Propagation analysis of flow like-mass movements to evaluate the effectiveness of passive control works

Abstract

Flow-like mass movements are catastrophic events occurring all over the world and may result in a great number of casualties and widespread damages. The analysis of the time-space evolution of the kinematic quantities is a useful tool to understand the propagation stage of these phenomena as well as for control works design. The thesis deals with study of flow regime of Newtonian and non-Newtonian fluids and provides a contribution to this topic through the use of numerical procedures based on FV (finite volume) scheme and SPH (smoothed particle hydrodynamics) method. The FV model, developed by Rendina et al., 2017, is a single phase equivalent model, while the Geoflow-SPH, developed by Pastor et al.2009, considers the propagating mass with an average behavior of solid skeleton and pore water pressure. The flow kinematics are analyzed through the Froude number, widely used in hydraulic engineering, discriminates two different kinematical features i.e. subcritical (slow) or supercritical (rapid) flows. The analysis concern a 1D/2D dam break of Newtonian (water flow) and non-Newtonian flows (in particular based on a viscoplastic and frictional laws). The numerical results highlighted flows are supercritical even in areas far from trigger zones and Froude numbers of viscoplastic flows are higher than frictional flows. Later, the Froude number is used as a quantitative descriptor of the control works response and, more generally, as an useful tool to estimate the efficiency of existing storage basins. The first case study regards Cancia, in the Dolomite Alps, where two storage basins dramatically failed on 2009 due to a short-time sequence of rainfall-induced debris flows and flash floods. The kinematic analysis highlighted that debris flow can be associated to a subcritical flow while flash flood is similar to a supercritical flow and for latter lower is the potential efficacy of control works. The second case study regards Sarno, in the Campania region, where one of the most complex systems of passive control works was built after the 1998 events. The performance of the protection system is analyzed referring to Froude number again which highlighted the importance of planning the emergency/ordinary maintenance of control works. Finally, a new type of passive control work is described, i.e. the permeable rack that has the function of decrease the pore water pressures at the base and inside the propagating mass, thus causing the landslide body to brake and stop. The rack performance is tested as adaptation structure in existing protection systems also.[edited by Author]