| The foundation pit of a subway station in Tianjin is close to a subway tunnel.The excavation depth of the foundation pit is up to 18 m,and the main scale is 186.4m×19.3 m.The minimum distance between the foundation pit and the metro shield tunnel is only 8.77 m,and the foundation pit is at a certain Angle to the adjacent tunnel.The traffic around the foundation pit is busy.In order to reduce the influence on the road traffic,the method of combining of direct excavation-shoring construction and cover-excavation method will be adopted in the construction of the station.To sum up,the foundation pit engineering on which this dissertation is based has the characteristics of large excavation area,large depth,small distance between the tunnel and the space relative position is not ideal.On the basis of summarizing and analyzing the relevant theories of foundation pit deformation,by combining with the space-time effect principle,this paper designs four kinds of excavation schemes.A three-dimensional finite element model is established by using Midas GTS NX finite element software,and numerical simulation method is used to study the influence of foundation pit construction on the deformation of adjacent tunnels under four kinds of excavation schemes.The main research contents and achievements of this dissertation are as follows:(1)Based on the analysis of domestic foundation pit engineering cases,Origin software is used to fit the relationship curve between the buried depth and the vertical deformation of the tunnel,the net distance between the tunnel and the foundation pit and the horizontal deformation of the tunnel,and the basic law of the deformation of the adjacent subway tunnel caused by the excavation of the foundation pit is summarized.(2)In the deep foundation pit project of a tunnel adjacent to the metro area in Tianjin,considering the engineering geology and hydrogeology,based on the space-time effect theory,the strip foundation pit is divided into several square foundation pits with a length-width ratio close to 1.Four excavation schemes are designed according to different zoning and excavation sequence..(3)Midas GTS NX finite element software was used to establish a three-dimensional finite element model of the excavation process.The process of foundation pit excavation and dewatering is simulated,and the recovery traffic condition by applying load in the covered excavation area is simulated.The calculation results show that the influence of different excavation schemes which own have different zones and construction sequence on tunnel deformation is different.The tunnel deformation is less affected by the zonal symmetric excavation scheme and the resumption of traffic has little effect on the deformation of the tunnel.(4)Based on the phenomenon of large heave in the simulation results of zoned symmetrical excavation scheme,the finite element model is improved to study the influence of foundation pit excavation on adjacent tunnels at different depth of pit reinforcement.The calculation results show that the influence of foundation pit excavation on the deformation of adjacent tunnels decreases after the pit bottom is strengthened.But when the reinforcement depth increases to a certain level,the effect of reducing the deformation of adjacent tunnels is not obvious. |
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