The 1963 Vajont landslide analysed through numerical modeling

The use of numerical modelling to simulate natural phenomena is increasingly widespread, mainly owing to computational capacity improving that makes it possible to face the complexity of the modelling techniques. The 1963 Vajont landslide represents a very interesting case study. The abundance of available data, before and after the event, allows the reconstruction of the initial and final mass morphology. Moreover, the mass compactness and the sudden velocity increase, as inferred from post-event observations and analyses, suggests the existence of a well-defined rupture surface, made of exposed clay layers on the western side of the detachment niche, also under the final deposit. Furthermore, the very high velocity attained by the sliding mass (presumably 20-25 m/s) is a hint for very low values of the bottom friction coefficient, considerably smaller than the usual value for clay material. In this work we apply to simulate the Vajont landslide an in-house built numerical code, UBO-BLOCK1, based on a Lagrangian approach: the sliding mass is split into several along-a-line interacting blocks, volume conserving and shape changing, and the motion of each block is computed numerically. This allows us to simulate the whole dynamics of the slide and to use observables (mainly the final deposit mass distribution) to constrain the parameter of the model, the most influential of which is the bottom friction coefficient. The main result of our analysis is that, if it is assumed that the west- and the east-side of theItalyslide move on a sliding surface with a different shape, as suggested in the literature, then the corresponding bottom friction coefficients result to be quite different from one another, which in turn demands an explanation in terms of lithological difference of the contact between the slide and the underlying rock body.