Study On The Development Characteristic And Influencing Factors Of Freezing Temperature Field In Cross Passages

The freezing method has been widely recognized in the construction of subway cross passages by virtue of its advantages,such as usability of numerous strata and lower pollution to the surrounding environment.According to the existing research results,the majority of scholars choose the development of the temperature field on any section of cross passage to replace the development of the temperature field on the whole cross passage,ignoring the influence of layout and deviation angle of freezing pipes,which cannot fully reflect the development law of the temperature field on the whole cross passage.Based on the engineering background of two cross passages between Luoxiu Road Station and Baise Road Station on Shanghai Metrol Line 15,the paper carries out a three-dimention numerical simulation of the deviation of the freezing pipes in the cross passage No.1 by the finite element software.Comparing and analyzing the development law of the temperature field of different sections of the cross passage,the weakest section of the cross passage and the closure time,thickness,average temperature of freezing wall on the corresponding secation are obtained.Sorting out and analyzing the brine temperature the brine temperature,formation temperature,and pressure relief hole pressure of the cross passage freezing project obtained on site,the similarities,differences and the reasons for the formation temperature reduction laws of the cross passages in the same interval are obtained.Moreover,the soil temperatures are substituted into the freezing wall thickness and average temperature calculation formulas with deviation coefficient,it is found that all freezing indicators can meet the design requirements.Finally,the numerical simulation is expanded to establish three-dimention models of cross passage with different brine temperatures and three dimention models of cross passage with different freezing pipes diameters.According to the three-dimention numerical simulation results of the cross passage with different brine temperatures,the time required for different thickness and strength of freezing wall to meet the design requirement at 15 days,30days,45 days and60days of freezing and temperature field are obtained,at the same time,the law of temperature field in cross passage with the change of freezing time and brine temperature are obtained.Based on the numerical simulation of three groups of cross passage with different freezing pipes diameter of 73 mm,89mm and 108 mm,the development law of the temeperature field of different sections is further studied.The result shows that in the section with large spacing of freezing pipes,it is longer time that the thickness of freezing wall to meet the design requirement,and the change of freezing pipes has a less effect on the required time for the thickness of freezing wall to meet the freezing design.Based on the above main work and results,the certain reference for the anlysis of the freezing effect on the similar cross passage could be provided in the future.Moreover,it is valuable to calculate the thickness and average temperature of the freezing wall.Meanwhile,it can provide a reference for the future cross passage freezing project in similar strata.