Research On The Properties And Structure Of Municipal Waste Contaminated Silty Clay In The Transition-acidification Stage

Municipal waste has become one of the important contaminant sources of geological environment.In the seepage process of municipal waste contaminant,the structure and mineral composition of soil are changed through physical and chemical actions,which leads to great changes in physical and mechanical properties,hydraulic properties and structural characteristics of soil.In this paper,the silty clay in Xuzhou is taken as the research object.On the basis of analyzing the composition of municipal waste contaminant and the degradation stage,the transition-acidification stage of municipal waste contaminant is determined as the research stage.Butyric acid,acetic acid and urea solution were selected as the contaminated solution.By measuring the shear strength,resistivity,permeability coefficient,moisture content and fracture structure parameters of the silty clay,the changes and influence mechanisms of the properties and structure of the silty clay in the transition-acidification stage are analyzed and revealed.The results show that:(1)The shear strength of contaminated silty clay is negatively correlated with the concentration of butyric acid and acetic acid,and positively correlated with the depth of seepage,and the shear strength of silty clay is less affected by urea;(2)The resistivity of contaminated silty clay is negatively correlated with the concentration of butyric acid and acetic acid,and negatively correlated with the depth of seepage,the resistivity of silty clay is less affected by urea.Under the same test conditions,the relationship of soil resistivity is: urea contaminated silty clay> butyric acid contaminated silty clay> acetic acid contaminated silty clay;(3)The permeability coefficient of contaminated silty clay is positively correlated with the concentration of butyric acid and acetic acid,and negatively correlated with the depth of seepage,the permeability coefficient of silty clay is less affected by urea;(4)The shape of natural water loss curve and water loss rate curve of butyric acid,acetic acid,urea contaminated silty clay and uncontaminated silty clay are the same.In the rapid water loss stage,acetic acid can promote the natural water loss of silty clay,while butyric acid and urea can obviously inhibit the natural water loss of silty clay;(5)Butyric acid and acetic acid have an obvious inhibitory effect on the development of the fracture structure of the silty clay.The fracture rate of urea contaminated silty clay is similar to that of uncontaminated soil.The relationship of fracture rate is: butyric acid contaminated silty clay < aceticacid contaminated silty clay < urea contaminated silty clay.(6)The fracture morphology of butyric acid and acetic acid contaminated silty clay is "saw-toothed",and the extension and development are "circular" and irregularly curved.The fracture morphology of urea contaminated silty clay and unncontaminated silty clay is smooth and flat,and the curve radian is small.Compared with uncontaminated silty clay,the average shape coefficient of butyric acid contaminated silty clay and acetic acid contaminated silty clay is significantly reduced.Based on the above analysis,the urea formed in the transition stage of municipal waste contaminant has little effect on the physical and mechanical properties and crack structure of the silty clay,but it has a very obvious inhibitory effect on the natural water loss of the silty clay.In the acidification stage,the formation of butyric acid reduces the shear strength and resistivity of the silty clay,increases the permeability coefficient,suppresses the natural water loss of the silty clay,and increases the complexity of the silty clay fracture structure.With the conversion of butyric acid and the formation of acetic acid,the shear strength and resistivity decreased further,the permeability coefficient tended to increase further,and the natural water loss rate increased significantly.The variation mechanism of physical and mechanical properties,hydraulic properties and structural characteristics of municipal waste contaminated silty clay in transition-acidification stage was revealed from the aspects of seepage transport,chemical action,ion adsorption,soil-water action,salt effect,crystallization and soil strength.The paper contains 37 figures,12 tables and 112 pieces of references.