| Subway construction is an important way to alleviate traffic congestion in modern cities and enhance the image of the city.After nearly two decades of development,in my country’s large and medium-sized cities the subway lines have gradually matured and the development intensity has gradually increased.In the process of connecting the subway lines into a network,a large number of proximity projects inevitably appear.The excavation of new tunnels disturbs the surrounding environment of the neighboring existing tunnels,which has become an important factor affecting the safety and operational stability of the tunnel structure.This has attracted the attention of relevant practitioners.Due to the irregular cross-section of the double-arch tunnel,the construction sequence is more,and the excavation disturbance to the surrounding rock and soil are more complicated.Therefore,it is particularly important to carry out research on the impact of double-arch tunnel construction on existing lines in the immediate vicinity.Based on the double-arch tunnel project of the Yanming Lake parking lot line of Xi’an Metro Line 5,numerical simulation is used as the main research method,supplemented by on-site measurements to study the influence of the near-parallel construction of a double-arch metro tunnel on the loess site on the deformation of the lining structure of the adjacent existing tunnel.What is more,it further analyzes the influence of the double-arch tunnel construction on the lining structure of the existing tunnel,and compares the force and deformation characteristics and differences of the existing line under three relative spatial positions.The main work content and results are as follows:(1)For the supporting project,conduct high-frequency monitoring and measurement of existing tunnels in the immediate vicinity,and establish a three-dimensional numerical model to simulate actual engineering conditions,and on the premise of verifying the simulation accuracy by comparing with the measured data,the impact of the shallow buried and near parallel construction of the double-arch tunnel on the lining structure of the existing tunnel is analyzed.Studies have shown that the near-parallel construction of the double-arch tunnel has an impact on the existing tunnel by 4.5 times the diameter of the double-arch tunnel.During the construction process,the existing tunnel has an overall offset without excessive self-deformation.The settlement of the existing tunnel is more sensitive to the staggered excavation method of the double-arch tunnel,and its lateral convergence is more sensitive to the clear distance.What’s more,during the entire excavation process,the existing tunnel deformation caused by the excavation of the pilot tunnel accounted for 60-65% of the total deformation.(2)Establish a numerical analysis model for the construction of the upper-span of a double-arch tunnel under the condition of different clear distances and crossing angles,and analyze and summarize the influence of the double-arch subway tunnel shallow-buried and under-excavated upper-span construction on the existing tunnel lining structure from the displacement and stress of the lining structure.Compared with the parallel construction conditions,it analyzes the influence of the relative position of the new double-arch tunnel on the force and deformation of the existing tunnel.Studies have shown that the upper span construction of a double-arch tunnel has an impact on the existing tunnel in the range of 2.5 to 3.5times the diameter of the double-arch tunnel,which is smaller than the nearly parallel construction;during the upper-span construction process,the deformation of the existing tunnel lining structure is mainly Uplift deformation,and the lateral displacement presents a Gaussian distribution along the longitudinal direction of the existing tunnel,but it is significantly smaller than the nearly parallel construction;at the same time,the impact of the over-span construction on the existing tunnels increases with the increase of the clear distance or included angle between the two tunnels.(3)Establish a numerical analysis model for the undercut construction of double-arch tunnels under the conditions of different clear distances and crossing angles,and analyze and summarize the influence of the double-arch subway tunnel shallow-buried and under-excavated undercut construction on the existing tunnel lining structure from the displacement and stress of the lining structure.Studies have shown that the impact of the underpass construction of the double-arch tunnel on the existing tunnel is 2.5 to 4.5 times the diameter of the double-arch tunnel,which is larger than the upper-span construction and is similar to the nearly parallel construction;During the underpass construction,the deformation of the existing tunnel lining structure is mainly settlement deformation.At the same time,the earth pressure plays a major role in the underpass construction.The displacement of the existing tunnel increases with the increase of the clear distance,which is different from the upper span construction;The impact on the included angle of the tunnel is basically the same as that of the upper span construction. |
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