Surface vibration propagation over a layered elastic half-space with an inclusion

The transmission of vibrations, and its reduction, in the far-held of the s urface of the ground due to a harmonic load acting over a strip, is investi gated theoretically. A possible vibration attenuation device that has shown some promise is the "wave impedance block" (WIB). The principle of this is to modify the modal wave propagation regime of the ground by introducing a n artificial stiffened layer (inclusion) under the load. The ground is mode lled as an elastic layered half-space and the inclusion is under the load w ithin the layered half-space. The performance of the inclusion in impeding wave transmissions at a number of receiver positions is studied and measure d in terms of insertion loss analogous to the study of noise barrier design s in outdoor sound propagation. A numerical model is presented which enable s the wave-field in the region of the inclusion to be determined. This is b ased on an integral equation formulation of the problem which is solved usi ng a boundary element approach. It is shown that an inclusion has a benefic ial effect at low frequencies. However, when the wavelength becomes short c ompared with the depth and width of the inclusion, adverse effects occur at some frequencies which are still observed in the far-field. The possible c auses are difficult to analyse as radiation, scattering and transmission of the shear and compression waves due to the inclusion must be taken into ac count. Various configurations of inclusion are studied and results presente d so that some preliminary conclusions may be derived. (C) 1998 Elsevier Sc ience Ltd. All rights reserved.