In practical engineering, earthquake-induced liquefaction can occur more than once in sandy soils. The existence of low-permeable soil layers, such as clay and silty layers in situ, may hinder the dissipation of excess pore pressure within sand (or reconsolidation) after the occurrence of liquefaction due to the mainshock and therefore weaken the reliquefaction resistance of sand under an aftershock. To gain more mesomechanical insights into the reduced reliquefaction resistance of the reconsolidated sand under aftershock, a series of discrete element simulations of undrained cyclic simple shear tests were carried out on granular specimens with different degrees of reconsolidation. During both the first (mainshock) and second (aftershock) cyclic shearing processes, the evolution of the load-bearing structure of the granular specimens was quantified through a contact-normal-based fabric tensor. The interplay between mesoscopic structure evolutions and external loadings can well explain the decrease in reliquefaction resistance during an aftershock.
