Mechanical Properties And Mechanism Analysis Of Saline Soil Modified By Lime-polypropylene Fiber

A large number of loess saline soils are distributed in northwest China,and its own undesirable characteristics will cause serious harm to infrastructure.Therefore,the saline soil needs to be modified before it can be used in engineering construction.Lime and polypropylene fiber are commonly used in engineering modified materials.Lime can significantly increase the strength of soil through chemical solidification and polypropylene fiber can improve the deformation property of soil effectively through physical reinforcement.However,both of the two materials will have some regeneration problems when improving the soil independently,such as the brittleness and easy cracking of the lime solidified soil,and the low strength and water stability of the fiber reinforced soil.Therefore,this study adhering to the idea of complementary advantages,using lime and polypropylene fiber to improve saline soil.Mechanical properties and microstructure of lime-fiber modified soils under three environments of ordinary state,water immersion and wet and dry cycles are investigated by the laboratory test.At the same time,response surface method is used to optimize the soil improvement process in thre e kinds of environment.The main research achievements are as follows:1.Under three environments of ordinary state,water immersion,an d wet and dry cycles,lime can effectively improve the compressive strength,deformation resistance and compactness of soil after adding fiber modified soil.The fiber can effectively reduce the brittleness of soil and improve the strength of soil after adding lime modified soil,but has little effect on the compactn ess of soil.With the increase of lime content,salt content and the proportion of Na₂SO₄ in salt,the compressive strength,deformation resistance,brittleness degree and compactness of soil of lime-fiber modified soil shows a trend of increasing first and then decreasi ng.With the increase of fiber content,the brittleness degree of lime-fiber modified soil decreases gradually,and the compressive strength increases gradually,but the compactness of the soil changes little.2.Under the water immersion environment and wet and dry cycles environment,with the increase of the number of water immersion days and wet and dry cycles,the compressive strength,deformation resistance and soil compactnes s of lime modified soil and lime-fiber modified soil shows a trend of weakening first and then increasing,but the brittleness degree of lime modified soil has little change and the brittleness degree of lime-fiber modified soil gradually increased.3.The compressive strength models constructed based on the Box-Behnken design principle for three environments of ordinary state,water immersion,and wet and dry cycles all have high accuracy and relia bility.After response surface methodology optimization,the maximum values of compressive strength of lime-fiber modified soil in ordinary state environment is 1044.83 k Pa and the best combination of test variables is 7.05%lime content,0.4%fiber conten t,1.11%salt content,and34.97%the proportion of Na₂SO₄ in the salt;the maximum values of compressive strength of lime-fiber modified soil in water immersion environment is 602.54 k Pa and the best combination of test variables is 7.41%lime content,0.38%fiber content,1.27%salt content,and 24.91%the propo rtion of Na₂SO₄ in the salt;the maximum values of compressive strength of lime-fiber modified soil in wet and dry cy cle environment is 610.43 k Pa and the best combination of test variables is 7.26%lime content,0.4%fiber content,1.35%salt content,and 30.25%the proportion of Na₂SO₄in the salt.