Analysis On Excavation Deformation Of Deep Foundation Pit In Soft Clay Subway Station And Its Influencing Factors

With the acceleration of urbanization in China,the problem of urban traffic congestion has become the main restricting factor on the development of cities.In recent years,the rapid development of urban railway has effectively alleviated the problem of urban traffic congestion.More and more cities throughout the country have built subways.Besides this,it is ineluctable that some subway lines are constructed in poor geological condition.Therefore,the construction of deep foundation pit of subway station is considerably challenging.In China there are deep soft soil layers in the vast coastal areas and areas that are abundant with waterways.The soft soil layers formed by silt and silt soil are distributed in Foshan area,and the soft soil layers are often partially mixed with clay layers of varying thicknesses,making the soil layer has the differences in every direction.Therefore,making the construction of the deep foundation pit at the station have an adverse effect.Based on the deep foundation pit engineering of Nanhai Square Station in Foshan City Rail Transit Line 3,using the combination of field measurement and numerical simulation,the model of foundation pit excavation is established by FLAC3D finite difference software.In this paper,the deformation law of deep foundation pit in Foshan metro station is studied,and the influencing factors of foundation pit deformation are discussed.The main findings are as follows:1.Through the analysis of the measured data and simulation results,it can be concluded that the horizontal displacement of the retaining structure of the foundation pit is mainly concentrated near the excavation surface with the shape of "bow",and the settlement area of the surface around the foundation pit is mainly concentrated within the range of 5 m and 15 m,which is in the form of a "groove".The axial force of the support is mainly concentrated on the first and the third beam,and the fourth beam is under the least force.2.The influence factors of foundation pit deformation are analyzed by using FLAC3D software.The foundation pit deformation is influenced by the wall thickness,embedding depth,support stiffness,pre-axial force and so on.The foundation pit deformation will decrease as the increase of these factors.3.There are busy roads in the vicinity of foundation pit construction,and the vehicles’driving on the top of the pit has a certain effect on the deformation of the foundation pit.The value of horizontal displacement and supporting axial force of retaining structure of foundation pit is large when the vehicle load influencing area is between 5m and 15m around the edge of foundation pit,and the magnitude of vehicle load has obvious influence on the axial force of support in shallow soil layer,but has little effect on the axial force of deep bracing of foundation pit.