Study On Frost Heave Effect Of Low Liquid Limit Silt Fillers In Seasonal Frozen Areas Based On Stress Release Hole

The frost damage of railway subgrade engineering in seasonal frozen soil area has always been an important factor affecting the normal operation and safety of railway lines.Various treatment measures have certain conditional applicability because of the uneven frost heave deformation of subgrade soil.In this paper,the subgrade filler at K222+700?K223+300 section of Shenmu-Shuozhou railway is taken as the research object,and a new idea of applying stress release hole to alleviate frost heave of soil is proposed innovatively.Combining with on-site data collection,laboratory test and numerical simulation,the basic geotechnical test of the filler soil was carried out,and its basic geotechnical characteristics and elastic modulus parameters of the filling material were determined.The influence of initial water content,compaction coefficient,hole ratio,type and proportion of filling material on frost heave characteristics of filler soil was studied through indoor unidirectional freezing column tests under different water supplement conditions.The hydro-thermal full-coupled model and frost heave model of soil column were constructed,and then the effects of hole ratio,depth and elastic modulus of filling materials on relieving frost heave deformation of soil columns werecompared and analyzed.The main conclusions of this paper are as follows:(1)The subgrade filler in this section is sensitive to frost heave,and the frost heave fluctuates greatly in winter.According to the results of basic geotechnical tests,it is considered that the filler belongs to a low-liquid limit silt with poor gradation,its optimum moisture content and corresponding maximum dry density are 14.4%and 1.886g/cm3 respectively.The elastic modulus of the filler soil is about 5-10 times that of the filling material.(2)The cooling process of soil samples is characterized by obvious stages,and the change of temperature field is less affected by stress release holes.The development trend of frozen depth of soil samples is basically the same,and the maximum frozen depth value increases with the increase of hole ratio.(3)Under the condition that there is no filling material in the stress release hole,the development of frost heave deformation of soil samples shows a trend of rapid,transitional and stable phase changes.In this process,about 70%to 90%of the frost heave deformation occurs in the early stage of rapid frost heave.Stress release holes have a significant effect on relieving frost heave of soil samples,which can effectively reduce the occurrence of frost heave deformation by more than 50%.The distribution trend of water content in soil samples is basically the same,but stress release holes will affect the migration path of water content in soil to a certain extent.(4)When there is filling material in the stress release hole,there is a small stage of deformation development in the early stage of frost heave,lasting for about 16 hours,and the frost heave deformation is only 36.8%?65.3%of that in the conventional frost heave.When the depth of filling material is close to the water level,the water migration effect will be aggravated,which indicates that the value of the depth of filling material needs to be strictly considered,and it is recommended to control the depth of filling material above the water level.Among the two types of filling materials selected in the paper,the effect of the filling material of rubber skeleton(R series)is superior to that of polystyrene skeleton(P series)in decreasing frost heave of soil samples.(5)When the stress release hole ratio of soil column is about 3%,it can play a more effective role in relieving frost heave deformation.When the hole depth is less than and close to the frozen depth of soil column,the effect of stress release hole on relieving frost heave is the best.When the elastic modulus of filling material in the hole is about 1/4-1/2 of the elastic modulus of soil column itself,the effect on releasing frost heave deformation of soil column is better,also,the influence on the overall strength of soil column is relatively small.The research results can provide technical and theoretical reference for relieving the frost heave of silt filler in seasonal frozen soil area.