Study On Physical Properties And Shear Characteristics Of Saline Soil Improved By Lime Silica Fume Under Freeze-thaw Cycle

Songnen plain area belongs to seasonal frozen soil area,and there are a lot of saline soil in this area.The special climatic conditions and hydrogeological environment lead to more and more serious salinization in this area.In this paper,the carbonated soil in Zhaodong area of Songnen Plain is taken as the research object.Firstly,the physical properties of the callie-silica-lime modified saline soil in this area are studied under the freeze-thaw cycle,including the limit water content test,the electrical conductivity test and the frost resistance test.By setting the number of freeze-thaw cycles,the amount of lime and silica fume and changing the vertical load,the shear properties of the improved saline soil were studied to explore the changes of mechanical properties under the influence of various factors,and the influence mechanism of the lime fume improvement under macro conditions was analyzed.Grey correlation analysis method was used to explore the correlation degree of each influencing factor to the shear strength of improved saline soil,and multiple linear regression model was established based on SPSS to analyze the functional relationship between the influencing factors of shear strength.The prediction model of shear strength under four influencing factors was constructed by MLP multilayer perceptron.The importance of each factor was analyzed and the difference between the detection model and the actual situation was analyzed.The results show that:(1)With the increase of lime content,the liquid limit and plastic index decrease,the plastic limit,shear strength,cohesion and internal friction Angle increase,the soil conductivity increases obviously,and the mass loss decreases continuously.(2)With the increase of wollastonite content,the shear strength,cohesion and internal friction Angle of the saline soil showed an increasing trend,and the liquid limit,plastic limit and plastic index decreased,the soil conductivity showed an obvious decreasing trend,and the mass loss decreased continuously.(3)With the increase of the number of freeze-thaw cycles,the limited water content and electrical conductivity of soil are less affected and the fluctuation is not significant,but the mass loss is increased and the frost resistance is weakened.As the shear strength and cohesion of saline soil decrease,the growth rate of cohesion degradation index becomes smaller and smaller,and the degradation index of internal friction Angle has an overall increasing trend.After seven freeze-thaw cycles,the cohesion and internal friction Angle degradation index of the modified saline soil were lower than that of the plain soil,and the freeze-thaw resistance was better.(4)The limited water content,electrical conductivity and frost resistance were improved significantly after double lime and wollastonite mixing,and the shear properties were enhanced more significantly than that of single lime and wollastonite mixing.(5)It was found that the plastic index,frost resistance,shear strength,cohesion and internal friction Angle of the sample with the ratio of6%L+12%SF had the best improvement effect,and the engineering properties were improved.To sum up,lime and silica ash can be added into the soil to improve the shear strength and freeze-thaw stability of the soil during the construction of Songnen Plain.