Attenuation of low frequency ground vibrations by means of resonant scattering of rayleigh waves on heavy masses

Although the main mechanisms of generating ground vibrations at source, e.g. by rail and road traffic, are now well understood, there are still very few investigations aimed to protect the affected buildings by influencing the propagation of ground vibrations, mainly Rayleigh surface waves, from a source to a receiver. A promising and cost effective method of screening the affected properties can be using heavy masses placed on the ground surface near the road (e.g. concrete or stone blocks, specially designed brick walls, etc). The principle of operation of such masses is based on the fact that their natural frequencies of vibration, which depend on the mass value and on the local ground stiffness, can be chosen within the frequency range of railway- or road-generated ground vibrations (normally from 5 to 50 Hz). When the mass is shaken under the impact of incident Rayleigh surface waves, it scatters the incident waves into the depth of the ground and at different directions on the surface, thus resulting in noticeable resonant attenuation of transmitted ground vibrations. Using suitable combinations of such mass scatterers, one can expect to achieve efficient vibro-isolation of affected buildings. While some initial efforts have been made in the past to investigate the above-mentioned mass scatterers, largely by means of numerical calculations, very little progress in understanding their behaviour has been made so far. The aim of the present paper is to give a brief introduction to the theory of resonant mass scatterers and to discuss some problems that still need to be considered to achieve a fuller understanding of their operation as means of damping of low frequency ground vibrations.