Creep, Relaxation, and Strain Rate Effects in Central Florida Silty Sand

Time and rate dependency studies of soil materials have been focused on clayey soils where the viscous effects are more pronounced for low confining pressures. In sandy materials, time-dependent and rate effects are usually considered negligible. Therefore, for practical purposes sands are deemed as non-viscous materials although there is experimental evidence that creep strains of 10% under monotonic loading can be developed. The viscous behavior of granular materials has been demonstrated to be stress dependent. For low confining pressures, it is attributed to particle rearrangement. Most studies on compressibility time-dependent effects of granular soils were developed in one-dimensional or triaxial conditions. The effects of different contents of non-plastic silts have been studied showing that granular soils with fine contents around the transitional limit of approximately 35%–45% start to behave in compressibility testing more like a fine grained material following isotach characteristic behaviors. The objective of the testing program presented herein, which was performed in a constant rate of strain apparatus for low confining pressures, was to evaluate the effects of fines in the material compressibility response of Central Florida silty sands. Control tests on several relative densities were targeted for clean sands. Creep, relaxation, and strain rate effects were evaluated in soil samples reconstituted to several effective axial stress conditions, and fines were added to the clean sand to target void ratios corresponding to the loose state. In this research, the concept of global void ratios versus skeleton void ratios was used to compare the silty sand behaviors up to a 20% of fine content in relation to control tests conducted in clean sands. This research concluded on the relative importance of considering the participation of fines up to 20% weight based on the compressibility response for several sample preparation techniques used to reconstitute the soil samples in the laboratory.