大直径土压平衡盾构下穿既有线U型槽结构变形

为确保盾构安全顺利地下穿地铁运营U形槽线路,避免下穿过程中引起U形槽结构过量沉降,影响运营安全,以北京新机场线2、3号风井盾构区间大直径土压平衡盾构下穿既有大兴线U形槽为工程背景,研究了砂卵石地层盾构隧道开挖对U形槽变形影响。通过对U形槽结构竖向位移、横向位移、轨道竖向位移、轨距等大量监测数据进行分析,得出盾构隧道开挖过程中既有结构的变形规律。结果表明:下方隧道开挖会造成U形槽和轨道结构产生不均匀隆起、沉降变形,竖向变形在2. 0 mm以内;隧道横向变形表现为不规则波动,变形在±0. 5 mm以内;轨距变化在±1 mm以内。既有U形槽结构竖向位移与盾构掘进参数关系密切;通过严格控制盾构施工参数,采用二次注浆、深孔注浆方式对管片背后进行填充,可大幅减少结构沉降。研究结果可为控制U形槽结构变形,确保既有线运行的安全提供借鉴。

Study on the Structural Deformation of U-shaped Groove Caused by Underlying Large-diameter Earth Pressure Shield Excavation

To make sure shield can safely and smoothly underlying operation U-shaped groove structure, to avoid excessive settlement and impact on the safety when existing line work, this paper based on the project that the new airport express line crossing beneath existing operating U-shaped groove of metro Daxing line in Beijing, the influence of shield tunnel excavation under U-shaped groove deformation was studied in sand-gravel stratum. Through the analysis of lots of monitoring data of vertical and lateral displacement of U-shaped groove structure, vertical displacement of track, track geometry and so on, the regulation of existing structure deformation was concluded during the construction process. The results of analysis indicate that the shield tunnel excavation will cause uneven uplift deformation of both U-shaped groove structure and track structure below and the uplift value can be controlled within 2.0mm by strict control of the shield excavation. The lateral deformation of the tunnel is shown as irregular fluctuation, and the deformation value is from-0.5mm to 0.5mm. The deformation of U-shaped groove structure is closely related to shield excavation parameter. By strict control of shield excavation parameters and secondary grouting to fill the space behind the lining, the deformation of structure can be reduced obviously. The results can be used as reference for controlling the deformation of tunnel structure and ensuring the safety of existing operating shield tunnel.