Study On Frost Heave Characteristics And Treatment Methods Of Subgrade In Seasonal Frozen Soil Area

Based on the research on freezing injury of seasonal railway subgrade,based on the railway subgrade in the West Lattice of Qinghai-Tibet Railway,the paper analyzes the main causes of the freezing damage of the railway subgrade in Xige section from the factors of temperature,soil and water.Taking typical soil samples 224 and 221,the indoor frost heaving test was conducted to study the relationship between frost heave and temperature,moisture,salinity and compaction degree.The formulas were fitted and the existing railway line Frost Heave Prediction Model of Subgrade and Frost Heave Prevention Model of Newly Built Railway Subgrade.Filling model and inlet frost heaving model tests were conducted indoors to analyze the variation of temperature,displacement and salt under the action of freeze-thaw cycles,and to verify the effect of salt injection method to treat subgrade freezing damage.The main conclusions of this paper are as follows:(1)Select the Xining-Golmud section of the Qinghai Tibet Railway typical scene digging and lots of frozen soil sample for indoor soil test.The main reason for the frost damage of the subgrade is that the shallow soil is silty clay,the content of the clay particles is larger and the water content is high.When the temperature is lower than the freezing temperature,the moisture in the soil is frozen and the rail surface is raised.Whether it is the new subgrade or the old subgrade,whether it is the thicker subgrade or the shallow Subgrade of the cushion,the frost damage of the subgrade of the Sieger section mainly occurs in the shallow layer,which belongs to the shallow frost damage.Temperature and salt content have a significant influence on the frost heave rate of subgrade soil,and water content has a significant influence on the frost heave rate of subgrade soil,and the interaction between the degree of compaction and the four factors has no significant influence on the frost heave rate.The main and secondary order among the four factors is temperature > salt content > water content > compaction degree.(2)Taking into account the four factors of moisture,salinity,temperature and degree of compaction,a small indoor frost heave test is carried out to get the frost heave rate of soil samples under different conditions.The frost heave ratio of soil under six kinds of salt and three compactness is comprehensively compared.When the moisture content is small,the compaction degree has great influence on the soil sample,and the influence is relatively weak when the water content is large.The salt content is lower than 1%,with the increase of the degree of compaction of frost heaving ratio increases,when the salinity is 2%,frost heaving ratio did not change with the degree of compaction and changes,further increase the amount of salt and frost heaving ratio increases with the degree of compaction will decrease,to control the Subgrade Frost damage need to control major the influence factors,each factor is controlled in a reasonable range,will maintain a relatively slow growth rate of frost.(3)The subgrade model is filled in the frozen soil model box;the ordinary test section and the salt injection test section are set up to monitor the displacement,temperature and salt.The overall trend of the different positions in the subgrade is consistent,and according to the law of cosine curve,it is consistent with the ideal control temperature.With the increase of depth,the temperature increases and the temperature fluctuates greatly.The closer to the slope,the closer to the cold end,the greater the temperature fluctuates.With the change of temperature,the subgrade soil presents a small range of periodic frost heave and thaw settlement.With the accumulation of time,the roadbed soil shows a certain settlement and consolidation.In the period of temperature variation,there is a regular variation rule.When the temperature is lower than a certain value,the frost heave starts.When the temperature is higher than a certain value,it begins to thaw,and the maximum value of frost heave and the maximum value of thaw settlement appear at the highest temperature and the lowest temperature.The maximum amount of frost heaving ordinary test section is 0.4mm,maximum amount of frost heaving salt note for the experimental section of 0.075 mm,after injecting salt subgrade soil frost heave decreases by 81.25%,indicating the subgrade soil after artificial salinization,can effectively restrain the frost heave of subgrade soil,the Subgrade Frost damage by injecting salt method is feasible.The effect of temperature on the migration of salt is very small and can be ignored.In closed environment,the salt does not migrate basically.(4)Salt injection is carried out at the site and the effect of salt injection is monitored.Through the monitoring data,it is known that salt injection is effective and feasible for seasonal subgrade disease.The frost heave of the four monitoring and salt injection sections is 45%,48%,47% and 175%,respectively,and the average decrease is 78.8%,compared with the non salt injection section.(5)According to the data of the small Zhang boss frost heaving test,fitting water frost heaving ratio and temperature,rate and the relationship between salt content,degree of compaction,and its verification.On the basis of the fitting formula,the forecast model of the existing line base frost heave and the prevention model for frost heaving and frost heaving of the newly built subgrade are put forward.At the same time,the frost heaving prediction model based on BP neural network is established and verified.