Effect of Relative Density on the Drained Seismic Compression of Unsaturated Backfills

Abstract

It is critical to accurately predict the seismic compression of backfill soils supporting bridge decks, pavements, or railways as small backfill settlements may have substantial impacts on the performance of these overlying transportation systems. Although several studies have evaluated the seismic compression of loose unsaturated soils, there has not been significant focus on the seismic compression of denser soils. This study presents the results from series of strain-controlled cyclic simple shear tests performed on unsaturated sand specimens having different initial relative densities and initial matric suctions representative of near-surface backfills. Although the seismic loading process may involve rapid, undrained shearing, the cyclic simple shear tests were performed in drained conditions with a slow shearing rate to isolate the effect of matric suction. The results showed that soils with higher initial suctions (or lower initial degrees of saturation) experienced smaller volumetric strains, but the effect of suction (or degree of saturation) decreases as the relative density increases.KeywordsSeismic compressionUnsaturated backfillsMatric suctionRelative density