Experimental Study on the Seismic Response of Embankments on Liquefiable Soils Improved with Stone Columns

Over the past few decades, methods used to reduce the liquefaction hazard in vulnerable areas have increased in number and complexity. On this subject, numerous studies have shown the insertion of granular columns to be an effective mitigation technique against settlement and lateral deformation by structures founded on liquefiable soil profiles. Granular columns are constructed by the insertion of coarse aggregate into the soil by means of compaction and vibration. The effectiveness of granular columns as a mitigation technique has been shown to involve three mechanisms: 1) ground densification during column installation; 2) shear reinforcement added by column stiffness, and 3) enhanced drainage capacity. There is, however, a lack of understanding concerning the extent to which each of the mechanisms contribute to the overall mitigation and what factors are improved by the process. Being able to comprehend the relative contributions of the mechanisms would lead to the development and refinement of a more efficient stone column mitigation system design. We used reduced scale centrifuge modeling to examine the influence of the three distinct aspects under controlled conditions and compared them to an unmitigated system. The system of interest was a 4 meter tall gravel embankment founded on dense Monterey sand (Dr≈90%) with a liquefiable layer of Ottawa sand (Dr≈40%) between it and a denser layer of Ottawa sand (Dr≈90%). The columns inserted had an area replacement ratio (Ar) of 10% and were modified as needed to isolate each mechanism. The experimental results will provide insight into the influence of this ground improvement technique on key engineering demand parameters of interest in design, such as acceleration and settlement. In a larger scope, it will also allow for the calibration of numerical models and advance understanding involving the ground improvement method based on granular columns