饱和黄土区桩基托换模型试验和数值模拟

Model Test and Numerical Simulation of Underpinning Pile Foundation in Saturated Loess Area

以兰州地铁一桩基托换工程为例,采用模型试验和数值计算相结合的方法对饱和黄土区桥梁部分既有桩截断前后的力学行为进行分析,探究了承台-桩基托换体系受力转换机理。结果表明:托换后体系力学性能更优越,桩基受力重新分配,有接近50%的荷载被传递至托换桩。部分既有桩被截断后上部荷载逐步分配到其周边桩和承台下部土体,周边桩沉降挤压邻近土体,使得截断桩下部土体向上移动,给承台一个上顶力,形成土体和承台的共同支撑体系,从而使桩基沉降趋于均匀。

Taking a pile foundation underpinning project of Lanzhou subway as an example,the mechanical behavior of some existing piles of bridges in saturated loess area before and after truncation was analyzed by combining model test and numerical calculation,and the stress conversion mechanism of pile cap-pile foundation underpinning system was explored.The results show that the mechanical performance of the system after underpinning is better,the stress of the pile foundation is redistributed,and nearly 50%of the load is transferred to the underpinning pile.After some existing piles are truncated,the upper load is gradually distributed to the surrounding piles and the soil under the pile cap.The settlement of surrounding piles compresses the adjacent soil mass,causing the soil under the truncated pile to move upward,giving a jacking force to the pile cap,forming a common supporting system of soil and pile cap,so that the settlement of pile foundation tends to be uniform.