Experimental Study On Cement-Silica Micropowder Improved Saline Soil Of Highway Subgrade

Saline soil is the soil with soluble salt content between 0.3%and 20%,including saline soil,alkaline soil and all kinds of salinized and alkaline soil.There are two main states of soluble salt in saline soil,i.e.salt solution in liquid phase and crystal salt particles in solid phase.When the external environment changes,such as winter cooling and summer rainfall,salts in the liquid phase and solid phase will transform each other,that is,the crystallization of salt solution or the dissolution of salt particles.If saline soil is used as the highway subgrade,the highway subgrade will suffer a series of hazards,such as,salt swelling and collapsing.When the soluble salt in subgrade soil transforms between solid and liquid state,the increasing porosity of soil makes the soil structure loose and damage easily under upper load,which will further affect the durability of highway.In this paper,the saline soil along the Shuangtao highway in Jilin Province is taken as the research object,and the improvement test of saline soil is carried out by using cement and silicon micropowder inorganic materials.Firstly,a series of physical and chemical tests are carried out on the local saline soil to determine its basic physical and chemical parameters.In addition,the mechanism of cement and silicon micro powder solidified soil is analyzed to determine the improvement materials and ratio.Subsequently,the compaction test,unconfined compression test,direct shear test,collapsing test and freeze-thaw cyclic test are carried out for the improved saline soil.The influence rule and improvement principle of the improvement materials on the performance of the saline soil are studied from the perspective of strength,deformation and durability.Finally,the micro characteristics,i.e.the shape of soil particles and the size and distribution of internal voids of the improved saline soil are analyzed by SEM and X-ray diffraction tests.The test results show that the water content of the achieved target compactness of the improved saline soil is increased by 36.1%～123.4%,and the strength of the saline soil is greatly increased by cement.The compressive strength,shear strength and collapsing resistance are linearly related to the cement content.The failure mode of the sample is brittle failure with lower durability of the freeze-thaw cycle,and the strength loss is around 80%.While the strength improvement of the silica micropowder improved saline soil is weaker than cement which shows plastic failure characteristics.The durability of freeze-thaw cycle is better,and the strength loss is about 10%.The strength of the composite material for the salinized soil shows the highest increase.The stress decreased linearly after reaching the peak,and gradually decrease with the increase of silica powder content.The strength loss of freeze-thaw cycle is about 50%.The microscopic characteristics test shows that the internal structure of the cement improved soil is formed by intersecting the cluster structure to a skeleton system to enhance the strength.The aggregates formed in the inner grains of the silica micro-powder improved soil make the soil structure dense with no obvious voids.A large amount of gel is formed between the composite material improved soil skeleton by the silicon micropowder.and the aggregates are transformed from hybrid to larger columnar with lower porosity.