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 (Gmax) 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 Gmax 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 Gmax and GC is related to the stress level. Under relatively low confining pressure, the Gmax remains nearly constant when GC increases from 0 to 80%, after which, Gmax increases rapidly until 100% GC. Under relatively high confining pressure, the Gmax increases slowly when GC increases from 0 to 40%, the rate of increase in Gmax becomes more rapid at 40–80% GC, and the Gmax increases most rapidly between 80 to 100% GC. The observed difference in the relationship between Gmax and GC is related to the stronger densification for specimens with between 40 and 80% GC at higher confining pressure. A Gmax 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.