Development of Engineering Continuum Models for Seismic Soil-Foundation Interaction

Soudkhah, Mahdi

Graduate Thesis Or Dissertation

Development of Engineering Continuum Models for Seismic Soil-Foundation Interaction Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/g158bh531

Abstract

To construct an improved experimental and analytical foundation for studying seismic soil-structure interaction, an integrated research program is pursued to examine the dynamic response of surface foundations on sandy soils under both forced and ground motion disturbance. By virtue of a set of developments of the centrifuge scaled modeling including the shake-table method, a comprehensive experimental database for the free-field ground motion problem of a stratum, multi-mode forced vibration response's dependence to foundation configurations, as well as their corresponding seismic behavior under general base motion were developed. Through a comparison of the generated data with those from the classical homogeneous and inhomogeneous shear modulus soil models, the limitations of conventional theories in capturing the general planar modes of vibration was demonstrated. The theoretical/computational development of the research includes the formulation and implementation of a set of new adaptive-gradient boundary elements, an improved treatment of corner and edge problems in BEMs, multi-domain rigid/deformable surface/embedded foundation problems under multi-directional seismic ground motion, and alternative decompositions of wave scattering problems. With the aid of these developments, the complex interaction of a granular soil layer with footings subjected to eccentric dynamic loads and seismic ground motion was investigated. In the experimental phase of the investigation, a variety of scaled-model surface foundations were designed and tested dynamically on a large geotechnical centrifuge and characterized in terms of multi-directional accelerance functions or transfer functions in the frequency domain. Among various findings, it was found that for the common range of footing configurations, capturing the in-situ variation of the shear modulus of the soil is not sufficient to describe the dynamic structural-soil problem comprehensively. Aimed at capturing the near-field and far-field site effects deemed critical for the problem, the new two-zone continuum model was found to perform well in both the radiation and seismic problems with economy, providing comprehensive agreement with both forced vibration and seismic data. On the basis of the experimental data obtained, a pair of compact evolution equations were also developed to express the 2 key physical parameters of the model directly in terms of the foundation configuration.

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