Cyclic Volumetric Strain Behavior of Sands with Fines of Low Plasticity

Abstract

This work investigates the seismic compression characteristics of nonplastic and low-plasticity silty sands with varying fines content (0≤FC≤60%). Cyclic simple shear testing was performed on various sand-fines mixtures at a range of modified Proctor relative compaction levels and degrees of saturation. Aside from the expected strong influence of relative compaction, increasing fines content is found to generally decrease volume change for fines fractions consisting of silts and clayey silts of moderate-to-low plasticity index (PI≤10). With truly nonplastic fines (rock flour), cyclic volume change increases with FC. Some materials also exhibit an effect of as-compacted saturation in which moderate saturation levels associated with high matric suction cause volume change to decrease. Additionally, the data consistently demonstrate that vertical strains decrease as overburden pressure is increased in a manner consistent with a previous clean sands model. This paper presents empirical equations to capture these effects, which extend a previous clean-sand volumetric-strain material model to account for the previously unconsidered effects of fines content and saturation.