The probable cause of the failure could be crushing of a weak rock mass owing to compression stresses under the downstream part of the dam base and subsequent uncontrollable deformation of the dam.
La cause probable de la rurture a ete un concassage de la roche faible au-dessous de la partie d'aval en base de barrage, entrainant une deformation incontrôlable du barrage.
Die wahrscheinliche Ursache des Bruches kann das Zerdruecken des Felsen durch Druckspannungen unter dem luftseitlichen Teil der Talsperrenbasis und nachfolgenden unkontrollierenden Deformationen des Talsperres sein.
The Malpasset dam failure has once given an impulse for a detailed study of the behavior of a „concrete dam - rock foundation" system. Numerous researches conducted by various experts and especially by Bureau Coyne et Bellier had revealed unknown features of the behavior of rock masses in the dam foundation and had formed the base for a detailed interpretation of the failure (Bellier 1967, Bernaix 1967, Londe & Sabarly 1966, Mary 1968 et al). The causes of this failure continue, however, to interest the engineering and scientific community, Wittke & Leonards (1987), Wittke (1990), PoiseI, Steger & Unterberger (1991) et al. presented a series of new studies of this problem. Using modem calculation methods, the authors had given a more thorough interpretation of the behavior of the Malpasset dam foundation.
A number of unforeseen seepage, deformation and other phenomena observed at numerous concrete dams constructed after the accident, at Malpasset and the regularities of shear failure of brittle materials, including the rock in concrete dam foundations, force us again to return to the causes of the Malpasset dam failure.
Numerous laboratory, in-situ, modelling and numerical studies have shown that under the complex stress state and, in particular, under constant normal and increasing shear stresses the failure of brittle materials proceeds in general in three stages: initiation of tension crocks - formation of crushing zones - sliding along the formed surface of damaged material. The important stage is the formation of crushing zones which coincide with the peak of the bearing capacity of the system. This stage determines finally the strength of the system and its failure kinematics (Fishman 1979, 1983, 1987 et al). Being inherent to brittle materials, the failure mechanism can manifest itself in different ways depending on a scale level, boundary conditions, loading methods, an extent of material continuity, and so on.
In general case an echelon system of tension cracks forms at first (fig. 1). They arise from defects of material structure and propagate along the planes of principal tension stresses. Narrow crushing zones (surfaces) begin to arise at a subsequent increase of shear load T or shear stress t. They propagate along the principal compression planes between the ups of tension cracks and the structure defects. At the moment they close, the shear stress t reaches its maximum value.
