Effects Of Existing Subway Tunnels Due To Adjacent Excavation Construction Of Foundation Pit

With the continuous development and utilization of underground space,more and more foundation pit projects appear in the vicinity of subway tunnels.The foundation pit project breaks the equilibrium state of the surrounding strata and causes the stratum movement,resulting in additive stress and deformation towards adjacent subway tunnels.Excessive additive deformation will affect the normal operation of subway and even threaten the safety of the subway structure.Therefore,it is necessary to study the influence of excavation construction of foundation pit on adjacent subway tunnels.In this study,10 foundation pit projects adjacent to subway tunnels in Suzhou were selected as research objects,and the spatial-temporal characteristics of subway tunnel deformation during the excavation of foundation pit have been studied by actual measurement and finite element modeling simulation.The main research contents and results are as follows:(1)Ten foundation pit projects adjacent to subway tunnels in Suzhou have been studied to classify the major influential factors,such as the plane and elevation dimensions,soil conditions,supporting structure,excavation method,reinforcement type,relative position of foundation pit and subway tunnel,deformation data of tunnel,etc.Characteristics of additive deformation of subway tunnels caused by excavation construction of foundation pit have been summed and analyzed from the following perspectives: mechanism,time distribution and spatial distribution.(2)The excavation process of the foundation pit has been simulated by the finite element analysis software MIDAS/GTS to solve the problems such as boundary selection,mesh partition,parameter and unit type selection,construction condition stimulation,etc.On the basis of that,the “foundation pit-soil-tunnel” three-dimensional finite element model is correctly established.(3)Taking the foundation pit of Suzhou Integrated Passenger Hub of the Automobile West Station for an example,the subway tunnel deformation during excavation has been analyzed dynamically based on the “foundation pit-soil-tunnel” three-dimensional finite element model.The rationality and correctness of the finite element model as well as the spatial-temporal characteristics of subway tunnel deformation are verified by comparing the finite element results with the measured data.(4)Using the foundation pit of Hengfeng Bank office building as another case study,set up a corresponding "foundation pit-soil-tunnel" three-dimensional finite element model,and dynamically analyze the tunnel deformation in the process of foundation pit excavation.By comparing the finite element calculation results and the measured data,the influential factors on the deformation of adjacent tunnel are analyzed,which are the stiffness of foundation pit supporting system and the distance between the foundation pit and tunnel.