Research On Temperature Field Of Shield Launching Horizontal Artificial Freezing Method

The artificial freezing method is used in urban subway projects due to its good sealing effect,strong soil formation,and less external influence on the construction.The artificial horizontal freezing method is gradually being used in the reinforcement of the shield starting end application.The changes in the freezing temperature field and the freezing effect directly affect the safety of the shield initiation.Therefore,this article combines the above problems with the Huangpi South Road Station Project of Shanghai Line 14 to focus on the influencing factors of frozen soil,artificial horizontal freezing temperature changes and effects,and freezing.The main research conclusions are as follows:(1)Summarized the thermal physical parameters of the soil including thermal conductivity,specific heat,latent heat,thermal conductivity,unfrozen water content,and related calculation formulas.According to the physical parameters of the soil measured on site,combined with the thermal physical parameter formulas of the soil And related codes,calculate the thermophysical parameters of the soil at different depths to the sea;(2)By analyzing the change of the main road and branch road and the change of the loop brine,the temperature difference between the main road and the branch road in the early stage and the loop tends to be stable in the later stage;the temperature change analysis of the temperature measuring hole shows that the deeper the soil,the slower the temperature drop.The temperature of the freezing hole in the inner ring is lower than that of the outer freezing hole,and the temperature drop rate of the inner ring is also greater than that of the outer ring;analysis of the development speed of the freezing wall,the freezing wall of the inner ring and the middle ring develops faster than the freezing wall of the outer ring;for the freezing wall According to the thickness analysis,the thickness of the frozen cup wall can reach 1.2-2m at a depth of3.4 meters,and the thickness of the bottom of the cup is greater than the design value to meet the design requirements;(3)Establish a three-dimensional numerical model of artificial horizontal freezing and reinforcement through finite element software.Comparing the simulated value with the actual measurement,it is found that the temperature simulation value of the freezing hole in the outer ring has a small difference from the measured value,and the difference in the temperature of the inner ring is large;Larger than the measured value;the denser the freezing pipes,the smaller the row spacing,the faster the soil temperature near the freezing pipes will drop.Generally speaking,the soil temperature of the inner circle drops faster than that of the outer circle;(4)It can be obtained by the path research method that the temperature distribution between adjacent freezing tubes is like a "hump",with the highest intermediate temperature,and the temperature near the freezing tube is low and the temperature is far away from the freezing tube.Through the path method and the graphic method,it is calculated that the active freezing thickness of the bottom of the freezing pipe is between 1.1 and 1.3m,and the bottom thickness of the outer ring freezing pipe is smaller than that of the inner ring freezing pipe;(5)The influence of brine temperature,initial ground temperature,soil thermophysical parameters,and concrete thermophysical parameters on the freezing temperature field is studied by the controlled variable method.The results show that the difference between the freezing brine temperature and the initial average temperature of the soil is 2℃.the temperature of the frozen brine has the greatest impact on the freezing effect,and the initial temperature has little effect on the freezing effect;for every 30% difference in the latent heat,specific heat capacity and thermal conductivity of the soil,the final temperature difference is 1～2℃.The effect is small;the thermal conductivity and specific heat capacity of the concrete of the ground connecting wall and the inner lining wall are about 0.02℃ for every 30%difference,which can be regarded as the ground connecting wall if the error is allowed.The parameters of the concrete have no effect on the final freezing.