软弱地层中基坑土体加固对下卧地铁隧道变形及开挖影响区的控制效果
Control effects of soil reinforcement on underlying metro tunnel deformation and influenced zone induced by deep excavation in soft strata
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摘要: 选择工程中常用的土体加固法,采用有限元数值方法研究软弱地层中坑内土体加固对基坑开挖引起下卧地铁隧道变形特性的影响,通过定义变形控制有效率指标表征隧道变形控制效果,综合考虑变形控制效果和工程经济性,给出坑内土体加固形式和加固强度建议方案,然后利用上述建议方案,研究坑内土体加固对开挖影响区的控制效果。研究表明,坑内土体平面满堂加固形式优于抽条加固和裙边加固,竖向分层加固形式优于回掺式加固和平板式加固;隧道变形控制有效率随加固土强度的增加呈非线性增长,加固土强度存在一个优化值;采用建议的平面满堂式和竖向回掺式(坑底以下加固土强度2.0 MPa、坑底以上加固土强度0.5 MPa)对坑内土体加固后,下卧隧道隆起变形显著降低,且隧道隆起分布特征和隧道变形影响区模式发生了改变,影响区范围也被缩小。Abstract: The commonly used soil reinforcement method is selected, and the finite element numerical method is used to study the influences of soil reinforcement in the pit on the deformation characteristics of the underlying metro tunnels caused by excavation. By defining the index of deformation control efficiency, the tunnel deformation control effect is characterized, and considering the deformation control effect and engineering economy together, the suggested scheme for soil reinforcement form and strength in the pit is given. Then, by using the above scheme, the control effect of soil reinforcement on the influenced zone induced by excavation is studied. There sults indicate that the control effect of the overall reinforcement is better than the strip-shaped reinforcement and the skirt-border reinforcement on the plane, and vertically the effect of layered reinforcement is better than the mixed reinforcement and the plate-type reinforcement. The tunnel deformation control efficiency increases non-linearly with the strength of reinforced soil, and there exists an optimal value for reinforced soil strength. After the soil in the pit is reinforced using the suggested overall reinforcement on the plane and the mixed reinforcement vertically (the reinforced soil strength below the base slab is 2.0 MPa, and that above the base slab is 0.5 MPa), the heave deformation of the underlying tunnel is significantly reduced, the distribution characteristics of the tunnel heave and the mode of influenced zone are changed, and the scope of the influenced zone is reduced.