Dynamic Properties of Residual Soil over a Wide Range of Strain

Dynamic properties such as shear modulus (G) and damping ratio (ξ) are important to understand the dynamic and non-linear stress-strain behaviours of soil from small to large strains. Limited studies have been done to understand dynamic and static properties of residual soil. The objective of this paper is to present the dynamic properties of saturated and unsaturated residual soil obtained using a modified cyclic triaxial apparatus. Undisturbed residual soil from Bukit Timah Granite in the northern part of Singapore was used. The test includes wave propagation test and cyclic triaxial test. Bender element based wave propagation test was used to determine the very small-strain shear modulus, G_max and small-strain damping ratio, ξ_min. Effects of varying net confining pressure and matric suction on P-wave, S-wave velocities, stiffnesses, and damping ratios (V_p, V_s, G_max, and ξ_min, respectively) for the residual soil are discussed. Very small-strain dynamic properties from bender element tests are compared with those in the literature. Shear modulus and damping ratio at strains ranging from 0.05 to 1% were estimated using strain-control cyclic triaxial test. The number of cycles applied on the soil specimen was 40 and the loading frequencies were 0.2 and 0.5 Hz. Shear modulus and damping ratio for a wide range of strain were obtained at various effective mean confining pressures for saturated soil and various matric suctions at constant net confining pressure for unsaturated soil. It is observed that effective mean confining pressure and matric suction are crucial parameters which affect shear modulus and damping ratio of soil. Finally, the damping ratio and normalized shear stiffness of the residual soil (ξ and G/G_max) for a wide range of strain are found to be consistent with previous studies.