The Malpasset Dam

The Malpasset Dam

Posted By: pmietlicki

Published to Work on Mar 29, 2017

The dam of Malpasset is notorious for the disaster that it caused the December 2, 1959 at 9:13 p.m. Its failure caused 423 deads or missing. This is the biggest disaster of its kind that has ever affected France.

This dam was built by a renowned engineer André Coyne then president of the International Association of Large Dams and an uncontested specialist in the construction of dams. He committed suicide six months after the disaster. Then how such a tragedy does happen? What is the level of responsibility of the different actors of this project? This is what we will try to determine in this report by analyzing the context, circumstances and the causes based on facts and concrete reports.

Context

At the end of the second World War, the Var must rebuild and equip itsef for its future. One of the main problems of this region concerning water scarcity, a problem that will become more pronounced each year because of considerable needs in particular for tourism. In addition, rains are very irregular; therefore the hydraulic equipment is a priority.

So it is a priority to find a solution as fast as possible. Any delay would have big consequences for the future of the region both in human terms, agriculture and tourism. So that departmental officials must respond as quickly as possible to these requirements to the benefit of citizens.

Thus, in 1946, the General Council launched a tender and began selecting a project. Given the number of projects and controversies, administration appealed to the high ministerial forums. Finally, the Ministry of Agriculture chose, in August 3, 1950, the dam project established on the Reyran rather than the one on the Siagnole area.

The General Council, anxious to quickly carry out this project of hydraulic equipment, for which "the financial assistance of the Ministry of Agriculture was essential," approved the principle of creating the dam on the Reyran. Especially since the Ministry of Agriculture promised a "60% granton the entire project (dam and agricultural irrigation)". The Interior Ministry also opened the possibility of subsidies for the development of drinking water to coastal cities.

On the other hand, the Siagnole dam project was not accompanied by any immediate promise of grant. This was of importance in view of the urgency of the work.

The preliminary study: a prediction of disaster

The dam was the work of the General Council of the Var. "Records show that all financial credits that have been requested were voted. Whether study or execution credits".

On the proposal of the General Counsel, Professor George Corroy of the faculty of sciences of Marseille was responsible for the preliminary geological survey, gave a favorable opinion. The appropriations necessary to first studies were then voted the "31 July 1946".

A first report was filed the november 15, 1946 by the professor. He had studied the rocks in the laboratory of Marseille. In a lengthy memorandum entitled "The water supply in the eastern region of the Var department and Malpasset dam near Frejus", the Professor told

Despite the multiplicity of the described details of accidents [...], the impoundment occurs in excellent geological conditions at the point of view of its sealing

As for the location of the dam and its location, the geologist finds

All these superficial observations show that the series of Reyran gneiss is far from homogeneous, and the foundations of a future dam in place should be prepared by research work. [...] The presence of pegmatite veins, with phenocrysts easily alterable, could likely cause more or less significant losses below the dam and in rocky shoulders of the dam

Unfortunately, the General Council and, subsequently, the Mr Coyne's office were met by the rather positive overall impression regardless research work suggested by the geologist. However, the procedure met the standards of the time that were then not as restrictive as current.

To study the draft of the dam, the General Council addressed the Mr Coyne's office, president of the International Association of Large Dams. In 1950, the consulting firm Coyne and A. J. Bellier asked three questions to the geologist :

Would you have any objection about :
1 - Moving the dam downstream ?
2 - Raising it to hill 130?
3 - Would it be any seling problem with the elevation of the water to point 130 ?

The geologist answered :

1 - It is possible to move the work of 200 meters. The anchorage does not present more difficulties on the left side than on the right side.
2 - It is not possible to raise the water level to point 130. The 120 point will be the maximum.
3 - The seal is not threatened by the water elevation

According to Professor Mr Roubault, who was asked what he thought of the geological study,

A preliminary geological study of the site was made and even well done. But from there, the construction work took place, unfortunately, under the sign of the fatal economy: research on the solidity of surveys and galleries were never executed [...] at the mere sight of rocks without systematic studies of their qualities and substantially complete absence of geological monitoring during the course of construction. Yet the crucial importance of the quality of support was unknown

Indeed, some samples of the study were considered representative of the geological structure of the field. The rest of the "audit" was simply done by sight.

The General Council, in the wake of the disaster, defends himself of trying to save money and stated that

We had even foreseen the possibility of an advance of 27 million for survey work [...] and Mr. Quesnel, the general inspector estimated that 8 million would be enough for these kinds of dams.

However, one can legitimately ask how and what criteria Mr Quesnel used to estimate that the usual surveys were "useless". Mr Quesnel said "we were sure to have a very safe anchorage." Thus Mr Quesnel, through an anchoring effect on the initial geological analysis, considered useless to make extensive studies.

