砂卵石地层基坑开挖对下卧运营盾构隧道结构变形研究

Study on the Structural Deformation of Underlying Operating Shield Tunnel Caused by Foundation Pit Excavation in Sand-gravel Stratum

砂卵石地层中进行基坑开挖会对周边环境产生较大影响,而基坑工程下方存在既有运营地铁线路时,基坑开挖将严重威胁到既有线路的安全运营。为研究砂卵石地层U形槽基坑开挖对盾构隧道的变形影响,以北京首条有轨电车西郊线上跨既有运营地铁10号线为工程背景,通过对监测数据进行分析,得出基坑开挖过程中既有结构的变形规律,并提出相应控制手段和措施。结果表明:U形槽开挖会造成下方隧道和轨道结构产生不均匀隆起变形,经采用深孔注浆进行土体加固后,隆起值控制在1.5 mm以内;隧道横向变形表现为不规则波动,变形值在±0.5 mm以内;开挖卸荷导致隧道受水平压缩、竖向拉伸的力,收敛为"竖椭圆"形状;轨距先拉开后缩小,最后再拉开,曲线呈"M"形,轨距值在±2 mm以内。

The excavation of foundation pit in sand-gravel stratum will have a great impact on the surrounding environment,and seriously threaten the operation of the existing subway line if it is under the foundation pit.In order to study the deformation of shield tunnels induced by excavation of U-shaped groove in sand-gravel stratum,the structure deformation law in the process of foundation pit excavation is identified and corresponding control measures are put forward through the analysis of monitoring data based on the project of the first tram of the western suburban line in Beijing overcrossing the existing operating shield tunnel of metro line 10.The results of analysis indicate that the U-shaped groove excavation causes uneven uplift deformation of both the tunnel and the track structure below and the uplift value can be controlled within 1.5 mm by using deep-hole grouting before excavation.The lateral deformation of the tunnel shows irregular fluctuation with deformation from-0.5 mm to 0.5 mm.The unloading of excavation causes the tunnel to be subjected to horizontal compression and vertical tension and converge to the shape of“vertical ellipse”.The gauge is pulled apart first,then reduced and pulled apart again,which makes the curve like an“M”with gauge value from-2 mm to 2 mm.