Numerical Simulation And Risk Assessment Of Deep Foundation Pit Of Aofeng Road Station Of Fuzhou Metro Line 4

Since China entered a new era,the development of national economy has also entered a new period.At the same time,the construction scale of urbanization is also gradually expanding,the foundation pit engineering of high-rise building and municipal engineering has gradually become an important project of urban development.Among them,the environment of deep foundation pit engineering in subway station is more complicated than that of general construction foundation pit engineering,construction conditions are more demanding,there is also a higher risk of safety.Therefore,the research on the deformation and stress characteristics of the deep foundation pit supporting structure of the subway station and the environmental impact is still a major issue and research hotspot of people’s concern.This paper take the deep foundation pit engineering of Aofeng Road Station of Fuzhou Metro Line 4 as an example,collect and sort out the design and construction data related to the foundation pit engineering of Aofeng Road Station,monitor and control the whole process of excavation of foundation pit,use Lizheng software and finite element software for design calculations and numerical simulations,discuss and study the characteristics of force and deformation during the excavation of the foundation pit,and using fuzzy mathematics combined with three-level alarm strategy,carry out foundation pit safety risk level evaluation,in order to provide reference for the construction,design and management of similar foundation pit projects in the future,this has important practical significance.The main research work and results are as follows:（1）Through the collection of research literature,summarize the relevant research theories of foundation pit deformation mechanism,foundation pit deformation influencing factors,and foundation pit risk assessment.（2）By sorting and analyzing the monitoring data obtained during the excavation of the station foundation pit,the deformation mode and law of the station foundation pit are studied.According to field monitoring and analysis,With the increase of the excavation depth of the foundation pit,the horizontal displacement of the diaphragm wall is also increasing,shows a"bow"-shaped distribution of"the upper and lower parts are relatively small,and the middle part is large".The position where the maximum horizontal displacement of the wall appears also changes with the change of the excavation depth,and it has been kept near the excavation surface.The maximum horizontal displacement detected is 55.4mm,at the wall-22m,the ratio of the maximum horizontal displacement of the ground connecting wall to the excavation depth was0.236%,this value is close to the average value of deformation ratio of deep foundation pits in Shanghai area.The calculation results using Lizheng software and finite element software are roughly the same as the monitoring situation,for example,the numerical simulation results show that the maximum horizontal displacement of the wall was46.5mm,which appears at-20.5m of the wall,showed that the use of theoretical calculation and analysis has a certain value.（3）The surface settlement monitoring around the foundation pit shows that the surface settlement curve is generally in a“parabolic”form of“concave”trough,the maximum value increases with the increase of excavation depth,when excavated to the bottom of the pit,the ground settlement reached 27.56mm,at a distance of 16m from the edge of the foundation pit,this position is consistent with the deformation law summarized in the《Foundation Pit Engineering Manual》of X_m=（0.5～0.7）h_0.Numerical simulation shows that the change trend of surface subsidence is roughly the same,the maximum settlement value is 23.4mm,which also appears at a distance of16m from the edge of the foundation pit,which is more consistent with the measured data.（4）The measured values of the axial forces of the six supports under all excavation conditions are all less than the design values,meet the design requirements,as the excavation depth increases,the axial force of each support first increases and then decreases,and then tends to stabilize.In addition,with the increase of the excavation depth,the sum of the axial forces of the various supports above the excavation surface has been continuously enlarged,it shows that the six supports have effectively played their respective roles in the process of foundation pit support,ensuring the safety of foundation pit construction.However,the actual monitoring value is slightly larger than the calculation result of the numerical simulation,which may be related to the impact factors such as the pile load around the construction site of the foundation pit or the traffic load.（5）The settlement monitoring values of the surrounding buildings（structures）and underground pipelines of the foundation pit are relatively small,the maximum value is18.36mm,which is within the monitoring warning value range,indicating that the supporting structure played a great role in the construction of the foundation pit excavation.（6）In this paper,a fuzzy comprehensive evaluation model for deep foundation pits based on entropy weight-AHP is established,combined with a three-level alarm strategy,to discuss and study the risk level evaluation methods of the foundation pit body,the surrounding environment of the foundation pit,and the overall foundation pit.And based on the monitoring data of the Aofeng Road station foundation pit project,the qualitative analysis of the deep foundation pit body and the surrounding environment safety conditions of the deep foundation pit,and then the overall risk level of the foundation pit is scored and evaluated.According to the normative standards,the comprehensive score of the overall risk assessment of deep foundation pits is 66.7points,and the evaluation grade is level I alert,which basically reflects the actual situation of the foundation pit.It shows that the foundation pit risk assessment method based on monitoring data in this paper is relatively objective,credible and reliable,which can provide reference for similar projects in the future and has a relatively large reference significance.