Effect of Fabric Anisotropy on Reliquefaction Resistance of Toyoura Sand: An Experimental Study

Recent earthquakes in New Zealand and Japan demonstrated that preshaking histories can significantly influence the liquefaction resistance of sandy soils, which has not been fully understood yet. It has also been reported that soils prepared with different depositional methods referred to as initial or inherent anisotropy show different liquefaction behavior. Therefore, a comprehensive experimental study was carried out for the first time to explore the combined effects of inherent anisotropy and induced anisotropy due to cyclic shearing on the reliquefaction resistance of loose (D_r = 45%) and dense (D_r = 70%) Toyoura sands subjected to various cyclic stress ratios (CSR). A hollow cylinder torsional shear apparatus (HCTSA) was used in this study since it can mimic the field stress conditions more realistically during earthquake events. In order to investigate the influence of inherent anisotropy on liquefaction and reliquefaction resistance of Toyoura sand, the hollow cylindrical specimens were reconstituted with different methods of dry deposition (DD) and moist tamping (MT), representing naturally and artificially deposited soils, respectively. Furthermore, sand specimens were cyclicly sheared up to medium and large shear strain levels, then reconsolidated at different states to evaluate the effect of induced anisotropy with different shear histories on reliquefaction resistance in the sand. A large preshearing reduces the reliquefaction resistance, while the reliquefaction resistance increases when the sandy soil is moderately presheared, irrespective of relative density and reconsolidation state. It was also found that the effect of reconsolidation state is more significant in the dense sand than the loose sand. Another key finding of this study is that the effects of initial fabric acquired by different reconstitution methods and reconsolidation states are lost in the reliquefaction tests once the loose Toyoura sands experienced large preshaking.