Experimental study on a partially saturated soil of a river embankment

River embankments are usually designed as earthen structures to retain hydrometric level fluctuations. Filling materials generally adopted are intermediate soils, consisting of natural silty soils with limited sand and clay content, compacted during construction process for both ensuring their mechanical stability and limiting the water flow through the embankment itself. The evaluation of time-evolving seepage and stability characteristics of riverbanks, which represents a crucial step for their vulnerability assessment, is strongly influenced by the unsaturated soil behaviour. In this framework, a comprehensive experimental study has been performed to explore the mechanical and retention properties of a river embankment silty soil in partially saturated conditions. Oedometric and direct shear tests under suction-controlled conditions have been carried out on soil sampled from an in-situ instrumented riverbank section, where an extensive monitoring system with suction and water content measurements has been recently implemented. The results of laboratory investigations are presented and discussed. Comparisons with monitoring data and similar laboratory tests performed in saturated conditions are also provided, in order to highlight the importance of an accurate characterization of the unsaturated soil behaviour as fundamental step for a realistic estimate of the river embankments slope stability and for reliable safety assessment.