Effect of Mean Particle Size and Uniformity on Modulus Degradation of Nonlinearly Graded Marine Sands

This study investigated the effect of gradation, especially of mean particle size and uniformity of gradation, on the shear modulus degradation of natural marine sands compared to regraded clean sands. A series of fixed-free resonant column tests were performed on graded clean sands and marine sands having similar uniformity coefficient values, $C_u$. It is observed that the modulus degradation of both clean sands and marine sands increased with the increase in $C_u$. However, the marine sands have degraded less than clean sands for the same $C_u$ and effective confining stress. The reasons can be attributed to the nonlinearity in the grain size distribution of marine sands above 60% finer and mean particle size, $D_{50}$, compared to graded clean sands. The overestimation of the modulus degradation of marine sands by the existing empirical equations is demonstrated. Considering the effects of uniformity coefficient, $C_u$, and mean particle diameter, $D_{50}$, a generalized calibrated modulus degradation model for a wide range of clean sands and marine sands is proposed with a high coefficient of determination. Good agreement is demonstrated between the estimated and experimental data from the literature.