Analysis of capillary barrier effects in the activation of debris avalanches in pyroclastic cover, Campania (Southern Italy)

On May 1998 many landslides involving pyroclastic covers lying on the slope of Pizzo D’Alvano relief hit the towns of Bracigliano, Quindici, San Felice a Cancello, Sarno (Campania, Italy). They were triggered by a prolonged and continuous rainfall event but certainly not extraordinary in terms of return time. The aim of the investigations carried out within this work, by means of in situ and lab testing, and by means of numerical simulations, is to point out some aspects related to triggering mechanisms of debris flows that appear relevant to the authors. In particular, attention is paid to retention phenomena of filtering waters due to the build up of capillary barriers in the interface between fine and coarser pyroclastic layers, causing suction head to drop to a level that triggers a landslide.