| Silty soft soil is widely distributed in coastal areas of South China,which has poor engineering properties,high water content and low bearing capacity.When soft soil is encountered in engineering construction,the traditional physical solidification treatment method is limited in practical engineering application,such as high cost and serious secondary pollution.Chemical solidification treatment technology refers to adding a certain amount of solidification agent according to the characteristics of soft soil to improve the mechanical properties of soft soil.At present,the most widely used solidification agent is cement,but there are serious environmental problems in its production process.Alkali-activated cementitious material is a new type of inorganic solidification agent with the characteristics of green environmental protection.This thesis attempts to use alkali-activated cementitious material to replace cement to solidify soft soil in South China.In this thesis,the silty soft soil in South China is selected as the research object,and sodium silicate is selected as the alkali activator to stimulate the potential activity of mineral powder and fly ash respectively.Static pressure method is used for sample preparation and a series of tests were carried out after solidifying to the set age.The strength characteristics of solidified soil under different mixing ratios were evaluated by unconfined compressive strength test,and the stability and durability of solidified soil were evaluated by water stability test and dry-wet cycle test.After drying and crushing the damaged soil samples,X-ray diffraction test and electron microscope scanning test were carried out to explore the changes in mineral composition and microstructure of soft soil before and after solidifying.The main research contents and conclusions of this thesis are as follows:（1）The solidification effect of single mineral powder on soft soil is limited,and single fly ash can even lead to the decrease of the strength of the sample.The addition of sodium silicate to stimulate the activity of solidification agent has a significant effect on the strength of the solidified sample,and the strength gradually increases with the increase of sodium silicate content.The maximum strength of alkali-activated mineral powder solidified sample can reach 0.85 MPa,which is 155% higher than that of single-doped mineral powder solidified sample.The maximum strength of alkali-activated fly ash solidified sample is 0.483 MPa,which is 70.7% higher than that of single-doped fly ash solidified sample.By comparison,it can be found that the strength of alkali-activated mineral powder solidified samples is higher and the solidification effect id better.Through the microscopic test,it can be observed that the cement cementitious material was formed in the solidified soft soil sample and cemented between soil particles,which is the hydration product C-（A）-S-H.（2）In water stability tests,under the condition of low sodium silicate content,all the samples were unformed disintegration within 24 h of immersion,and the water stability was extremely poor.With the increase of immersion age,the peak stress of the rest mixing proportion sample increases gradually,the unconfined compressive strength increases gradually,and the water stability is better.The sample with G20S4 mixture ratio reached the maximum strength of 1.933 MPa after 40 d immersion.（3）The samples with 10 % mineral powder content all disintegrated in three dry-wet cycles,and the durability was extremely poor.The mass loss rate of the rest mixing proportion sample under the ratio of dry-wet cycle test was analyzed.The results show that the cumulative relative mass loss rate of all samples is within the failure standard value（< 30 %）,which meets the requirements of relevant specifications.Overall,the durability of dry-wet cycles of G20S3 and G20S4 is better,while the durability of G15S3,G15S4 and G20S2 is poor,which is not suitable for geotechnical engineering with more alternation of dry and wet environments. |
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