Suction fluctuations in unsaturated slopes: evindeces from two test sites in Southern Italy

Slope failures in partially saturated pyroclastic slopes are often induced by rainwater infiltration. Monitoring pore pressure in the subsoil makes it possible to identify the most critical period for slope stability and to determine whether current site conditions are critical for slope failure (according to a Civil Protection approach). This paper deals with the behaviour observed from 2002 to 2011 in two test sites in southern Italy. Using the data obtained, typical aspects of groundwater regime are de-scribed. The effect of single rainfall events is recognized only in the shallowest lay-ers, with a relatively small perturbation in the suction trend compared to the ampli-tude of seasonal fluctuations (that reach 80 kPa). Minimum suction values occur during winter in all layers. Therefore, we can conclude that the critical period for landslide triggering is between January and April