Physical and mathematical modeling of infiltration through layered pyroclastic covers

摘要

In recent years, a number of flowslides and debris flows triggered by rainfall affected a wide mountainous area surrounding the "Piana Campana" (southern Italy). The involved slopes are constituted by shallow unsaturated air-fall layered deposits of pyroclastic nature, which stability is guaranteed by the contribution of suction to shear strength. To understand the infiltration process and the soil suction distribution in such layered deposits, strongly affecting slope stability, infiltration tests in a small-scale layered deposit have been carried out. The results highlight that the presence of a coarse-textured pumiceous layer interbedded between two finer ashy layers, in unsaturated conditions, delays the wetting front advancement, thus initially confining the infiltration process within the uppermost finer layer. However, when high hydraulic gradients establish across the pumices, water infiltration into the deepest layer starts. Thus, in presence of long lasting intense rainfall, the presence of a coarse-gained layer does not necessarily impede the progressive saturation of the lowest soil layer. The interpretation of the experimental results has been supplemented with the simulations carried out with a mathematical model based on the integration of 2D Richards equation.