Vajont dam
| Vajont dam | |||||||||
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| Coordinates | 46 ° 16 '2 " N , 12 ° 19' 45" E | ||||||||
| Data on the structure | |||||||||
| Construction time: | 1956-1959 | ||||||||
| Height above valley floor: | 261.6 m | ||||||||
| Building volume: | 360,000 m³ | ||||||||
| Crown length: | 190.15 m | ||||||||
| Crown width: | 3.4 m | ||||||||
| Base width: | 22.1-27 m | ||||||||
| Data on the reservoir | |||||||||
| Storage space | 150 million m³ | ||||||||
| Particularities: |
Arch dam |
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The Vajont dam in the Alps in northeast Italy (100 km north of Venice ) was built from 1956 to damming the river Vajont . It became known through the "Catastrophe of Longarone" ("Catastrophe of the Vajont"; Italian strage del Vajont , disastro del Vajont or tragedia del Vajont ) on October 9, 1963.
The damming of the Vajont reservoir led to a landslide from Monte Toc into the lake. This caused a large tidal wave that poured over the top of the wall into the narrow valley and completely destroyed the town of Longarone , the villages of Faé, Villanova, Erto and five others. Around 2000 people died in the disaster. More than half of the bodies were not found. The dam was largely undamaged during the disaster and is still there today, but the lake was not dammed again.
The project
The project for a dam in the Vajont Valley was operated by the company SADE (Società Adriatica di Elettricità) , which was particularly active in the electricity market in northeastern Italy towards the end of the 19th and during the first half of the 20th century.
The aim of the project was to provide large water reserves in the middle of the foothills of the Alps in order to be able to generate enough electricity for the city of Venice during the dry season. The Piave River and its tributaries carry sufficient water in the autumn and spring months, but very little in the winter and summer months.
The gorges of the Vajont river (which has its source in the Friulian Dolomites and flows into the Piave after flowing along Monte Toc) were particularly suitable for the project. Along the course of the river, near the mountain villages of Erto e Casso , the geologist Giorgio Dal Piaz and the civil engineer Carlo Semenza found an apparently suitable place to build what was then the highest double arch dam in the world; Until the construction of the Grande Dixence dam in 1965, it was the highest dam on earth.
The initial project envisaged a 202 meter high arch dam with a storage capacity of 58.2 million cubic meters. The plans were later modified so that the wall should reach a height of 261.60 meters with a storage volume of 152 million cubic meters. The volume of the reservoir was therefore much larger than in any previous project that had been carried out in the Piave Valley.
The Vajont project received full approval from the relevant ministry on July 17, 1957.
Planning and construction of the dam
Preliminary work
In 1929 Dal Piaz and Semenza made their first ascent in the valley. The project work for the Vajont dam began around 1940, and the project came before the responsible authorities in 1943 under the name “Grande Vajont”. Since most of the members of the commission were at war and could not vote, the "Grande Vajont" was approved without reaching a minimum number of voters. In the following years this result was never questioned.
After the Second World War, the Vajont project, for which SADE exerted great pressure, began to take shape and was finally presented to the Genio Civile, the competent authority. The first thorough geological surveys were carried out in 1949. At the same time, the protests of the valley communities involved in the project, Erto and Casso, began, because the new lake was intended to flood numerous residential buildings and a lot of agricultural land.
Despite strong protests from the valley residents and doubts from the responsible control authorities, the first expropriations took place in the mid-1950s, and preparations for the large construction site continued. The actual construction work began in 1956 without the approval of the responsible ministry.
Construction work
During the construction work, unforeseen adjustments had to be made to the project as a number of minor landslides occurred on the flanks on which the wall was based. For this reason, cement injections had to be pressed into the rock.
After the start of work, a few small earthquakes occurred , so that SADE had to apply for further geological surveys that uncovered the remains of an ancient landslide from the Paleolithic on Monte Toc . These rock masses threatened to slide into the lake when the water level rises at the foot of the landslide. SADE never sent these new findings to the responsible control bodies.
The construction work was progressing: On February 2, 1960, the lake was partially filled up to 600 m , later that year the water level rose to 650 m . On November 4, 1960, the first landslide occurred: 700,000 cubic meters of loose rock and rock fell into the lake without causing any major damage.
