Deformation Characteristics And Numerical Analysis Of Subgrade Soil Under Freezing And Thawing Cycle

In order to study the frost heaving characteristics of the subgrade soil in the northeast seasonal frozen area and the effect of different freeze-thaw cycles on the long-term stability of the subgrade,the subgrade soil of a highway section in Jilin Province was used as the research object,and basic physical and mechanical tests,frost heave test and creep test under different freeze-thaw cycles were carried out on the sample soil.The grading test,limit water content test and compaction test were carried out on the test soil samples to obtain the liquid limit,plastic limit,optimal water content,maximum dry density and other parameters of the soil samples.This provided basic indicators for subsequent frost heave tests and creep tests.Considering the axial deformation and radial deformation of the test soil samples,the frost heaving characteristics of the soil samples were described by linear frost heaving rate and volume frost heaving rate,respectively.The effects of different freezing temperatures,different water contents,and different compaction degrees on the frost heave index of soil samples were analyzed,which laid the foundation for the subsequent establishment of the relationship between three factors and the characteristics of frost heave.Considering that the deformation of frozen soil is not only the transient deformation of vehicle loads,most of the deformation of frozen soil was based on the creep deformation under long-term load.Therefore,the creep deformation law of soil samples under different freeze-thaw cycles,creep Poisson's ratio,creep rate,isochronous stress-strain curve,etc.This would further understand the creep characteristics and failure characteristics of frozen soil after different freeze-thaw cycles.Finally,numerical calculations were performed for 7 times of freezing and thawing cycles,and the stress-strain variation trend of the soil sample model was analyzed.The comparison analysis between the numerical calculation curve and the test curve was used to predict the deformation characteristics of the actual soil sample.The main conclusions were as follows:(1)The influence of water content and freezing temperature on the subgrade soil in the depth direction was much greater than that of compaction.At the same time,the degree of compaction had a certain law to follow in the depth direction,but the freezing temperature and water content could not directly predict its change law in the depth direction.(2)Under the action of moderate stress,after a period of decay creep,the creep rate of frozen soil will not decay to zero.On the contrary,when the creep ratedecreases to a certain value,it will remain unchanged,and a straight line segment of stable creep will appear in the creep curve.Taking the freeze-thaw cycle 5 times as an example,when the stress level is 42 kPa,there is only attenuation creep in frozen soil.When the stress level increases to 50 kPa and 59 kPa,the frozen soil will stabilize and accelerate the creep deformation.(3)The instantaneous creep of frozen soil will also reduce the proportion of total creep.After 7 freeze-thaw cycles,under the first load of 40 kPa,the instantaneous creep was 0.0263%,and the final creep was 0.0281%,which accounted for about93.59%.When the third-level load is applied,the instantaneous creep is 0.172%,and the final creep is 0.0189%,accounting for about 91.01%.By the time of the final load,the instantaneous creep was 0.233%,the final creep was 0.0318%,and the proportion was about 73.27%.(4)The vertical stress cloud diagram under the effect of the initial stress showed more obvious stratification.At a certain point,the horizontal node displacement cloud map gradually expanded outward,forming a ring-shaped change law that diverges outward.The change of the cloud image presented by the lower model was roughly consistent with the change of the actual initial stress.The vertical stress cloud diagram showed obvious horizontal layering characteristics.The maximum vertical stress of the model was at the foot of the embankment,and its maximum value was about 0.4MPa.Its distribution characteristics were basically consistent with the actual monitoring situation,which showed that the calculation results of establishing the roadbed model were more reliable.