Experimental Study On Strength Deterioration And Microscopic Mechanism Of Loess Under Freeze-Thaw And Salt Interaction

With the increasing construction of loess area,the shallow soil exfoliation disease of loess slope has attracted much attention.The freeze-thaw and salt erosion are the important factors that cause the loess slope to peel off.Therefore,the study on the strength degradation of loess by freeze-thaw-salt interaction The microscopic mechanism is of great significance.In this paper,the freeze-thaw cycle test,the triaxial compression test,the scanning electron microscopy test and the nuclear magnetic resonance test were used to study the strength degradation and microstructure change of the loess by freeze-thaw-salt.The main work and results are as follows:(1)Through the indoor freezing-thawing cycle test and the triaxial compression test,the changes of the stress and strain curves of loess were studied by freeze-thaw and salt interaction.The results show that the stress-strain curves of the samples are hardened under different conditions;The peak intensity of the stress-strain curve decreases with the increase in the number of cycles and the increase in salt content.(2)Through the analysis of the stress-strain curve of the sample,the freeze-thaw-salt interaction was studied to study the strength deterioration of loess.The research shows that the cohesive force of the undisturbed soil decreases linearly with the increase of salt content,and the internal friction angle varies with salt.The increase of the amount increased linearly,and the increase was not large.The maximum increase was 1.0.80.The cohesive force of undisturbed soil decreases exponentially with the increase of the number of freeze-thaw cycles,and the internal friction angle increases with the increase of the number of freeze-thaw cycles.The amplitude is not large,the maximum increase is 1.44°;the change law of remolded soil is the same as that of undisturbed soil,and the variation is smaller than that of urndisturbed soil;the equation of strength deterioration of loess under the action of freeze-thaw and salt is obtained.(3)Scanning electron microscopy(SEM)experiments were carried out to study the changes of micro-parameters of loess with freeze-thaw and salt interaction.The results show that as the number of freeze-thaw cycles increases.,the average particle size increases,the particle size distribution decreases,and the particle abundance When the salt content increases,the average particle size increases,the particle size distribution dimension increases,the particle abundance decreases,and the orientation probability entropy is basically unchanged.(4)Through the nuclear magnetic resonance test,the effects of freeze-thaw-salt interaction on the micropore characteristics of loess were studied.The results show that the T2 spectrum of the soil samples after freezing-thawing-salt shows two peaks,with the increase of the number of freeze-thaw cycles.The total area of the T2 spectrum increases,and the total amount of soil pores increases,showing a logarithmic growth type.As the salt content increases.,the total area of the T2 spectrum increases,showing a linear growth type,the T2 spectrum distribution shifts to the right,and the micropores are small.Hole transformation;the change of soil cohesive force is mainly related to the change of soil particle size and the arrangement of soil particles.The change of internal friction angle is mainly related to the change of pore number and particle shape.