Laboratory Investigation into the Effect of Fines Plasticity on the Mechanical Behavior of Sand/Fines Mixtures

This paper presents a laboratory study carried out to investigate the mechanical behavior of Chlef sand emphasizing the effect of non-plastic fines content (silt) and plastic fines content (clay) on the sand-silt-clay mixture behavior. For this purpose, a series of direct shear tests were performed. The samples under study were taking account two initial relative densities for their preparation (RD = 55 and 85%). The test results showed that the shear strength of Chlef sand decreases with the increase of silt content from 0 to 40%, and for sand-clay and sand-silt-clay mixtures, the variation of shear strength has a threshold value; a decrease until 20% fines content followed by an increase considering the percentage of fines is higher. Cohesion increases with the increase of silt content, while for the sand-clay and sand-silt-clay mixtures, the cohesion increases until a threshold of 20% fines content with a same tendency as the variation of the direct shear strength. Contrariwise, a slight variation of the friction angle at the peak has been observed.