A slope stability failure is more commonly known as a landslide, particularly among non-engineers. This type of failure occurs when the weight of a soil mass overcomes the soil’s shear resistance along a failure plane. Water within soil increases its unit weight, while reducing the shear strength. As a result, water and water pressures often play a role in triggering a slope stability failure.
The Vaiont Dam disaster of 1963 was a classic slope stability failure. Ironically, the dam itself did not fail and stands today. The dam is a thin concrete wedge in a narrow gorge. A vast soil mass falling into the reservoir triggered a massive wave that blew over the dam and destroyed villages downstream.
The
Vaiont Dam was part of an extensive system of dams, reservoirs, and
hydroelectric powerhouses located in the
On October 9, 1963, at 10:41 p.m., approximately 270
million cubic meters (353 cubic yards) of rock fell into the reservoir, moving
as fast as 25 m/s (82 fps). A
tremendous wave of water blew over the dam, virtually the entire reservoir,
sending a 70 m (230 ft) wall of water down Vaiont gorge.
It destroyed the town of
The slide moved a 250 m (820 ft) thick mass of rock
about 300 – 400 m (980 – 1300 ft) horizontally.
It pushed the old slide mass up the far slope.
Trees and soil along the
The dam, however, stood. It had withstood a force of approximately 4 million metric tons (4 million tons) of water, roughly eight times the force for which it had been designed. The dam is still there, but there is no water behind it (Wearne 2000, p. 217 – 219). There was a small gouge in the concrete about 1.5 by 9 m (5 by 30 ft) along the crest near the left abutment (Ross 1984, p. 132).
The volume of the slide was slightly larger than the
working volume of the Vaiont Reservoir. It
was more than twice the volume of the largest earthen dam ever built, the Fort
Peck Dam on the Missouri River in
The key document on this case study is The Vaiont Slide: A Geotechnical Analysis Based on New Geological Observations of the Failure Surface, Volume I, Main Text, Technical Report GL-85-5, published by the U.S. Army Corps of Engineers, U.S. Army Engineer Waterways Experiment Station, Vicksburg, Mississippi (Hendron and Patton 1985). It may be difficult to find except on loan from some large university engineering libraries.
The Vaiont Dam case study is covered in pages 206 through 225 of collapse by Wearne (2000) as well as pages 127 and 130 through 139 of Ross (1984). Wearne’s chapter contains accounts from engineers and survivors of the disaster. Engineering News Record reported on the case in the October 17, 1963 and December 7, 1967 issues, and published an editorial in the October 24, 1963 issue.
A very similar mechanism caused the 2005
This case study is discussed in Chapter 7 of the book Beyond Failure: Forensic Case Studies for Civil Engineers, Delatte, Norbert J., ASCE Press.
