Research On The Changing Law And Mechanism Of Engineering Properties Of Expansive Soil Under Heavy Metal Pollution

With the rapid development of modern industry,the problems caused by heavy metal polluted soil become more and more serious,bringing serious harm to the engineering construction.Expansive soil,as a kind of clay with special properties is more harmful to heavy metal pollution.At present,most researches at inland and abroad focus on the direction of general clay polluted by heavy metals.Three heavy metals,lead,zinc and chromium,have serious pollution to the environment,and have different effects on the properties and action mechanism of expansive soil.There are few systematic studies on the engineering properties and reaction mechanism of heavy metal contaminated expansive soils.In order to further study how heavy metals affect the properties of expansive soils,systematic laboratory experiments were carried out to artificially prepare lead,zinc and chromium contaminated expansive soils.Based on the National Natural Science Foundation of China(NO.4167020957)as the backing,with heavy metals lead,zinc,chromium pollution of expansive soil as the research object,the pollution that the engineering properties of expansive soil from the macroscopic and microscopic structure,the mechanism of the two aspects of indoor experiment study,through the law of macro and micro mechanism of the method of combining research is mainly focused on the pollution of the expansive soil basic properties,strength,deformation,permeability,and the change rule of the microscopic properties,and from the micro perspective,heavy metals and the mechanism of the expansive soil with each other.The main research results are as follows:(1)The basic physical properties of expansive soils polluted by heavy metals of different types and concentrations were compared and analyzed.The results showed that with the increase of heavy metal concentration,the clay content,specific gravity and consistency of expansive soil decreased rapidly.(2)The change rule of engineering properties of expansive soils polluted by heavy metals of different types and concentrations was discussed.The results showed that the strength of expansive soil decreased obviously due to heavy metal ions,and the cohesion decreased significantly(the cohesion of lead-polluted soil increased).The permeability of expansive soil is changed and the permeability coefficient increases with the increase of heavy metal concentration.The compressibility of polluted expansive soil becomes larger,and it is found that heavy metal ions can inhibit the expansion and shrinkage of expansive soil.(3)The microstructure of heavy metal contaminated expansive soil was analyzed by microcosmic test.The results show that heavy metal ions change the structure of soil,the volume of aggregate pores and macroscopic pores increases,and the structure of soil tends to be loose,which verifies the change law of engineering properties.The reaction mechanism between heavy metals and expansive soil is explained from two aspects: the commonness and particularity of heavy metal ions.