Research On The Influence Of Pile Group On Neighboring Metro Tunnels

This paper uses numerical simulation software of ABAQUS and combine field monitoring to analyze the influence of pile group construction on tunnels based on a road reconstruction project in Hangzhou.On this basis,this paper applies the numerical simulation method to analyze the influence of the whole process of pile construction and the sequence of pile group construction on tunnels.The main work and results in this paper are as follows:1.The field monitoring results and numerical simulation results are collated and analyzed.The deformation trends of these two results are basically matched.In the process of pile group construction,tunnels show the trend of keeping away from pile in the horizontal direction and the trend of sinking in the vertical direction.The larger the depth of the tunnel,the larger the horizontal displacement and the small the vertical displacement.And the the horizontal displacement of each tunnel is larger than the vertical displacement.The displacement growth rate is closely related to the construction number of the pile on that day.The number of pile construction is small,the change of the displacement of the tunnel is slow and the change of the displacement is quick when the number of pile construction is big.2.Through the numerical simulation,it can be found that the influence of single pile construction on tunnels is far less than the influence of pile group construction on tunnels.This is because the stress generated by single pile during pile group construction superimposes each other,so that the stress of pile group and pile bottom soil is much larger than that of single pile,and the stress influence depth and width are much more than that of single pile.3.Through analyzing the result of numerical simulation of single pile,it can be found that pushing steel sleeve and pouring concrete make tunnels move away from pile in the horizontal direction and make tunnels uplift in the vertical direction.This is due to the squeezing effect of these two construction processes on the surrounding soil.In the stages of mud protection with earth excavation and hardening of concrete,because the soil stress reduces and diffuses,tunnels move close to pile in the horizontal direction and sink in the vertical direction.4.In the pressure stage of steel casing,the change in the left and right lines of the metro tunnel No.1 is obviously lager.This is mainly due to the fact that when the pressure depth of the steel casing is greater,the steel casing and the soil column in the pipe together form a whole pile,and the squeezing effect is more obvious.Due to the protection of steel casing,the horizontal displacement of each tunnel varies little in the stage of mud wall protection and soil collection,concrete pouring and concrete hardening.At construction process of the vertical displacement change,the change in the outgoing line of the metro tunnel No.1 is the largest.This is mainly due to the superposition effect of the shallow tunnel in the vertical displacement.This explains why the greater the depth of the tunnel is,the larger the horizontal displacement is,the smaller the vertical displacement is.The rule is consistent with that of pile group construction.5.Through comparing the numerical simulation results of two sequences of pile group construction,it can be found that when the pile group was constructed from both sides of the tunnels from near to far,the influence on tunnels is less than the influence on tunnels when the pile group was constructed from both sides of the tunnels from far to near.This is because when pile groups are being constructed from both sides of the tunnel from near to far away,the constructed piles have a barrier effect on the post-construction piles.