| Saline soil is widely distributed all over the world.China's saline soil is mainly distributed in inland arid and semi-arid areas,riversides,coastal areas and other regions.The high sulfate content in the saline soil in Ningxia region,combined with the special climate,in the weathering process caused by complex environmental conditions,the salt and alkali components in the soil continuously crystallize and dissolve with the migration and aggregation of water,and the process of salt accumulation and desalination get on.When the outside temperature drops,the sulfate in the soil will crystallize out,because the sulfate will increase the volume of water absorption when crystallizing,and the phenomenon of salt frost heave occurs.Although there has been a relatively systematic understanding of the research on saline soil,and some valuable research results have been obtained in the mechanism and influencing factors of saline soil-based diseases,most of the previous studies have focused on the curing of sulfate by different curing agents.The research on the strength growth of the soil and the inhibition mechanism of salt swelling,and less attention has been paid to the deterioration of the engineering properties of the cured sulfate soil after being subjected to long-term environmental impact To this end,this thesis uses the orthogonal test analysis method(range analysis,analysis of variance,etc.)for the deterioration of engineering properties of solidified sulfated saline soil after long-term environmental impact,through triaxial test,collapse test,SEM scanning Tests and diffraction analysis tests were conducted in terms of strength characteristics,salt expansion characteristics,and collapse characteristics of solidified sulfated saline soil.The main research results are as follows:(1)The extremely poor analysis of the strength test results of the sulfated soil after solidification shows that the number of freeze-thaw cycles has the greatest influence on the cohesion of the soil sample,followed by the amount of calcium chloride.Regarding the salt frost heave test,a comparative analysis believes that:only blending fly ash and calcium chloride has a certain inhibitory effect on salt swelling,but its effect is not as good as that of blending fly ash and calcium chloride.(2)With the increase of salt content,the collapse rate of sulfated saline soil increases linearly.The range analysis shows that the influence of different factors on the collapse rate is in order of salt content,calcium chloride content,the amount of fly ash.(3)X-ray diffraction analysis shows that a dense and low-difference diffraction peak group appears in the diffraction pattern of sulfated soil samples solidified with fly ash and calcium chloride,indicating that the action of the curing agent and salts is easy to form amorphous Cementitious substances,thereby enhancing the bonding strength between soil particles.SEM experimental analysis shows that the fly ash alone can fill the pores between the soil particles at the beginning of the freeze-thaw cycle,improve the structure of the soil,and thus significantly enhance the cohesion of the soil.However,as the number of freeze-thaw cycles increases,the structure of the soil gradually decreases,and some of the bonding points are spalled,and the strength decreases as the structure decreases.(4)Comprehensive macro-test,micro-test and engineering economic analysis,when the salt content is 2%,it is recommended to mix fly ash 15%+calcium chloride 2%;when the salt content is 5%,it is recommended to mix Fly ash 15%+ calcium chloride 4%;when the salt content is 8%,the proportion of the soil to achieve maximum cohesion is:fly ash 15%+calcium chloride 4%.Under this ratio,it can not only meet the strength characteristics and salt swelling suppression effect of saline soil under the condition of long-term freeze-thaw cycles,but also suppress the sagging of saline soil to a certain extent. |
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