软土地区河道开挖对下方地铁隧道变形的影响及其控制措施

Influence of Soft Soil Area River Excavation on Underlying Metro Tunnel Deformation and Control Measures

[目的]地铁盾构隧道因上方河道开挖卸荷产生隆起变形,可能会影响地铁隧道的正常运行。为此,应就软土地区河道开挖工程对下方地铁隧道的变形影响进行研究,并制定地铁隧道变形控制措施。[方法]介绍了案例工程的概况,采用有限元方法对其实测数据进行分析,验证了土体本构模型及参数的合理性。基于具有典型软土特征的宁波地区地层剖面和土层参数,建立了土体简化模型,依次分析了河道开挖宽度变化对下方地铁隧道变形的影响、河道开挖深度变化对下方地铁隧道变形的影响、软土层埋深对地铁隧道变形的影响。介绍了门架式土体加固措施及门架式梁板加固措施两种变形控制措施,将考虑了控制变形措施的计算模型与基准模型的有限元计算结果进行了比较分析。[结果及结论]在土体加固和河道开挖阶段,下方地铁隧道变形分别表现为沉降和隆起;河道开挖断面面积相同时,减小河道的开挖深度、增加河道开挖宽度,有利于减少下方地铁隧道变形;地铁隧道竖向位移主要由其下方土体回弹变形产生;门架式梁板加固措施对于地铁隧道隆起变形的控制效果明显。

[Objective]The unloading-induced upheaval deformation resulting from river excavation above metro shield tunnels may affect metro tunnel normal operation.Therefore,it is necessary to study the deformation effects of soft soil area river excavation on underlying metro tunnels and formulate control measures for metro tunnel deformation.[Method]The general overview of a case project is presented,and finite element method is conducted on its field-measured data analysis to validate the reasonability of the soil constitutive model and parameters.Based on the characteristic soft soil profile and soil parameters of Ningbo region stratum,a simplified soil mass model is established.The impact of changes in river excavation width,depth and the burial depth of soft soil layers on the deformation of underlying metro tunnels is analyzed sequentially.Two deformation control measures of gantry-type soil reinforcement and gantry-type beam-slab reinforcement,are introduced.A comparative analysis is performed between the finite element calculation results considering the control deformation measures and the baseline model.[Result&Conclusion]During soil reinforcement and river excavation stages,the deformation of underlying metro tunnel manifested as settlement and upheaval,respectively.When maintaining the same cross-sectional area for river excavation,reducing the river excavation depth and increasing the river excavation width are conducive to minimizing underlying metro tunnel deformation.Vertical displacement of the metro tunnel is primarily influenced by the rebound deformation of the soil below it.The gantry-type beam-slab reinforcement measure exhibits a noticeable control effect on metro tunnel upheaval deformation.