Shear-Induced Instability of Sand Containing Fines: Using the Equivalent Intergranular Void Ratio as a State Variable

Abstract

In this work, the influence of different types of fine materials on the shear-induced instability of sand–fines mixtures was studied from various aspects. For this purpose, clean sand was mixed with three kinds of fines with different plasticity indices (PIs)––silt (PI =15), clay (PI =21), and diatomaceous silt (PI =70). A new fines classification system was used that suggested that the high PI of diatomaceous silt is not due to electrochemical forces, but to the porous skeletons of diatoms producing high Atterberg limits. Multiple series of undrained triaxial tests were performed in order to evaluate the collapsibility potential of the mixtures. The equivalent intergranular void ratio, as a state variable, was used to evaluate the behavior of the mixtures. It was found that the equivalent intergranular void ratio can reduce the influence of fines and provide a strong correlation bearing several aspects of the mechanical behavior of coarse-grained–fines mixtures.