Effect of the fines content and its characteristic grain shape on the undrained strength of loose silty sands

Static liquefaction of loose saturated granular soils has caused several catastrophic failures of earth fills, tailings storage facilities and waste dumps. It is well known that the liquefaction potential strongly depends on state parameters. However, the influence of grains’ intrinsic properties has attracted less attention. In this paper, comprehensive experimental work on non-plastic silty sands is presented. The main objective is to study the effects of the characteristic grain shape of the fines content (FC) on the undrained behavior of loose cohesionless silty sandy materials. Samples of Ottawa sand mixed with varied amounts of fines were prepared, to obtain the common FC scenarios of underfilled, transitional and overfilled packings. Two types of fines were used: glass beads and mine tailings. Constant volume and constant stress ring shear tests were carried out at large shear strains of around 100%. The results show that transitional cases exhibit higher residual strength under constant volume conditions. Moreover, data on mixtures indicate that angular fines content significantly increases the critical friction angle, while it decreases when rounded FC are used. The same trend is observed in the undrained (i.e., constant volume) peak and critical strengths. The results help to understand the effect of intrinsic characteristics of soils on static liquefaction potential. The main application is the assessment of the undrained behavior of granular mixtures that can drastically vary their properties in industrial processes, such as mine waste production.