Vajont Dam
Failure
A Slope Stability
Problem
Vajont Dam, Italy
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Completed in 1961
Located 100km North of Venice
One of the tallest thin arch dams
in the world
Stands at 265.5m tall
27 m thick at base
3.4 m thick at top
115 million m3 of water retained
by dam
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Located on a very deep and narrow gorge in the
Varjont valley.
Geology of the valley was thought to be known.
Analysis of ancient landslides carried out
Areas of weakness not identified in test borings
Believed to be sufficiently stable
October 9th 1963
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3rd drawdown of the reservoir
and heavy rains trigger
enormous landslide
260 million m3 of valley falls
into reservoir at speeds of up
to 110km/hr
This causes 50million m3 of
water from the reservoir to be
swept over dam in a 250 m
high wave
Effects
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Dam was relatively unaffected. Only top
1m or so of masonry washed away.
Flooding caused a landslide which
destroyed the nearby villages of
Longarone, Pirago, Rivalta, Villanova and
Fae.
Reports of up to 2000 deaths
Damage also caused by air displacement
from the “splash” in surrounding villages.
Longarone, in the morning, 9th
October, 1963
Longarone, in the morning, 10th
October, 1963
Causes of Failure
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Speculation of location of sliding surface. Recent
studies confirm it was located in thin clay layers
(5-15cm)
Claims that it was a reactivation of an old
landslide
Others claim it was first time movement
Increase in level of the reservoir drove up pore
pressures in clay layers, reducing the effective
normal stress and hence the shear resistance
Failure occurred in brittle manner resulting in a
catastrophic loss of strength