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A series of bender element tests was carried out to investigate the variation of small-strain stiffness (Gmax) of sand–granulated rubber mixtures under long-term loading. Comparisons were made using two different host sands: a non-crushable material called Sydney sand and a crushable material composed of completely decomposed volcanic rock (CDV). The test results suggested that, at the selected stress states in the study (mean effective confining stress ranged from 250 to 333 kPa), the influence of creep on the stiffness of the pure sand specimens was more pronounced for CDV compared with Sydney sand and the presence of rubber amplified creep effects on both types of mixtures. The influence of creep on Gmax was therefore associated with two major mechanisms: the increased compressibility of specimens predominantly because of grain crushing (contribution of sand fraction), and the increased compressibility because of the presence of soft rubber grains (contribution of the rubber fraction). The significant influence of grain breakage on the relationship between stiffness and creep was confirmed by post-test examination of the grain-size distribution curves of pure CDV samples. For rubber–CDV mixtures, the inclusion of soft and viscoelastic rubber grains prevented breakage, in this way reducing the creep mechanism due to grain crushing, but increased the overall influence of creep on stiffness. These conclusions were drawn based on 20% of rubber by mixture weight, and very similar behaviour was observed for 10% rubber. It was therefore understood that the aggravation of creep induced by the increased deformations due to the presence of rubber, for the given contents of rubber included in the study, was more dominant compared with the adverse influence of rubber on samples’ creep by preventing sand grain breakage.

A micromechanical experimental study is presented in this paper investigating the normal contact response of quartz sand grains under cyclic loading. Sand grains with clean surfaces, termed uncoate...

This technical note presents the calibration exercise of a Hardin-type resonant column of fixed–partly fixed ends, which is capable of exerting dynamic torsional vibration on the specimen. The apparatus uses a mechanical system connected to the drive mechanism which works as a massless torsional spring–dashpot and can apply axial load of compression or extension to the specimen. Thus, the vibration of this system follows the physics of oscillators (spring-type model), which is highly strain-rate dependent. The calibration exercise led to the estimation of the apparatus rotational inertia (JA). The calibration exercise was carried out using aluminium bars of known stiffness and of variable dimensions covering a range of frequencies from about 60 to 95 Hz, as well as real soil specimens, which were used as calibration rods covering an additional range of frequencies from about 85 to 170 Hz. This allowed a wide range of frequencies to be captured, which are representative of resonant frequencies of soil specimens of 70 mm dia. and 140 mm long. For the real soil specimens, which were used as calibration rods, the rotational stiffness necessary for the estimation of JA was estimated from bender elements inserted into the resonant column. It was shown that JA was frequency dependent, which is in alignment with the vibration of oscillators.

While it has been acknowledged from cyclic laboratory tests that the inclusion of rubber particles increases liquefaction resistance, little attention has been paid to the influence of rubber conte...

This study reports on the significance of particle shape on the small-strain damping ratio of dry sands in shear (Ds,min) through a comprehensive set of torsional resonant column tests. Sands with a variety of grain shapes prepared at variable initial densities are studied. The samples are subjected to torsional resonant column tests under isotropic confining pressures (p′) ranging from 50 to 800 kPa. Small-strain damping ratios are derived based on the free-vibration decay mode of the samples and the results are compared with the half-power bandwidth method. The effects of grain size distribution, particle shape and effective confining stress on Ds,min are thoroughly discussed, and a new model for the prediction of small-strain damping ratio of dry sand is proposed.