Study On The Influence Of Dynamic Load And Freeze-thaw Cycle On Deformation Of High-speed Railway Subgrade In Seasonally Frozen Soil Region

The variation mechanism of stress and deformation in subgrade soil of high-speed railway in seasonal frozen soil area is particularly complex under the interaction of temperature change,repeated freeze-thaw cycles and repeated train vibration and impact.At present,the research results of roadbed settlement and deformation are mostly focused on static load or ordinary train.The study of roadbed deformation under dynamic load and freeze-thaw cycle is not yet mature.This paper takes Harbin-Dalian high-speed railway project as the research object,refers to the predecessor's research on the design characteristics and working characteristics of frost-proof layer of Railway Subgrade in seasonal frozen zone,according to thermodynamic theory,adopts coupled thermo-hydrodynamic analysis model(flow deformation)numerical model,uses PLAXIS finite element software to realize THM(hydro-thermal coupling)numerical simulation analysis of subgrade soil,and uses PLAXIS software.The HSS constitutive model(hardening model of small strain soil)provided by this paper is used to study and analyze the temperature distribution and settlement deformation of high-speed railway subgrade under freeze-thaw cycles,taking into account the changes of temperature,frost heave rate of subgrade fillers and thermal conductivity of anti-freezing layer.On this basis,PLAXIS dynamic simulation and time-history analysis are used to study the residual deformation and final settlement deformation of frozen ground under freezing and thawing conditions,calculate the final settlement of roadbed under dynamic load,and analyze the settlement deformation law of frozen soil roadbed under dynamic load and freeze-thaw cycle.This paper mainly achieves the following results:(1)The influence of temperature in the formation is attenuated as the depth of the soil deepens.The maximum thickness of the ice layer in the soil is between the lowest temperature and the freezing temperature date.The thermal conductivity of the anti-freezing layer of the railway subgrade will affect the thickness of the ice layer of the subgrade.The thickness of the icing under the anti-freezing layer is significantly smaller than that of the two sides.Therefore,rational design of the anti-freezing layer can effectively control the freezing and thawing state of the subgrade soil.The thickness of the ice layer of the soil is determined by the combination of temperature changes,temperature in the depth of the formation,thermal conductivity of the formation and the basic structure.(2)As the temperature decreases,the high railway foundation will undergo subsiding.When the temperature reaches the lowest in the year,the settlement of the high railway base reaches a steady state.As the temperature rises above the freezing point,the icy layer of the subgrade will gradually melt from top to bottom,and then the high railway base will thermally expand.The specific settlement and rebound amount of the high railway foundation is obtained through numerical analysis,which provides a reference for the design of railway subgrade engineering.(3)Applying traffic load to the roadbed soil in the icing state and the melting state respectively,and analyzing the influence of the ice layer of the roadbed soil on the stiffness of the soil.The results show that the stiffness of the roadbed soil is larger under icing conditions.According to the machine factor,the stiffness of the subgrade soil is even increased by about 1 times,indicating that the THM numerical model can fully consider the influence of the physical state on the mechanical state.(4)Perform a variable analysis on the thermal conductivity of the anti-freezing layer of the subgrade soil(see Figure 3.11).The specific laws are as follows: the thermal conductivity of the anti-freezing layer is increased from parameter 1 to parameter 2,and the thickness of the ice layer in the subgrade is reduced by 14%.The maximum settlement value of the subgrade is reduced by 10%,and the subgrade rebound is reduced by 33%.However,if parameter 1 is raised to parameter 3 and parameter 4,the antifreeze effect is significant attenuated.in the antifreeze design of the roadbed soil,a material with certain thermal insulation properties can be used as the antifreeze layer.(5)Under the dynamic load of train,there is no significant difference in residual deformation between icing and melting.This is because the thickness of the icing layer is small relative to the entire subgrade and foundation depth,and has little effect on residual deformation..For the settlement peak in the dynamic loading time of high-speed rail,the settlement of the subgrade at low temperature is 2.5%~6.0% smaller than that of the high temperature state.This is due to the increase of the stiffness of the subgrade soil due to the presence of 1m thick ice layer at low temperature.The surface ice layer of the subgrade soil will increase the stiffness of the subgrade soil and cause the stress concentration of the subgrade soil below the railway track.The curve results show that the dynamic stress changes by no more than 100 kPa,in line with the specifications.(6)Repeated application of train load by numerical simulation,analysis and obtain residual settlement of railway subgrade,and calculate the cumulative settlement law according to the calculation method of cumulative plastic deformation under repeated load of train.Through the above methods,the cumulative settlement of 14.8 mm can be obtained,which meets the requirements of subgrade settlement design specifications and provides reference for the design of railway subgrade engineering.