Effects of Moulding Water Content on the Stress-Strain Behaviour of a Compacted Silty Sand

Abstract

Compacted soil is often employed in geotechnical constructions. A set of triaxial compression tests was executed on fully saturated specimens of a medium-fine compacted soil to investigate the influence of preparation water content on the stress-strain behaviour. Specimens were prepared by compacting at different water contents on the dry and wet sides of the optimum and around the optimum for different compaction energy levels. A state-of-the-art triaxial apparatus, which allows investigation into soil behaviour from very small strains up to failure, was used. It is shown that, as previous researches have indicated, compacting soil at different moulding water contents produced materials with different microstructures. The test results showed that the effect of soil microstructure was noticeable at small strains but it decreased with an increase in the strain and had little or no effect on the shear strength envelope in terms of effective stresses. Particularly, it is shown that, even after removing the effects of compacted dry density, the specimens compacted at the optimum water content presented not only the lowest isotropic compressibility, but also the highest initial stiffness and damping ratio at small strains. As the strain level increased, the stress-strain behaviour tended to be more uniquely controlled by the instantaneous dry density. It was also the case of the dilatancy characteristics, which controlled the pattern of effective stress path.