Analysis Of The Influence Of Foundation Pit Excavation On The Adjacent Subway Tunnels Under Complex Conditions

Based on an example of the foundation pit of a near subway tunnel in Shanghai soft soil area,this paper analyzes the influence of the foundation pit construction on the deformation of the adjacent tunnel and the foundation pit by the finite element simulation software of the geotechnical engineering Midas the GTS NX model.The foundation Pit is in Shanghai soft soil area,its structure is special,it is composed of adjacent deep foundation pit and shallow foundation pit,and the subway tunnel is located under the shallow Foundation pit,and it is located on the side of the deep foundation pit,the situation is more complicated.The main contents of this paper are as follows:(1)Three kinds of construction schemes for excavation of foundation pit under more complicated conditions are proposed,and the deformation of model under different schemes is analyzed through Midas software simulation.In this paper,the influence of different excavation methods on foundation pit and tunnel under complicated conditions was obtained by comparing and analyzing pit bottom heave of foundation,horizontal displacement of enclosure structure,settlement of soil mass outside the pit as well as horizontal and vertical deformation of tunnels.It is found that deformation of foundation pit and tunnel will be obviously affect by different excavation schemes unde complex conditions.Especially,the excavation of foundation pit on the side of the tunnel will have a great influence on the horizontal deformation of the tunnel,and the excavation of foundation pit above the tunnel will have a great influence on the vertical deformation of the tunnel.(2)This paper simulates and analyzes the influence of the scope and depth of the foundation pit on reducing the deformation of the foundation pit and adjacent tunnel,and chooses the reasonable reinforcement scheme to ensure the safety and stability of the project.It is found that soil consolidation in the passive area of foundation pit is beneficial to reduce the deformation of foundation pit and adjacent tunnel,but for the effect of reinforcement depth and reinforcement range on reducing the deformation of foundation pit and tunnel,the reinforcement effect is not obvious with the increase of reinforcement depth under the premise of the same cost.But the larger the reinforcement range,the better the reinforcement effect.