J. E. Luco

Response of a layered viscoelastic half-space to a moving point load

Abstract A procedure to obtain the steady-state displacements and stresses within a multi-layered viscoelastic half-space generated by a buried or surface point load moving with constant speed parallel to the surface of the half-space is presented. The approach is based on an integral representation of the complete response in terms of wavenumbers. The effects of layering are included by use of an exact factorization of the displacement and stress fields in terms of generalized transmission and reflection coefficients. The results in the time domain are obtained by Fourier synthesis of the frequency response which in turn is obtained by numerical integration over one horizontal wavenumber. Numerical results for the displacement and stress fields on the surface and within the half-space are presented for surface and buried loads moving with various subsonic and supersonic speeds.

Dynamic interaction between rigid foundations in a layered half-space

Abstract A computationally efficient boundary integral equation technique to calculate the dynamic response of a group of rigid surface foundations bonded to a layered viscoelastic half-space and subjected to external forces and seismic waves is presented. The technique relies on an iterative scheme which minimizes in-core memory requirements and takes advantage of any geometrical symmetry of the foundations. Extensive results for the case of two rigid square foundations placed at different separations and bonded to a viscoelastic half-space are presented. It was found that the choice of discretization of the foundations has a marked effect on the calculated impedance functions for extremely small separations. Illustrative results for a case of several closely-spaced foundations bonded to a layered half-space are also presented.

A comparison of soil-structure interaction calculations with results of full-scale forced vibration tests*

The capability of a simple soil-structure interaction model to predict the response of structures during forced vibration tests is evaluated by comparison of the theoretical and experimental response of a nine-storey reinforced concrete building. A very good agreement between theoretial and experimental results was obtained for vibrations in which the foundation acts as a rigid body. It was also found that simple models may not be applicable when the foundation is highly deformable.

Stresses and displacements in a layered half-space for a moving line load

Abstract The dynamic displacements and stresses within a multilayered viscoelastic half-space produced by a buried or surface line load moving with constant speed parallel to the surface of the half-space are calculated by Fourier synthesis of the frequency response which in turn is obtained by analytical integration over horizontal wavenumbers. The effects of layering are included by use of an exact factorization of the displacement and stress fields in terms of generalized transmission and reflection coefficients. The procedure is tested by comparison with previous analytical solutions for the case of a uniform half-space and new numerical results for the displacement and stress fields on the surface and within the half-space are presented for surface loads moving with various subsonic and supersonic speeds.

Dynamic response of embedded foundations: a hybrid approach

Abstract A hybrid approach is presented to obtain the dynamic response of foundations of arbitrary shape embedded in a layered viscoelastic half-space when subjected to external forces and elastic waves. The approach is based on the use of Greens functions for the half-space continuum combined with a finite element discretization of the finite portion of soil excavated for the foundation. Compared with direct or indirect boundary integral equation methods this particular combination permits a reduction of the number of calculations of Greens functions at the expense of additional finite element calculations. The validity and accuracy of the hybrid approach is investigated by comparison with solutions obtained by other methods for axisymmetric foundations embedded in a uniform viscoelastic half-space and in a layered medium. It is found that the proposed hybrid approach with an appropriate discretization of the soil excavated for the foundation can achieve excellent accuracy.

Diffraction of obliquely incident waves by a cylindrical cavity embedded in a layered viscoelastic half-space

Abstract The three-dimensional harmonic response in the vicinity of an infinitely long, cylindrical cavity of circular cross-section buried in a layered, viscoelastic half-space is obtained when the half-space is subjected to homogeneous plane waves and surface waves impinging at an oblique angle with respect to the axis of the cavity. The solution is obtained by an indirect boundary integral method based on the use of moving Greens functions for the viscoelastic half-space. Numerical results describing the motion on the ground surface and the motion and stresses on the wall of the cavity are presented for obliquely incident P-, SV-, SH- and Rayleigh waves with different horizontal angles of incidence.

Dynamic response of a two-dimensional semi-circular foundation embedded in a layered viscoelastic half-space

Abstract The dynamic response of a massless rigid strip foundation of semi-circular cross-section embedded in a uniform or layered viscoelastic half-space is considered. The foundation is subjected to external harmonic forces and moments and to plane homogeneous P-, SV- and SH-waves. Numerical results are obtained by two indirect boundary integral equation methods: a reciprocity-based approach and a version of the least squares approach. The results for a uniform half-space are tested against the exact solution for longitudinal vibrations and against earlier results for the in-plane impedance functions and for the in-plane response to plane waves. The deffects of Poissons ratio, material attenuation and layering on the impedance functions and on the scattering coefficients (response to waves) are described in some detail. The appearance of fictitious eigen-frequencies at which the solution may fail is also discussed.

On The Three-dimensional Seismic ResponseOf A Class Of Cylindrical Inclusions EmbeddedIn Layered Media

In this paper we examine the three-dimensional response of a class of cylindrical inclusions of infinite length embedded in a layered viscoelastic half-space and subjected to plane waves impinging at an oblique angle with respect to the axis of the inclusion. The cases considered include topographical canyons of arbitrary cross section, buried cavities or unlined tunnels, buried pipelines or lined tunnels, and layered sedimentary basins or valleys. All of these cases are formulated and solved by means of a unified indirect boundary integral method based on the use of moving Greens functions for a layered viscoelastic half-space. Results for the three-dimensional response of canyons, cavities, pipelines and valleys as well as comparisons with previous solutions for simple cases are presented for excitations corresponding to P, SV and SH-waves.