Numerical Simulations For Freezing Method In Metro Connecting Channel In Water Rich Sand Layer

Compared with other construction methods,the artificial horizontal freezing method has the advantages of environmental protection,high reliability,good permeability resistance and less impact on the surrounding environment.The stratum of the connecting passage in Nanchang area is saturated sand,so freezing method is often used to excavate the connecting passage.Based on the project background of the connecting passage between Normal University South Road Station and Pengjiaqiao Station of Nanchang Metro Line 1,the temperature field of freezing and thawing,seepage field of underground pore water and displacement field of frost heave during the construction of freezing method are studied deeply in this paper.The main research contents are as follows;(1)The parameters of sand samples with 10%,15%,20%,and 25% water content were tested,and the variation rules of freezing temperature,specific heat capacity,thermal conductivity and frost heave rate were obtained.Then the parameters of soil layer needed for simulation were collected by consulting geological survey reports.(2)After the collection of parameters,taking the engineering case of the connecting passage between Normal University South Road Station and Pengjiaqiao Station Metro as the background,ABAQUS finite element software is used to model the frozen soil temperature field and its development law,the frost heave displacement of the soil,the influence of seepage field on the change of temperature field,and the thawing period of 120 days.The melting condition of the melting,etc.Then compare with the actual engineering monitoring data to verify the accuracy and rationality of the numerical simulation,so as to facilitate the next simulation work.(3)Based on the simulation of engineering cases in Chapter 5,the data of parameter test in Chapter 4 are summarized,and the temperature field development and distribution law and frost heave displacement of sandy soil under different water content are analyzed by ABAQUS finite element software.Finally,the simulation results are compared horizontally,The results show that the greater the saturation ofsand,the better the freezing effect of freezing method.(4)Based on the coupled theory of heat and flow,considering the influence of convective heat transfer under groundwater seepage,the simulation calculation is carried out by using COMSOL,a finite element software which studies the coupling of multi-physical fields.The coupling of heat transfer in porous media and Darcy's law is selected to study the distribution and development law of freezing temperature field under different groundwater seepage conditions,and two monitoring points T1 and T2 are extracted..By comparing the temperature curves,it is found that the faster the seepage speed is,the more cold the groundwater takes away,and the greater the influence on freezing effect is.