Study On Mechanical And Microscopic Properties Of Solidified Zn²⁺ Polluted Red Clay

With the continuous improvement of modernized national construction,urban planning adjustments have been completed one after another throughout the country,leading to the relocation of many industrial and mining industries,leaving behind a large number of heavy metal contaminated sites.After entering the soil,the heavy metal pollutants react with the minerals inside the soil and destroy the structure of the soil,which has an adverse effect on the physical and mechanical properties of the soil and directly affects the development and utilization of the contaminated areas.In order to reuse these legacy sites,it is necessary to study and improve the environmental conditions around the sites as well as the engineering properties of the soils.This paper takes Zn²⁺contaminated red clay as the research object,uses calcium superphosphate as the main curing agent and calcium oxide as the auxiliary agent,analyzes the mechanical properties and the change law of resistivity of contaminated soil under different test conditions,combines the test results of microstructure test（SEM,XRD）,illustrates the curing treatment effect,and provides theoretical support in the application of this type of curing agent in the field engineering of Zn²⁺contaminated red clay covered area.The main conclusions are as follows:（1）The shear strength of red clay and the simultaneous measured damage resistivity both gradually decreased with increasing pollution concentration;the curing effect of red clay with different pollution concentration was different,and the shear strength of cured soil increased about 1.25-2.91 times more than that of polluted soil;the cohesive force of Zn²⁺polluted red clay decreased with increasing pollution concentration,and the angle of internal friction increased slightly with increasing pollution concentration;the shear strength index of Zn²⁺contaminated red clay increased significantly after curing.（2）Different contamination concentrations show different degrees of weakening effect on the lateral limit compressive strength of red clay;the lateral limit compressive strength of Zn²⁺contaminated red clay increases significantly after curing,increases linearly with the increase of curing agent incorporation rate and increases with the increase of curing age;the initial resistivity and damage resistivity of soil measured simultaneously in the lateral limit compressive strength test decrease with the increase of contamination concentration,and numerical fit was performed and found that the two conformed to a power function relationship.（3）Indoor standard consolidation tests found that the contaminated soil compression coefficient falls within the range of 0.1 to 0.5MPa^-1,as a medium compressibility soil,and the cured soil compression coefficientis less than or equal to 0.1MPa^-1,as a low compressibility soil,indicating enhanced soil compression properties after curing.（4）The test results of four-phase electrode method showed that the resistivity of Zn²⁺contaminated red clay decreased with the increase of contamination concentration after curing,and the resistivity and the contamination concentration were in accordance with the exponential function;it kept decreasing with the increase of water content,and the two were in accordance with the power function;it increased with the increase of porosity,and the two were in accordance with the logarithmic function.（5）From the SEM of microscopic test,it can be seen that Zn²⁺contamination destroys the internal structure of red clay and increases its porosity;a large amount of generation material is attached to the surface of cured soil,which gels with red clay particles and forms a more stable structure of agglomerates.At the same time,the large amount of products can effectively fill the soil pores,reduce the porosity and make the soil become dense.Combined with the X-ray diffraction test,it can be seen that there are gypsum Ca SO₄·2H₂O,hydroxyapatite Ca₁₀（PO₄）₆（OH）₂and Zn（PO₄）₂·4H₂O and other products attached to the surface of the cured contaminated soil.