Full-scale testing of liquefaction mitigation using Rammed Aggregate Piers in silty sands.

Liquefaction mitigation in silty sands is a major challenge for geotechnical engineers, specialty contractors, and owners. An extensive literature is available for studying densification of vibratory methods whose effectiveness decrease as the fines content increases, while few information are known on the increment of lateral pressure and of the composite stiffening response of piers. In this respect, a full-scale testing was performed in Bondeno (Ferrara, Italy) where liquefaction was observed in the 2012 Emilia earthquake. In this study, ground improvement in silty sand, produced by a group of 16 Rammed Aggregate Piers (RAP), was tested using in situ tests and controlled blasting. An adjacent untreated test area with no RAPs, which experienced liquefaction and significant settlement (70 to 100 mm) following controlled blasting, was also characterized for useful comparison. Relatively high excess pore pressure ratios were recorded in both the panels, while the measured settlement (20 to 40 mm) in the improved panel was significantly lower than in the unimproved panel and sand boils did not develop.