Simulating triggering and evolution of debris-flows with sph

Abstract

Recently, debris-flow kinds of phenomena have been reproduced by means of Lagrangian methods, such as Distinct Element Method (DEM) or Lagrangian Finite Element Method (LFEM). Among the others, meshless, Lagrangian numerical method, known as Smoothed Particle Hydrodynamics (SPH), is here applied to simulate debris-flow initiation and propagation over the slope of a mountain located in the city of Nocera Inferiore (Southern Italy). Debris-flows have been simulated since long time for hazard mitigation assessment or deposit evaluation via Eulerian-based methods. Since they may feature mesh distortion as the computational domain evolves, heavy grid refinement algorithms are sometimes necessary, especially for those problems characterized by large deformations. SPH overcomes such difficulties since no mesh is needed over the physical domain. Spatial discretization is indeed carried out with a collection of particles without connectivity bonds among them. While boundary particles are fixed over time, computing particles are free to move in response of external and internal forces such as gravity and pressure. More in detail, computing particles are all initially frozen. Once a particle located in the upper region of the slope is set free, the others close to it move if a pressure threshold plim is reached. Other particles are subsequently triggered where the mentioned condition occur, as a domino effect. Runout velocity is controlled by handling the shear stress τbed with the fixed bed. Results show how different are the conditions of motion, by varying the location of the triggering area, the pressure threshold plim and the shear stress τbed. In order to measure the capability of SPH into simulating such events, some comparisons are made with corresponding Flo 2D results.