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

摘要

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 V_s-σ_m' and Go-σ_m relationships are dominated by particle type in terms of mineralogy and morphology; plastic response at particle contacts of the pumice samples led to higher n_v and n_G 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 n_D 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.