Experimental Study On Unsaturated Properties Of Acid Contaminated Expansive Soil Remediation By Alkali Residue

Expansive soil is a special kind of soil that is easy to cause disasters and is difficult to handle.In addition,its properties are greatly affected by changes in environmental conditions,so the properties of expansive soil under the influence of acid pollutants are more complicated and difficult to predict.The alkali residue repairing acid contaminated expansive soil is an ideal method,but its mechanism has not yet been revealed.For this reason,based on the unsaturated direct shear test and the consolidated undrained triaxial test,this article explores the hydrochloric acid concentration,alkali residue content,matrix suction,The influence of net normal stress,curing age and confining pressure on the strength of the improved soil.At the same time,SEM is used to study the corresponding microstructure characteristics,and the IPP software is used to analyze the quantitative characteristics of the microstructure of soil samples under different conditions,provide a certain reference for engineering construction in expansive soil areas.The main conclusions are as following:(1)Results of unsaturated direct shear test show that the failure modes of hydrochloric acid contaminated samples and plain soil samples show the characteristics of plastic failure,and the strength increases with the increase of displacement.There is a turning point of 6%for the effect of hydrochloric acid concentration on the strength of expansive soil,that is,when the hydrochloric acid concentration is less than 6%,the strength of samples decreases with the increase of hydrochloric acid concentration,and when the hydrochloric acid concentration exceeds this value,the strength increases.The unsaturated direct shear strength of 6%hydrochloric acid contaminated sample is 145k Pa,which is 17%lower than that of plain soil sample(175k Pa).Under the condition of 6%hydrochloric acid concentration,the strength of expansive soil polluted by hydrochloric acid first increases and then decreases with the increase of alkali residue content,and there is an inflection point of 40%,at this time,the strength of the sample is 271k Pa,which is 86%higher than the sample polluted by hydrochloric acid,and the sample shows obvious brittle failure characteristics after adding alkali residue.The larger the alkali residue content is,the more obvious the brittle characteristics are.The strength growth rate of the samples with alkali residue is also much faster than other samples.The results show that the shear strength increases with the increase of matric suction and net normal stress.When matric suction is 200k Pa,the unsaturated direct shear parameters of acid contaminated samples are c′=189k Pa,?~b=22.05°and when net normal stress is200k Pa,the unsaturated direct shear parameters c′=190k Pa,?′=22.27°。(2)Results of consolidated undrained triaxial test show that the failure mode of plain soil and 6%hydrochloric acid contaminated sample are waist drum and it is plastic failure.The maximum deviator stress of plain soil sample increases with the increase of curing time,and the peak deviator stress is 595k Pa after 28 days of curing.The peak deviator stress of 6%hydrochloric acid contaminated sample decreases at first and then increases with the increase of curing time.After curing for 7 days,the peak deviating stress of the sample reaches the minimum value of 452k Pa.The shear failure crack of the sample repaired by 40%alkali residue is brittle failure.The peak deviation stress increases with the increase of curing time.The peak deviation stress of the sample cured for 28 days is1937k Pa.The peak deviation stress of the sample cured for 7 days increases by 365k Pa compared with the sample not cured.The results show that the maximum deviation stress increases with the increase of confining pressure,and the internal friction angle and cohesion of the samples polluted by hydrochloric acid decrease,while both increase significantly with the addition of alkali residue,which indicates that alkali residue can enhance the internal friction angle and cohesion of the samples polluted by hydrochloric acid,so as to improve the strength of the samples.(3)Results of microscopic tests show that the expansive soil has the typical microstructure characteristics of clay,and the unit body is in the form of sheet structure,which is mainly connected with each other in the form of plane to plane.With the addition of hydrochloric acid,hydrochloric acid will corrode oxides,etc.,leading to a decrease in the proportion of small and micro pores,while an increase in the proportion of large pores.6%is an inflection point under the influence of hydrochloric acid.After the addition of alkali residue,the proportion of small and micro pores in the soil increased significantly.The small and micro pores of the sample with 40%alkali residue content are 10%higher than those of the hydrochloric acid contaminated sample,and the proportion of large and medium pores decreased.The pore area,pore diameter and pore perimeter are improved with the increase of alkali residue content.