Study On The Frost Heave Behavior And Strength Of Coarse-grained Fillings From High-speed Railway Subgrade In Cold Region

With more and more high-speed railway across cold regions,which the seasonal frozen soil is widely distributed,many anti-frost problems influence the operation of subgrade.Among them,anti-frost heave is the basic but most important issue.In order to prevent subgrade from frost heave behaviors,series of anti-frost measures has been adopted.However,the monitoring results of subgrade of High-speed railway(HSR)showed that smoothness was deteriorated due to uneven frost heave.Therefore,in order to understand the mechanism of frost heave and the variation of strength in coarse-grained fillings to provide basis for HSR construction design and safety evaluation in cold region,this paper carry out the following work:(1)Through researching the frost heave development and its effect on subgrade in several HSR and monitoring temperature and deformation in sections of Ha-Qi HSR,it could be concluded that although the overall frost heave deformation was small,the uneven frost heave appeared very irregular,resulted in serious damages to the smoothness of subgrade(2)With coarse-grained fillings from surface layer and bottom layer in HSR in cold region,including Graded crushed rock and Group A,B soil,one-dimensional frost heave experiments with different temperature,fines content,water content,compactness and freeze-thaw cycles were carried out.Three-dimensional frost heave experiments and frost heave model experiments also were supplemented.The variation regularity of temperature in the freezing or melting process in the field of sample,freezing depth,freezing rate,the frost heave deformation and frost heave ratio in coarse-grained fillings were analyzed.It was found that in combination with certain conditions,even coarse-grained fillings can also produce a considerable amount of frost heave amount or frost heave ratio.And water content and fines content were the most important factors affecting the frost heave.(3)By applying static and dynamic load,the frost heave deformation experiments of coarse-grained filling with load were carried out.It is found that the inhibitory effect of load with frost heave on coarse-grain filling.In closed system,the amount and ratio of frost heave of coarse-grain filling under static load are the least.The amount and ratio of frost heave appeared to be larger with no load and dynamic load.In open system,the frost heave ratio of coarse-grain filling under no load is greater than under static load and dynamic load.The magnitude of load also affect the frost heave deformation and water distribution after freezing in both system.(4)Though researching the classification standard and the research methods of frost heave of coarse-grained soils at home and abroad,it could be concluded that frost heave ratio is not suitable index for high-speed railway deformation.Based on the hazards may be caused by frost heave deformation in HSR operation,maintenance standards in railway and results of frost heave experiment,this paper proposes classification scheme of coarse-grain fillings,which suitable for high-speed railway in cold region.(5)Large scale direct shear experiments of coarse-grain fillings under the condition of unfrozen and frozen had been carried out by using the direct shear experiment system.The shear stress displacement characteristics,shear strength and shear strength index changes of coarse-grained fillings with different temperature,vertical pressure,water content under were analyzed;Considering temperature,moisture content,vertical pressure,vibration frequency as factors influence dynamic characteristics,with direct shear apparatus of frozen soil,experiments of coarse grain filling were carried out with unfrozen and frozen state.The results of dynamic strength and cumulative plasticity strain with factors were compared with both states.