Study On Expansion And Shrinkage Properties Of Expansive Soil Modified By Polyaluminium Chloride Compound Activated Silicate

Expansive soil is widely distributed in China.It is a kind of high plastic clay mainly composed of hydrophilic clay minerals,montmorillonite and illite.Because of its engineering characteristics such as strong expansion and contraction,multi-fracture,over-consolidation and strength attenuation,it is easy to cause roadbed deformation,slope instability,building instability and other damage,which brings huge hidden dangers to the construction of expansive soil area.Therefore,it is necessary to modify expansive soil and study its modification mechanism.In this study,polyaluminium chloride and activated silicic acid are used to modify expansive soils in Yangxian County either alone or in combination.Firstly,the effects of different modifiers on the physical and mechanical properties of expansive soil and its swelling and shrinkage deformation characteristics are analyzed.Then,with the expansion and contraction as the index,a modifier ratio of activated aluminum chloride as the solidifying agent and activated silicic acid as the coagulant is determined.Finally,by analyzing the changes of physical properties,mineral composition,electrochemical properties and microstructural characteristics of expansive soil before and after modification,the mechanism of the modified expansive soil is explored.The research conclusions are as follows:（1）Both modifiers can improve the swelling and shrinkage properties of expansive soils.According to the change rule of expansion index,the modification effect of PAC is better than that of activated silica,and the modification effect is the best when PAC content is 6%.According to the shrinkage index,the modification effect of activated silica is better than that of PAC.（2）After modified by PAC and activated silicic acid,the physical and mechanical properties of expansive soils change greatly.The content of clay fraction of modified soil decrease greatly,the liquid limit and plastic index decrease,and the shear strength index increase obviously.Under the same dosage,the physical properties of expansive soil are obviously affected by PAC,and the shear strength index of expansive soil is obviously affected by activated silicic acid.（3）According to the change rule of swelling and shrinkage index of modified soil,the modified effect of PAC compound activated silicic acid on expansive soil is obviously better than that of PAC alone.The optimal ratio is 6%PAC and 6%activated silicic acid.（4）Through boundary moisture content test,ζpotential test,grain size analysis test,clay minerals content analysis,scanning electron microscopy and BET specific surface area test,the mechanism of PAC compound activated silicic acid modified expansive soil is that its hydrolysis to produce a large number of high[Al]^m+and flocculate can lessen combined water film thickness and cement effective adsorption by ion exchange and electricity neutralization,and flocculation net trapping effectively cemented clay particles,so as to enhance the overall structure of the soil and reduce soil swell-shrink property.