Effects Of Freezing And Thawing Cycles On Engineering Properties Of Cement Stabilized Lead Contaminated Soil And Its Mechanism

With the adjustment and upgrading of the industrial structure of our country and the acceleration of urbanization process,many enterprises with pollution risks move away from the original site,leaving a large number of industrial pollution sites.The soil heavy metal pollution is an important pollution type of the contaminated site.At present,the treatment method of heavy metal contaminated sites in China is mainly solidification / stabilization technology,Soil temperature changes,as an environmental factor,can affect the nature of cement stabilized soil.Therefore,the properties of soil will change after freeze-thaw cycles.The study on the changes of the properties of cement solidification / stabilization heavy metal contaminated sites is of great significance to the remediation of heavy metal contaminated sites in seasonal frozen areas of china.Based on this background,this paper is based on the scientific research foundation of the returned overseas Chinese researchers of Ministry of education,and takes the engineering mechanics properties of cement solidified heavy metal lead(Pb)contaminated soil as the main research contents.Through indoor soil test,freeze-thaw cycle test and theoretical analysis on cement solidification of Pb(Pb)contaminated soil freeze thaw condition at room temperature and under the variation of the unconfined compressive strength,anti shearing strength;the microstructure characteristics of cement stabilized heavy metal lead(Pb)contaminated soil subjected to freeze-thaw cycles were revealed by means of SEM electron microscopy;the prediction model of unconfined compressive strength of cement solidified heavy metal lead(Pb)contaminated soil with the variation of freeze-thaw cycles and cement content was constructed.The main research results are as follows:(1)The influence of cement content on unconfined compressive strength,shear strength and modulus of deformation of cement stabilized lead contaminated soil under normal temperature was investigated.It is pointed out that cement mainly improves the compressive strength,shear strength and resistance to deformation by means of hydration hydrolysis reaction;(2)The influence of lead ion content on unconfined compressive strength,shear strength and modulus of deformation of cement stabilized lead contaminated soil under normal temperature was investigated.It is pointed out that the heavy metal lead ion affects the compressive strength,shear strength and resistance to deformation of the solidified soil mainly by affecting the hydration hydrolysis reaction and the hardening reaction of the cement.The results show that the compressive strength,shear strength and cohesion of cement stabilized soil decrease and the resistance to deformation decreases with the increase of lead ion content;(3)The influences of freeze-thaw cycles and freezing temperature on unconfined compressive strength and shear strength of cement stabilized lead contaminated soil were investigated,The results show that with the increase of the number of freeze-thaw cycles,the specimen unconfined compressive strength Qu value,shear stress,cohesion decreases,the internal friction angle increases;as the temperature decreases,the stress-strain curve characteristics change,no reduction of compressive strength and cohesion of the lateral limit,internal friction angle the change and the dosage of cement and lead ion content;(4)According to the existing predictions on cement solidification of heavy metal pollution in soil strength and ideas,combined with the fitting method of data analysis data,put forward the cement solidified lead(Pb)prediction model of soil pollution intensity,and verified by the data;(5)The effect of freeze-thaw cycles is mainly by changing the sample size and the pore size,the macro parameters of specimen change.