Study On Deformation Law Of Subway Station Excavation By Tunnel First And Station Later Method In Frozen Soil Area

In recent years,with the continuous development of China’s rail transit,the traditional construction methods have been unable to meet the needs of modern urban development.Therefore,scholars at home and abroad have carried out relevant research and put forward the technology of "tunnel before station" to expand the subway station,that is,to excavate the tunnel first,and then to construct the station by expanding the existing tunnel after the tunnel is completed.This method can effectively solve the contradiction between the construction period of station and interval tunnel,improve the utilization rate of shield,shorten the construction period and save the cost.However,most of our country has begun the construction of subway tunnels in the cold and frozen regions,but few scholars consider the applicability of "tunnel before station" in the frozen regions.Therefore,this paper takes a station construction project of Harbin Metro Line 3 phase II as the background,and studies the technology of "tunnel before station" in permafrost area.The contents of this paper are as follows:(1)Analytical solution of ground displacement in Permafrost RegionConsidering the frost heaving effect of soil in permafrost region,based on Mindlin basic solution,the stiffness layer method is used to transform the parameters of permafrost layer in permafrost region,and the three-dimensional elastic solution of ground deformation during tunnel construction in permafrost region is obtained,which is solved by MATLAB.Taking a station construction project of Harbin Metro Line 3 phase II as the background,the corresponding deformation curve is drawn,The deformation law of stratum under different freezing temperature is analyzed.(2)Numerical simulation of subway station in Permafrost RegionUnder the above engineering background,the paper compares and analyzes the medium tunnel method and CRD method to expand the subway station by using the unit temperature field built in Midas software,and considers the frost heaving effect of soil.The vertical displacement,horizontal displacement and the deformation law of the station structure under the two schemes are studied.It is concluded that the middle tunnel method is better than the CRD method in controlling the deformation of the stratum and the station structure.On this basis,the analytical solution and numerical simulation results are compared.The optimization of reinforcement scheme,excavation scheme and excavation procedure is carried out for the middle tunnel method.The deformation law of stratum and structure is obtained.The above research shows that the analytical solution and numerical model can better reflect the ground and structure deformation law caused by "tunnel before station" expansion excavation in permafrost region,and can be used for the deformation prediction and analysis calculation of actual engineering construction.