Mechanical Model And Numeircal Prediction On Deformation Of Soil Under The Action Of Frost Heave

The environment has an impact on the physical state and mechanical property of soil.The periodic freeze of soil in the seasonally frozen soil region due to the temperature variation is typical of the change of soil form.The soil freezes when the temperature drops below freezing temperature.The frost action of soil intuitively changes the form and mechanical property of soil.The laboratory tests and field observations show that the frost action doesn’t reduce the strength and stability of soil,but may cause excessive deformation.The adverse effects of frozen silty clay lift the superstructure and cause potentially serious damage on soil and superstructure.The nonuniform deformation of the base of superstructure will cause larger additional stress and possible damage.Therefore,the frost action of soil is one of the main causes of the damage of infrastructure in cold region.The problems of the law of frost heave developments and deformation prediction for silty clay during soil freezing in seasonally frozen soil were investigated.The law of frost heave developments and its influence factors were also discussed using the method of the laboratory test,theoretical analysis and numerical simulation.The main content and understandings are listed as follows:Firstly,based on the characteristics of seasonally frozen soil during the frost heave process,the freezing heave test in open-system under step cooling temperature was performed.The effect of overburden stresses was also considered.The distribution rule of temperature field,the development rule of frost heave process,and their effect factors were also discussed based on the experimental results.Combination with the frozen fringe theory,a frost heaving layering method was developed for saturated silty clay.Subsequently,the correlation between freezing rate and temperature gradient was evaluated.The Takashi’s model for predicting the the frost heave ratio of saturated silty clay was modified.The the freezing rate parameter was replaced by the temperature gradient parameter in this modified model.The research illustrated that the overburden stress played an inhibiting role in the water flow of freezing soil and had little impact on the temperature distribution.The amount of frost heaving in the specimen surface during soil freezing was accumulated by the amount of frost heaving in first soil layer to the third soil layer.The results of forecast model of frost heave rate for saturated silty clay were in good agreement with that of experimental measurements.Then,the governing equations（energy conservation equation,mass conservation equation,and correlation equation）of water-thermal coupling for frozen soil were established based on the experiment of the soil water characteristic.Frost heaving test for saturated silty clay was simulated by the finite element software Abaqus.The coupled heat and moisture transfer during soil freezing was also considered in this study.Furthermore,the calculated results are in good agreement with the experimental measurements throughout the test,showing the correctness of the water-thermal coupling theory.Secondly,the mechanical model of saturated silty clay during soil freezing in k₀ state was established based on the results of one dimensional frost test for saturated silty clay.Also,the incremental non linear elastic theory and the concept of the biggest frost heaving force were used in this mechanical model.Mechanical model of saturated silty clay during soil freezing in general stress state was obtained with further revision and development.Thirdly,a one-dimensional analytical mechanics model for the frost-heave deformation of horizontal ground was established using the frost-heave mechanics model in k₀ state from the point of view of engineering.This model well predicts the stable stress field and strain field,and analyzes the influence factors of frost-heave force and deformation of soil surface,after freezing process with different boundary of load and displacement.This research shows that the frost-heave deformation of ground surface decreases with the increase of the initial loading on the surface,and increases with the cooling temperature.Finally,based on the aforementioned frost heave tests in laboratory and empirical prediction model on frost heave of saturated silty clay,a hydro-thermal-stress indirectly coupled numerical model of the freezing process of the saturated silty clay was developed with unsteady state temperature control equation,water migration control equation,and stress-strain control equation considered,which takes the phase change into account.This model can be used to solve heat transfer,seepage and deformation with unsteady state characteristics of model parameters.It can simulate the freezing process of the saturated silty clay under step by step cooling.The numerical model was validated with the soil frost heave test results in laboratory.At last,a symmetric model considering different overburden pressures was constructed to research the evolution rules of frost heave of a typical subgrade in seasonal frozen region.