基坑开挖引起邻近地铁隧道变形简化计算方法

Simplified Calculation Method for Deformation of Adjacent Metro Tunnels Caused by Foundation Pit Excavation

为探究基坑开挖对邻近地铁隧道变形的影响,基于XGBoost算法对典型案例中影响地铁隧道水平变形的因素进行重要度排序统计,提出可用于预测隧道水平变形的经验公式。通过两阶段分析方法建立地铁隧道竖向变形理论计算模型:首先基于Mindlin解计算考虑基坑坑底及侧壁卸荷作用引起的隧道竖向附加应力;进而将隧道视为搁置于Winkler地基上Eular-Bernoulli无限长梁,引入考虑隧道埋深影响的修正地基基床反力系数,建立隧道竖向变形微分方程进行求解。文中计算方法与实测数据、数值模拟结果对比分析结果表明:(1)本文方法相较于传统方法计算地铁隧道的变形精度更高;(2)在临近地铁隧道的基坑施工时,可通过控制基坑与临近地铁隧道之间的距离,分块分层开挖基坑等来控制地铁隧道的变形。

In order to explore the influence of foundation pit excavation on the adjacent metro tunnels,the importance ranking of the factors affecting the horizontal deformation of tunnels in typical cases were analyzed based on the XGBoost algorithm.Then an empirical formula to predict the horizontal deformation of metro tunnels was proposed.The theoretical calculation model of the vertical deformation of the metro tunnel was established by the two-stage analysis method:Firstly,the Mindlin solution was used to calculate the vertical additional stress of the tunnel caused by the unloading of the foundation pit bottom and side walls.Then,the tunnel was regarded as an Eular-Bernoulli infinite beam on the Winkler foundation.A modified foundation bed reaction coefficient that can take into account the influence of the tunnel burial depth was proposed,and a differential equation for the vertical deformation of the metro tunnel was established.The comparison and analysis results of the calculation method in this paper with the measured data and numerical simulation method show that:(1)Compared with the traditional method,the improved method calculates the deformation of the metro tunnels with higher accuracy;(2)When excavating the foundation pit adjacent to the metro tunnels,the deformation can be controlled by paying attention to the distance between them,and dividing the foundation pit into layers and blocks.