Research On Unloading Soil Characteristics And Deformation Laws During Excavation Of Deep Foundation Pit Of Metro Station

With the rapid economic development of our country,the road traffic is becoming more and more congested,and underground rail transit has become the first choice for people to travel.Compared with other cities,Shijiazhuang has a larger population.To facilitate people’s travel,Shijiazhuang is vigorously building underground rail transit.In the process,controlling the deformation during the excavation of the foundation pit has always been the focus of the project.Based on the engineering background of a deep foundation pit of a subway station in Shijiazhuang,this paper conducts research and analysis on the deformation of the foundation pit during construction.Through physical mechanics experiments and microscopic analysis,and with the help of Origin data analysis software and finite element analysis software,the foundation pit excavation is carried out.The soil properties and deformation mechanism in the process have been systematically studied,mainly including:(1)Aiming at the change of soil properties during the excavation of foundation pits,indoor experiments are used to compare the experimental results with those before the soil is unloaded,revealing the law that the strength of the soil decreases as the load is removed;on this basis,On this basis,the scanning electron microscope was used to observe the unloaded soil at different depths,and combined with the results of the indoor test,the filling and cementation of the surface debris of the soil was investigated,and the influence mechanism of the strength of the lower soil was increased.At the same time,it is recommended that when designing the excavation in this area,the soil parameters should be 90% to 95% of the original soil parameters.(2)Based on the basic principle of soil nonlinear change,ABAQUS finite element software is used to simulate,and according to the on-site monitoring results,the deformation of the foundation pit during the construction process is analyzed,and It is concluded that during the excavation of the foundation pit,the surface settlement exhibits a groove-shaped change trend from the edge of the foundation pit,the horizontal displacement of the pile body shows a bow-shaped change trend,and the supporting axial force shows a stepwise growth law and has a negative effect on adjacent buildings.The impact of the material is very small,revealing the deformation characteristics of the foundation pit during the excavation process.The simulation results are compared with the measured results to verify the feasibility of simulating the excavation of foundation pits.(3)The feasibility of the model is verified based on(2).On the basis of this model,By analyzing the influence of steel supports at different positions on the lateral deformation of the structure,it is recommended to place steel supports 3m,8m,and 13 m from the ground;the depth of the pile body has little effect on the lateral deformation;when the design is two steel supports,The lateral displacement of the pile is about to exceed the limit,it is not recommended to use two steel supports.