Study On Dynamic Characteristics Of Silty Clay Of Wetland Subgrade In Seasonal Frozen Area

With the planning of the northern traffic arteries,the road project construction is increasing with each passing day.Pavement cracks,road mud squeezing,and uneven foundation settlement often occur in seasonally frozen areas.After the seasonal frozen soil is affected by a large temperature difference,the nature of the soil is more complex,especially for some special areas.In particular,the research on some special areas is still not fully perfect.This paper selects the undisturbed soil of the roadbed under construction in the Heilongjiang wetland area to study the changes of related parameters under the action of dynamic loads.The specific contents are as follows:(1)Through foundation drilling,the original silty clay of highway subgrade is selected as the research object,and the geotechnical foundation experiment is carried out to measure the moisture content,specific gravity,and liquid plastic limit.According to the temperature change in the area where the soil sample is located,15 freeze-thaw cycles are set.Use electron microscope to scan microstructure change characteristics.Under the effects of freezing and thawing,ribs,faults,and cavities gradually appear on the surface of the structure.The pore imaging technology is used to select the representative pores,and it is found that the variation characteristics of pores with freeze-thaw action are the cone-shaped development trend towards the surrounding direction.(2)The undisturbed soil is subjected to a freeze-thaw cycle treatment,and then a dynamic triaxial test is carried out,and a sinusoidal waveform is used to simulate the traffic load cumulatively for 5000 times.The cumulative plastic strain changes with the number of cyclic loadings and the influence of different test factors on the data are studied.The concept of freeze-thaw average growth ratio is proposed;a new fitting model is proposed.Compared with the exponential model,this model reduces the degree of development of the curve with the increase of the number of cycles of loading,and is more in line with the experimental data.(3)Analyze the change characteristics of the undisturbed soil dynamic elastic modulus under the influence of different vibration frequencies,confining pressure,dynamic load,and freeze-thaw cycles,and conduct a significant analysis of the interaction of the combination of various factors,and find that the confining pressure and dynamic stress There is a restrictive relationship between them.When the confining pressure and dynamic stress increase proportionally,the test data will not be affected.Combined with the new model of cumulative strain,the relationship between dynamic elastic modulus and cumulative strain is verified according to Lagrange’s median theorem.(4)Using the graded loading method,the ultimate bearing strength of the undisturbed soil of the subgrade under dynamic load was measured,the dynamic strength attenuation ratio formula was proposed,and the exponential model was used to fit the ultimate dynamic strength after one freeze-thaw cycle,and combined The exponential model and the damage mechanics formula are used to derive the dynamic strength freeze-thaw damage prediction model,which can be used to predict the damage of the subgrade soil dynamic strength after different freeze-thaw times.