Characterising the effect of particle size disparity on liquefaction resistance of non-plastic silty sands from a critical state perspective

Widespread liquefaction has been frequently observed in silty sand deposits during recent large earthquakes. How to properly evaluate the liquefaction potential of silty sands has emerged as a matter of great concern. This paper presents an investigation into the problem through a comprehensive experimental programme in conjunction with a newly developed framework of analysis. Focus is placed on the effect of particle size disparity and its interplay with the effect of fines content – two fundamental issues for which current understanding is limited. A novel finding of the study is that the liquefaction resistance of sand–fines mixtures, defined as the cyclic resistance ratio (CRR) leading to failure at a specific number of loading cycles, is almost uniquely related to the state parameter (ψ) defined in the critical state theory, regardless of particle size disparity and fines content. To quantify the combined effects of fines content and particle size disparity, an empirical model is put forward along with a practical method for estimating the critical state parameters of silty sands. The model is evaluated using experimental data on a range of sand–fines mixtures in the literature, showing a reasonably good performance and attractive advantages. A grain-scale mechanism is also suggested to explain the observed effects.