Research On Single Pipe Freezing Temperature Field In Pipe-roof Freezing Under The Arrangement Of Different Freezing Implement

The pipe-roof freezing method is the combination of the pipe curtain method and the artificial ground freezing method.The pipe screen formed by the pipe-jacking is used as the bearing structure,and the frozen soil curtain formed by freezing is used as the waterproof structure between the pipe-jacking.This construction method fully combines the advantages of the pipe curtain method and artificial ground freezing method,it has been successfully applied in the construction of Gongbei Tunnel of Zhuhai Cable in Hong Kong-Zhuhai-Macao Bridge in China.The structure type and arrangement method of the freezer in the pipe jacking method play a decisive role in the application effect of the pipe-screen freezing method.For this reason,in this paper,a combination of model test and numerical simulation is used to deeply analyze the single pipe freezing temperature field in pipe-roof freezing under the arrangement of different freezing implement in order to obtain the optimal type and arrangement of the freezer.The main research contents and achievements of this article are as follows:(1)Considering the three different arrangements of solid tube-circular freezer,empty tube-double circular freezer,and empty tube-special shape freezer,a large-scale model test system with single tube freezing was established,based on the similarity criterion.The single-tube freezing temperature field was tested and compared.The results show that: at 21 h,the temperature drop rate of the solid tube-circular freezer is 0.05 ℃h faster than that of the empty tube-double circular freezer in the same position.The temperature drop rate of the empty tube-special shape freezer is 0.1℃h faster than the temperature drop rate of the solid pipe-circle freezer at the same position,and the rate of temperature drop of the three types of freezers was not much different afterwards.(2)Considering the three different arrangements of solid tube-circular freezer,empty tube-double circular freezer,and empty tube-special shape freezer,ANSYS finite element program was used to conduct a numerical simulation study of single tube freezing temperature field.The results show: at 21 h,the temperature drop rate of the solid tube-circular freezer is 0.16 ℃h faster than that of the empty tube-double circular freezer at the same position,and the temperature drop rate of the empty tube-special shape freezer is 0.19 ℃h faster than that of the solid tube-circular freezer at the same position,and the rate of temperature drop of the three types of freezers was not much different afterwards.(3)According to study of model tests and numerical simulations,the freezing effect of the empty tube-special shape freezer is the most effective in the three different arrangements of solid tube-circular freezer,empty tube-double circular freezer,and empty tube-special shape freezer.However,empty tube-special shape freezer are welded in the form of angled arcs,which is difficult to process,and there are many welds and a large number of overhead welds.The requirements for welding are high,and the problem of leakage of refrigerant is prone to occur.The cost of maintenance in the later period is higher.Therefore,an empty tube-double circular freezer can be considered instead of an empty tube-special shape freezer.The research results of this paper have important guiding significance for the design and construction of the pipe-roof freezing method,and can be applied to the shallow-buried over-large cross-section tunnel construction in water-rich ground.