Study On The Development Law Of Freezing Temperature Field Of Metro Ultra-Long Connecting Channel In Coastal Stratum

Artificial freezing has been widely used in the construction of metro connecting channel in coastal region of China where is water-rich weak stratum almost by its excellent advantages under water-rich conditions.Conventional connecting channel freezing technique has been a proven technique,but engineering experience and research about ultra-long connecting channel are scarce,which cause frozen wall unable to closed,the unsatisfactory freezing effect,engineering accident even.This paper uses a research methods that combination of theoretical calculation,numerical analysis,and field monitoring,to conduct systematic research about the development law of freezing temperature field of metro ultra-long connecting channel which based on a construction of connecting channel in Fuzhou Metro line 2.The main research contents and conclusions are as follows:(1)Based on freezing temperature field mathematical model,the applicability of methods which calculating average temperature of frozen wall was analyzed under common freezing hole arrangement in the construction of metro connecting channel.Research results show that equivalent model method is suitable for application under the ideal condition of flat frozen wall which can reflect the freezing temperature field fine.The general empirical formula is convenient for practical engineering application which is simple and uniform,but there will be some errors when the freezing radius is much larger than the freezing hole spacing in the late freezing period.(2)3D FEM of metro ultra-long connecting channel is used to analyze the model longitudinal section result of the bilateral development law of freezing temperature field and research four feature areas which divided according to the freezing hole arrangement by unilateral freezing range.The out of sync development law of freezing temperature field of metro ultra-long connecting channel is obtained and calculation results show that frozen wall of right side connecting channel close completely need at least 22 d under ideal conditions.The freezing effect of the expected weak area is poor in which thethinnest thickness of freezing wall is 2.27 m and average temperature of freezing wall is-12.19℃ when frozen for 50 days.(3)The change law of soil temperature is summarized of the metro ultra-long connecting channel by the engineering measured data.Calculation results of key freezing technical indicators show that the thinnest thickness of freezing wall is 2.29 m in the area of trumpet mouth and pump room,2.04 m in the main part of connecting channel,and average temperature of freezing wall is-11.43℃ when frozen for 50 days,which meet the design and construction requirements.Above conclusion that the freezing effect of the expected weak area is poor is proved by compared the measured data with the numerical simulation results.Simulation effect is accurate on account of the error that is within acceptable limits and speculating that the reason of error is deflection of freezing hole in actual construction.(4)Freezing hole random deflection model is established for analyzing the influence of freezing hole random deflection on the development law of freezing temperature field of metro ultra-long connecting channel.Research results show that freezing hole random deflection will affect the freezing process of local soil.It obviously affects the flatness and stability of the freezing wall,and it is easy to form a weak freezing location as the difference is 0.26 m in the thinnest thickness of freezing wall with or without freezing hole random deflection when frozen for 50 days,that mean the influence of freezing hole random deflection should be fully considered and the quality of borehole should be strictly controlled before the construction of metro ultra-long connecting channel and strictly control the drilling quality in the construction of metro ultra-long connecting channel.