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Meisam Goudarzy, Debdeep Sarkar

• Resonant column tests were carried out on Hostun sand mixed with 5%, 10% and 20% non-plastic fines (defined as grains smaller than 0.075 mm) in order to quantify the combined influence of the void ratio \(\it (e)\), anisotropic stress state (defined as \(\sigma_v\)'/\(\sigma_h\)') and fines content \((f_c)\) on the maximum small-strain shear modulus \(G_{max}\). A significant reduction in the \(G_{max}\) with increasing \(f_c\) was observed. Using the empirical model forwarded by Roesler, the influence of e and \(\sigma_v\)'/\(\sigma_h\)' on \(G_{max}\) was captured, although the model was unable to capture the influence of varying fines content using a single equation. From the micro-CT images, a qualitative observation of the initial skeletal structure of the 'fines-in-sand' grains was performed and the equivalent granular void ratio \(\it e*\) was determined. The e was henceforth replaced by \(\it e*\) in Roesler's equation in order to capture the variation in \(f_c\). The new modification was quantified in terms of the mean square error \(R^{2}\). Furthermore, the \(G_{max}\) of Hostun sand–fine mixtures was predicted with good accuracy by replacing e with \(\it e*\). Additionally, a micromechanical interpretation based on the experimental observation was developed.