Study On The Influence Of Foundation Pit Excavation On The Existing Side Tunnel

Foundation pit engineering is one of the important factors that affect the normal operation of subway.In the process of foundation pit excavation,the bending moment and displacement of the lining on the side of the tunnel will produce a series of changes,and the earth pressure on the outside of the lining will also change.This series of changes may cause the crack deformation of the tunnel,and even affect the operation safety of subway in serious cases.Therefore,it has become a very important topic to study the influence of foundation pit excavation on the side existing tunnel and put forward corresponding control measures.In this paper,through indoor model test,numerical analysis and other methods,the influence of foundation pit excavation on the side existing tunnel is studied under different tunnel space location conditions,and some data are compared with engineering examples and their simulation.By embedding different length of isolation piles,the protection effect of isolation piles on the tunnel in the process of foundation pit excavation is studied.The main research results are as follows:(1)The influence of the initial excavation of foundation pit on the tunnel is very small.In the later stage of foundation pit excavation,the bending moment at both ends of the tunnel increases,the upper and lower bending moment decreases,and the tunnel shows the trend of tension and compression at both ends;the horizontal and vertical displacement at the upper right part of the tunnel are greater than that at the lower left part,and there is a trend of uneven displacement;the earth pressure at the far side of the tunnel foundation pit increases,and the earth pressure near the foundation pit decreases.(2)The tunnel close to the foundation pit and shallow in depth is greatly affected by the excavation of the foundation pit.The specific performance is that the bending moment,lateral and vertical displacement values of the tunnel are larger,the displacement and deformation trend of the tunnel are more obvious,and the influence on the displacement is greater than the influence on the bending moment.(3)The longer isolated pile support system can obviously reduce the bending moment,displacement and earth pressure change value of the tunnel,which plays a better role in protecting the tunnel.The shorter isolated pile support system can also reduce the bending moment,displacement and earth pressure change value of the tunnel,but the reduction range is limited,which can not play an effective role in protecting the tunnel,and the efficiency cost is relatively low.(4)The longer the isolation pile is,the smaller the bending moment and displacement value of the tunnel is,but the shorter the isolation pile whose length does not exceed the excavation depth of the foundation pit has limited reduction range and low efficiency and cost;the longer the isolation pile whose length is above and below the embedded depth of the foundation pit can greatly reduce the deformation and displacement value of the tunnel,which has a better protection effect on the tunnel.However,the long isolation pile can not play a greater role in the control of the tunnel,so choosing the appropriate length of the isolation pile can protect the tunnel and achieve a better economy.