软土地区长条形基坑开挖对下卧既有地铁隧道影响的实测分析

Field study on the effect of excavation of strip-shaped foundation pit on existing underlying subway tunnels in soft soil

为了研究软土地区长条形基坑开挖对下卧既有地铁隧道位移和变形的影响规律及控制措施,依托杭州某快速路隧道基坑正交下卧地铁隧道的工程,介绍了该快速路隧道基坑的分坑分区开挖方案:采用分隔桩将长条形基坑分为上跨基坑与东西两侧基坑,先分层分块开挖上跨基坑,后由远及近对称分块开挖东西两侧基坑。对上跨基坑和旁侧基坑相继开挖过程中下卧地铁隧道的竖向位移、水平位移及水平收敛变形进行了监测,监测结果表明:上跨基坑开挖使下卧地铁隧道产生隆起变形;东、西两侧基坑开挖引起下卧地铁隧道的进一步隆起变形;随着上跨基坑开挖,下卧地铁隧道上、下行线主要产生向上跨基坑内侧的水平位移,下卧地铁隧道水平收敛变形主要呈减小趋势,而东、西两侧基坑开挖对下卧地铁隧道水平位移和水平收敛变形的影响不明显。本工程的设计方案和施工方案有效保护了下卧地铁隧道,为类似上跨地铁隧道的长条形基坑的设计和施工提供了经验和指导。

In order to study the influence of excavation of strip-shaped foundation pit on the displacement and deformation of underlying subway tunnels in soft soil and the relevant control measures,the excavation project of an expressway perpendicular to existing underlying subway tunnels in Hangzhou is introduced.The zoned excavation scheme of this excavation project includes:(i)the strip-shaped foundation pit is divided into one overlying foundation pit and two lateral foundation pits(i.e.,eastern one and western one)by dividing piles;(ii)the overlying foundation pit is excavated by districts and layers;and(iii)the lateral foundation pits in the east and west are excavated symmetrically by blocks from far to near.The vertical displacement,horizontal displacement and horizontal convergence of the underlying subway tunnels during the zoned excavation are monitored.The monitoring results show that the uplift deformation of the recumbent subway tunnel is caused by the upper span foundation pit excavation,and the further uplift deformation of the recumbent subway tunnel is caused by the excavation of the foundation pit on the east and west sides.With the excavation of the upper span foundation pit,the upper and lower lines of the recumbent subway tunnel mainly produce the horizontal displacement across the inside of the foundation pit,and the horizontal convergence deformation of the recumbent subway tunnel mainly decreases.However,the influence of the excavation of the foundation pit on the east and west sides on the horizontal displacement and horizontal convergence deformation of the recumbent subway tunnel is not obvious.The design and construction schemes of this project effectively protect the underlying subway tunnels,which could provide references for the design and construction of similar strip-shaped foundation pit above existing underlying subway tunnels.