Evaluation of void ratio and elastic modulus of unsaturated soil using elastic waves

The void ratio and elastic modulus of a soil influence the soil's behavior. In unsaturated soils, soil parameters can be easily affected by the matric suction and specimen component. The object of this study is to evaluate the elastic moduli and void ratios of unsaturated soils using compression and shear waves. The analytical equation for the void ratio in unsaturated soils is derived from the elastic wave velocities. The volumetric pressure plate extractor (VPPE) is improved for the application of axial load. The compression and shear waves are measured using piezo disk elements and bender elements, respectively, installed on the confining cell. For the preparation of the specimens, sands are mixed with silts of two different volume fractions (vf), 0 and 20%. The specimens are subjected to the axial stresses of 100 or 350 kPa to control the matric suction. The experimental results show that the shear wave velocities in the specimens with vf = 20% increase with increasing matric suction, while the shear wave velocities in the sandy soils (vf = 0%) remained almost constant. The compression wave velocities increase with increasing axial load, while the compression wave velocities remain constant with changes in the matric suction. The void ratio values determined from the elastic wave velocities agree well with void ratio values determined on the basis of the volume of the unsaturated soils. This study suggests that elastic waves can be effectively used to estimate the void ratios and elastic moduli of unsaturated soils.