Wave dispersion in granular soil by DEM analysis in two and three dimensions

Numerical studies are conducted to investigate the existence of wave dispersion in resonant column tests on dry granular soil. The distinct element method (DEM) in the time domain is employed in two and three-dimensions to simulate the laboratory apparatus. The investigations focus on the effect of sample width, voids ratio. viscous damping and wavelength, on propagation velocities of longitudinal harmonic waves in rectangular samples consisting of uniform grains. It is shown that granular materials may exhibit anomalous dispersion that is, wave velocities that increase with increasing excitation frequency. This increase may be significant for squatty samples, yet becomes less pronounced for slender samples. The dispersion effects tend to be more pronounced in 2D over 3D analyses which suggests waveguide dispersion. Similar findings have been reported in some 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 elucidate the salient features of the problem.