The effect of plastic fines on the shear modulus and damping ratio of silty sands

The dynamic behavior of soil material is of importance in construction and geotechnical engineering. This study focuses on the dynamic properties of silty sands, particularly on the effect of plastic fines content (FC) on the shear modulus and damping ratio. Natural sand (Taiyuan sand) and fines (Taiyuan loess) were collected from an engineering site in China. Fujian standard sand, kaolin, and stone powder were also used for comparison. Fines plasticity, FC, effective confining pressure, and relative density were considered. A series of tests were conducted using a Stokoe-type resonant column apparatus manufactured by GDS Instruments, UK. The small strain shear modulus (G_max) of the samples were investigated under various test conditions. Hardin’s function was used to fit the experimental data. The results indicate that the shear modulus changes non-linearly with increasing FC. The shear modulus of various mixtures initially decreases and then increases. The threshold FC (FC_th) of Taiyuan and Fujian sand mixtures is 30% and 20%, respectively, which indicates that the FC_th is related to the host sand. The addition of plastic fines will decrease the shear modulus. The effect of non-plastic fines on the shear modulus of sand–fines mixtures is dependent on FC. The damping ratio of various mixtures initially increases and then decreases with increasing FC. The addition of fines will increase the damping ratio. Moreover, the damping ratio of plastic fines mixtures is higher than that of non-plastic fines mixtures. The values of the fitting constant, namely, A, n, and d, are related to fines plasticity. The findings of this study can provide a reference for engineering designers.