Study On The Physical And Mechanical Properties Of The Acid-Stained Red Clay

In recent years,with the rapid development of China's social economy,more and more environmental issues occurred and more scholars have begun to pay more attention to studying the contaminated soil.This research was supported by Guangxi Key Project of Department Study on geotechnical engineering properties of the polluted red clay in Guilin karst areas(KY2015ZD055).The test soil samples,red clay,were selected from the Yanshan area in Guilin.We took the hydrochloric acid solution as the acid contaminant,took the concentration of hydrochloric acid solution and the immersion time of red clay in acid solution as influencing factors,so as to study the physical and mechanical properties of the acid-stained red clay.The main research results are as follows:(1)Through the method of pumping and saturating,we made acid-stained red clay samples by soaking them in different concentrations of hydrochloric acid solution and different soaking time.After soaking,there were no significant changes in the appearance of red clay,but pungent smell.The color of the acid solution changed from clarification into yellow-green.(2)We obtained the physical properties of the acid-stained red clay through the ring cutting quality test,drying the moisture content test,specific gravity test and liquid plastic limit joint test.The result showed that with the increase of the concentration of hydrochloric acid solution and the soaking time being longer,the quality and density of acid-stained red clay decreased,the water content increased,the void ratio of the soil increased after acid contamination,and the proportion of red clay particles decreased as a whole;at the same time,the liquid limit,plastic limit and plasticity index of red clay also decreased after being polluted.The reason for the change of the physical properties was that with the loss of oxide and soluble salt in red clay after pollution,the soil cementing ability and hydrophilic ability became weakened and the soil became rough and loose.(3)We studied the change rule of compressional property and shear strength of red clay after pollution through consolidation test and unconsolidated undrained triaxial shear test.The result showed that with the increase of the concentration of hydrochloric acid solution and the soaking time being longer,the compressibility and the coefficient of compressibility of acid-stained red clay increased;the modulus of compressibility,shear strength and cohesion decreased;while the internal friction angle had no obvious change.The main reason was that after the red clay was corroded by hydrochloric acid solution,the oxide,which plays the cementation role,was dissolved,the pores of the soil became lager and the cementation capacity of soil particle decreased.(4)We explored the corrosion mechanism of acid-stained red clay from the perspective of chemical reactions by combining the characteristics of physical and mechanical properties of acid-stained red clay.The half-oxide and silica in the secondary mineral reacted chemically with the hydrochloric acid solution,during which the silica was hydrolyzed in solution and the hydrolysis reaction was a two-way reversible.The half-oxide reacted with hydrochloric acid and generated new salts and water.The water soluble salts in red clay also dissolved in hydrochloric acid and produced ions,and the ion-exchanged reaction was generated between new ions and hydrochloric acid solution,all of these reactions caused the changes in the physical and mechanical properties of acid-stained red clay together.