Study On Freezing Pipe Position Layout Of Artificial Freezing Method In Harbin Metro

With the continuous development of urbanization and the gradual increase of urban population,the above-ground rail transit planning has become more and more difficult to meet people’s daily travel needs.People began to focus not only on the above-ground spatial structure,in recent years,major cities began to build large-scale subway and river tunnel,greatly.It has alleviated the pressure of urban traffic,and its convenient,fast and economical travel mode has been recognized by the broad masses of people.However,the excavation of the end shaft and the connecting passage in the complex geological conditions of the river tunnel has emerged.The conventional grouting reinforcement has been difficult to meet the construction requirements.The artificial horizontal freezing method has the advantages of good water sealing,strong adaptability,little disturbance to the surrounding environment,and comprehensive informationization of the construction to ensure the construction safety.Auxiliary tunnel excavation is more and more popular in engineering.Artificial freezing pipe arrangement is an important part in the construction process.Reasonable pipe arrangement can not only reduce the input of resources cost,but also control the ground frost heave displacement more reasonably,reduce the influence on Subgrade and surrounding buildings,and make the artificial freezing process freezing.The study of the rule of pipe layout becomes very important.Taking the excavation of the contact passage of Harbin metro line three as the background of the project,the following studies are carried out.(1)experimental study on deformation and strength characteristics of frozen soilIn the process of artificial freezing,the strength of frozen soil is the important basis for evaluating the stability of frozen wall.Therefore,the triaxial tests of silty clay,fine sand and coarse sand under different water content,confining pressure and freezing temperature are carried out and the strength analysis is carried out.(2)experimental study on water movement in freezing processThe volume expansion of water from liquid phase to solid phase is only a part of frost heave in the process of soil freezing.The water migration under the combined action of negative temperature and ice crystals is the most important part of frost heave.The frost heave experiments of silty clay and fine sandy soil under closed conditions and water supplement conditions were carried out respectively,and the law of water migration during the frost heave process was explored,providing a basis for the later verification of the water-heat coupling finite element model.(3)establishment of coupled finite element model for artificial freezing methodThe temperature field and moisture field of saturated frozen soil during freezing process are obtained by establishing the water-heat coupling equation of saturated frozen soil with temperature and porosity as dependent variables.The relationship equation between frost heave and porosity is given,and the temperature field and moisture field are linked with displacement field.Finally,the soil is saturated by using COMSOL Multiphysics mathematical module.The freezing process was simulated and compared with the results of indoor water migration experiment to verify the accuracy of the model.(4)numerical simulation analysis of different pipe layout schemes based on multi field coupling model.Considering the size,number,spacing,row of Freezing Holes and other factors,a variety of freezing pipe layout schemes are determined,and the law of pipe layout is obtained by numerical simulation analysis.The rationality of pipe layout is measured by the surface frost heave displacement,the time of cross-circle frost heave,the completion time,and the cooling amount needed in the plan,and the reasonable pipe layout scheme is determined.(5)Field monitoring of temperature field and displacement field in artificial freezing constructionDuring the artificial freezing synchronous construction process,the frozen wall temperature field and the landmark displacement field are monitored on site to obtain the actual results of the temperature field and the surface displacement field.While guiding the construction of the project,the actual results and numerical simulation results of the on-site monitoring can be compared and verified.The accuracy of the finite element model is to prove that the model is universal and can be widely applied in the early stage of the artificial freezing method.