The Montaguto earthflow: A back-analysis of the process of landslide propagation

Earthflow and mudflow processes represent a class of landslides that, owing to their typical long run-out, may generally induce huge damages to infrastructure lines, with negative economic impacts. Therefore, the analysis of the landslide propagation with time in such cases can provide useful information to mitigate landslide risk. The present paper discusses the case history of a huge earthflow developed in 2005-2006 in the area of Montaguto town (Southern Apennines, Italy), that produced significant damages to a national road and a national railway at the slope toe. The average displacement rate during the first critical stage of propagation was of some m/day. The aim of this contribution is the reconstruction of the propagation stage of this landslide during the first high-mobility stage. A detailed geomorphological analysis aimed at defining the main features of the in-situ landslide propagation is firstly described. Later on, a back-analysis of the kinematical features of the same landslide process, based on a simple infinite-slope sliding-consolidation model, is presented to investigate the role of different factors in the process of landslide propagation. The application of this analytical solution suggests that the development of high excess pore water pressures due to undrained loading processes and the consequent consolidation process can represent a reasonable way to explain the earthflow mobility. The application of the analytical model to the specific case study is also supported by the field evidence of the existence of excess pore water pressures in the landslide mass which have been measured in situ during the recent monitoring campaign and the corresponding data are also discussed in the work.