Study On Engineering Properties Of Loess Contaminated By Heavy Metal Ions

The contamination of heavy metal ions causes different influences on engineering property of soil and dangerous on construction safety. Loess contains amounts of carbonate and porosity, which makes loess has a strong ability of heavy metal ions absorption and can be used in construction as a material for pollution prevention.The studyused artificial polluted loess which contained Yangling loess, chromic nitrate, zinc nitrate and cupric nitrate to stimulate loess contaminated by different concentration of heavy metal ions in practical engineering. The influence of heavy metal pollution on physical-chemical properties of loess were studied through grading test, soluble salt content test, pH value test, liquid limit-plastic limit joint test, soil gravity test and permeability test. The compression test, SEM test and triaxial test also be conducted to study the engineering property and microstructure of loess contaminated by heavy metal ions. The conclusions of study are as follows:（1） The result of soil gravity test showed that the soil gravity decreased with the increase of Cr³⁺, Zn²⁺ and Cu²⁺ concentration. The clay content and pH decreased with the increasing of heavy metal ions content. Liquid limit-plastic limit of loess contaminated by Zn²⁺ and Cu²⁺ had a slight change, but loess contaminated by Cr³⁺ changed from silt clay to silt according with the increase of Cr³⁺. The permeability test showed that Cr³⁺ had a limit influence on permeability coefficient of polluted loess, the permeability coefficient of polluted loess increased significantly after contaminated by Zn²⁺ and Cu²⁺. The content of soluble salt and Ca²⁺、Mg²⁺、Na+、K+ increased obviously with the increase of heavy metal ions.（2） The results of compression test indicated that contaminated loess by Cr³⁺ had a decrease in compressibility and compressive deformation with the increase of Cr³⁺ content. On the contrary, contaminated loess by Zn²⁺ and Cu²⁺ had a slight increase in compressibility and compressive deformation with the increase of Zn²⁺ and Cu²⁺. The results of triaxial test showed that the cohesion of loess contaminated by heavy metal ions all decreased with the increase of heavy metal ions content. The internal friction angle increased with the increase of heavy metal ions content. Loess contaminated by Zn²⁺ and Cu²⁺ had a slight increase on internal friction angle, and loess contaminated by Cr³⁺ had an obvious increase on internal friction. The shear strength of loess contaminated by Cr³⁺ had a significant increase according with the increase of Cr³⁺ content.（3） The results of SEM test showed that Cr³⁺, Zn²⁺ and Cu²⁺ have significant influences on microstructure of Yangling loess. The cementation of clay and carbonate between soil particles vanished partly, the surface of soil particle became rough and aperture of porosity increased with the increase of Cr³⁺ content. The porosity number increased and the edge of soil particles became smooth with the increase of Zn²⁺ and Cu²⁺ content. The contact between soil particles of loess contaminated by Zn²⁺ and Cu²⁺ became unconsolidation because of decrease of cementation and increase of porosity.