Numerical Simulation Of Moisture And Heat Stability Of Closed Embankment Structure In Seasonal Frozen Soil Regions

In the seasonal frozen soil zone,the roadbed is deformed under the effect of freeze-thaw cycle,resulting in a series of diseases such as cracking and mud turning in the road surface.The reason is the migration and phase change of the water in the embankment soil during the freeze-thaw process.It can be seen that the freeze-thaw deformation of the embankment is controlled by the law of temperature and moisture in the soil,which is essentially caused by the interaction of soil particles,ice and unfrozen water in the soil water potential and pressure.At present,for the freeze-thaw damage of roads,a variety of measures have been proposed,including improvement of embankment soils,thermal insulation methods,improvement of embankment water conditions,improvement of roadbed,pavement structures and overall measures.The closed embankment is proposed based on a comprehensive consideration of various factors that cause freeze-thaw damage to the embankment of permafrost.It lays heat and water insulation materials on the slope,top of the embankment and the junction between the roadbed and the natural foundation,so as to keep insulation and improve the water condition of embankment.This embankment structure has not been applied practically at present,and lacks corresponding monitoring and experimental data.In this paper,the COMSOL Multiphysics finite element software is used to simulate the distribution and evolution of the temperature field,the water separation field and the displacement field of the ordinary embankment and the closed embankment under the seasonal climatic conditions.Compared and evaluated the hydrothermal stability and the effectiveness of anti-freeze-thaw damage of the closed embankment.In addition,the reasonable burying depth of the insulation and waterproof materials in the closed embankment is also studied.By comparing the hydrothermal stability and deformation characteristics of the closed embankment with insulation and waterproof materials different embedment depths,the reasonable embedment depth is obtained.The purpose is to provide design basis and theoretical guidance for popularizing the roadbed in seasonal frozen soil area.The main conclusions of this paper are as follows.(1)The closed subgrade has better thermal stability.It's internal soil temperature of the subgrade unchanged.Only the temperature of the external soil temperature changed with the seasonal variation.The heat and water insulation material prevents the moving forward of the freezing front,and effectively improves the adverse effect of the temperature change at the foot of the subgrade.At the same time,under the influence of thermal insulation material,the closed roadbed freezed quickly,thawed slowly,and the low temperature area after freezing is larger.(2)At the time of freezing and thawing,the closed subgrade is less affected by the change of water,and the moisture in the soil is not changed,only the moisture redistribution of the external soil is affected by the temperature.According to the distribution of the total volume water content along the depth,the water migration phenomenon in the subgrade soil freezing process is obvious.The water content of the soil in a certain range below the freezing and thawing interface is significantly reduced,the total volume water content of the frozen soil mass increases obviously,and the maximum can reach 26.7%.In addition,moisture migration occurs not only in the freezing process of soil,but also before freezing.(3)During the freeze-thaw process,the deformation law of the ordinary roadbed and the closed roadbed is the same.After freezing,the vertical deformation at the top of the subgrade slope is larger than that at the center of the roadbed,and the top surface of the roadbed is concave.In contrast,the vertical deformation of the closed subgrade surface is significantly reduced,with a reduction of 66%.In addition,there is no frost heave at the foot of the closed subgrade,and the relative displacement of the top surface decreases significantly.This change reduces the damage caused by the uneven deformation and is beneficial to the stability of the pavement structure.After the thaw settlement,the top surface of the roadbed is convex,the maximum settlement occurs at the shoulder of the road,and the settlement of the ordinary roadbed is larger than that of the closed roadbed.(4)After a comprehensive comparison of the temperature,the ice content and the displacement of different closed embankment.it is concluded that the buried depth of the insulating water insulating material in the closed embankment should be less than 0.7m.Under this depth,the temperature field of the embankment is relatively stable,the total ice content is relatively small,the pavement deformation is uniform,the effect of the freezing and thawing cycle on the stability of the embankment is weakened,and the performance of frost thawing and thawing of embankment is effectively exerted.According to the law of water heat stability and deformation of the closed embankment,the embankment has better water thermal stability and smaller frost heave deformation.It can significantly improve the uneven deformation of the embankment's top surface freezing and thawing,and weaken the damage caused by the uneven deformation.It's a better embankment structure of freezing and thawing disease.