Environmental Engineering Reference
In-Depth Information
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FIGURE 9.19
Map of Vaiont Reservoir slide. (From Kiersch, G.A., in
Focus on Environmental Geology
, Tank, R., Ed., Oxford
University Press, New York (1973), Section 17, 1965, pp. 153-164. With permission.)
probably remained as residual stresses in the mass. Erosion of the valley caused some
stress relief of the valley walls, resulting in numerous rebound joints that produced blocky
masses. In addition, groundwater had attacked the limestone, leaving cavities and con-
tributing to the generally unstable conditions (Kiersch, 1965).
The slide history is given by Kiersch (1965). Large-scale slides had been common on the
Vaiont valley slopes, and evidence of creep had been observed near the dam as early as
1960, when the dam was completed at its final height of 267 m. During the spring and
summer of 1963, the slide area was creeping at the rate of 1 cm/week. Heavy rains
occurred during August and September and movement accelerated to 1 cm/day. In mid-
September, movement accelerated to 20 to 30 cm/day, and on the day of failure, 3 weeks
later, it was 80 cm/day. Since completion of the dam, the pool had been filled gradually
and the elevation maintained at about 50 m below the crest or lower. During September,
the pool rose at least 20 m higher, submerged the toe of the sliding mass, and caused the
groundwater level to rise in the sliding mass. Collapse was sudden and the entire mass to
a depth of 200 m broke loose and slid to the valley floor in 30 to 60 sec, displacing the
reservoir and causing a wave that rose as much as 140 m above reservoir level. The dam
itself was only slightly damaged by the wall of water but was rendered useless.
Sliding was apparently occurring along the clay seams, but the actual collapse is
believed to have been triggered by artesian pressures and the rising groundwater levels
that decreased the effective weight of the sliding mass and, thereby, the resisting force at
the toe.