After this first landslide , the Institute for Hydraulics and Hydraulic Engineering at the University of Padua was commissioned to create a simulation for a disaster in the Vajont Valley. In a model, the consequences of a 40 million cubic meter landslide were simulated using gravel. According to this simulation, which turned out to be wrong in the following years, a water level of up to 700 m would have been considered safe, because it would not have caused any damage. Simulations that were carried out after the disaster, considering the correct extent of the landslide and with the help of connected concrete slabs, led to a result comparable to reality. These studies had to be commissioned abroad, because no institute in Italy wanted to question the results of the first simulation and thus embarrass the University of Padua.
Between 1961 and 1963, the lake was filled and emptied several times to prevent the risk of landslides in the surrounding area. On September 4, 1963, the water level even rose to a level of 710 m . The inhabitants of the valley complained about the ground movements accompanying the damming and the numerous earthquakes, while loud noises could be heard from the mountain. In order to counter the risk of the rear storage space constricting, a bypass tunnel was built during this time. A controlled damming would no longer have been possible due to a mass movement into the reservoir. The Vajont River is still routed through the tunnel today before flowing into the gorge via a waterfall below the lock.
Protest of the residents
Ever since the SADE appeared on Monte Toc, the inhabitants of the Vajont Valley tried to assert their claims to property by defending themselves against the expropriations and complaining about obvious errors in the project. Two citizens' initiatives emerged, the "Comitato per la difesa del Comune di Erto" and the "Consorzio Civile per la rinascita della Val Ertana", but their concerns and reports were never heeded by the authorities.
Tina Merlin (1926–1991), a journalist for the communist newspaper " L'Unità ", published several articles on the subject and was therefore charged with defamation and disruption of the public peace. However, in a trial she was acquitted of the allegations.
Flood disaster and the consequences
The catastrophe
At 10:39 p.m. on October 9, 1963, the catastrophic landslide occurred, with 270 million cubic meters of rock (almost twice the storage volume) slipping from Monte Toc towards the lake over a length of 2 kilometers, largely filling its basin. The sudden displacement of the dammed water caused a huge tidal wave that missed the villages of Erto and Casso on the opposite slope by a few meters before flowing up the valley and destroying a few small towns there. About 25 million cubic meters of water (about one sixth of the storage volume) overflowed the wall and reached the small town of Longarone, located at the end of the narrow valley: This and some of the surrounding villages were completely destroyed. About 2,000 people died immediately (official sources say 1917 victims, others more; the number has never been determined). Few people - mostly children - were found alive. The wall itself remained largely undamaged.
After the disaster
The Ministry of Public Works ("Ministero dei Lavori Pubblici") immediately opened an investigation into the causes of the disaster. Civil engineer Pancini, one of the defendants, committed suicide shortly before the trial. The trial began in 1968 and ended a year later with the sentencing of all the defendants involved to 21 years in prison for the disaster and multiple murders involved.
The appeals court reduced the sentences for some of the defendants and acquitted the others for lack of evidence. In 1997, Montedison , which had bought SADE, was ordered to pay damages to the affected communities. A small memorial chapel was built on the right mountain slope.
For survivors of the Longarone disaster ( Disastro del Vajont ), the state founded a new town called Vajont in 1971 . Longarone was also rebuilt in the 1960s and 1970s.
The journalist Tina Merlin wrote a book about the disaster ( Sulla Pelle viva. Come si costruisce una catastrofe. Il caso del Vajont ). But it wasn't until 1983 that she found a publisher for this. Further editions appeared in 1993, 1997, 2001 and 2016.
Geological analysis
The Vajont landslide had several causes. First of all, it is undisputed that the creeping , i.e. the movement of the slope, only became apparent when the lake was dammed. As a result, the lower, supporting part of the slope was lifted and weakened. At the same time, thin, swellable clay layers only centimeter thick ( smectite , montmorillonite and other clay minerals ) soaked up with water deep below the surface of the terrain. As a result, their strength - their resistance to shear , which is not great anyway - decreased further. This created a sliding joint, or, as some authors assumed, a sliding layer created by a landslide from much earlier times was reactivated.
So the slope started moving. As long as no buildings or structures on the slope were affected, this creeping was not dramatic. The slope was not so steep that a sudden failure had to be feared, because even in the clayey slip joint there was still so much friction that the movement could not become extremely fast. In the worst case, it was thought that part of the slope would slide more or less slowly into the lake or the rock would block itself after a certain distance. The cross-section of the slope resembled a chair with a 40 ° steep, sloping back and an almost horizontal, supportive seat. Smaller, harmless slides were factored in, and at some point the seat would bring the back to hold. An attempt was made to enforce this through the several damming and lowering phases until 1963. Unfortunately, the expectations placed on this measure were wrong.
