LIQUEFACTION BEHAVIOR OF SAND GRAVEL COMPOSITES

To quantify the effect of gravel content on the liquefaction resistanc e of sand-gravel composites, a series of undrained cyclic triaxial tes ts was performed on sand-gravel composite specimens with gravel conten ts of 0%, 20%, 40%, 60%, and 100%. Test results show that the liquefac tion resistance of sand-gravel composites may increase significantly w ith increasing gravel content. This increase was observed even for com posite specimens tested at the same relative density. It was found tha t at 40% gravel content, a 40% relative density composite with 40% gra vel will behave like a 65% relative density sand for the soils tested in this study. A methodology is described to estimate the cyclic stren gth of the composite soil by testing the finer fraction soil alone. Sc alping oversized particles from gap-graded soils may result in signifi cantly underestimated prototype cyclic strength when the scalped soil is tested at the same relative density as either the total composite o r the finer fraction of the composite. For loose composite specimens w ith 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 t he finer fraction is proposed to account for the effect of gravel incl usions on the liquefaction behavior of the composite.