Monitoring And Numerical Simulation Of Deformation Law Of Foundation Pit In Subway Tunnel

With the development of economic construction,the construction of various cities is in full swing,and housing construction projects,road and bridge projects and underground tunnel projects cross each other.Especially in the construction of deep foundation pits on the top of existing subway tunnels,the stability of supporting structures and foundation pits will be greatly affected.Based on the monitoring of the foundation pit engineering of the southern extension of Wuhan Optics Valley Avenue,theoretical analysis is adopted.The combination of on-site monitoring and numerical simulation studies the foundation pit monitoring technology and deformation law,and achieved the following results:(1)According to the special geological and hydrological conditions of the subway tunnel foundation pit under the south extension of Guanggu Avenue,two support schemes of steel sheet pile + graded grading support system and cast-in pile + graded grading support system are proposed.A detailed monitoring plan has been developed.(2)Through the analysis of the monitoring data,the variation law of the horizontal displacement of the supporting structure(slope),the supporting axial force and the deep horizontal displacement of the supporting structure under different working conditions during foundation excavation are obtained.The monitoring results show that with the excavation of the foundation pit,the axial force value of the steel support will increase first and then decrease;the deep horizontal displacement of the cast-in-situ support structure will gradually increase with the excavation of the foundation pit.The increase is generally in the form of a "bow" with a small middle and a large middle.(3)Using MIDAS/GTS finite element,a three-dimensional numerical model of the foundation pit of the subway tunnel under the south of Guanggu Avenue was established,and the parameters of the modeling were reviewed with the monitoring values.The model is used to compare the horizontal displacement of the supporting structure(slope),the supporting axial force and the horizontal displacement of the supporting structure under the subway condition at the top of the foundation pit.The simulation results show that the support is not under the subway condition.The horizontal displacement of the supporting structure(slope),the supporting axial force and the deep horizontal displacement value of the supporting structure have a certain range of variation,indicating that the foundation pit construction under the subway is very dangerous,and certain construction must pay attention to the construction.The determination of the protection system and the inspection during the construction process can ensure the safety and stability of the foundation pit during construction.(4)Through comparative analysis,during the excavation of the foundation pit of the subway tunnel,the horizontal displacement of the supporting structure(slope),the axial support of the steel support and the monitoring of the deep horizontal displacement of the supporting structure have certain values.The deviation is mainly manifested by the fact that the measured value is larger than the simulated value.The analysis is numerical simulation of the foundation pit excavation process under ideal conditions.The actual construction is inevitably affected by the external environment,but the overall trend of the two is The same is gradually increased with the excavation of the foundation pit,and reaches the maximum when excavation to the bottom layer.This shows that the numerical analysis model of this paper can predict the deformation trend of various parts during the excavation process.This can provide a basis for the design of the foundation pit support scheme,the selection of construction methods and the layout of monitoring points.