Exploration of the Kinematics of the 1963 Vajont Landslide, Italy, using a numerical modelling toolbox

The Vajont Slide has been studied for half a century, yet questions about its kinematics and dynamics still remain. Application of state-of-the-art numerical techniques aids in understanding the slide’s mechanical behaviour. In the current paper, we use four two- and three-dimensional finite element, distinct element, and lattice-spring modelling codes in a toolbox approach to conduct a forensic, exploratory investigation of the kinematics of the slide. We examined the influence of rock mass properties and friction along the failure surface using the 2D finite element code. Preliminary results indicate that weaker units within the sliding mass deformed more than stronger units, and that a Prandtl wedge zone of transition developed between the active upper and passive lower blocks of the slide mass in the west. The difference between the biplanar western sliding surface and the more circular eastern surface proves to be significant in terms of stability. Models suggest a critical friction angle of approximately 18°, above which the slope is stable. The 2D distinct element modelling results indicate that both failure surface morphology and block size are important. Planar and arc-shaped failure surfaces are most unstable, whereas rough undulating surfaces are stable. As block size increases, overall slope stability increases and a lower friction angle along the failure surface is required to initiate sliding. Block kinematics were further investigated using a 3D distinct element code. This numerical code illustrated the controls of bounding structural features such as the Col Tramontin Fault and Erto Syncline, as well as block size, on the failure. Finally, preliminary simulations in a new 3D lattice spring code show that crack clusters developed, and became concentrated in the transition zone between the back and seat of the chair-shaped failure surface.