Research On P-y Curves Of Pile-Soil Interaction During Liquefaction Of Saturated Sands

It is very important for the design of foundations to evaluate lateral bearing capacity of piles under seismic loads. Although some researches were done on the lateral bearing capacity of piles in liquefied sand, the conclusion which was widely accepted has not obtained. It is observed that the saturated sand would be degraded because of the residual pore water pressure despite it was not liquefied under seismic loads. There are few researches on lateral bearing capacity of piles in degraded saturated sand so far. Therefore, Model tests of the soil-pile interaction were conducted to research lateral bearing capacity of a single pile in degraded stratum and p-y curves of the stratum in this dissertation. Main achievements are described as follows:Firstly, a model test method was developed to simulate the interaction of pile and saturated sands with the excess pore water pressure from seismic loads based on the principle of effective stress, in which the residual pore water pressure was simulated by applying the back pressure to the saturated sand stratum. Model tests of the soil-pile interaction corresponding to different degradation state strata were conducted to research the effect of residual pore water pressure on the lateral bearing capacity of the single pile. The results showed that lateral bearing capacity of piles gradually decreased with an increase of residual pore water pressures and model test results were consistent with shaking table and centrifugal model test results for liquefied sands.Further, the relationship between p and y of degraded saturated strata was analyzed to research variations of parameters determining p-y curves of degraded saturated strata. The method to determine ultimate lateral resistances based on soil strength parameters was established by analyzing the failure mode of liquefying saturated strata. Variations of characteristic lateral displacements, yu and ym, and subgrade reaction modulus coefficient were analyzed to determine degradation p-y curves of three segments frame using the three-dimensional finite element method. Relationships of these parameters with the pile diameter and the degradated strata strengths were established. Methods to determine characteristic lateral displacements and the subgrade reaction modulus coefficient of degraded strata were developed using characteristic parameters of soils and piles. Finally, methods determining the three segments frame p-y curve and the hyperbolic p-y curve of degraded saturated strata were analyzed based on research results and referencing to methods suggested by Reese and API Code. P-y curves determined by those methods were basically consistent with model test results, and responses of the pile determined using calculated p-y curves were also consistent with model test results, which showed that the lateral capacity of the pile in saturated degradation sand strata could be evaluated using those methods. Comparing to the method to determine degradation p-y curves of three segments frame, the method to determine hyperbolic degradation p-y curves is more convenient and will be easy accepted in engineering practices.