The Deformation Monitoring For Operating Subway Tunnel Under The Influence Of Foundation Pit Engineering

In under construction project of foundation pit like metro tunnel which had big scale and large excavating detph had complecated enviroment and located close to buildings.The three of foundation pit、soil mass and tunnel interacted on each other.The excavtion project of the doundation pit leaded to the disturbance of soil mass and the destruction of the original stress of the soil mass,causi-ng the deformation of metro tunnel under operation.While the deformation would lead to serious consequences without effective method to take it under control,the analysis and monitoring for the metro tunnel under operation and understanding for the deformation of the tunnel were necessary.This paper took the metro tunnel under operation which located below the foundation pit of a hotel as an object to carry out the study.(1)The analysis concluded the factors contributing to the deformation of the foundation pit and the causes of the deformation of the metro tunnel as well as the mechannism how excavting of the foundatin pit affected the nearby the me tro tunnel.By analysising for the excavting process、engineering geology and dy drogeology and other related information,using large sacale finite element software FLAXIS to simulating the excavting process of the foundation pit,adopting linear elastic model(LE),Mohr-Coulomb model(MC),soil hardening model(HS),considerating model parameter selection,iterative method,the error parameters,boundary setting,tunnel buried deep,segment lining,foundation pit support an d excavation model and other related factors comprehensively the fea-sibility of the model would be verified.(2)Taking the simulating results under design specification as a reference,the monitoring programme confirming the monitoring scope,purpose,warning value,frequency and other element were formulated.Auto-monitoring was taken for the real-time monitoring the metro tunnel under the foundation pit of a hotel,acquiring the monitoring data and analysis for the deformation.In the process of the foundation pit construction,actual horizontal displacement of the tunnel was greater than vertical displacement.The largest horizontal displacement,11.05 mm appeared in the tunnel arch and the largest vertical displace ment appeared in the tunnel vault.The horizontal displacement decreased when the horizontal distance between the continuous wall of foundation pit and the central axis of the tunnel had increased.With the comparative analysis between finite element numerical simalation reasults and auto-monitoring numerical reasults,it’s known that numerical simulation reasults and monitoring reasults were roughly similar as well as the change trend.This conclution showed that finite element numerical simalation reasults has certain applicability in analysing the infulence on nearby metro construction caused by foundation pit construction and can be applicated to similar engineering.