Effects of reconsolidation degree on reliquefaction resistance under mainshock-aftershock sequences: A DEM investigation

Aftershock events may immediately follow mainshock events. In liquefiable deposits, the excess pore pressure caused by mainshock events may not dissipate completely in a short time interval between the mainshock and the aftershock. Sandy soil with different reconsolidation degrees (U-r) may present different reliquefaction resistances during the aftershock, which was not fully considered into the previous studies of reliquefaction. In this study, discrete element method (DEM) was employed to simulate a series of cyclic triaxial tests to evaluate the effects of U-r on reliquefaction resistance under mainshock-aftershock seismic sequence. The initially liquefied specimen was reconsolidated from two states with small and large residual shear strain respectively. Reconsolidated specimens reliquefied under different cyclic stress ratios (CSRs). Simulation results show that reliquefaction resistance increased gradually with increasing U-r, which was closely related to the previous residual shear strain during the first liquefaction event. Specimens that having large residual shear strain reliquefied easily, and the reliquefaction resistance of those specimens increased slightly with increasing U-r. On the contrary, reliquefaction resistance of the specimens that having small residual shear stain increased obviously with increasing U-r. The ratio of initial mechanical average coordination number to initial mesoscopic fabric anisotropy of reconsolidated specimens had a good correlation to the contraction potential and increased gradually with increasing U-r.