Numerical simulation of the groundwater flow leading to sand boil reactivation in the Po River

The reliability of river embankments is essential for flood risk management. The Po River, which flows through the North of Italy, is safeguarded over half of its length by major river embankments. Performance assessment of such water-retaining structures has become a major concern following some significant flood events in the past. Among the possible initiating causes of failure, backward erosion piping turns out to be particularly threating in the middle-lower stretch of the river. In particular, the November 2014 high-water event triggered the formation or reactivation of a few important sand boils. The paper presents a preliminary 3D finite element model of the groundwater flow through a selected cross section of the Po river, located in the Province of Reggio Emilia, which experienced a reactivation of piping phenomena after the 2014 event. The numerical model, based on a detailed geotechnical characterization obtained from in situ tests, was calibrated on the basis of the 2014 high-water event measurements and verified for a subsequent event that took place in November 2016, though without any relevant sand boil reactivation. Results are discussed with the aim of providing some insight into the mechanism under study.