Deformation Characteristics Of Foundation Pit And Optimization Design Of Retaining Structure Based On Deformation Control

The foundation pits of urban subway stations have the characteristics of large excavation depth,large plane size of foundation pits,and complex surrounding environment,which bring more stringent deformation control requirements to foundation pit engineering.In the design of subway station foundation pits,due to the complexity of the surrounding environment and the differences in soil properties,some of the foundation pit retaining structure designs have large safety hazards,and some foundation pits are excessively pursuing safety.The structural design is too strong,resulting in unnecessary cost waste and reducing the economics of the project.Therefore,how to achieve a balance between safety and economy in the design of foundation pit engineering is the current research focus of foundation pit engineering.This paper takes the foundation pit of the Sumiao Station of Wuxi Metro Line 3 as the engineering background.Aiming at the stratum conditions of Wuxi area dominated by clay and silty clay,this paper uses a combination of numerical simulation and measured data analysis to analyze the "ground connection".The deformation characteristics of the foundation pit in the form of "wall +internal support" support,and the factors affecting the deformation characteristics of the foundation pit are analyzed.On this basis,the foundation pit retaining structure is optimized based on pipeline deformation control.The main work content and results are as follows :(1)After sorting and analyzing the measured data of the foundation pit at Sumiao Station of Wuxi Metro Line 3,it is concluded that during the excavation of the foundation pit,the ground settlement around the foundation pit,the horizontal displacement of the ground connecting wall,the deformation characteristics of the surrounding pipelines,and the The development law of supporting axial force.In general,the deformation value of the foundation pit is much smaller than the engineering control value,the safety reserve is too large,the overall rigidity of the enclosure structure is too strong,the design is conservative,and the engineering economy is reduced.Therefore,the optimization of the foundation pit enclosure structure is determined necessity.(2)The numerical simulation results based on the HS hardened soil constitutive model are basically consistent with the measured data.On this basis,a three-dimensional numerical model of the standard section of the foundation pit was established.Using the single variable principle,the thickness of the ground connecting wall,the elastic modulus of the ground connecting wall,the insertion ratio of the ground connecting wall,the crosssectional area of the first concrete support,and the steel support were studied.The influence of six groups of different influencing factors of cross-sectional area and horizontal spacing of supports on the settlement of the ground and pipelines around the foundation pit.The curve relationship between the above 6 groups of influencing factors and the maximum surface settlement of the surrounding area and the settlement value of the pipeline are established respectively to make certain preparations for the follow-up research.(3)By comparing the above 6 groups of influencing factors on the ground settlement and pipeline settlement around the foundation pit,it is concluded that the thickness of the ground connecting wall and the horizontal spacing of steel supports have a more obvious influence on the deformation of the foundation pit.Determine the values of these two parameters according to the deformation control value.(4)Based on the relationship curve between the parameters of the enclosure structure and the deformation above,three optimization schemes were determined with pipeline deformation as the control;and the safety of the enclosure structure itself,the stability of the foundation pit,and the effect of deformation control were determined.Project economics and construction factors are compared with the original plan comprehensively.While the deformation of the three optimized plans meets the control requirements,the project economics is improved and the expected optimization goal is achieved.