Effects of soil heterogeneity on pile foundations under seismic loads

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Seismic induced liquefaction of saturated soil is still a major cause of earthquake damage to deep foundations, in spite of relatively large safety margins used in design. This proposal outlines a combined experimental and numerical study aimed at addressing a series of questions regarding failure mechanisms and interaction forces for piles in liquefying soil that have not been answered yet, and at providing the industry with a reliable tool and guidelines for seismic design of deep foundations. It is well understood today that soil properties vary from one point to another even within geologically distinct layers. The effects of this natural soil heterogeneity on soil liquefaction and soil pile interaction will also be addressed. In this respect, recent theoretical research identified a very interesting behaviour of such natural soils subjected to seismic loads that is likely to have significant influence on design practices in earthquake geotechnical engineering. To date, there is no experimental verification available to the practicing engineering community to help in recognizing, quantifying and accepting the above-mentioned behavior of heterogeneous soils.   A series of original centrifuge experiments for seismic analysis of pile foundations in randomly heterogeneous soil are proposed in this research program to investigate the atypical soil behaviour identified in theoretical studies and to quantify its effects on deep foundations. A state-of-the-art finite element code for dynamic effective stress analysis of soil-structure systems will be calibrated based on the experimental results and used to expand the scope of the experimental program. Both experimental and numerical results will then be used to develop, calibrate and validate a computationally effective tool for seismic analysis of pile foundations, readily available for current design applications. Finally, the new tool will be used in a systematic numerical study to provide design guidelines for a wide range of field situations and seismic loads. The soil materials for experiments and the examples for theoretical developments will be selected from the Fraser River Delta in British Columbia, a densely populated region highly vulnerable to earthquake hazards and soil liquefaction.