EFFECTS OF LIQUEFACTION ON PILE FOUNDATIONS

[mahyarov]

EFFECTS OF LIQUEFACTION ON PILE FOUNDATIONS

Author: Horne, J C Kramer, S L | Size: 5.29 MB | Format: PDF | Quality: Original preprint | Publisher: Washington State Transportation Center | Year: 1998 | pages: 140

Liquefaction of soils has caused considerable damage to pile-supported structures such as bridges and buildings in earthquakes. This project attempted to identify the most important impacts of liquefaction on pile foundations and to develop and verify new tools that allow those effects on pile foundation performance to be evaluated. A literature review indicated that the majority of damage to pile foundations has been caused by lateral movement of liquefied soil. Evaluation of the effects of lateral spreading on pile foundations requires that the soil displacements caused by lateral spreading be predicted and that the response of a pile foundation to those lateral displacements be predicted. In answer to the shortcomings of currently available estimation procedures, this project developed computational models for predicting lateral spreading deformations and pile-soil interaction. To validate the models against closed-form elastic solutions, they were compared with other computer programs that have some of the capabilities of the models and with field performance from available case histories. Free-field ground surface displacements produced by lateral spreading vary widely, but they are influenced most strongly by the initial and residual shear strength of the liquefiable soil, the gradation of the liquefiable soil, the initial state of shear stress within the deposit, the earthquake magnitude, and the distance from the site to the fault rupture zone. Pile response to lateral spreading is strongly dependent on surface slope, soil strength, and pile flexural stiffness, but it is relatively independent of groundwater table depth, pile diameter, pile length, and p-y curve stiffness. Both models developed in this study account for nonlinear, inelastic soil behavior and consider the development of excess porewater pressure and its effects on soil stiffness and strength. The pile-soil interaction model accounts for frequency-dependent radiation damping behavior in the time domain and allows computation of dynamic pile displacements, bending moments, shear forces, and soil reactions. By allowing computation of free-field displacements both at and below the ground surface and by considering the effects of those motions on the pile throughout earthquake shaking, the proposed model offers a practical, rational tool for evaluating lateral spreading effects on pile foundations.

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