Study On The Frost Heave Characteristics Of Railway Filling Roadbed In Seasonal Frozen Areas

With the rapid development of China’s railway industry,multiple railways in the seasonal freezing zone are currently in operation and construction.Although some railways have taken measures to prevent frost heave,railway lines still experience varying degrees of frost heave.This article mainly focuses on the deformation law of the roadbed near the Chagan Lake Station in Songyuan,Jilin Province during filling and frost heave.By numerical simulation,the settlement characteristics during the layered filling process of the Chagan Lake station roadbed were studied.Considering the freeze-thaw cycle effect on roadbed models with different filling heights,a systematic study was conducted on the frost heave law of railway roadbed,as well as the temperature field and frost heave displacement field caused by the frost heave effect.The main research content includes:During the layered filling process of the roadbed,as the filling height increases,the settlement gradually increases,while the increment gradually decreases.The maximum settlement at the center of the line is 15.112 mm,and the settlement on both sides will gradually decrease as the distance from the center of the line increases;After layered filling,the horizontal displacement of the soil is relatively small compared to the vertical displacement.As the filling thickness increases,the horizontal deformation of the roadbed bed increases,and the horizontal displacement direction of the soil on both sides of the roadbed faces away from the centerline of the line;For soft soil roadbed,adding mixing piles to the foundation soil to reinforce the soil will significantly reduce the settlement.When the filling height is larger,the increase in the thickness of the reinforcement area has a greater impact on the post construction settlement.At different filling heights,the maximum freezing depth of the soil occurs in mid April.As the filling height increases,the freezing depth line will also rise at the maximum freezing depth,and the maximum freezing depth values for different filling heights are not significantly different.At a filling height of 2.5m,the soil exhibits a freeze-thaw process in which the freezing process develops from top to bottom of the surface soil,while the melting process occurs simultaneously from top to bottom of the surface soil and from bottom to top of the deep soil.This characteristic is called "unidirectional freezing,bidirectional melting";Compared to miscellaneous fill soil,weak frost heave soil is less affected by temperature during the same period,which will make the freezing depth of some soil layers in weak frost heave soil smaller;The cold energy in the soil undergoes a certain hysteresis in the process of transferring downwards to the interior of the soil layer,resulting in the maximum freezing depth occurring at the end of March.The maximum freezing depth of the soil near the roadbed is 1.35 m.The results of the thermal coupling analysis show that the frost heave changes with time at different filling heights,increasing first and then decreasing.The maximum frost heave at the center of the line varies,and the higher the filling height,the smaller the maximum frost heave.The development of frost heave and frost depth is mainly divided into three stages: the first stage is a rapid development period,during which the frost heave deformation increases rapidly;The second stage is a stable development period,where the amount of frost heave and depth show a stable development phenomenon,lasting for a long time until the maximum freezing moment;The third stage is the rapid melting period,during which the vertical displacement decreases rapidly and the duration is relatively short.