Investigating the effect of gravel content on the small-strain shear modulus of sand-gravel mixtures

Most previous studies have focused on the small-strain shear modulus (G_max) of clean sand or sand-silt/clay mixtures, while little attention has been given to sand-gravel mixtures which are extensively used in many construction projects, such as railway foundation, rockfill dam and artificial slope. This study investigates the effect of gravel content (GC) on the G_max through a series of shear wave velocity tests on specimens with 0 to 100% GC in a large-scale triaxial apparatus. The results show that the relationship between G_max and GC is related to the stress level. Under relatively low confining pressure, the G_max remains nearly constant when GC increases from 0 to 80%, after which, G_max increases rapidly until 100% GC. Under relatively high confining pressure, the G_max increases slowly when GC increases from 0 to 40%, the rate of increase in G_max becomes more rapid at 40–80% GC, and the G_max increases most rapidly between 80 to 100% GC. The observed difference in the relationship between G_max and GC is related to the stronger densification for specimens with between 40 and 80% GC at higher confining pressure. A G_max model considering the effect of GC was established and verified using the test data. The model can assist with rapid estimation of the small-strain shear modulus of sand-gravel mixtures.