Influence of fines on the collapse of loose sands

A study has been carried out to investigate the influence of fines and gradation on the skeletal collapse behaviour of loosely prepared sand samples. Loose sand samples, formed by moist tamping and consolidated to the same effective stress level, were prepared with varying percentages of both plastic and non-plastic fines (< 74 μm) and non-plastic fine sand (> 74 μm). Samples were isotropically consolidated and subjected to monotonic undrained triaxial compression. Results indicate that increased percentages of fines (< 74 μm) have a pronounced effect on the monotonic undrained behaviour at large strains (> 0.5%). This change is represented by a decreased strain softening behaviour and a shifting of the steady-state line. Variation of the gradation of the host sand appears to have little effect on the monotonic undrained behaviour. A supplemental study, involving use of the scanning electron microscope, was carried out to evaluate the findings of the test program in terms of sand fabric.