The dynamics of a pumice granular soil in dry state under isotropic resonant column testing

The response of soils under vibrations strongly depends on the type of particles which reflects the behavior at particle contacts and the micro-mechanisms that dominate granular assemblies. In this paper the dynamic properties of a pumice soil of low bulk density and high porosity were investigated. As a reference soil, a quartzitic crushed rock with hard particles was used. The experiments were performed on dry samples of sand to gravel size under isotropic conditions of confinement in a fixed-free resonant column apparatus. In the range of small strains, the Vs–σm′ and GO–σm′ relationships are dominated by particle type in terms of mineralogy and morphology; plastic response at particle contacts of the pumice samples led to higher nV and nG exponents in comparison to the quartz ones. The small-strain damping ratio values were fairly similar for pumice and quartz soils, while the values of the exponent nD were more scattered. At higher shear strain amplitudes, the pumice soils showed higher linearity in comparison to the quartz ones. This is attributed partially to micro-crushing at particle contacts that occurs during the dynamic loading of the pumice soils which shifts the elastic and volumetric thresholds to higher strains and plays an important role in the energy dissipation in granular assemblies.

► The paper examines the response of pumice soils of low unit weight and high porosity. ► A fixed-free resonant column apparatus is used, while dry samples are studied. ► The pumice soils exhibit significantly more linear response in comparison to quartz soils. ► The pumice soils exhibit lower stiffness but similar damping compared to quartz soils. ► Micro-mechanical interpretations are also presented and discussed.