Application of CPT to the evaluation of permeability in a Po riverembankment prone to backward erosion piping

Backward erosion piping is one of the most critical issues for the stability of river embankments worldwide. The article presents results from an extensive geotechnical campaign carried out on a section of the Po river embankments (Italy), prone to backward erosion piping. The aim of the investigations was twofold: firstly, identifying the stratigraphic arrangement of the river system causing favourable conditions for piping occurrence, and secondly determining the permeability of the aquifer and the finer top stratum (blanket) in their undisturbed state, as well as that of the pre-existing eroded zone in proximity of the sand boil. Indeed, analytical and numerical approaches available in the literature are particularly sensitive to the value of permeability of the aquifer, which should therefore be determined in undisturbed conditions. CPT tests turned out to be suitable and economical to this scope. This study presents an integrated analysis of in situ testing data, collected from boreholes, piezocone test and Lefranc test, aimed at estimating the saturated permeability of the different soil units using different experimental methods and interpretation approaches. A comparison between alternative CPT-based methods and field permeability tests is proposed. A good agreement between the different methods was found, thus suggesting the suitability of CPT for the hydraulic characterization of soils.