Determination of shear modulus and damping ratio of normally consolidated unsaturated kaolin

Abstract

Shear modulus (G) and damping ratio (D) are efficient and important parameters in estimation of seismic response of a site. Recently by development of the advanced experimental equipment, some studies have been presented based on the dynamic parameters of unsaturated soils. It is tried to find the variation of the cyclic parameters of the unsaturated soil alluvium in the current research. This is done in following to previous studies, by the determination of the shear modulus and damping ratio parameters at medium to large strain levels using suction controlled cyclic triaxial apparatus along with modelling the effects of changes in matric suction and mean net stress on these parameters in unsaturated fine grained material. In this regard, a special type of fine-grained soil with plasticity index of 12 is selected. Experiments are performed on different stress paths including three suction levels (zero, 150 and 300 kPa), three mean net stress levels (100, 200 and 300 kPa) and three deviatoric cyclic stress amplitudes (18, 42 and 81 kPa) up to 60 loading cycles. The tests show that increase in suction results in rising shear modulus and decreasing in damping ratio values. Increasing of the mean net stress enhances the stiffness of normally consolidated samples and leads to increase shear modulus and decrease in damping ratio. Finally, according to the results of the current investigation and other available data from the literature, the prior equations for estimation of the normalized shear modulus (G/G0) and damping ratio of unsaturated soils are modified.