Study On The Effect Of Deep Foundation Pit Excavation On Adjacent Subway Tunnel

In the wake of constant development and construction of cities that China promote,underground rail transit,one of the important parts of urban transportation network,has made a significant contribution to alleviate the problems of traffic congestion and land shortage in cities.Along with the continuous increase of metro lines construction,the number of deep foundation pit adjacent to subway tunnel construction is getting increasing.The transform of stress field and displacement field of surrounding soil caused by the excavation of deep foundation pit causes the deformation of adjacent subway tunnel as a result of additional force of soil.If the tunnel deformation can not be accurately predicted and reasonably controlled,the tunnel structure may be damaged in the coordinated deformation with surrounding soil during foundation pit excavation,which will affect the subway operation’s safety.On the basis of summarizing the mechanism of excavation unloading and tunnel deformation,the deep foundation pit of an electric power tunnel is taken as the background.Combined with field monitoring and numerical simulation analysis using Midas GTS NX software,this paper systematically analyzes and studies the influence of deep shaft foundation pit excavation process on the deformation of adjacent track interval,and also provides some design reference value for some similar foundation pit engineering in the future.The main research contents and results of this paper are as follows:（1）By summarizing the research status at home and abroad on the displacement and deformation of adjacent tunnels caused by foundation pit excavation,this paper summarizes the characteristics of foundation pit deformation and the main influencing factors and control measures of tunnel deformation.（2）By integrating the deep foundation pit project to establish a three-dimensional finite element model,this paper analyze the construction status.The results show that the maximum horizontal displacement of ground wall increases with the excavation condition.The occurrence position of the maximum horizontal displacement keeps moving down along the depth direction of the diaphragm wall.When the excavation is completed,the maximum horizontal displacement of the diaphragm wall is 9.42 mm.The external surface settlement of the largest pit near the tunnel side reaches 4.87 mm,and the maximum settlement occurs 10.69 mm away from the pit edge.Under various working conditions,the influence of foundation pit excavation on left line tunnel is obviously less than that on right line tunnel.The positions of different sections of the same tunnel are also significantly different under the influence of excavation.The horizontal displacement of the tunnel increases with the excavation.The vertical displacement is affected by the spatial relationship between the foundation pit and the finished surface under different working conditions.It gradually decreases in working conditions 4-6,and increases continuously in working conditions7-10.The maximum horizontal and vertical displacement of the tunnel are 2.87 mm and 2.31 mm,respectively.（3）By comparing the numerical simulation results with the field monitoring results,I found that both the numerical simulation of the deformation of the foundation pit itself and the deformation of the tunnel were basically consistent with the field monitoring results,and the trend of the two numerical displacement curves was roughly identical.This verifies the rationality of the model and the reliability of the subsequent analysis results.（4）By studying four different factors between the foundation pit and the tunnel,namely,different horizontal distance,tunnel buried depth,the thickness of the diaphragm wall,the cross section area of the internal support,this paper highlights the analysis of the influence of the foundation pit excavation process on the deformation of the interval tunnel.We can draw the following conclusions: when the buried distance of tunnel is more than once the depth range of foundation pit excavation,the influence of foundation pit excavation on tunnel deformation is greater;When the buried distance of tunnel is more than 1.5 times of the excavation distance,the excavation has little influence on tunnel deformation.When the depth of the tunnel exceeds the depth of foundation pit,it will change the regularity of the horizontal and vertical displacement of the tunnel.The depth of foundation pit has great effect on the horizontal and vertical displacement of tunnel.The increase of the thickness of diaphragm wall and the cross section area of inner support can control the deformation of tunnel well.The effect of the increase of inner support area on vertical displacement is slightly higher than that on horizontal displacement.Figure [44] Table [6] Reference [58]...