Shear stiffness of sand-fines binary mixtures: Effects of sand gradation and fines content

Abstract

In this study, a comprehensive experimental programme was carried out on five clean sands of different gradations mixed with low plastic fines using an apparatus that incorporates both resonant column (RC) and bender element (BE) functions. The sand gradation is characterized by uniformity coefficient of host sand (Cus) and grain size ratio (Rd), which is defined as the ratio of the mean grain size of sand to that of fines. The effects of fines content (FC) and sand gradation on small strain shear modulus G0 are analyzed from the experimental results. Both RC and BE test results show that G0 continuously decreases in a non-linear manner as FC increases to 30% and becomes as low as nearly 50% of that of clean sand at the highest FC. The reduction rates with respect to FC are similar regardless of the testing type and the stress dependence of G0 is insensitive to FC. Meanwhile, G0 decreases as Cus or Rd increases at a given FC and void ratio or at a fixed equivalent skeleton void ratio e*. A new predictive model in terms of e* is proposed to evaluate the G0 of sand-fines mixtures to account for the effects of void ratio, confining pressure, FC, and sand gradation within ±20% deviation. Moreover, the rate of shear modulus degradation with shear strain and the damping ratio are higher for sand-fines mixtures with higher FCs.