Wave dispersion studies in dry granular materials by the distinct element method

Wave dispersion in resonant column tests on dry granular soil is explored. Numerical investigations in two and three-dimensional Distinct Element (D.E.) elastodynamic analyses are reported, implemented by means of the commercial computer platforms PFC2D and PFC3D. The investigations focus on the effect of dimensionless sample width, H/B, dimensionless grain size d/B and wavelength, d/l, on propagation velocities of longitudinal waves in the samples. It is shown that granular materials may exhibit anomalous dispersion that is, wave velocities that increase with increasing frequency over certain frequency ranges. This increase may exceed 10% for squatty samples, but becomes less pronounced for slender samples. Similar fi ndings have been reported in experimental NDT studies of concrete materials and a number of experiments on granular materials, but have not been systematically explored by numerical means. Results are presented in the form of dimensionless graphs and charts that provide insight into the physics of the problem.