservoir was 4.8
m below the normal level. The hydraulic head above the ground surface was about
8.0 m when the earthquake occurred. Liquefaction caused a global movement to
downstream, with contraction and lifting up of two slabs above the upstream toe and
a sliding of the downstream toe, which filled the downstream drainage channel.
Despite the liquefaction, the embankment did not fail (see Figure 10.1).
Figure 10.1. Mean profile of the Romanian embankment damaged by the Vrancéa earthquake
(1990)
10.2.8. Earthquakeperformanceofsmallearthdams
Failure of the 12 m Lo Ovalle Dam (1932) and the 18 m Lliu-Lliu Dam (1934)
during the earthquake of March 3, 1985 in San Antonio is indicated by the ICOLD
Bulletin 99 , but not confirmed by Bulletin 120 [ICO 01]. One explanation is that
sliding occurred, but no water was released.
In Japan, the number of irrigation dams in 2000 was over 100,000, with 1,872 of
them exceeding 15 m, out of which 1,688 are embankment dams. Several seismic
failures were reported among embankments built before 1945 (the oldest is 1,600