Study Of The Engineering Property Evaluation Method For Organic Contaminated Sites Based On The Electrical And Thermal Parameters

During the urbanization of China,organic compounds have been found as one of the main pollutants in industrial sites.It was found that the engineering properties of soils are significant changed after contamination,hence,it triggers the needs in rapidly evaluating and classifying organic contaminated sites.Electrical resistivity and thermal resistivity are two basic properties of soil,their performance is changed before and after contamination.Hence,the changes of electrical resistivity and thermal resistivity in organic contaminated soils are studied,and an evaluation system of the engineering properties in organic contamination site soils is built based on the Analytic Hierarchy Process,so as to provide a scientific basis for the evaluation of organic contaminated sites.This dissertation is under the financial support of the Key Project of Natural Science Foundation of China(Grant No.41330641)and the National Natural Science Foundation of China(Grant No.41202203).Typical soils of Yangtze River backswamp silty clay and Xia-shu clay were used in this study,0#diesel,kerosene and 4.5%pesticide cypermethrin were used as typical organic pollutants.The engineering properties of organic contaminated soils(e.g.the physical,mechanism,electrical and thermal properties)were studied by laboratory tests,model tests,theoretical analysis and field tests.An evaluation system of organic compounds in influencing the engineering properties of site soils was built as well.The main contents and conclusions of this dissertation are shown as following:(1)Estimate methods of the engineering properties changes in organic contaminated soils are reviewed.The physical and mechanical properties,electrical resistivity,thermal resistivity and engineering estimation methods of organic contaminated soils are analyzed.The existing problems are critically reviewed.(2)The variation in the physical and mechanical properties and microstructures of contaminated soils are thoroughly studied.The effects of contamination dosage on the basic physical property indices and mechanical characteristics were carried out by laboratory tests.The results indicate that the liquid limit,plastic limit and the plasticity index of oil contaminated soils all decrease with the increase of oil added.While the liquid limit,plastic limit and the plasticity index of pesticide contaminated soils all increase with the increase of the pesticide added.The shear strength of organic contaminated soils is decreasing with the water content;the cohesive force and the friction angle of organic contaminated soils both decrease with the increase of contaminants.The microstructure of soil particles changes after the contamination of organics.It was found that particles aggregate after contamination.And organic contamination has no effects on soil minerals.(3)The Wenner four electrodes method is used to measure the electrical resistivity of organic contaminated soils,the effects of water content,contaminants dosage,saturation degree and the porosity on the electrical resistivity of soils are analyzed.For oil contaminated soils,two indexes(the volumetric liquid content and the water and oil saturation degree)are introduced here to study the influence of the water and oil two-phase on the electrical resistivity of oil contaminated soils.The electrical resistivity of oil contaminated soils is normalized based on the electrical resistivity of uncontaminated soils.The soil electrical contamination coefficient PΩ and the volumetric liquid content ratio θ are defined,and the four phase electrical resistivity model of oil contaminated soils is established.Results show that under the same saturation degree,the electrical resistivity of contaminated soils increase linearly with the increase of the volumetric liquid content.While under the same volumetric liquid content,the electrical resistivity of which decrease in power function with the increase of the water and oil saturation degree.When other conditions are the same,the electrical resistivity of pesticide contaminated soils increase in power function with the increase of the contaminants content and their porosity,decrease in exponential function with the increase of the water content and the saturation degree.In addition,the resistivity variation range has nonlinear correlation with the soil contamination level,the electrical resistivity can be used as a soil contamination evaluation index.(4)A non-steady-state thermal probe test is used to measure the thermal resistivity of soils before and after contamination.The effects of the factors,such as the water content,the contaminants content,the saturation degree and the dry density on the thermal resistivity of contaminated soils are discussed.Relationships among the volumetric liquid content,the water and oil saturation degree and the thermal resistivity are built.The thermal resistivity of contaminated soils are normalized based on the thermal resistivity of uncontaminated soils,and then a thermal resistivity calculation model using the soil thermal contamination coefficient PK is established for oil contaminated soils.Results show that under the same oil content,the thermal resistivity increase in exponential function with the increase of the water content and the saturation degree;while under the same water content,the thermal resistivity increases linearly with the increase of the oil content,decreases in non-linearly with the increase of the dry density.Under the same water saturation degree,the thermal resistivity of contaminated soils increases linearly with the increase of the volumetric liquid content;while under the same volumetric liquid content,the thermal resistivity of which decreases in power function with the increase of water and oil saturation degree.Furthermore,the relationship between the electrical resistivity and the thermal resistivity has linearly relation in the double logarithm coordinate system.(5)A model test apparatus is designed to conduct the electrical cone penetration test(RCPTu)in diesel contaminated soils with different water contents and oil contents.The cone resistance,the sleeve friction resistance and the electrical resistivity of different soils are obtained.Meanwhile,the two electrodes method is used to measure the electrical resistivity of different soils during penetrating.Results show that the electrical resistivity values measured by the RCPTu and the Wenner four electrodes method are very close to each other,while the resistivity measured by the two electrodes method is a little bit higher than these measured by RCPTu.Under the same oil content,the electrical resistivity of soil decreases with the increase of water content;under the same water content,the electrical resistivity of soil increases with the increase of oil content.The cone resistance and the sleeve friction resistance of soil decrease with the increase of the water content and the oil content.In addition,the contamination level of oil contaminated soil can be estimated by the amplitude of variation of the cone resistance,the sleeve friction resistance and the electrical resistivity.(6)Electrical cone penetration tests were conducted in a combined polluted site.The values of the cone resistance,the sleeve friction resistance and the electrical resistivity of site soils were obtained.X-ray fluorescence,volatile organic compounds tests and conventional tests were conducted on soil and water samples.Results show that different pollutants have different influence on soils’ electrical resistivity,cone resistance,sleeve friction and soil particle distribution and their pH,the depth of soils affected by contamination is found at about 4 m below the ground level.(7)The evaluation system of the impact of organics on site soils’ pollution characteristics is built based on the Analytic Hierarchy Process.In this system,index properties reflecting changes in soil behavior,mechanical properties,and properties reflecting chemical characteristics of contaminants are considered as parameters for the criteria;while the elements in the system consists of type of contaminant,contaminant concentration,land planning,soil electrical resistivity,and soil thermal resistivity.Weights of each element were given by calculation according to the states of the element,varying from 0 to 100,the index of site contamination SQ is calculate by weighted calculation,the states of contaminated sites are estimated by the index of site contamination SQ.The results obtained from laboratory test and field investigation indicate that the resulting evaluation as per the proposed evaluation system is consistent with the real condition,which proved that the evaluation system built in this study has the value of application.