上穿既有隧道大直径管棚支护效果研究

Supporting Effect of Large-Diameter Pipe Shed in Tunneling Up-Crossing Engineering

北京地铁大兴机场线在上穿既有10号线盾构隧道过程中,采用大直径管棚控制既有隧道隆起。以此为工程依托,研究在大直径管棚支护下既有线的隆起变形。首先,通过分析现场实测数据,得到既有线位移随施工进度的变化规律和最终既有线竖向位移曲线,得出既有隧道隆起集中在2倍开挖区宽度内的结论。然后,通过三维有限差分法,分别建立有管棚和无管棚的数值模型,将模拟数据的既有隧道竖向位移变化与实测数据对比,验证数值模型的有效性。最后,通过对有无管棚两种工况的模拟结果对比分析,得出结论:管棚施工使既有隧道在打设管棚的阶段多发生了0.5 mm左右的沉降,但管棚可以减少既有线1.5~2 mm最终隆起值。这说明,通过采用超前管棚,可以有效地控制上穿工程中既有盾构隧道发生的隆起,研究成果可为类似上穿工程提供一定的借鉴。

In up-crossing the existing line 10 shield tunnel of Daxing Airport Express tunnel,the large-diameter pipe shed method was employed to control uplift.Based on the foregoing project,this study investigates the uplift deformation of an existing tunnel supported by a large-diameter pipe shed in an up-crossing project.First,the curves of the existing line displacement that change with the construction and existing line of the final vertical displacement are obtained by analyzing the field measurement data.The uplift of the existing tunnel is found to increase by up to twice the width of the excavation area.Then,three-dimensional numerical models with and without pipe sheds are formulated using the finite difference method.The simulation data of the vertical displacement of the existing tunnel are compared with the field measurement data to verify the effectiveness of the models.Finally,the comparative analysis of the simulation results of the tunnel with and without the pipe shed leads to the conclusion that the construction of the pipe shed causes a settlement of approximately 0.5-mm during its setting.Moreover,the pipe shed can reduce the final uplift value of the existing tunnel by 1.5–2 mm.The foregoing shows that a pipe shed laid in advance can effectively control the uplift of an existing shield tunnel in up-crossing engineering.The results of this study can be used as reference for similar projects.