Liquefaction Behavior of Sand-Gravel Composites

Abstract

To quantify the effect of gravel content on the liquefaction resistance of sand-gravel composites, a series of undrained cyclic triaxial tests was performed on sand-gravel composite specimens with gravel contents of 0%, 20%, 40%, 60%, and 100%. Test results show that the liquefaction resistance of sand-gravel composites may increase significantly with increasing gravel content. This increase was observed even for composite specimens tested at the same relative density. It was found that at 40% gravel content, a 40% relative density composite with 40% gravel will behave like a 65% relative density sand for the soils tested in this study. A methodology is described to estimate the cyclic strength of the composite soil by testing the finer fraction soil alone. Scalping oversized particles from gap-graded soils may result in significantly underestimated prototype cyclic strength when the scalped soil is tested at the same relative density as either the total composite or the finer fraction of the composite. For loose composite specimens with a small percentage of gravel particles, a more reasonable estimate of the prototype cyclic strength may be obtained by testing the fine material at an equivalent relative density. An equivalent density of the finer fraction is proposed to account for the effect of gravel inclusions on the liquefaction behavior of the composite.