基坑全过程开挖及邻近地铁隧道变形实测分析

Measurement analysis on whole excavation of foundation pit and deformation of adjacent metro tunnel

根据邻近已运营地铁隧道的基坑工程监测数据,对基坑开挖全阶段施工过程的深层土体侧向位移与邻近地铁隧道变形之间的规律展开研究,探讨基坑开挖的施工危险节点与重点影响区域。研究发现,基坑开挖前期围护结构施工和降水均对地层和邻近地铁产生了不容忽视的初始位移影响,围护结构长时间无支撑暴露是基坑侧移快速增长的危险时段;基坑开挖具有空间效应,中部侧向变形要大于边角,且单向开挖易造成后挖区土体的位移场和应力场叠加,引起邻近隧道的最大变形向后挖区偏移;基坑开挖深度与邻近地铁埋深相近时,隧道结构产生显著的水平位移和'横鸭蛋'式收敛变形,竖向位移波动不大;深层土体侧移曲线表现为'阶梯鼓肚形',土体最大水平位移与隧道变形在小范围内呈线性关系,但随着侧移量的增大,隧道变形发生偏离拟合曲线的超线性增长,在工程中应值得关注。

Based on the monitoring data of the foundation pit project in the adjacent metro tunnel in operation,the relationship between the lateral displacement in the deep soil and the deformation of the adjacent metro tunnel during the excavation process of the foundation pit has been studied.The dangerous nodes and key affected areas during the excavation of foundation pit are identified and discussed.It shows that the construction of retaining support structure and the precipitation at the early stage of foundation pit excavation have an initial displacement effect on the stratum and adjacent metro.The long-term unsupported exposure of the retaining structure results in the rapid growth of the lateral deformation of the foundation pit.The excavation of foundation pit has a spatial effect.The lateral deformation is greater at the center than the corner of the foundation pit.The one-way excavation easily causes the superposition of the displacement field and the stress field of the soil in the post-excavation area,causing the maximum deformation of the adjacent tunnel to be moved to the back excavation area;When the excavation depth of the foundation pit is close to that of the adjacent metro,the tunnel structure produces significant horizontal displacement and convergence deformation with'transverse duck egg'type,but the vertical displacement fluctuates little;The lateral displacement curve of the deep soil presents the stepped belly-shape,and the maximum horizontal displacement of the soil is in linear with the tunnel deformation in a small range.However,with the increase in the lateral displacement,the deformation of tunnel deviates from the fitting curve and tends to the superlinear increase,and this should be paid more attention in engineering.