Study On The Mechanical Characteristics And Deformation Prediction Of Subgrade Fill Under The Action Of Freeze-thaw

The Qinghai-Tibet Plateau and regions of China are the main distribution areas of frozen soil.In recent years,the construction speed of highways in permafrost regions in China is gradually accelerating.However,due to the fact that permafrost is prone to produce obvious freeze-thaw changes with temperature rise and fall,the roadbeds in permafrost regions suffer from freezing,thawing and other diseases serious.As the temperature changes periodically,the subgrade continuously undergoes a freeze-thaw cycle,resulting in a new arrangement and structural connection of the soil particles in the subgrade fill and the active layer,thereby changing the mechanical properties of the soil.At the same time,the construction activities of the highway changed the water-heat balance inside the frozen soil,causing a rise in the internal temperature of the frozen soil and an increase in the upper limit of the frozen soil,which affected the stability of the roadbed.This article studies the development trend of subgrade filling mechanical properties in permafrost regions and the prediction of future deformation of subgrade.The conclusions are as follows:(1)Through the consolidated undrained triaxial shear test(UU test),the effects of moisture content,confining pressure,and number of freeze-thaw cycles were studied,and the single-factor freeze-thaw cycles were analyzed for failure strength,stress-strain curve,elastic modulus,and Influence of shear strength index.The results show that:under the action of freeze-thaw,the stress-strain curve of the soil will not change the reflection form,the elastic modulus and the failure strength will reach the minimum after 7 freeze-thaw cycles,and the cohesion of the soil will continue to decrease.The effect of freeze-thaw cycles on the internal friction angle is not significant.(2)Based on the orthogonal test,using intuitive analysis method and analysis of variance,the influence factors such as freezing temperature,freezing and thawing times,compaction degree,confining pressure and water content and their interactions were studied.Significance.The results show that the compaction,water content,and interaction between confining pressure and freezing temperature have the most significant effect on the mechanical properties of the fill.(3)Through the indoor frost heave and thaw settlement test,the variation law of soil thawing coefficient and frost heave rate under different water content,dry density and load conditions are analyzed,and the prediction models of stable frost heave ratio and stable thawing sink coefficient are established.The results show that the thawing settlement coefficient and frost heave rate increase linearly with the increase of water content.The frost heave rate increases with dry density and then decreases first,and decreases linearly with the increase of load.The change in sink coefficient is the opposite.(4)By establishing a coupled model of frozen soil water and heat considering the dynamic equilibrium relationship between pore ice content,negative soil temperature and water migration,the distribution characteristics of subgrade temperature field in permafrost region were studied,and combined with stable thaw settlement coefficient and stable frost heave The research results of the rate predict the long-term deformation of the roadbed.The results show that the cumulative deformation in the center of the subgrade within 15 years is 101mm,and the cumulative deformation of the shoulder is 97mm.The long-term deformation of the two is basically the same.