Strain-dependent dynamic properties of compacted clay-sand mixtures

Abstract

Compacted clay-sand composites, as a type of gap-graded soils, are widely used in a variety of geotechnical engineering projects such as the core of embankment dams, the foundation of offshore structures, and impermeable blankets in waste disposal landfills. In this study, a comprehensive series of resonant column and torsional shear tests is carried out to investigate the strain-dependent dynamic shear modulus and damping ratio of clay-sand mixtures. The significant effects of isotropic confining pressure, relative compaction, aggregate content, and plasticity index of the fines portion on the shear modulus degradation curve, strain-dependent normalized shear modulus, and damping characteristics of compacted clay-sand mixtures are systematically examined. The results show that the shear modulus of the composites increases with increasing isotropic confining pressure and decreasing plasticity index. It is also observed that the effect of sand content on the strain-dependent shear modulus increases with increasing confining pressure. In addition, the normalized shear modulus decreases and the damping ratio increases with the increase in the sand content of the compacted mixtures. Relative compaction is also observed to have an insignificant effect on the strain-dependent shear modulus and damping characteristics of composites. Based on the experimental results and considering the influences of all controlling parameters, several empirical equations are developed to evaluate the strain-dependent shear modulus and damping ratio of compacted clay-sand composites. The proposed equations could be readily utilized in practice for the seismic stability analysis of various geo-structures comprising compacted gap-graded composites.