Analysis Of The Influence Of Different Vertical Freezing Schemes On The Reinforcement Effect Of Shield Launching End

With the rapid development of urbanization in our country,underground rail transit is developing rapidly in order to relieve the pressure of surface transportation,and subway has become one of the main options for people’s daily travel.The artificial freezing method has become the most commonly used reinforcement technique in subway tunnel because of its good water-stopping performance,high flexibility and green environment protection.However,with the development of frozen temperature field,it is easy to cause freeze-heave and thaw,which can affect surface buildings and destroy underground pipelines.Therefore,this paper based on a shield inlet and exit hole in fuzhou as the engineering background,by establishing different numerical analysis models and combining with the field measurement data,compares and analyzes the development rule of frozen temperature field in whole section and segmented.(1)Firstly,compare the different freezing schemes at the beginning of shield,analyze the characteristics and applicability of different freezing schemes,minimize the volume of frozen curtains to reduce the construction volume,and obtain the best technical and economic benefits.(2)The cooling law of low temperature brine and soil freezes is obtained by analyzing the temperature data of desalination,loop brine and different soil measurement points in the field.Based on the monitoring of frost heave displacement,the deformation law of the shield tunnel caused by the whole section freezing,section freezing,and field measuring data,the thickness and average temperature of the frozen curtain are calculated.(3)Using finite element software,numerical models of total block freezing and segmented freezing were established to simulate the freezing cross circle under different freezing modes,and the development of freezing temperature field on the special path was studied.The end of the frozen pipe is the weakest part of the construction.The frozen design should be strengthened to ensure the quality of the construction.(4)Taking into account the variation of freezing temperature field with different factors during segmental freezing,the results show that: larger thermal conductivity,smaller specific heat capacity,smaller density,lower initial ground temperature and faster cooling of soil layer;The temperature of saltwater had a great influence on the final freezing effect,but the soil had not reached freezing temperature at 12 d before freezing,at which time the cooling effect of different saltwater temperatures did not vary much.Based on the above research contents and progress,it can be used as a reference for similar shield starting end reinforcement design and for the development of freezing temperature field in the future.