Study On The Coupling Law Of Water And Heat In The Frozen Reinforced Contact Channel Between Gongfu Station And Hohhot Stadium Station

Compared with the traditional construction method,the artificial ground freezing method can effectively prevent groundwater seepage,the construction environment pollution is small,has the applicability to a variety of soil layers,has been widely used in the subway tunnel construction project.The construction of contact channel is an essential process in subway construction,and the construction is very difficult,especially in the soft soil layer rich in water,and there are risks of collapse and frozen soil curtain failure in the construction process.The freezing method runs through the active freezing stage and the thawing and thawing process of frozen soil before the excavation of the contact channel,during which the construction risk is bound to cause certain casualties and economic losses.In order to improve economic benefits,it is necessary to deeply study the changes of frozen soil curtain in the freezing process under the action of groundwater seepage.In this paper,combined with the construction project of No.2 contact channel between Gongfu Station and Hohhot Sports Station of Metro Line 2 in Hohhot,Inner Mongolia Autonomous Region,ADINA and COMSOL software were used respectively to simulate and study the numerical calculation values and the in-situ measured data,so as to verify the reliability of the numerical simulation method.This paper focuses on the development process of frozen soil curtain and the rule of soil temperature evolution under the condition of groundwater seepage,and explores the sensitivity analysis of each stage.The main conclusions are as follows:(1)Based on the concrete engineering data obtained from field measurement,it is found that the temperature development and change of the observation point with a deep depth of temperature measuring hole is relatively stable,which can be used as the analysis point for sensitivity analysis of numerical model;Under the two conditions with or without percolation,the numerical calculation results of measuring points at the same position were compared with the measured data,and the curves with similar cooling rules were obtained,and the maximum temperature difference values were always less than 5℃,which proved the feasibility of the finite element method.(2)Under static water conditions,for different Y profiles,the freezing effect caused by the density of cryotube is very different;The earliest freezing time for X=-3.1m interface related parameters to meet the requirements of subsequent excavation construction is about 18 d of active freezing,and the average temperature in the frozen wall reaches-10℃ at 16.3d.By simulating the development process of frozen soil curtain,the weak link in freezing construction can be found in advance.The thermal conductivity of soil and different brine cooling schemes have great direct influence on the final effective thickness of frozen wall.(3)Considering the seepage of groundwater and the migration of water molecules,the frozen soil curtain will migrate.When there is no seepage,the frozen wall is symmetrical,uniform and regular.When there is percolation,the cooling range and freezing wall thickness of the downstream percolation are higher than that of the upstream percolation,indicating that the effect of groundwater percolation on the frozen soil curtain in the actual project cannot be completely ignored,and the simulation results will be closer to the actual project after adding the percolation field,so the freezing measures at the beginning of the percolation direction should be strengthened.When the flow direction is vertical flow direction,the freezing construction will be greatly affected.(4)The time it takes for soil to enter the phase transition stage in the middle period of forced thawing is mainly determined by the distance between soil and thawing tube.The smaller the distance is,the earlier the soil enters the phase transition stage.With 70°C circulating hot water,it takes 33.5 days to defrost for 60 days.In the early stage of melt grouting,the side and top of the structure on the contact channel should be mainly used,and in the later stage,the bottom should be mainly used.