A suction-controlled laboratory campaign for assessing the hydro-mechanical properties of a compacted silty sand mixture|Indagini sperimentali a suzione controllata per la valutazione delle proprietà idro-meccaniche di una miscela sabbio-limosa compattata

Due to continuous water level fluctuations and changes in climatic boundary conditions, river embankments experience frequent variations in the degree of saturation and suction distributions, which strongly influence earthworks performance, both in terms of infiltration regime and stability conditions. For these reasons, an experimental campaign aimed at investigating the hydromechanical response of a compacted silty sand mixture, representative for the embankment earthfills of the river Po tributaries (Italy), has been carried out and the main results are reported and discussed in this paper. To promote homogeneity and initial conditions consistency, the specimens were reconstituted at target dry unit weight and moisture content, by using the standard Proctor compaction energy. Suction-controlled triaxial and oedometer tests were designed and carried out to highlight the effect of drying and wetting stress paths, as well as confining stresses, on strength and compressibility characteristics of the tested material. The well-established axis translation technique has been used for controlling matric suction inside the samples. Typical suction ranges for the embankment, assessed through field monitoring of seasonal and daily hydraulic changes, have been imposed during the tests. Unsaturated specimens consistently exhibited a higher shear strength and stiffness with the increase of suction, compared to the saturated samples. The outcome of the present mechanical characterization may provide some meaningful geotechnical insights for the assessment of river embankment actual safety margins under transient seepage groundwater flow.