基于动力BNWF法的冻土-桩相互作用模型研究

Study on Frozen Soil Pile Interaction Model Based on Dynamic Beam on Nonlinear Winkler Foundation Method

基于水平循环荷载作用下不同负温冻土环境中单桩动力特性模型试验结果,在已有分析桩-土-结构相互作用的动力BNWF模型的基础上,提出改进的冻土-桩基动力相互作用非线性反应分析模型。在该模型中,利用改进的双向无拉力多段屈服弹簧考虑桩侧冻土的水平非线性力学特性,同时兼顾桩侧与冻土间的竖向非线性摩擦效应、桩尖土的挤压与分离作用以及远场土体阻尼对桩基动力特性的影响。其中桩侧水平多段屈服弹簧参数根据冻土非线性p-y关系获得,该关系曲线以三次函数曲线段及常值函数段共同模拟,并由室内冻土压缩试验结果确定。最后基于改进的动力BNWF模型,提取动位移荷载作用下该桩顶力-位移滞回曲线及桩身不同埋深处的弯矩动响应数值分析结果,并与相应的模型试验结果对比,二者具有较好的拟合度,表明本文所提出的改进模型在分析冻土-桩动力相互作用时有较好的适用性。

Permafrost is distributed widely in our country.Although pile foundation is the main foundation form for large bridges in frozen zones,few studies have been conducted regarding the dynamic characteristics of pile foundation construction in permafrost.An improved nonlinear analytical model for frozen soil-pile dynamic interaction was developed on the basis of model test results of the dynamic characteristics of pile foundations in various subzero temperature soils under lateral dynamic loads and an analytical model of pile-soil-structure interaction with the dynamic beam on nonlinear Winkler foundation model.This improved analytical model simulates the nonlinear lateral pressure effect of the frozen soil around the pile with an improved bidirectional compression-only multi-yield spring.Vertical friction effects between the frozen soil and pile,extrusion and separation effects of frozen soil under pile tips,and damping effects of the farfield soil on the dynamic characteristics of pile foundations are also considered in this analytical model.The parameters of the bidirectional tensionless multi-section yield spring are determined by the nonlinear p-y relationship of frozen soil.The p-y relationship whose parameters were based on the results of the indoor frozen soil compression test was simulated by the combination of a cubic function and a constant function.Displacement-force response of the pile head and pile shaft responses to bending moments at different depths under dynamic forces were very similar to the model test results.Results indicate that the improved analytical model is potentially helpful during the analysis of frozen soil-pile dynamic interactions.