Influence Of Double-line Shield Tunnel Crossing Construction On Frame Structure And Surface Deformation

At present,our country is at the peak of urban rail transit construction.While building urban subways on a large scale,there are more and more engineering cases under construction of shield tunnels under existing buildings.However,the construction of shield tunnel underneath adjacent buildings will disturb the stratum and destroy the original in-situ stress balance of the surrounding stratum.In-situ stress adjustment and formation deformation will be transmitted to the position of the superstructure,resulting in uneven settlement and deformation of the superstructure.When severe,it will affect the normal use of the superstructure and even cause major engineering accidents.Therefore,it is of great significance to study the influence of shield tunnels on the frame structure and ground surface deformation during dynamic construction,and to effectively control and protect them.This article is based on the Hunan Natural Science Foundation project "Surface settlement mechanism based on the coupling effect of subway tunnel-stratum-upper frame structure"(No.S2017JJQNJJ1586).Take the Changsha Rail Transit Line 2 under a frame structure as the engineering background.Using Midas GTS/NX,the influence of the double-track shield tunnel construction on the frame structure and ground deformation was analyzed.The main contents are as follows:(1)Taking the Changsha Metro Line 2 from below through a surface six-story frame structure building as the engineering background,and using Midas GTS/NX for numerical analysis.By comparing the simulation results with the monitoring data,it is found that the finite element numerical simulation results are in good agreement with the measured values.It shows that the selection of calculation parameters in the model is reasonable,and Midas GTS/NX finite element software can simulate subway tunnel construction more accurately.Therefore,it is possible to predict the influence of the underpass construction of the double-line shield tunnel on the frame structure and ground deformation.(2)According to the difference of the excavation position of the double-track shield tunnel under the frame structure,it is divided into three working conditions,namely:the double-line tunnel passes through the frame structure directly below,the left-line tunnel passes directly underneath,and the right line tunnel passes through the frame structure,Double-line tunnel side through the frame structure.The finite element software was used to simulate the dynamic construction process of the shield tunnel.The influence of the construction process on the upper frame structure and ground deformation is analyzed.The analysis shows that:1)During the process of shield tunnel excavation,all structural columns and beams of the frame structure have different degrees of settlement.The frame structure column drives the beams rigidly connected to it to deform,causing torsion or tilt deformation of the entire frame structure building.With the deformation of the frame structure,its internal force will also change.However,the internal force of the frame structure changes little.2)When there is a tunnel excavation on the lower right of the frame structure building,the tunnel excavation will disturb a certain range of surrounding soil and cause the soil to loosen.During the excavation of the shield tunnel,the surface deformation at the location of the frame structure is small.However,the surface deformation is very large within a certain range directly above and to the right of the tunnel.This shows that the surface deformation of the frame structure itself has a restraining effect.3)The excavation position of the double-line shield tunnel has a great influence on the additional stress and additional deformation of the frame structure.The maximum stress value of the frame structure under the construction condition of the double-line shield tunnel side-penetrating frame structure is the largest,which is easy to cause the lateral tilt of the frame structure.The maximum stress value of the frame structure under the construction condition of the double-line shield tunnel passing under the frame structure The smallest,it is easy to cause longitudinal tilt of the frame structure.(3)According to the difference in the construction sequence of the two-line shield tunnel under the frame structure,it is divided into three working conditions,that is,the left and right line tunnels are synchronously constructed,the left and right line tunnels are synchronously constructed,and the left and right line tunnels are synchronously constructed in reverse.The finite element software was used to simulate the dynamic construction process of the shield tunnel.The influence of the construction process on the upper frame structure and ground deformation is analyzed.The analysis shows that:1)During the excavation of the shield tunnel,the digging pressure reacts to the soil in front of the excavation surface,and the squeezing of the soil causes uplift deformation at the surface location.The stress release of the soil body at the tail of the shield causes the elastoplastic deformation of the soil body,which in turn causes the settlement and deformation of the surface above.2)Construction of double-line shield tunnels at different excavation locations will cause different surface deformations.However,with the excavation of the tunnel,the surface deformation at different excavation locations tends to be consistent.That is,the surface deformation curve is symmetrical about the centerline of the two-line tunnel.When the tunnel is excavated to the center of the frame structure,the lateral deformation of the ground surface caused by the construction of the double-track tunnel through the frame structure is the largest.3)The construction sequence of the left and right tunnels has little effect on the additional stress and deformation of the frame structure.4)When the tunnel is excavated to the center of the frame structure,the simultaneous excavation of the left and right tunnels will cause large surface deformation.The excavation conditions of the left and right line tunnels in the same direction and the reverse synchronization of the left and right line tunnels will cause secondary interference to the ground.Therefore,special attention should be paid to the ground settlement caused by tunnel excavation.