Study On Mechanical Properties And Microscopic Mechanism Of Improved Clay Under Freeze-thaw Cycles

In recent years,with the continuous growth of China’s comprehensive strength,the construction of highways and railways has been carried out.In road engineering construction,soil is an unavoidable engineering material.Jilin Province belongs to the seasonal freezing area,and most of the province is clay,clay roadbed under the action of freeze-thaw cycle,road often appear various diseases,seriously affecting traffic safety.The use of lime to improve the clay can improve the mechanical properties of the soil,and this paper conducts mechanical experiments on lime improved clay under the action of freeze-thaw cycle.In order to explore the mechanical properties and microscopic mechanism of lime-improved clay under freeze-thaw cycle,five kinds of lime content improved clays were selected in this paper,0%,1.5%,3%,4.5% and 6%,and the optimal moisture content(WOPT)and ±2% WOPT control moisture content conditions were prepared,and the freeze-thaw cycle times were selected 0,1,2,4,6 and 8 times.The effects of lime content and freeze-thaw cycle on soil static and dynamic parameters were obtained by freeze-thaw cycle test,static triaxial test and dynamic triaxial test.The microstructure image was obtained by electron scanning microscope,and the microstructure parameters of the soil were quantitatively analyzed,and the correlation degree between the microscopic parameters and the macroscopic mechanical parameters was explored by using the gray correlation method.The specific work of this article is as follows:(1)Through the static triaxial test,the change law of shear strength,cohesion and internal friction angle with lime content,moisture content and freeze-thaw cycle times was obtained.It is found that the freeze-thaw cycle will reduce the cohesion,internal friction angle and shear strength,and the incorporation of lime will increase the optimal moisture content of the soil,and when the lime content is 4.5%,the improved soil has the best resistance to freeze-thaw cycle.(2)Through the dynamic triaxial test,the variation law of the dynamic elastic modulus,dynamic shear modulus and damping ratio of the soil with the number of freeze-thaw cycles and loading cycles of the improved soil with 4.5% lime content was studied under the action of freeze-thaw cycle.The results show that the dynamic elastic modulus,dynamic shear modulus and damping ratio decrease with the increase of the number of freeze-thaw cycles.(3)Microscopic photos of soil samples were taken with the help of scanning electron microscope,and microscopic photos were graphically processed and relevant parameters of microstructure features were extracted through Image-Pro Plus 6.0.The distribution of structural elements,average particle size,abundance(flatness),fractal dimension and directional probability entropy were selected as representatives of microstructure characteristics,and the effects of lime content and freeze-thaw cycles on the microstructure of lime-improved clay were studied and analyzed.Studies have found that the freeze-thaw cycle makes soil particles loosely distributed.The reaction between lime and soil causes soil particles to develop in an equiaxial direction,and the destruction of soil by freeze-thaw cycle also leads to greater abundance,and particles and pores develop in an equiaxial direction.Under the same lime content conditions,the fractal dimension of lime-improved clay decreased first and then increased with the increase of freeze-thaw cycles.The directional probability entropy of lime improved clay increases with the increase of freeze-thaw cycles,and the incorporation of lime can slightly delay the time when the directional probability entropy of improved clay is affected by freeze-thaw cycles.