The failure of the dam Vaiont is a catastrophic event not due to structural failure of the arched double curvature dam, but in a huge landslide slope of a flood basin. Despite the fact that in the area of Vaiont there was every indication of a "problem" area, though political-economic interests, combined with the absence of a common language among geologists and engineers, led to disastrous errors and omissions.
Failure Date: October 9, 1963
Casualties: Approximately 2,600 deaths and destruction of cities, Longarone and Villanova Valley Piave.
History: The Vaiont dam was completed in 1960, at a high altitude valley in the Italian Alps and was 266 meters tall, making it the second highest dam in the world after the dam Cupola.
The geomorphology of the area indicated that there was risk for the southern slopes, mainly. Nevertheless it was decided by the engineers of the project that there was no reason for concern.
Not having sufficient geotechnical data, it was decided to draw up a typical geotechnical analysis. the existence of a prehistoric landslide which is still active was noted. But the company had already spent a huge amount of money, so they did not want to stop the project.
During the first filling of the reservoir (February to November 4, 1960), movement was seen in the southern slope. While at the beginning the landslide was ranged a few mm / day, in October the landslide was ranged at about 4cm / day. As the reservoir began to reach the planned level of filling, a large crack opened (tension crack), 300 m length and 1,5 m width. On 4 November, while the filling of the reservoir was continuing, a part of the landslide, measuring 500x500m, (700.000 m3), slid into the reservoir within 10 minutes.
The engineers tried to control the rate of movement of the slope through decreasing and increasing the reservoir level.
After 3 years it was found that the slip rate was increased dramatically. Engineers had no longer the control. Heavy rains made worse the situation. Immediate reduction in reservoir level was decided in an effort to check the landslide which was moving uncontrollably at up to 0,4m / day, without success but with terrible consequences.
The latest measurements on 9 October that were recorded were 80cm / day in a large area of the landslide. The same day at 22:15, the landslide accelerated. A large block with length 2km, width 1,5km, and a thickness of several hundred meters (2.7 × 10 8 m3) slid from the hillside to the reservoir at a speed of 110km / h. The induced wave outstripped the dam at 70m and the downstream valley was flooded destroying cities Villanova, Longarone and Casso.
The most tragic failure in history with 2,600 dead people.
Sources: landslideblog.org, wikipedia
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