THE RESPONSE OF PILES DURING EARTHQUAKES: DYNAMIC SOIL-PILE-SUPERSTRUCTURE INTERACTIO

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THE RESPONSE OF PILES DURING EARTHQUAKES: DYNAMIC SOIL-PILE-SUPERSTRUCTURE INTERACTIONS

Author: Boulanger, R W Kutter, B L Wilson, D W | Size: 5.83 MB | Format: PDF | Quality: Original preprint | Publisher: University of California, Davis | Year: 1998 | pages: 125

The dynamic response of pile foundations in soft clay and liquefiable sand during strong earthquake shaking was evaluated. The research consisted of two major components: (1) a series of dynamic centrifuge tests of pile-supported structures in soft clay and liquefiable sand; and (2) an evaluation of dynamic "beam on a nonlinear Winkler foundation" (BNWF) analysis methods against the centrifuge model results. The dynamic centrifuge modeling techniques were critically evaluated in detail because these tests were among the first performed using the new shaking table on the 9-m radius centrifuge. The results of this evaluation will benefit other current and future projects utilizing the large centrifuge. Several BNWF computer programs were shown to give consistent results for similar idealizations of a physical problem. Two new p-y elements were implemented into the program GeoFEAP. The representation of radiation damping was shown to be important in certain cases, with series radiation damping being technically preferred over parallel radiation damping in such cases. Calculated responses for a single pile in soft clay were in good agreement with the centrifuge data when using series radiation damping and a p-y element with gapping ability. The p-y resistance of liquefied sand was shown to be strongly dependent on relative density and displacement level. Time histories of p-y resistance were obtained by backcalculation techniques for the soft clay and liquefied sand tests. The p-y resistance of liquefied sand shows characteristics that are consistent with the expected stress-strain behavior of liquefied sand, including the effects of relative dentify, dilation, cyclic degradation, and prior displacement history. If a scaling factor approach is used to approximate the effects of liquefaction on p-y resistance, then pseudo-static p-y analyses suggest a scaling factor of about 0.1-0.2 would be appropriate for Dr=35-40% sand and a scaling factor of about 0.25-0.35 would be appropriate for Dr=55-60% sand. It is emphasized that the use of an apparent p-y scaling factor for liquefied sand was shown to be a simplistic approximation to a complex phenomenon, and therefore its use in design requires considerable judgment.

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