Investigating the liquefaction resistance and initial shear modulus of silty sands from equivalent intergranular void ratio concept

Multiple series of laboratory undrained cyclic triaxial tests and bender element tests are conducted to obtain pairing data for R l and G o for laboratory reconstituted samples of silty sands. Several categories of silty sands in a ‘fines in sand’ matrix are prepared using coarse, medium, and fine sands as the host sands and non-plastic fines with different fines contents of F c = 0–30% as the guest silt. The concept of the equivalent intergranular void ratio is that it is used to deduce the b -values for R l and G o . Instead of applying the empirical expression, as employed in past studies, the b -values are determined by directly fitting the silty sand data to the corresponding backbone clean sand relation. The fictitious active fines content, defined as F c * = bF c , is then introduced, which bears a good physical meaning for mechanical interpretations of the test results. F c * tends to increase rapidly as F c increases, following the empirical expression of F c * = μF c 2 . The corresponding values for F c.l * and F c.s * for large-strain R l and small-strain G o , respectively, are directly compared. It is found that they take different values, and that the ratio of F c.l */ F c.s * is dependent on the size disparity ratio for χ and F c . The implications of this experimental finding are discussed with respect to the micromechanical modelling of the silty sand behaviour. The differences in the values for F c.l * and F c.s * are found to lead to multiple series of cyclic resistance ratio CRR and shear wave velocity V s relations for silty sands with different F c , which are comparable to the empirical relations given in past studies.