Research On Automated Monitoring And Deformation Control Of Foundation Pit Construction Safety In Urban Metro Station

With the rapid development of the national economy and the tight urban land use,the subway has been selected by more and more cities as the best solution to effectively solve the traffic congestion problem because of its safe and efficient transportation.However,most of the subway stations are located in the central area of the city.The geological conditions are complex,the surrounding buildings and underground pipelines are densely distributed.If the supporting structure stability and deformation of the surrounding environment are controlled improperly during the construction process,it will have a serious impact.Therefore,real-time safety monitoring of the station foundation pit,and analysis of the force and deformation law of the foundation pit,and the control of the deformation during construction are of great significance for ensuring the safety and stability of the foundation pit construction.Taking the foundation pit of Liuting Airport Station of Qingdao Metro Line 1 as the engineering background,and uses the combination of theoretical analysis,on-site monitoring and numerical simulation to carry out the following aspects:(1)This paper firstly combines the research status of safety monitoring and deformation control of foundation pit construction,analyzes the deformation mechanism and calculation method of station foundation pit,and discusses the main influencing factors of station foundation pit deformation from three aspects: engineering geology and hydrogeological conditions,structural form and design,construction scheme and management.(2)A three-dimensional numerical simulation model for the foundation pit of Liuting Airport Station of Qingdao Metro Line 1 is established by using Midas GTS NX finite element software.The simulation results show that the deformation curve of the retaining structure is a small "big bow" curve,and the surrounding ground settlement is "groove".The main influence area of foundation pit excavation on the ground settlement is 0~30m(1.8H)from the edge of the pit,the surrounding surface settlement exceeding the range of 42m(2.5H)is basically not affected by the excavation of the foundation pit.The supporting axial force is gradually increased with the increase of the excavation depth of the foundation pit.When excavating to the bottom of the pit,the axial force of each support reaches the maximum.The foundation pit excavation has obvious three-dimensional effect.During the construction process,the internal force and deformation of the middle part of the standard section and the section change should be monitored to ensure the safety and stability of the foundation pit.(3)Taking the Liuting Airport Station of Qingdao Metro Line 1 as the engineering background,the automatic monitoring scheme and manual monitoring scheme are respectively determined,and the application of the “Knowledge Cloud” automatic monitoring system is introduced.The results of automated monitoring show that with the excavation of the foundation pit,the lateral deformation of the retaining structure develops from the "cantilever type" in the previous stage to the "arch" curve in the middle of the small head.The maximum horizontal displacement occurs at the second position of maximum excavation depth of the foundation pit.The surface settlement around the envelope structure has developed from the “triangle” in the previous period to the “groove shape” distribution.The maximum surface settlement occurred at the position 9m(0.53H)from the edge of the foundation pit.The support axial force increases gradually with the increase of the excavation depth.When excavating to the bottom of the pit,the second support axial force is the largest,which corresponds to the lateral deformation of the retaining structure.(4)The numerical simulation results are compared with the results of automatic monitoring and manual monitoring.The analysis shows that the calculated values are almost the same as the overall trend of the measured values,and the simulation results are in line with the actual situation of the project.The artificial monitoring data has greater volatility.In contrast,the automated monitoring data is more stable,and the monitoring results are more consistent with the development trend of the calculation results.In the process of on-site construction,we should pay attention to real-time monitoring work to truly achieve information construction.(5)The sensitivity analysis of the deformation control of the foundation pit of urban metro station is carried out,and the influence of the rigidity of the retaining structure,the insertion ratio of the retaining structure,the prestress of the steel support and the over-excavation of the foundation pit on the deformation control of the pit of the station are studied,which provides effective reference for the design and construction of urban metro stations.