Soil elements in situ are subjected to multidirectional shearing during earthquakes. Ignoring the effect of two horizontal shear components generally results in an underestimation of the liquefaction resistance of soils during earthquakes. The actual earthquake sequence generally consists of a mainshock and subsequent aftershocks. Soils may experience liquefaction during the mainshock and then reliquefy again during the subsequent aftershocks. Previous studies on multidirectional loading paths have mainly focused on single liquefaction events. This study employs 3D discrete element modeling to simulate reliquefaction behavior of sands with various multidirectional cyclic simple shear loading histories. The specimens are initially subjected to various strain histories under multidirectional loading paths and then reconsolidated to initial stress states. Subsequently, each soil specimen is subjected to unidirectional cyclic loading in two different directions in the reliquefaction tests. The influence of multidirectional cyclic loading histories on the post-liquefaction drainage compression and reliquefaction resistance are analyzed. Moreover, the evolution of soil fabrics and interaction between fabric orientation and loading direction in the reliquefaction test are investigated. The results highlight that reliquefaction behavior of soils depends on both the fabric and the interaction between the fabric orientation and the loading direction. This study aims to provide micromechanical insight for understanding the effects of multidirectional shearing histories on reliquefaction resistance of sands.

Examining the reliquefaction resistance of sand deposits is more challenging due to the complex interplay of several factors that may increase or decrease the resistance. This resulted in severe limitations in understanding the reliquefaction mechanism of sand deposits subjected to repeated shaking events. The present study attempted to overcome this limitation by examining the reliquefaction resistance using 1-g shaking table experiments. A total of 65 shakings were performed on saturated Solani sand with varying acceleration amplitude, dynamic frequency, shaking duration, and relative density of the sand specimen. All the above factors were experimented with three different shaking patterns (incremental, uniform and decremental) and independent events. For each shaking event, generation and dissipation of excess pore pressure, soil subsidence, and relative density variations were presented. The beneficial effect of seismic preshaking were applicable in partially liquefied soils that were subjected to incremental shaking pattern. On the other hand, contrary results were reported for uniform and decremental shaking patterns, where the later found to be more damaging. The state of the soil (partially or completely liquefied) governs the reliquefaction resistance, as the beneficial effect of preshaking was applicable only in partially liquefied soils, irrespective of the shaking pattern. Whereas complete liquefaction disturbs the structure of existing sand specimens and results in reduced reliquefaction resistance for future seismic events.