Influence of Soil Suction on Small-Strain Stiffness of Compacted Residual Subgrade Soil

Abstract

The small-strain stiffness of compacted residual lateritic subgrade soil was determined. A bender element apparatus and the filter paper method were integrated to develop a systematic testing procedure to investigate the influence of matric suction on small-strain stiffness, including small-strain shear wave velocity and small-strain shear modulus, with different wetting paths. Soil specimens were compacted at three moisture contents (optimum moisture content, dry of optimum, and wet of optimum), then wetted to various moisture contents by using an environmental simulation apparatus developed to simulate in-service moisture conditions. Test findings indicate that specimen moisture contents increase gradually and finally attain equilibrium in the wetting process. Suction decreases with increasing moisture content and degree of saturation; consequently, small-strain shear wave velocity and small-strain shear modulus decrease. The specimens compacted at dry of optimum have a much lower small-strain shear wave velocity and small-strain shear modulus than specimens compacted at wet of optimum. Nevertheless, the small-strain shear modulus exhibits higher linearity with matric suction than with moisture content. Results indicate that matric suction is a key parameter for evaluating the dynamic properties of compacted soil.