Frozen Expansion Characteristics And Numerical Simulation In The Dark Dig Area Of Fuzhou Metro Line 4

With the large-scale development and utilization of underground space in Fuzhou area,artificial freezing method in rich soft soil construction is more and more widely used,but permafrost swelling melting phenomenon at the same time has great influence on the safety of the top structure,as the frozen tunnel under wear cover structure engineering increased year by year,the influence of the top cover structure has attracted the attention of more and more scholars.The study of the engineering characteristics of soft soil in Fuzhou area can provide some reference for the artificial freezing method construction of underground space in Fuzhou.At present,there is not much research on this topic.This paper takes the silt soft soil in the dark excavation area of Fuzhou Metro Line 4 as the research object,and analyzes the engineering characteristics under the artificial freezing construction conditions in this area:The basic physical parameters of the silt soft soil in the dark excavation area of Fuzhou Metro Line 4 will be determined,and at the same time,the local construction environment will be analyzed to determine the boundary conditions of the soil,and a set of freezing and expansion device that can realize single bidirectional freezing,water replenishment and applying overburden load will be designed according to the experimental requirements.Through the experiment of different factors(temperature,initial moisture content,salt content,loading load)under the influence of frost swelling characteristics of silt soft soil,found that the cold end temperature reduction,the increase of the soil frost swelling effect,and the loading load and the increase of soil salt content will inhibit the soil frost swelling effect.Analysis of the stability value of the increase of the decrease of the temperature.The initial water content,salt content and overburden load of the soil are all related as a secondary parabolic relationship.When one of the boundary conditions continues to increase,the frost swelling force of the soil will not change.According to the order of change of the solid-liquid phase in the solution,the change of the non-frozen solution in the water-salt system is analyzed,and the coupling equation of hydrothermal force and crystallization is established according to the law of conservation of mass,energy,quantity of matter and related knowledge of elastic mechanics.The hydraulic-thermal force coupling model was established by the Comsol Multiphysids software PDE module and the results were analyzed,while comparing the simulation results and verifying the applicability of the model.In addition,according to the thermal coupling model of the multilayer soil water according to the actual layout position of the frozen pipe in the project,the temperature field and water field are calculated according to the boundary conditions such as local hydrology,geothermal and temperature change in the frozen pipe,and the field monitoring data are compared with the calculation results to verify the reliability of the model.