Study On Influence Of Foundation Pit Construction On Lining Structure Of The Subway Tunnel And Control Measures

With the rapid development of modern cities,there are a large number of subway to facilitate the passage of residents.At the same time the rapid development of real estate around the subway causes a large number of the foundation pit engineering around subway tunnels.The excavation of deep foundation pit by the side of subway tunnel is one of the most common outside work forms.The excavation of the lateral foundation makes the stress field and displacement field of the existing subway tunnel change greatly,which resulting in secondary stress strain,combined with the complexity of engineering geological conditions,the construction process is easy to lead to excessive displacement of the tunnel or even crack disease.This article takes a subway shield tunnel side of foundation pit engineering as the background,establishing a numerical calculation model with ansys finite element method.Analyze the influence of foundation pit excavation on the cracking of side tunnel shield tunnel.In this paper,the specific research work are as follows:(1)Based on the finite element method,simulation and analysis of the influence on the segment cracking by excavation,emphatically analysis of the changes of axial force and bending moment of the segment after excavation.Calculate the maximum tensile stress of the segment structure based on the axial force and bending moment.Research show that the segmental cracking site is apex of arch?the bottom of arch and the middle of arch near the foundation pit side.This is consistent with the actual monitoring of the results of the segmental cracking site.It is concluded that the sudden increase of bending moment caused by excavation of the foundation pit is the main reason for the cracking of the segment structure.(2)Analysis the cracking of the related influencing factors of by the side of subway shield tunnel,detailed analysis of the influence of the soil parameters,excavation width of the foundation pit,horizontal pit distance of the foundation pit,thickness of the underground continuous wall and the excavation depth.Study the influence law of the maximum tensile stress of three different parts of tunnel segment structure under different influence factors.(3)Summarize the control measures of the displacement of the tunnel structure caused by the foundation pit engineering,Focusing on the application of grouting reinforcement and steel plate reinforcement in practical engineering and summarizes the application of the two methods.Based on the background of this project,the effect of soil grouting reinforcement method is evaluated.When the elastic modulus of the soil is 240 MPa,the maximum tensile stress of the tunnel structure is 2.6MPa,the tunnel structure does not crack.At the same time,the influence of grouting reinforcement range on grouting effect is analyzed.The results show that the grouting reinforcement can effectively reduce the bending moment of the tunnel structure.When the reinforcement range is increased from 0.8m to 1.2m,the maximum bending moment is reduced by 13.1%,the maximum tensile stress is reduced by 16.8%.The grouting reinforcement scope has a great influence on the grouting effect.