四线隧道密贴下穿既有车站施工参数优化分析

Optimization Analysis of Construction Parameters in the Four-line Tunnel Closely Passing under the Existing Station

为确保既有结构在隧道下穿施工中的安全,以北京地铁19号线四线隧道密贴下穿既有4号线新宫站工程为背景,通过现场监测和数值模拟,分析既有结构在不同导洞开挖顺序、开挖进尺、掌子面错距、临时支护拆除长度等工况下的沉降变形特征。研究结果表明:(1)导洞开挖顺序为“先上后下、先边后中”引起的既有结构沉降变形最小;(2)其他条件一定时,既有结构沉降随着开挖进尺的增大而增大,本项目开挖进尺取2 m为宜;(3)其他条件一定时,既有结构沉降随着掌子面错距的增大而减小并最终趋于稳定,本项目掌子面错距取6 m为宜;(4)其他条件一定时,既有结构沉降随着临时支护单次拆除长度的增大而增大,本项目临时支护单次拆除长度取6 m为宜;(5)既有站东西两侧布设围护桩可以有效控制既有结构沉降。

In order to ensure the safety of the existing structure in the process of underneath-crossing tunnel construction,the settlement and deformation characteristics of the existing structure under the conditions of different excavation sequence,excavation footage,working face distance,single demolition length of temporary support are analyzed by means of on-site monitoring and numerical simulation based on the project of the four-line tunnel of Beijing Metro Line 19 closely passing under the existing Xin Gong station of line 4.The research results show that:(1)The settlement and deformation of the existing structure caused by the excavation sequence of“first up and then down,first side and then middle”are the least;(2)When other conditions are certain,the settlement of the existing structure increases with the increase of the excavation footage.It's advisable to take 2 m as the excavation footage for the project;(3)When other conditions are certain,the settlement of the existing structure decreases with the increase of the working face distance.The working face distance of this project should be 6 m;(4)When other conditions are certain,the settlement of the existing structure increases with the increase of the single demolition length of temporary support.It's appropriate to take 6 m as the single demolition length of temporary support in this project;(5)The settlement of the existing structure can be effectively controlled by placing retaining piles on the east and west sides.