地铁盾构长距离下穿对既有铁路框架桥影响的数值与实测分析

Numerical simulation and field monitoring of influence of metro shield tunnel undercrossing the existing railway frame bridge by long distance

地铁盾构近接施工产生的地层扰动与变形会对既有敏感构筑物使用安全造成威胁。为分析盾构下穿施工对既有铁路建构筑物变形的影响,以长沙地铁6号线盾构长距离下穿京广铁路客货运框架桥为工程背景,建立盾构下穿施工的三维数值模型。研究不同注浆压力、土仓压力及地层加固情况下框架桥和轨道的变形受力特性,并结合现场实测数据分析盾构掘进参数的变化特征及既有结构的变形规律。模拟结果表明:盾构左线先行施工对框架桥和轨道变形的影响大于右线;注浆压力和土仓压力的提高,以及地层加固措施的采取,能有效控制框架桥和轨道的沉降变形;轨道结构变形随注浆压力和土仓压力的提高而减小,分别达到0.30 MPa和0.16 MPa后继续提升时对沉降控制效果逐渐减弱。实测数据表明:右线盾构掘进参数相比左线较小且更稳定,总推力和刀盘扭矩控制在13000 kN和3500 kN·m以下可确保安全快速掘进;框架桥和轨道变形随盾构掘进变化明显,下穿前变形较小,下穿时变形开始增大,下穿后变形逐渐稳定;框架桥整体变形在-1.75~1.37 mm之间,轨道变形在-3~2 mm之间,轨道高低偏差和变形速率均小于控制标准。在施工过程中应重点关注先行隧道的施工影响,并严格控制盾构掘进参数,合理选择地层加固措施,以保证既有铁路构筑物的运营安全,研究结果可为今后类似下穿工程设计与施工提供参考。

The ground disturbance and deformation caused by the close construction of metro shield pose a threat to the safety of the existing sensitive structures.In order to analyze the influence of shield undercrossing construction on the deformation of existing railway structures,with the engineering background of the Changsha metro line 6 undercrossing Beijing-Guangzhou railway passenger and freight frame bridge,the three-dimensional numerical model of shield tunnel excavation was established.The influence of frame bridge and railway track in different grouting pressure,soil warehouse pressure and strata reinforcement condition were investigated.The change of shield tunneling parameters and the deformation law of the measured data were analyzed.The results are drawn as follows.The influence of left shield line on the deformation of frame bridge and track is greater than that of right shield line.The settlement deformation of frame bridge and track can be controlled effectively by increasing the grouting pressure and soil warehouse pressure and adopting the measures of stratum reinforcement.The deformation of track structure decreases with the increase of grouting pressure and soil warehouse pressure,and the control effect of track structure on settlement gradually decreases when it reaches 0.30 MPa and 0.16 MPa respectively.According to the measured data,compared with the left line,the shield tunneling parameters of right line are smaller and more stable,and the total thrust and cutter head torque are controlled below 13000 kN and 3500 kN∙m to ensure safe and rapid tunneling.The deformation of frame bridge and track changes obviously with shield tunneling.The deformation is small before undercrossing,begins to increase when undercrossing,and becomes stable after undercrossing.The overall deformation of the frame bridge is-1.75~1.37 mm,and the track deformation is-3~2 mm.The height deviation and deformation rate of the track are less than the control standard.In order to ensure the safety of the existing railway structures,it is necessary to pay attention to the influence of the construction of the antecedent tunnel,strictly control the shield tunneling parameters,and choose the stratum reinforcement measures reasonably.The research results can provide a reference for the design and construction of similar undercrossing projects in future.