Deformation Monitoring Of Foundation Pit Construction And Numerical Simulation Analysis Of Hongshan Station Of Wuhan Metro Line 8

In recent years,the rapid growth of the Chinese economy and urbanization caused increasing pressure on transportation.In order to alleviate the traffic pressure and improve citizens’ quality of life,the Wuhan government is making efforts on the underground space.Vigorously develop subway projects,and at the same time,more and more complex deep foundation pit projects have been generated mainly from urban subway projects.This paper will focus on the deformation rule of ground settlement and retaining structure around the foundation pit in Wuhan area.It is of great engineering significance to optimize the safety of foundation pit monitoring and support design.Based on the deep foundation pit of Hongshan station in the second phase of Wuhan Metro Line 8,the monitoring was planned under the guidance of theoretical analysis.According to the monitoring data,the surface settlement and the deformation of the retaining structure on the standard section were analyzed,and the settlement law of the surrounding surface of the foundation pit and the influence of the supporting structure on the deformation of the foundation pit were obtained.Through the finite element software PLAXIS,the model of the standard section of Hongshan station was established.Differentiating different working conditions according to excavation depth,comparative study was performed through simulation results and actual test results.The main research work is as follows:(1)Research on deformation law and mechanism of foundation pit.The deformation mode,types and mechanism of foundation pit were obtained through consulting literatures.Deformation types of foundation pit mainly include surface settlement which consists of triangle and groove settlement,horizontal displacement of retaining pile and base uplift.In terms of changing law,the maximum displacement of triangle settlement is near the wall while the maximum displacement of groove shape is at a certain distance from the wall.The horizontal displacement of retaining pile can be divided into cantilever type,parabola type and mixed type under different excavation depth,and its shapes are inverted triangle,parabola type and wave type.(2)Collect and sort out field monitoring data in the stage of construction.The monitoring data collected in the field were classified,sorted and tabulated to obtain the ground settlement law and the horizontal displacement law of the pile.The largest part of the surface settlement is about 10 m away from the edge of the foundation pit,and the deformation curve conforms to the groove surface settlement law.The horizontal displacement curve of the pile is similar to "bow shape" and conforms to the deformation law of parabola shape.(3)The model was established by the standard section of PLAXIS.In order to simulate the excavation process of foundation pit,different conditions were distinguished according to different excavation depth.The results showed that the largest part of the surface settlement is about 10 m away from the edge of the foundation pit;the support form of bored cast-in-place pile + steel pipe internal support can effectively control the horizontal displacement,vertical displacement of foundation pit retaining pile and the settlement of soil behind the wall,so that it is in a safe range.At the same time,the layout of monitoring points and monitoring scheme are reasonable and feasible.The monitoring point is set here to monitor the construction of the foundation pit,which can help us to understand the change trend of the displacement of the foundation pit.The monitoring data feedback analysis can better predict the change trend.(4)Before and after the erection of the fourth steel support in the whole foundation pit construction process,the surface settlement and the deformation of the retaining structure reach the maximum value,which is the most dangerous period in the whole construction process.Although the stability of the retaining structure meets the requirements of the specification,it is also necessary to pay attention to whether other factors will affect the construction safety.(5)The numerical simulation of the whole process of the excavation of the deep foundation pit of the subway station was carried out,and the results obtained were compared with the monitoring data.The results show that numerical calculation results of each construction stage are relatively consistent with the field monitoring results.This study provides a scientific basis for the rational design and safe construction of the deep foundation pit project of Wuhan Metro station.