Understanding fabric evolution and multiple liquefaction resistance of sands in the presence of initial static shear stress

Abstract

Recent field observations have shown that mainshock and subsequent aftershock events can induce multiple-liquefaction events, in which soil liquefies several times at the same site. However, the fundamental mechanism of multiple liquefaction in most previous studies is under level ground conditions, and the cyclic loading condition is symmetric under such conditions. In this study, we conduct 3D DEM simulations of multiple-liquefaction processes considering initial static shear stress. 14-sphere clumped models are used to reconstruct the realistic grain shape of Toyoura sand particles. Cyclic liquefaction and reconsolidation tests are carried out alternately five times. The soil samples with various initial static shear stresses are sheared up to different maximum shear strains in each liquefaction stage. We investigate the liquefaction behavior and volumetric compression during multiple-liquefaction stages considering initial static shear stress. In addition, the evolution of contact-based fabrics, including coordination number (Z) and degree of fabric anisotropy (ac), are analyzed during the whole liquefaction and reconsolidation tests. Furthermore, we establish the relations among contact-based fabrics (Z and ac), volumetric compression and liquefaction resistance. The results reveal that in stress reversal cases, the maximum shear strain is the governing factor that influences the multiple-liquefaction resistance. Conversely, the static shear stress becomes the dominant factor affecting the multiple-liquefaction resistance in non-stress reversal cases. Moreover, changes in multiple-liquefaction resistance are attributed to the microstructure of soils represented by Z after reconsolidation.