| In recent years,the development of China's highways and railways has been extremely rapid,the scale of road networks has continued to expand,and the volume of transportation has continued to increase.China's road and railway construction has entered a new stage.The roadbed filler is exposed to the natural environment and undergoes at least one freeze-thaw cycle every year.Under strong melting and freezing,the roadbed is prone to weakening,fouling and other diseases,which seriously affect the normality of roads and railways.Operational and driving safety.With the construction of highways in seasonally frozen areas,the requirements for the overall stability of the roadbed,the smoothness of the roadbed and the freeze-thaw resistance of the roadbed fillers are constantly increasing.Due to the complicated changes in geological conditions along the highway,some roadbed fillers cannot be directly applied,and it is unlikely to use high-quality fillers.Therefore,it is important to use the near-soil and improve the soil with poor mechanical properties while satisfying the freeze-thaw resistance.On the basis of summarizing the research status of lime-modified soil in the seasonal frozen area at home and abroad,the deformation characteristics,strength characteristics and microscopic characteristics of lime-modified soil under the freeze-thaw cycle were studied experimentally.The research results will provide reference for the selection of lime content in the lime-cured soil in the seasonal frozen area,and provide a basis for the determination of the mechanical properties of the subgrade soil and the freeze-thaw resistance performance index.The main content of the paper is as follow:1.Routine physical property index test and CBR test of lime-modified soilIn this paper,five different types of lime-modified soils were selected.First,theV physical properties of five kinds of lime-modified soils were determined,including water content,particle analysis,boundary moisture content,optimum moisture content and maximum dry density.After the 0-time and 6-time complete freeze-thaw cycles were carried out on the samples under the optimum moisture content,the CBR test was carried out to obtain the CBR values of the five different lime-modified soils before and after freezing and thawing.The results showed that before and after freezing and thawing,the CBR value of 6% lime modified soil was the largest compared with that before the improvement.The lime-containing 6% lime-modified soil has the least loss during the 6 freeze-thaw cycles.The lime-modified soil with6% lime content is tightly connected between the soil particles before freezing and thawing,and the soil particles are destroyed after freezing and thawing.The smallest.Therefore,for the optimum lime content of cohesive soil with Ip>20,6% can be used as a reference value.2.Experimental study on static triaxial compression of lime-modified soil after freeze-thaw cycle.In the state of optimum moisture content and optimum moisture content ± 5%,the lime-modified clay with the lime content of 0%,2%,4%,6% and 8% is prepared,and the number of cycles of the freeze-thaw cycle test is selected as 0.1,2,3,4,6,8,10 times,the sample that reached the freeze-thaw cycle was taken out for static triaxial test.The results show that under the condition of less than 6% of lime,the cohesive force of lime-modified soil increases with the increase of lime content.The cohesion of lime-added soil is more than 6%.Reduced.The lime-modified soil with a lime content of 6% has the least fluctuation in the percentage loss compared to the cohesion force in the unfrozen-thaw state after each freeze-thaw cycle.The lime-modified soil with a lime content of 2% has the greatest fluctuation in the percentage loss compared with the cohesion force in the freeze-thaw state after eachVI freeze-thaw cycle.The higher the water content of lime-modified soil,the smaller the cohesive force,the smaller the internal friction angle and the smaller the shear strength.Under the same confining pressure and the same number of freeze-thaw cycles,the shear strength increases with the increase of lime content.The increase is the highest in shear strength when the lime content is 6%.3.Study on static and dynamic modulus of lime-modified soil before and after freezing and thawing cyclesThe triaxial compression test data of all the test pieces were processed,and the straight line segment was selected on the deviatoric stress-strain curve,and the linear slope was the elastic modulus by straight line fitting.When the water content is Wopt,the number of freeze-thaw cycles is constant,and the static modulus of elasticity increases with the amount of lime,which increases first and then decreases.The static modulus of elasticity is the largest when the lime content is 6%.When the lime content is 6%,the number of freeze-thaw cycles has the least influence on the static elastic modulus.When the water content is Wopt+5%,the number of freeze-thaw cycles is certain,and the static elastic modulus increases with the increase of lime content.After the trend of reduction.The static modulus of elasticity is the largest when the lime content is 4%.The dynamic strength characteristics of lime-modified soil with 0% and 6%lime were tested.The results show that when the water content is Wopt,the dynamic elastic modulus of 6% of lime content is less than that of lime-modified soil with 0%lime content.After the freeze-thaw cycle,the skeleton between the particles is destroyed,and the dynamic elastic modulus of the lime-modified soil decreases with the increase of the number of cyclic loadings.After 4 freeze-thaw cycles,the dynamic elastic modulus of lime-modified soil with 6% lime content is almost unchanged.4.Microstructure analysis after lime-modified soil freeze-thaw cycleThe same batch of test pieces using static triaxial test,after 0,1,4,and 8freeze-thaw cycles,the microstructure images of different freeze-thaw cycles were extracted by electron microscope,and Image-Pro Plus(IPP)software was used.The microscopic images were processed and the selected microscopic parameters were measured.The results showed that the lime-modified soils with 0%,2%,4%,and 6%lime-modified soils increased the agglomeration of lime-modified soils after undergoing freeze-thaw cycles.After the lime-added 8% lime-modified soil experienced a freeze-thaw cycle,the agglomeration was generally weakened.With the increase of the number of freeze-thaw cycles,the average particle size of soil samples with 0% and 2% lime content increased and the average pore diameter decreased.The average particle size of lime-modified soil with 4%,6%,and 8% lime content was basically reduced,and the average pore diameter was basically increased.Under the action of freeze-thaw cycle,the particle size distribution of lime-modified soil is uneven,and the difference in abundance is small.The number of freeze-thaw cycles is certain.With the increase of lime content,the surface fractal dimension is basically reduced.5.Macromechanics and microstructure analysis of lime-modified soil before and after freezing and thawing cyclesThe relationship between macroscopic mechanical properties and microstructure was analyzed by grey correlation method.The results show that when the water content is less than or equal to the optimum water content,the incorporation of lime mainly improves the cohesion,thus improving the shear strength of the improved soil.When the water content is large,the amount of lime has an effect on the cohesion and internal friction angle of the modified clay.The effect of lime content on the elastic modulus increases with increasing water content.Under the optimal moisturecontent state,the number of freeze-thaw cycles has the least influence on the static elastic modulus when the lime content is 6%.The correlation between the cohesion of lime-modified soil and the fractal dimension of particle size is calculated by the grey correlation method.The cohesion is positively correlated with the fractal dimension of the particle size.The incorporation of lime mainly changes the cohesive force by changing the content of the fine particles.The smaller the cohesive force,the smaller the water content of the microparticles.The cohesive force was positively correlated with the microparticle content;the internal friction angle of lime-modified soil was the most correlated with the average particle size,and the internal friction angle of lime-modified soil was negatively correlated with the average particle size. |
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