北京市轨道交通基坑工程桩体变形特性

Deformation characteristic of piles foundation pit engineering of urban rail transit in Beijing

根据基坑开挖深度、地层条件的不同,对北京市轨道交通80个明挖顺作法基坑工程实测结果进行统计分析,研究确定北京砂卵石和黏性土地区深基坑开挖引起的桩体变形规律。研究表明:1围护桩顶和桩体均存在向基坑内和基坑外两个方向的水平位移,水平位移实测结果分布形态均近似符合正态分布。2围护桩整体最大变形均以桩体变形为主,桩向基坑内水平位移平均值约为0.05%H^0.12%H,向基坑外水平位移平均值约为0.02%H^0.07%H。3插入比、长宽比、基坑系统刚度等对桩的最大水平位移有一定的影响。4桩向基坑内水平位移最大值主要出现在0.26H^0.45H处,向基坑外水平位移最大值主要出现在0.18H^0.20H处。研究成果可对未来北京及其他地区城市轨道交通基坑工程变形大小及安全性的预测和评估,指导基坑工程设计与施工工作,对防止基坑事故的发生具有重要意义。

According to the difference of excavation depth and the formation conditions, 80 case histories of foundation pit engineering of urban rail transit in Beijing are analyzed. The deformation laws of piles excavation induced by foundation pit engineering are studied in Beijing sand & gravel zone and clay soil zone. The results show that: (1) The horizontal displacements of retaining piles at top and body are in two directions, that is, towards and out of the foundation pit and the measured displacements are approximately in normal distribution. (2) The maximum pile deformation is the pile body deformation. The maximum pile deformation is about 0.05%H^0.12%H towards the foundation pit and about 0.02%H^0. 07%H out of the foundation pit. (3) The insertion ratio, the ratio of length to width and the system stiffness have certain influence on the maximum pile deformation. (4) The maximum value of horizontal displacement of piles towards the foundation pit mainly appears at 0.26H^0.45H, and the maximum value of horizontal displacement of piles out of the foundation pit mainly appears at 0.18H^0.20H. The results can be used to predict the lateral deformation of similar projects in Beijing and other areas and to guide the design and constructions. It also has great significance for preventing accidents foundation pits.