Study On The Law Of Artificial Freezing Frost-heaving And Thawing-settlement Of Cross-passage In Coastal Stratum

The coastal areas are mostly soft and rich water strata,the cross-passage is usually constructed by artificial ground freezing method.The artificial ground freezing method is an environment-friendly construction method,which has the advantages of no pollution to the environment,low noise,little influence on the surrounding underground structures,stable bearing,and good resistance to permeation.However,after the soil has been frozen,its physical and mechanical properties will change.The most important performance is the phenomenon of frost-heaving and thawing-settlement,Surface buildings,underground structures,underground pipelines,etc,will be affected by frost heaving,cracks may occur,and the more serious situation is the destruction of the structure.This paper uses a research methods that combination of theoretical analysis,numerical simulation,and construction monitoring.Combined with Fuzhou rail transit line 2 project Shangjie station-Jinyu station cross-passage and pump station project,a systematic study of the frost heaving,thawing settlement and its.main influence factors in the horizontal freezing of subway cross-passages have been done.Combined with the actual project,the freezing process,excavation process and natural thawing process are further analyzed.The main research contents and conclusions are as follows:(1)Based on the stochastic medium and numerical analysis theory,an analytical and predictive mathematical model for surface deformation caused by frost heaving and thawing settlement in a horizontal freezing tunnel is established.The mathematical model established was applied to the project prediction of the cross-passage.(2)Considering the initial position and direction of the actual layout of the freezing pipe,the variation of the thermal conductivity with the temperature,the latent heat of the soil phase change,the penetration of the soil,and the boundary conditions,creat Thermal-seepage coupled finite element analysis model for temperature field,seepage field and stress field,the temperature field,penetration field,displacement field distribution and development law of active freezing,cross-passage and pumping station excavating and natural thawing were analyzed.The surface frost heaving displacement curve after completion of the active freezing and the surface thawing settlement displacement curve after completion of natural thawing are obtained.(3)Monitor freezing temperature and surface deformation in the process of artificially freezing in the cross-passage,compare the results of finite element simulation and predictivemathematical models of frost heaving and thawing settlement prediction with measured data,The three results are basically the same,which verifies the reasonableness of the prediction model and the finite element simulation method.Use the model to predict the final thawing settlement results of natural thawing.