Numerical modelling of entrainment/deposition in rock and debris-avalanches

Abstract

Rock and debris avalanches, as well as debris flows, are characterized by peculiar behaviour influenced by geometry of the initial failure surface, topography, involved materials involved and water content. During their motion rock avalanches can entrain large volumes of sediments both in a dry and in a saturated state. Entrained dry material has generally the consequence to reduce the total landslide runout, whereas entrainment of almost saturated material can have more complex consequences. We use a finite element code to simulate the motion of a moving landslide mass on materials with different properties and along very sharp topographies. Erosion and deposition can be modelled as well as interaction with obstacles of different characteristics. We present two examples of the modelling problems and capabilities. We simulated the runout of a rock avalanche on a ground formed by alluvial material under dry and saturated conditions. This material can be entrained and plowed by the impacting and running rock avalanche material. Sensitivity of the erosion and transport mechanisms has been analysed by performing different analyses. The simulated case study is the 6 ⁎ 10 5 m 3 Arvel rock-avalanche (1922, Switzerland) for which a reliable set of pre- and post-failure observations is available. Final geometry, mass redistribution, velocities and runup are used to validate the model capabilities and study the effects of different material properties.