| Earthquake damage investigation indicates liquefaction is one of the main reasons of earthquake-induced damage to the pile-supported bridge, the domestic seismic design codes only provide some general provisions on the horizontal bearing capacity in liquefying ground so that some blindness and arbitrariness is coming out when carried out, which reveals some problems in aseismic design of pile foundation. The study on pile-soil-structure dynamic interaction is the key to solve this problem in liquefying ground. Dynamic p-y curve method is an important method to investigate pile-soil dynamic interaction, which has the advantages of clear conception, simpleness, easy implementation-numerically and avoidance of choosing complex constitutive model, in addition, it also can take the nonlinear characteristic of soil into consideration. Beacause of the above-mentioned advantages of dynamic p-y curve method, increasing attention has been paid to this method in recent years.A series of large-scale shaking table tests were conducted successfully corresponding to liquefiable ground covered with clay layer at the surface layer, a simplified numerical model was established based on the Winkler theory and combined a new p-y curve, which took the effect of mass in the vicinity of pile and pore pressure on the dynamic reponse and stiffness of sand into consideration, to research pile-soil-bridge structure dynamic interaction in liquefying ground. Based on the free site analysis, the simplified model was verified by two shaking table tests which proved its reliability and rationality, and then the sources of residual errors between model and tests were analysed. Strong emphasis was placed on the parameter sensitivity analysis of p-y method. A series of understandings are obtained; some suggestions about seismic design of pile foundation are proposed based on the damage mechanisms and parameter analysis.The main research contents and understandings obtained in this study are as follows:Some test results under different frequencies and vibration amplitudes are shown to demonstrate frequency and vibration amplitude significantly affect the dynamic response of pile and the development of excess pore pressure; the camparison betweent sinusoidal wave and earthquake motion indicates the response of pile and pore pressure is much intenser under earthquake motion. The calculated results are very consistant with the test results after the verification, which proves Beam on Nonlinear Winkler Foundation Method is a simple but reliable method to analyse the dynamic response of pile foundation. The spectrum analysis reflects displacement of pile is controlled by low frequencies while acceleration and bending moment are controlled by relative high frequencies, especially for acceleration.There will be higher stability and safety for larger pile diameter and higher stiffness ratio between pile and soil. The dynamic response of pile is intenser for larger mass of superstructure while damping reduces the response, the analysis on excess pore pressure indicates the effect of soil displacement on the pile-soil dynamic interaction is more obvious than that the reduction of stiffness of soil. The response of pile will be halved or doubled when the vibration amplitude is halved or doubled, and the hysteresis of acceleration and displacement of pile is reverse compared with bending moment.The efforts and conclusions, especially the simplified model in this paper, have certain theoretical and practical significance for the further investigation on earthquake-induced pile-soil-bridge structure dynamic interaction as well as the seismic analysis and design of pile foundation, even for the development of deformation-based aseismic design for bridge pile foundation in liquefying ground. |
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