Field data based numerical analysis of sand boil reactivation along river embankments

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The Po River, the longest watercourse in Italy (652 km), flows eastward from the western Alps to the Adriatic Sea confined for half of its course within major river embankments. Over the centuries, many urban centres, industrial and agricultural settlements developed near these structures and today 16 million people reside here. Among the possible failure mechanisms affecting these structures, backward erosion piping (BEP) results one of the most threatening. BEP refers to the process in which, in presence of high-water events, seepage forces gradually erode the coarse material of the embankment foundation, creating a shallow pipe at the interface with the cohesive top layer.
The paper addresses the safety assessment of river sections to sand boils reactivations. The focus is on the modelling of water dynamics in proximity of the sand ejection pipe able to reliably simulate the phenomenon at the verge of activation. The study refers to a section in Mazzorno Sinistro (RO) along Po River affected by recurrent phenomenon reactivations. A 2D FE model of the section is developed to reproduce accurately the hydraulic behaviour upon transient seepage. The distribution of the hydraulic parameters of the different soil units has been estimated initially from in-situ and laboratory tests then validated in back analysis on piezometric data. Finally, the variations in the hydraulic gradients and in the flow rate in proximity of the pipe are traced upon increasing stationary hydrometric levels and the obtained results compared to literature critical gradients.

28th European Young Geotechnical Engineers Conference (EYGEC2024)

Keynote Papers