Effects of state of test sample, specimen geometry and sample preparation on dynamic properties of rubber–sand mixtures

The study presents resonant column test results on sand mixed with granulated rubber. The experiments were carried out on samples within a range of rubber content from 0 to 15% by dry weight of sand–rubber mixtures, at variable isotropic effective stresses, p′, state of test sample and sample preparation method. Both small-diameter specimens of 36 mm × 82 mm in size and large-diameter samples of about 70 mm × 140 mm in size were tested in torsional mode of vibration at very small shear strain amplitudes, in general less than 10−5. Specimens were tested in a dry state, a moist state with a very small water content inclusion and a fully saturated state. The data indicated that for a given p′, the increase of rubber content shifted the obtained resonant frequencies to lower values, the small-strain shear modulus, G0, decreased, whereas small-strain material damping, Ds0, increased. The state of test sample, namely dry, moist or fully saturated, did not affect the obtained small-strain shear modulus values but did affect the obtained Ds0. G0 could efficiently be described through typical formulas of G0 against p′ used for sands, by treating the volume of rubber particles as part of the total volume of voids into the void ratio function of the G0–p′ relationship. By preparing the samples at variable initial void ratios, comparisons could be obtained between samples of variable rubber contents and state of test sample but at a given resonant frequency. This is very important in capturing the behaviour of the mixtures in resonant column test which is a non-frequency-controlled method and thus the effect of rubber content and loading frequency could be de-coupled in the experiments.