With increasing damming, the creeping movements increased more and more, until then on October 9, 1963, in a lowering phase (the mirror was a good 9 meters lower than the previous damming) the previously "leisurely" crawling movement (a few centimeters a day) dramatically within a few minutes increased and the rock masses finally hit the lake at a good 100 kilometers per hour.
A study from 1985 came to the conclusion that heavy rainfall and the simultaneous lowering of the congestion target could have been enough for the failure. In vertical crevices - many of them had surely opened up due to the sliding movement - water could have penetrated, but no longer drained. At the same time, the water trapped in the slope could not have drained quickly enough when the water level fell . The hydrostatic height of the water alone causes an enormous horizontal pressure, which is just as great in a gap just millimeters wide as in the sea ( hydrostatic paradox ). Both of these certainly weakened the slope even more, but were probably not the final trigger for the dramatic landslide, because the crawling speed inexplicably increased in the weeks before, even though it had not rained during this time.
If this increase in creeping speed cannot be reconciled with the damming of the lake, there must be other explanatory models. In the shear joint, the friction must have suddenly disappeared. Leopold Müller , one of the experts after the disaster, was of the opinion that the behavior of the sliding joint was thixotropic , i.e. the strength of the material must have decreased due to the movement. One explanation for this loss of friction would be that the pressure in the tiny, water-filled pores of the thin layers of clay must have increased so much that it was finally sufficient to support and lift the entire weight of the slope. The slope could then fall into the lake with practically no friction.
Such an explanatory model, which presumably also applies to some failure of embankments in earthquakes, was developed at the University of Padua. The constant creeping (viscoplastic flow) of the slope resulted in frictional heat in the sliding joint. This had been the case for years, because the slope had been crawling for just as long, and for just as long it had flowed back into the surroundings without a significant rise in temperature in the water-saturated clay. If the pore water is heated, however, the pressure in the pores increases (because the very impermeable clay drains only slowly), the strength of the layer decreases and the creeping movements increase. Initially only imperceptibly and slowly, but always continuously, the speed increased within 5 months from less than one centimeter per day to up to 10 centimeters on the day of the disaster. The calculated temperature in the interior of the clay layer initially rose by just over 3 ° C to around 23 ° C compared to that in the rock.
About three weeks before the disaster, according to the model, which was subsequently calibrated with the measured values of the slope movement, a change occurred. From now on, the increase in temperature concentrated more and more on the thin shear zone, the significantly deforming area in the middle of the clay layers. The state became increasingly adiabatic , the warmth remained in the clay. Previously, at least as much heat was given off to the environment as was produced, but now a state was reached where the increasing temperature weakened the shear zone and the slope speed increased as a result. For this reason, there was even more frictional heat, which in turn influenced the shear strength. The system rocked to a critical state, but this still happened slowly and almost imperceptibly.
Within the last 3 weeks the temperature rose to about 36 ° C. But this is the calculated critical temperature from which the clay wants to release its bound water. This effect then suddenly, within minutes, leads to a large, almost explosive increase in pore water pressure, which then led to a catastrophe. The shear strength was lost, the slope swam up and slid into the lake.
Summary
The landslide flank gave cause for concern even before the disaster and during the construction of the barrier due to various smaller landslides and earthquakes. At the same time, geologists discovered a massive landslide that was far back in history. An expert report by the University of Padua , using a scientific simulation, came to the conclusion that a catastrophic demolition scenario could also be managed. These decision-making bases were available to those responsible - operator, building consortium and state approval authority - when, shortly before the disaster, further warning signs such as weak earthquakes and unusual noise noises in the mountain increased a month before the event. Based solely on the Padua report, which can be proven to be false from today's perspective, the various warning signs were ignored and the damming process continued undeterred - with fatal consequences.
Similar event in the Pontesei warehouse in 1959
It is largely unknown that as early as 1959 in the valley opposite Forno di Zoldo, when the Pontesei reservoir was first dammed, a "small vajont" occurred. Accelerated slope movements of the left storage system from 13 m below the stowage destination prompted the operator to stow quickly. Presumably due to the excess pore water pressure in a comparable slideway, approx. 3 million cubic meters of material were mobilized and slipped into the storage space. A 20 m high tidal wave overflowed the crown only slightly, the barrier keeper Arcangelo Tiziani (Cagno Padéla) was killed. The operator - SADE - downplayed this incident. Today the first flood relief structure , an open-air tower with an overflow funnel , bears witness to this "mishap"; Since 1959, the flood relief has been provided by a second, lower-level structure.
