Analysis Of The Impact Of Deep Foundation Excavation On The Deformation Of Adjacent Underpass Tunnels

In order to relieve urban traffic congestion,China has built a large number of subways,and many new pit projects have been built adjacent to subways,and the excavation construction of pit projects will have adverse effects on subway tunnels.Therefore,it is important to study the impact of excavation construction of foundation pit project on the adjacent subway tunnel for the safety of foundation pit and subway tunnel.In this paper,the actual foundation pit project adjacent to the subway tunnel in Beijing College Road Science and Technology Park Dongsheng Park is taken as the research object,and the deformation of the foundation pit and tunnel in the excavation and unloading stage is simulated by using the finite element numerical software MIDAS GTS NX,and the displacement change law of the underground diaphragm wall,subway station and tunnel interval in the excavation and unloading stage of the foundation pit is analyzed,and compared with some of the actual measured values of site monitoring;the Tongji The control scheme for the deformation exceedance of the underground diaphragm wall was reviewed and analyzed by Tongji Qixing calculation software;the control effect of the double-row pile parameters in the foundation pit on the deformation of the adjacent underpass tunnel was discussed.The main research contents and results are as follows:(1)Finite element numerical simulation software is used to simulate the foundation pit project and study the deformation law of the foundation pit and the adjacent subway tunnel.With the increase of the excavation depth of the foundation pit,the deep horizontal displacement of the underground diaphragm wall gradually increases,and the horizontal displacement and vertical displacement of the subway station and tunnel interval show a growing trend.Influenced by the excavation range of the foundation pit,the horizontal displacement and vertical displacement of the station in the excavation range of the foundation pit grow faster displacement deformation,the station in the excavation range outside the parts of the horizontal displacement increment is smaller,displacement deformation is smaller.The simulated value is compared with the actual measured value on site,and the displacement deformation trend of both is basically the same.(2)The control scheme of the underground diaphragm wall deformation exceeds the limit was reviewed and analyzed.In view of the deformation of the underground diaphragm wall exceeding the limit,the design and construction measures were proposed,and the deformation of the underground diaphragm wall under three different working conditions was reviewed and calculated using Tongji Qixing calculation software.It is further suggested that the hardening and drainage measures should be strengthened at the surface above the subway station,and the continuous deformation monitoring of the station and the underground diaphragm wall structure should be enhanced.(3)The control effect of double-row pile parameters in the pit on the deformation effect of the adjacent underpass tunnel is discussed.The maximum horizontal and vertical displacements of the subway station are reduced by 24.1%,7.8% and 15%,11.1% respectively when the thickness of the double-row pile wall in the pit is increased from 0.7m to 1.0m.The pile length of underground diaphragm wall is increased from 23 m to 29 m,and the maximum horizontal displacement of the subway station is reduced by 13.2% and 9.6% respectively.The maximum horizontal displacement of the subway station is reduced by 7.8% and 5.0% respectively when the thickness of the diaphragm is increased from 0.6m to 1.0m.Increasing the thickness of the underground diaphragm wall has a good effect on controlling the displacement and deformation of the subway station,and can be combined with the method of increasing the thickness of the connecting slab to control the displacement and deformation of the adjacent subway station.