Combined effect of fines content and uniformity coefficient on cyclic liquefaction resistance of silty sands

Cyclic liquefaction of silty sands remains to be very intriguing for both research and practice. Even though many factors are known to influence the liquefaction resistance of sands, the effect of fines content is perhaps one of the most studied yet still a controversial one. Effect of grain size distribution by means of uniformity coefficient is also studied in literature but not as much as fines content influence. Moreover, to date, no clear relationship has been established between the uniformity coefficient and cyclic liquefaction resistance of clean or silty sands. This study adopts a distinct methodology by considering the effects of fines content and uniformity coefficient together, which were typically considered separately as two isolated parameters in previous studies (i.e., typically, only one of them was considered or focused). A series of constant volume cyclic direct simple shear (CDSS) tests were performed on mixtures of two base sands and four non-plastic silts at different fines contents, which also enabled authors to observe the liquefaction response of silty sands with different gradations. Based on the analysis, a new equation was developed which predicts the cyclic liquefaction resistance of silty sand by considering the uniformity coefficients of the sand (CU_sand) and silt (CU_silt) fractions forming the soil together with its fines content (FC). The proposed equation was also demonstrated to work very well on six distinct silty sands having different gradations and fines contents from literature. The level of the combined influence of fines content and uniformity coefficient on cyclic liquefaction resistance of silty sands is also shown to be considerably affected by the magnitude of relative density. Practical implications and limitations of the new equation are discussed as well.