Seasonal groundwater regime in an unsaturated pyroclastic slope

Rainwater infiltration is the mechanism that leads or predisposes unsaturated pyroclastic slopes to failure by reducing matric suction and hence reducing the shear strength. Therefore, groundwater flow analysis is an important tool to investigate slope stability as well as predict conditions caused by heavy rainfall. Analysis and prediction quality can be greatly improved by in situ monitoring. In this framework, this paper describes the results of an ongoing experimental research project on mudflows, based on monitoring of a test site in a typical geological environment in western Campania. The site was selected to carry out extensive laboratory and in situ experimentation, consisting of field monitoring of climatic conditions, matric suction and water content. The suction data span about 4 years, while water content data cover about 2 years. Considered together, these data allow clear identification of seasonal fluctuations of the hydraulic properties in the subsoil, while giving interesting information on the hysteretic hydraulic behaviour of pyroclastic soils. Suction measurements were elaborated to obtain groundwater heads in the subsoil and then equipotential lines and flow vectors.