See also
literature
- Rinaldo Genevois, Monica Ghirotti: The 1963 Vaiont Landslide. In: Giornale di Geologia Applicata. Volume 1, 2005, pp. 41-52. Chronological summary with presentation of the explanatory models for the landslide and references to relevant scientific work on the Vajont catastrophe, (English).
- Marco Paolini, Gabriele Vacis: The flying lake. Chronicle of an announced disaster. ISBN 3-88897-207-8 .
- Paperback edition rororo 2000, ISBN 3-499-60841-3 .
- Tina Merlin: Sulla pelle viva. Come si costruisce una catastrofe. The caso del Vajont. 1st edition. 1983. (2001, ISBN 88-8314-121-0 )
- Axel Bojanowski : Natural disaster: When the mountain fell into the lake . In: Süddeutsche Zeitung . October 29, 2007 ( sueddeutsche.de - Archived May 19, 2010).
- Giovanni Barla, Paolo Paronuzzi: The 1963 Vajont Landslide: 50th Anniversary . In: Rock Mechanics and Rock Engineering . tape 46 , no. 6 , September 26, 2013, p. 1267-1270 , doi : 10.1007 / s00603-013-0483-7 .
- Axel Bojanowski: Vajont disaster: Why the mountain fell into the reservoir. In: Spiegel Online . April 20, 2015.
- Georg Lux, Helmuth Weichselbraun: Derelict & Forgotten - Lost Places in the Alps-Adriatic Region . Styria Verlag, Vienna / Graz / Klagenfurt 2017, ISBN 978-3-222-13551-4 , pp. 120–127.
- Georg Lux, Helmuth Weichselbraun: Forgotten & Displaced - Dark Places in the Alps-Adriatic region . Styria Verlag, Vienna / Graz / Klagenfurt 2019, ISBN 978-3-222-13636-8 .
Movie
documentation
- Daniela Agostini, Hannes Schuler: The conquest of the Alps. (4/5) hydropower. Germany, 2009, 43 min. Link at the Graz Film Festival 2009.
motion pictures
- Renzo Martineli: Vajont - La diga del disonore . Italy 2001
Web links
- Vajont - La diga del disonore in the Internet Movie Database (English) (film about the disaster)
- Human disaster
- Vajont dam. In: Structurae
- the history of the Vajont (Italian or French)
- ProgettoDighe: Vajont - with lots of photos and technical information
- Vajont dam
- Il disastro del Vajont - successione cronologica dei principali eventi (Italian)
- Lost Places - The Dolomites Dam (video about the disaster, with simulation of the landslide)
Individual evidence
- ↑ Felice Dal Monte: Your fate was called SADE . In: The magazine . February 1964, p. 54-56 .
- ^ Toni Sirena: Tina Merlin: partigiana, comunista, giornalista
- ↑ Tina Merlin: Sulla pelle viva. Come si costruisce una catastrofe. Il caso Vajont. Cierre Edizioni, 2016. (Details on the older editions also here )
- ^ E. Semenza: Sintesi degli Studi Geologici sulla frana del Vajont dal 1959 al 1964. Mem. Mus. Tridentino Scie. Nat., XVI, 1965, pp. 1-52.
- ↑ Alessandro Pasutoa, Mauro Soldati: The use of landslide units in geomorphological mapping: an example in the Italian Dolomites. 1991.
- ↑ David Petley: Landslide information: The Vajont (Vaiont) Landslide. ( Memento from August 13, 2006 in the Internet Archive ) Land-Man.Net. Retrieved September 28, 2015.
- ^ AJ Hendron, FD Patton: The Vaiont slide, a geotechnical analysis based on new geologic observations of the failure surface. Technical Report GL-85-5, US Army Corps of Engineers , Washington DC 1985.
- ↑ Emmanuil Veveakis, Ioannis Vardoulakis, Giulio Di Toro: Thermoporomechanics of creeping landslides: The slide 1963 Vaiont, northern Italy. In: Journal of Geophysical Research. Volume 112, F03026, 2007, doi: 10.1029 / 2006JF000702 (PDF; 670 kB).
- ↑ When the mountain masses slid into the lake. In: derstandard.at . October 30, 2007.
- ↑ Charles Perrow , who wrote in Normal Disasters , argues in the same way . 1988 on p. 286 speaks of the "ignoring alarming information" and writes that "bureaucratic botch" has taken place.
- ^ Daniela Agostini, Hannes Schuler: The conquest of the Alps. Part 4: hydropower. Germany, 2009, in: Karl Schreiber's YouTube channel, uploaded on January 17, 2014
- ^ In the Internet Movie Database IMDB: Vajont - La diga del disonore