Study On Engineering And Environmental Stability Of Compound Solidified Lead Contaminated Soil Characteristics Under Long-term Freeze-thaw Cycles

Because people worldwide rapid advance agricultural intensification,industrialization and urbanization,industrial structure upgrade and city layout adjustment,a lot of(water,air,soil,etc.)to the environment caused serious damage to the high pollution risk enterprises were shut down or moved,how to effectively manage its legacy of heavy metal pollution site problem also with the people environmental protection consciousness enhancement.At present,the mainstream remediation technology for the treatment of soil contaminated by heavy metals in various countries is solidification/stabilization technology(S/S).However,treatment after pollution soil curing repair effect tends to produce with the change of the environment deterioration,the freeze-thaw cycle,as a kind of important external forcings,change of soil temperature field of solidification/stabilization repair engineering and the stability of the environment of soil heavy metal pollution worthy of in-depth study,through the system research under the action of freeze-thaw alternation of curing the variation regularity of heavy metal pollution soil engineering and environmental stability,reusing the heavy metal pollution in permafrost regions site long-term stability and guarantee the stability of its curing/effect is of great significance.This paper is based on the research of national Natural Science Foundation of China on the decomposition mechanism(41772306)of the long-term frozen melting engineering of the solidified soil layer with high concentration of heavy metals Taking the long-term freeze-thaw cycle as the main influencing factor and combining with the engineering practice,the degradation law of engineering characteristics and environmental stability of composite solidified lead-contaminated soil was preliminarily explored through indoor geotechnical test,leaching test and analysis of metal occurrence morphology by setting different curing ratio and heavy metal pollution concentration.The main research results are as follows:(1)The effects of short-term freeze-thaw cycle and long-term freeze-thaw cycle on the unconfined compressive strength of composite solidified lead-contaminated soil have different mechanisms.The main influencing mechanism of short-term freezing-thawing cycle is the degree of hydration and hydrolysis of the curing agent,while the main influencing mechanism of long-term freezing-thawing cycle is the degree of damage to the structure of the sample.(2)After a long-term freeze-thaw cycle,laboratory geotechnical tests were carried out on the cured lead-contaminated soil in the ratio of C2.5S5F5,C5s2.5F2.5 and C5S5.The results show that the addition of cement,lime and fly ash can effectively resist the freeze-thaw cycle’s effect on the unconfined compressive strength of samples,and the higher the content of cement + lime in curing agent,the less the freeze-thaw cycle’s effect on the strength of samples.At the same time,the addition of fly ash can be a very good sample of antifreeze performance,improve sample in long-term strength and stability of freezing and thawing.(3)Heavy metal ions can inhibit the hydration hydrolysis reaction of curing agent,and thus have a deterioration effect on the compressive strength of the samples,and significantly affect the solidified lead-contaminated soil samples with a high cement content in the total amount of curing agent(4)Long-term freeze-thaw cycle will reduce the acid resistance of composite solidified lead-contaminated soil.In the toxic leaching test,the p H value of the extract decreased with the increase of freeze-thaw cycles.In the semi-dynamic leaching test,the p H value of the filtered solution of the solidified ratio sample with more freeze-thaw times will peak earlier than that of the solidified ratio sample with less freeze-thaw times.(5)In the toxicity leaching test,the lead ion leaching concentration in the samples increased with the increase of freeze-thaw cycles.Compared with other samples,the leaching concentration of lead ion in the samples with the content of cement + lime making up a large proportion of the total amount of curing agent is significantly reduced,while the leaching concentration of lead ion is significantly increased when using fly ash instead of cement and lime as curing agent.In the semi-dynamic leaching test,with the increase of the number of freezing-thawing times,the time point of lead ion leaching peak in the filtered solution will be delayed,and the peak value of lead ion leaching of the sample with more freezing-thawing times is larger than that of the sample with less freezing-thawing times.Cement and lime or higher total curing agent were less effective diffusion coefficient De C5S5 sample C5S2.5 f2.5 samples and C2.5 S5F5 sample,at the same time the lime content is higher C2.5 S5F5 De effective diffusion coefficient of sample is less than C5S2.5 f2.5 sample,cement and lime content will affect the effective diffusion coefficient of lead in the sample De,cement and lime content more sample,the effective diffusion coefficient of lead De is small,and the influence of the lime content is more apparent.(6)Long-term freeze-thaw cycle effect mainly influence the lead form in the distribution of ion exchange state is combined with carbonate state,reduce stability strong carbonate combination state of metal content,increase the content of the poor stability of metal free,make originally by curing the stability of the reactivation of lead ions,destroyed the stability of the curing,reduce the overall stability of solidified soil sample.