Modelling a sand boil reactivation in the middle-lower portion of the po river banks

The Po River, which flows eastward through the Northern of Italy, is the largest and most important watercourse in the country. A system of major embankments safeguards over half of its length, existing since the XVI century. The stability of such structures has become a crucial issue following some significant flood events in the past. Among the most common collapse triggering mechanisms for Po river embankments, backward erosion piping turned out to be particularly menacing during the last most important high-water events (e.g. 1951, 1994, 2000 and 2014). In particular, the November 2014 high-water event led to the reactivation of a few relevant sand boils along the middle-lower stretch of this watercourse. This paper presents a 3D finite element model of the groundwater flow within a specific segment of the Po River, located in the province of Ferrara, which underwent piping reactivation during the 2014 event. The numerical model has been developed taking into account a detailed geotechnical characterization obtained from both site and laboratory investigations along with the available 2014 high-water event measurements. The effectiveness of the model is then validated with reference to a piping event recently occurred. Results are discussed with the aim of providing some insight into the most significant factors governing initiation of piping mechanism.