Changes in sand mesostructure under repeated seismic liquefaction events during centrifuge tests

Abstract Previous studies have revealed that past shaking can substantially affect sand reliquefaction resistance. Researchers have attributed these effects to the formation of stable or vulnerable sand mesostructures during previous shaking events. However, no experiment has been performed to directly visualize how sand particles evolve into stable or vulnerable mesostructures. In this study, a sand deposit was shaken by four repeated seismic motions in centrifuge model tests, and simultaneously, mesoscopic images of sand particles were recorded by a newly developed microimage acquisition system. The mesoscopic images showed that pore fluid seepage caused particles previously in contact to be separated and form large voids during sand reconsolidation stages. The sand with large voids quickly contracted during the subsequent shaking event, exhibiting a decreasing sand reliquefaction resistance. The sand reliquefaction resistance gradually increased as the seepage damage effects attenuated, and the number of sand particle contacts increased with sand densification under multiple shaking events. The testing results suggested that influences of the excess pore pressure dissipation on the sand mesostructure should be considered in assessing sand reliquefaction resistance.