Surface waves attenuation in granular media through a small-scale Metabarrier

The present thesis describes a small-scale experiment, carried out in the laboratory of the Swiss Federal Institute of Technology of Zurich (ETH). The research focuses on metamaterials, locally resonant structures able to affect the propagation of waves passing through them. The present thesis investigates an innovative method to attenuate Rayleigh waves through the insertion of a barrier of scaled resonators into the soil, capable of generating a bandgap in the dispersion relation. Waves, whose frequency fall within the bandgap, cannot propagate through the resonant structure. Each resonator is constituted by a steel mass mounted on top of a spring made with 16 beams forming a truss. Taking advantage of the results of A. Palermo et al [1] as a starting point, we carried out a small-scale experiment in a big wooden box filled with glass beads in order to investigate the effectiveness of the designed metabarrier in attenuating surface waves generated by a metal rod exciting the surface every 300 ms. We found a stop-band in the dispersion relation inside the metabarrier, generated by the coupling between the vertical component of Rayleigh waves and the longitudinal resonances of the resonators. In parallel with the laboratory experiment, some numerical simulations have been performed with the software Comsol Multiphysics in order to compare the results obtained experimentally.