砂土中桩-土-承台协同作用下桩基承载特性细观研究

Mesoscopic study on bearing characteristics of pile foundation under pile-soil-cap combined interaction in sand

为探究桩-土-承台协同作用下,带承台单桩极限承载力大于其单桩及承台基础单独作用下极限承载力之和的强化机制,在砂土地基中分别建立能够反映单桩、带承台单桩及承台基础静载试验全过程的二维离散元模型,并通过与室内模型试验荷载-沉降曲线变化规律对比,验证了模型的合理性。基于验证后的数值分析模型,从细观的角度对砂土地基的变形机制和桩基的承载特性进行分析。结果表明:地基变形机制方面,相对于单桩与承台基础,带承台单桩对地基土的扰动程度更显著,台下抗载土体范围更大;桩基承载特性方面,在带承台单桩桩侧一定范围土体出现成拱现象,成拱作用加强了桩侧、桩端附近土体的密实度,提高了桩侧摩阻力及端承力,进而使得整体承载力得到提高。该离散元数值模拟结果可以为带承台桩基设计和承载力估算方法提供参考。

In order to explore the strengthening mechanism that the ultimate bearing capacity of single pile with cap is greater than the sum of the ultimate bearing capacities of single pile and cap foundation under the synergistic action of pile-soil-cap,two-dimensional discrete element models(DEMs)which can reflect the processes of static load test of single pile with cap,single pile only and cap foundation only in sand are established,and the rationality of the models are verified by comparing the model-predicted results with the variation laws of load-settlement curve in the laboratory model test.Based on the validated DEMs,the deformation mechanism of the sand foundation and the bearing characteristics of pile foundation are analyzed from the microscopic perspective.The results show that,in terms of the sand foundation deformation mechanism,compared with single pile and cap foundation,the foundation soil is more significantly disturbed by the single pile with cap,and the soil in a large range under the cap participates in the process of resisting the load.As for the bearing characteristics of the pile foundation,the compactness of the soil near the pile side and pile end is strengthened by the effect of the arch formation that occurs around the pile side of the single pile with cap,which improves the lateral friction resistance and the bearing capacity of pile end.As a result,the overall bearing capacity of the single pile with cap is improved.The results of DEM can provide references for the design of pile foundation with cap and the bearing capacity estimation method.