Elastic wave fields in a half-plane with free-surface relief,tunnels and multiple buried inclusions

In this work, we study the elastic wave fields that develop in an isotropic half-plane which contains different types of heterogeneities such as free-surface relief, unlined and lined tunnels, as well as multiple buried inclusions. The half-plane is swept by traveling harmonic waves, namely pressure waves, vertically polarized shear waves and Rayleigh waves, as well as by waves emanating from an embedded source. The computational tool used is the direct boundary element method (BEM) with sub-structuring capabilities. Following development and numerical implementation of the BEM, two stages of work are performed, namely a detailed verification study followed by extensive parametric investigations. These last numerical simulations help determine the dependence of the elastic waves that develop along the surface of the half-plane, as well as of the dynamic stress concentration factors in the different types of buried inclusions, to the following key factors: geometry of the free-surface relief, geometry, depth of burial and separation distance of the inclusions, wavelength to inclusion diameter ratio and dynamic interaction phenomena between the multiple heterogeneities. In closing, the potential of the enhanced BEM formulation to treat dynamic soil-structure-interaction problems with the kind of complexity expected in realistic engineering applications is discussed.