Study On Influence Mechanism Of Freezing Of Connecting Passage On Upper Existing Tunnel

As the underground traffic network becomes more and more complex,the freezing method is adopted to reduce the deformation effect of the surrounding lines.At present,the research on the influence of the existing tunnel has achieved fruitful results at home and abroad,but the research on the influence of the freezing process of the connecting passage on the existing tunnel in the upper part is still lacking,and the understanding of it is still insufficient.In this paper,by means of theoretical calculation,field measurement and numerical simulation,the project of freezing connecting passage under the section of shangyang-gushan station of Fuzhou Metro Line 2 is studied,the influence of freezing on the deformation of the upper existing tunnel and the surrounding soil is studied as follows:(1)according to the elastic theory and the simplified calculation of the frost heaving force of the frozen soil mass of the tunnel in the cold region,the relationship between the frost heaving force on the outside of the frozen wall and the additional stress transfer and attenuation in the soil is obtained,based on the analysis of the vertical deformation of the central point and the longitudinal axis of the existing tunnel in the freezing process of the connecting tunnel,it is found that the area affected by the frost heave of the existing tunnel in the upper part is 5 times the width of the frozen soil mass,the frost heaving stress increases linearly with the increase of frost heaving rate.(2)through the analysis of the measured displacement data of the existing tunnel and the ground surface,the heat dissipation of the entrance and exit of the connecting passage,the temperature field of the soil layer and the development of the frozen wall are explored,the displacement of the soil around the freezing pipe,the displacement of the ground surface and the displacement of the existing tunnel in the upper part of the connecting passage are changed,and the measured data are fitted,the average growth rate was 0.59 mm/d ～ 1.01 mm/d.The time-dependent displacement of measured points in the upper existing tunnel accords with the logistic function.(3)the finite element software ANSYS is used to simulate and calculate the freezing underpass project,and the results of temperature and displacement are compared with the measured data,furthermore,the displacement variation of soil layer,upper existing tunnel and corresponding ground surface during active freezing period is studied.The results show that the frost heave can be divided into three parts: the weakest,the strongest and the transition zone,and the influence radius of the frost heave on the existing tunnel is about 21 m.(4)on the basis of the finite element model mentioned above,by changing the diameter of the existing tunnel in the upper part of the model and the clear distance between the tunnel and the connecting passage,the horizontal angle and the elastic modulus of the soil layer,etc.,the displacement variation law of the existing tunnel and stratum during the freezing process is further studied.The results show that the angle and net distance are the most important factors to the displacement and deformation of the existing tunnel.The greatest influence on surface displacement and deformation is the included angle.Based on the above research progress and results,it can provide some references for the design,construction and surrounding area protection of similar connecting passage or tunnel freezing engineering.