Experimental Study On The Influence Of Silica Fume On The Engineering Properties Of Cement Reinforced Soil

Cement reinforced soil is a kind of artificially improved soft soil material with certain strength and relative stability formed by mechanical compaction and curing with cement as the main agent.Cement reinforced soil is not only characterized by low compressibility and high strength,but also widely used in various fields because of its low price and obvious reinforcement effect.However,with the continuous improvement of building requirements and more and more complex construction sites,the strength and deformation of cement-soil also put forward higher requirements.The thesis is based on the National Natural Science Foundation project"Control Effect and Mechanism of Combined Water on the Mechanical Behavior of Soft Clay"?No.41572257?,and Ningbo Soft Clay as the research object,based on the characteristics of silica fume,uses silica fume as an admixture into cement reinforced soil.From the role of silica fume-soft soil,cement-soft soil,to explore the role of silica fume,cement,soft soil.The thesis analyzes the effect of silica fume with different dosage on the shear strength index of soft soil,the deformation resistance of soft soil and the change of pores in soft soil;The change rule of unconfined compressive strength of cement reinforced soil without silica fume;Under the condition of a certain amount of cement,explore the effect of the amount of silica fume on the stress and strain of cement reinforced soil;At the same time,the electron micrographs of silica fume reinforced soil,cement reinforced soil and silica fume reinforced cement soil were used to analyze the changes in microstructure and the effect of silica fume.According to the study:?1?Through the triaxial test,it was found that silica fume can improve the cohesion of soft clay well.As the amount of silica fume added increases,the cohesion increases;Silica fume can improve the ability of soft soil to resist deformation well.As the amount of silica fume added increases,the deformation resistance of silica fume-reinforced soil increases first and then decreases.?2?The influence of silica fume on soft soil is mainly achieved by the filling effect of silica fume particles and the adhesion of tiny soil particles to form aggregates and enhance the overall density of soft soil.As the amount of silica fume added increases,large pores in soft soil gradually decrease,and small pores gradually increase.?3?Through the unconfined compressive strength test,it is found that with the increase of curing time,the maximum stress of cement soil is increasing,and the failure strain corresponding to the maximum stress decreases with the increase of age;When the amount of silica fume mixed is 1.5%²%,that is,the amount of silica fume accounts for 1.5%²%of cement,the effect of increasing the strength of cement reinforced soil is the best;Deformation modulus is obtained from the stress-strain curve of silica fume reinforced cement soil,which is then fitted with the compressive strength to obtain the relationship E₅₀=44q_u.?4?Scanning electron microscopy experiments showed that the hydration products of cement first filled and closed the pores of soft soil,and then covered the surface of the soil particles with a network of C-S-H gel,which made the soil more structural;Silica fume can promote the hydration products of cement,consume Ca?OH?₂,and inhibit the growth of Ca?OH?₂ crystals;The cementing material can better cement the soil particles and the flake clay minerals,so that it forms a space skeleton with a certain strength.?5?The enhanced strength of silica fume reinforced cement soil is the result of the filling effect of silica fume and cement,cement hydration,and pozzolan reaction of silica fume.