Research On The Theory And Application Of Volatile Organic Contaminants In-situ Investigation Based On MIP-CPTU Testing

Volatile organic compounds(VOCs)contaminants of underground soil and groundwater has become one of the problems of environmental governance in China.At present,the evaluation methods of VOCs contaminants distribution were time-consuming and expensive.The traditional techniques of contaminated site investigation include drilling,sampling and laboratory analysis.Due to the limited geological information,the location arrangement of many soil drilling and monitoring wells were inappropriate,and the obtained information were not ideal to contribute to the investigation accuracy.In addition,it usually takes weeks for soil drilling and monitoring wells samples to be analyzed in the laboratory.The membrane interface probe(MIP)has been widely used as an efficient tool of organic contaminated site investigation in foreign countries.However,at present,the application of MIP data only determines the relative concentration distribution of contaminants through the absolute value of the signal value.In contaminated site investigation,the influences of geotechnical engineering properties differences of soil layers on the test results were ignored.Piezocone penetration test(CPTU)is one of the most important in-situ test method in the field geotechnical engineering property investigation in the world,which can be used for high-resolution soil layer identification and horizontal permeability coefficient evaluation.These factors can reflect the influence of soil layer difference on MIP test results.Therefore,the combination of the two techniques can improve the test accuracy of the contaminated site,and at the same time more accurately acquire the site geological information,which provides support for the subsequent design of treatment and reuse plan.Under the situation of vacant research of domestic organic contaminated site investigation based on MIP and CPTU techniques(MIP-CPTU)and combined with domestic and foreign literature,the detection mechanism and application were studied.First of all,the principle of MIP test and Comsol numerical simulation are used to determine the test influence area,and then the laboratory tests are designed and carried out to study the influence of fines content on MIP test results.MIP field test was carried out,supplemented by resistivity piezocone penetration test(RCPTU)to obtain and interpret the site geotechnical parameters,and to evaluate the impacts of geological difference on MIP test results.Finally,the test data were modified to obtain the site contaminants concentration distribution map.The main contents of this paper are as follows:(1)Based on the analysis and introduction of MIP testing mechanism and RCPTU,the existing characteristics of organic contaminated soil are analyzed and summarized,mainly including soil thermal characteristics and electrical characteristics.This paper summarized the application of MIP test system in the investigation of contaminated sites,and analyzed the problems existing in the extension of MIP tests in-situ investigation of contaminated sites in China.(2)Combined with MIP probe size and testing mechanism,laboratory model tests were designed.Because the hollow cylindrical soil sample should be prepared in the test,it is necessary to design the sample mold.Through in-situ thermal piezocone penetration test(TCPTU)of the tested soil,the thermal characteristics of the soil were obtained.Then,the influence area of MIP test was analyzed by numerical simulation using Comsol software,and the sample size was determined.In addition,the laboratory model tests were carried out to study the influence of soil fines content on MIP test.(3)The MIP tests was carried out in a waste gas station site in Nanjing,and the operation procedure of MIP test in this site was described.In addition,the site sampling analysis was carried out to find out the types and concentrations of contaminants in this site,which was used as the benchmark for MIP site analysis.Through the statistics and interpreting of the MIP test data,the differences between the MIP data and the sampling data are determined,and the factors which lead to the inconformity were analyzed.The correlation between Total Petroleum Hydrocarbon(TPH)and MIP test signals and the influence of the surface soil-groundwater combination zone on the test were analyzed.(4)MIP test data as the main research objective,supplemented by RCPTU to provide site geotechnical engineering characteristics to support the analysis of influencing factors of MIP test,and at the same time,the acquired soil resistivity was used as the inversion parameter of contaminants concentration to support the results of MIP test.Based on the analysis results,the MIP test results were modified and the site contaminants distribution map was drawn.