A new interpretation of the geotechnical context of the Vajont rockslide

This study presents the detailed reconstruction of the entire structure of the oldest Vajont rockslide (270-300 million of m3) for the first time, describing the complex geometry and the characteristic superimposition of distinct rigid blocks on a very thick shear zone (40-50 m thick) made up of a chaotic assemblage of rock blocks, limestone angular gravel and high plasticity clays. Typical back-calculated values of the friction angle φm, obtained for the 1963 Vajont slide, ranged essentially from 17° to 27° but these are mean values referring to the entire slip surface and can differ considerably from the true shear strength properties of the materials effectively involved in the failure. This explains the difference between the friction angles measured by means of different shear tests on various Vajont clay samples (φc = 6-15°, prevailingly) and the typical back-calculated mean values. The recognition of the bottom shear zone is decisive both for the geotechnical and the hydrogeological modelling of the huge Vajont landslide (Oct. 9, 1963). © Springer-Verlag Berlin Heidelberg 2013.