Development Of TDR Penetrometer And Using For The Investigation Of Contaminated Site

With the development of society and economy, the problem of contaminated site becomes more and more serious. The affairs of soil and water pollution (e.g. heavy metal, NAPLs) have frequently occurred and caused high attention. However, little attention has been paid on the survey of contaminated site. In this paper, numerical analysis, unite tests and model tests have been used to research the sample area and skin effect of three rod TDR probes; the applicability of using TDR method to detect the NAPLs contaminated soil; the optimization of electrode array for the TDR penetrometer and detection of soil water content, leachate and NAPLs contaminated soil. Several significant conclusions are achieved.(1) The sample area and skin effect of three rod TDR probe could be analyzed by SEEP/W module in the software of Geostudio. For the three rod TDR probe with rod diameter and rod spacing ranging from4mm to8mm and15mm to60mm respectively, the sample area increases significantly with the increasing of rod spacing and this two parameters satisfy a quadratic curve relationship, the rod diameter has insignificant effect on the sample area; the skin effect becomes serious with the increasing of rod spacing and improves with the increasing of rod diameter, Similarly, the skin effect and rod diameter-rod spacing ratio also satisfy a quadratic curve relationship.(2) For the specimens of NAPLs-water-air-sand mixtures:When the θw was kept constant, insignificant change in the dielectric constant was observed as θdiesel increased, and the electrical conductivity changed insignificantly and irregularly. When the θdiesel was kept constant, both the dielectric constant and electrical conductivity increased significantly as θw increased. When the θliquid was constant, both the dielectric constant and electrical conductivity increased significantly as the ratio of θw to θdiesel increased. In this case, the dielectric constant can be will predicted by using the a model.(3) For the specimens with diesel contaminated sand layer being sandwiched in sand layer: When being sandwiched between two saturated sand layers, the contaminated sand layer resulted in a significant change in dielectric constant, and the interfaces could be identified by analyzing the recorded reflection waveform. When being sandwiched between two dry sand layers, the contaminated sand layer resulted in insignificant change in dielectric constant, and the interfaces could not be identified. When the diesel contaminated sand layer being sandwiched between the dry sand layer and the saturated layer, the interface close to the saturated sand layer could be identified.(4) With the proposed weight allotion equation and its numerical method, the sensitivity of measuring target medium of two current TDR penetrometers is analyzed. Through the analysis resluts, unreasonable design of TDR penetromenter could affect its sensitivity to the target medium and then, its measurement accuracy would be reduced.(5) By the numerical method, the array of electrodes of the TDR penetrometer is optimized and a new TDR penetrometer is designed. Comparing with the current TDR penetrometers, the proposed TDR penetrometer increases20%in the sensitivity to target mediums, therefore, its measurement accuracy improves. The reflection signal of the proposed TDR penetrometer is stable and easy to identify the characteristic reflection points in the laboratory calibration tests. The calibration equations to measure dielectric constant and electrical conductivity have high linearity.(6) Through model tests, the TDR penetrometer could measure dielectric constant and electrical conductivity in different soil layers effectively. With these two electrical parameters, the soil water content, leachate contaminated soil and NAPLs contaminated soil could be well detected.