Improved Liquefaction Resistance with Rammed Aggregate Piers Resulting from Increased Earth Pressure Coefficient and Density

During the last decades, liquefaction damages induced by earthquakes have underlined the importance of identifying effective soil improvement techniques for mitigation purposes. Vibratory methods, such as rammed aggregate piers, are commonly used to densify sands and silty sands, erroneously neglecting the influence of the lateral stress. This paper presents the results of a series of liquefaction mitigation case studies carried out using rammed aggregate piers in Christchurch (New Zealand), Boca de Brice˜no (Ecuador), and Bondeno (Italy) following the 2010–2011 Canterbury seismic sequence, the 2016 Muisne earthquake, and the 2012 Emilia seismic sequence, respectively. The availability of coupled piezocone and seismic dilatometer tests before and after treatment enabled a geotechnical characterization of the three sandy sites to be made, along with estimating the at-rest lateral earth pressure coefficient, and comparing the effectiveness of the treatment at the trial sites. Finally, the paper proposes an updated procedure for liquefaction assessment that takes into account both the increase in soil density and lateral stress produced by ground improvement.