Drained Seismic Compression of Unsaturated Sand

Abstract

Seismic compression of unsaturated soils occurs due to particle rearrangement during large-strain cyclic shearing, which may be resisted by interparticle stresses that depend on the matric suction and degree of saturation. Due to the high rate of shearing in earthquakes, seismic compression is expected to be an undrained phenomenon with changes in total volume, matric suction, and degree of saturation along with an evolution in soil hydromechanical properties during cyclic shearing. To simplify this problem and better understand the mechanisms of seismic compression, this study seeks to isolate the effect of matric suction through a series of drained cyclic simple shear tests on unsaturated sand subjected to different shear strain amplitudes. These tests were performed in a cyclic simple shear apparatus with suction-saturation control using a hanging column and suction monitoring using an embedded tensiometer. Matric suction values in the funicular regime had the greatest effects on the magnitude and rate of development of seismic compression with cyclic shearing, and values in the capillary regime were similar to those in dry and saturated conditions. The volumetric contractions also caused the soil-water retention curve and suction stress characteristic curve to shift toward higher suctions during cyclic shearing.