The dam

The engineer André Coyne was then famous for regiving honor to the arch dams in France. He had already built almost "a hundred dams with a quarter abroad".

The arch dam is the synthesis of an audacious mathematical formula. Indeed, "the dynamic shape of an arc of concrete returns the strong pressure of water trapped in each bank." In short, the clever form of arch dam is somehow "insensitive" to pressure: the more pressure, the more it tightens the wall and the dam "anchor" in the rock. This makes it an extremely durable type of dam and allows engineers to leverage this pressure to reduce the thickness of the dam without affecting its strength. It is also important to indicate that the dam Malpasset with 6,78m wall thickness made it "the thinnest dam in Europe".

But "it is obvious that this type of work requires that the banks receiving the bulk of the pressure are of maximum robustness".

Multiple problems

After the construction and up to the disaster, it was not possible to fill the dam. On the one hand, because of the lack of rain and, secondly, because of legal proceedings relating to expropriation issues initiated by the company that operated the fluoride Spath mines located within the perimeter of the lake.

But, the first filling phase is extremely delicate.The stresses then exerted on the structure resemble those caused by an earthquake. It is important that the first impoundment is regulated, controlled, gradual and monitored to study the behavior of the structure during this critical phase.

The end begins

André Ferro, the valve keeper initially worried about deformations of the vault but engineers reassure him, stating that this proves the "satisfactory elastic behavior of concrete arch".

In November 1957 the work of the highway Esterel-Côte d'Azur trigger, within 300 meters, major mine fires. André Ferro making his rounds on the vault, felt the blast under his feet. He organizes a seminar with officials of Agricultural Engineering. The reassuring conclusions formulated that the shots have no inconvenience to the dam and they started again ... Afterwards, André Ferro testified that when the shooting occurred, the surface of the water rippled.

In November 1959, after a long period of drought, the region had to face 3 weeks of intermittent torrential rain. So much so that the dam was filled completely and suddenly. It was in fact the first filling, the most critical phase of the life of a dam. However, this filling has not been controlled neither tested.

The disaster

So on the evening of December 2 1959, all ceded by releasing a wave of 60 meters high (the height of the dam) and 50 million cubic meters of water that swept at a speed of 30 km/h on Fréjus in just 20 minutes. It spared the district located high and walked around it but devastated everything else and caused real family dramas : children have been spared for being gone to bed on the first floor and took refuge at the top of the wardrobe while the parents staying on the ground floor did not survive.

Results : 423 deaths and 951 affected buildings, including 155 totally destroyed.

Technical analysis

As often, when such disasters occur, it is a convergence of many factors that explain the event. First, it's the type of rock that is predominantly responsible. Once the dam filled with water, pressure on the rocks from the ground, 60 meters deep, is at maximum. It therefore sought to escape through loopholes. With the study and homogenization of the rock having been rough, she had no trouble finding ones. Gradually, the Archimede pressure exerted by the water will rise until the dam bursts.

This is where the thinness of the dam was an aggravating factor. Small illustration: throw a bowling ball against a window it will break. Replace the bowling ball by a puck (with the same hardness and weight) and project it flat against the glass. More the puck will have a large diameter, and more likely the glass will resist. Thus, the higher the point of impact is concentrated then the impact is more violent, and more the impact surface is wide then the shock will be more diffuse even if the force is of the same intensity. Thus, the thinness of the dam acted on the anchor points in the rock just like a bowling ball, constraints suddenly increased by the raising of the dam, focused on a weakened rock by its nature, and then by the vibrations caused by the explosions of the construction site from the nearby highway....

It is not the fragility of the dam that is in question (even today, engineers agree that the structure was perfectly sized) but the anchors in the surrounding rock weakened and inadequately consolidated and therefore unable to resist and withstand the stresses.

Conclusion

This event profoundly shocked public opinion and has provided a vivid memory for all civil engineers. So that the standards have undergone a major overhaul and because André Coyne, deeply affected by this tragedy, has committed suicide a few months later. This project would have unfortunately been subjected to various means of treatment : the representativeness for geological analysis, anchor for the inclusion of warning events concerning the keeper's concerns (deformation of the structure, blasting for the construction of the highway ...) who yielded to the comforting words of the hierarchy. And no doubt, the escalation of commitment which, once built, the engineers did not want to consider the warning signals. Not to mention the lack of money which faced the General Council and influenced the selection of a heavily subsidized project. Hopefully this kind of drama with these heavy human consequences have allowed this type of situation does not happen ever again.

Sources

  1. Malpasset une tragédie déjà entrée dans l’histoire (P.E.M.F)
  2. Barrage de Malpasset – De sa conception à sa rupture (Valenti, Vito | Bertini, Alfred | Fréjus Leroy)
  3. La catastrophe de malpasset
  4. Barrage de Malpasset


Tags: Barrage, Dam, Malpasset

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