The Combined Effect of Particle Size Distribution and Relative Density on the Large Strain Behavior of Sandy Soils

Sandy soils were investigated by means of a new ring shear device to understand the combined effect of particle size distribution and relative density on the soils’ deformation characteristics at large strains. The soils were sheared in undrained condition to at least 10 m to observe their responses before and after the attainment of steady state. Two main responses—purely contractive and partially contractive—were identified. Loose specimens were purely contractive and mobilized peak strength at small strains before undergoing rapid loss of shear resistance until steady state strength was achieved. On the contrary, dense soils exhibited partially contractive behavior by first contracting and then dilating as shearing progressed. Analyzed shear resistance-pore pressure relationships indicated that changes in relative density induced corresponding changes in dilation characteristics. The shear behavior of the soils at critical density demarcated the behavior of the loose from that of the dense soils. At densities below the critical, the specimens exhibited purely contractive behavior, and above the critical, the specimens’ behavior was defined by three distinct stages of deformation of phase transformation, peak and steady states. A comparison of the friction angle at phase transformation, steady state and critical state in all the soils revealed only little difference. At a given normal stress, the friction angle at phase transformation was equal to the friction angle at steady state in specimens at critical density. This study shows that the large strain behavior soils can offer valuable insight on the mechanism of rapid, long-travel slope movements that are often catastrophic.