Temporal GPR Imaging Of An Oil Release Within Undergound Sandy Soil

The spilled out oil leakage, under the joint action of its own gravity and capillary force, along the solid skeleton particles into the vadose zone, the void among the unsaturated layer first suffer from pollution, excessive oil continue to form free fluid infiltration to the underground water surface, and with the groundwater flow diffusion, more pollution area.Underground oil pollution area spatio-temporal evolution at different stages, this paper presents the dielectric characteristics and ground penetrating radar (GPR) to detect ability to carry out the experiment and forward modeling, analysis of different stages of the dielectric medium follow pollution model, the anomaly characteristics of the GPR detection section and describe the assessment method, to determine the differences of different phase, improve the pertinence of ground-penetrating radar data processing and interpretation accuracy.Researches show that:(1)Compared to clean unsaturated sand, the polluted soil’s dielectric constant in unsaturated zone Significantly larger, The greater the initial water content, the greater the increase amplitude, the polluted soil’s dielectric constant mainly controlled by moisture content, although dielectric constant increases with the increasing oil content, the increase amplitude is less than I. Mixed dielectric constant and Dielectric constant of components follow the CRIM dielectric model. Unsaturated soil pollution on the GPR profile shows characteristics of high amplitude and low frequency anomaly, anomaly amplitude is correlated with soil initial moisture content When the initial water content below 10% volume, It is difficult to identify the anomaly. The greater the initial water content, the more obvious anomaly features. Pollution area travel time anomalies are not obvious.(2) Free fluid in the capillary zone pollution area is also characterized by high-amplitude and low-frequency, intersects with reflection axis in the surface of water table. With the expanding of pollution area, abnormal area also increases accordingly, both have good corresponding relation. Due to permittivity decreased significantly in the pollution area, the corresponding Reflection axis at the bottom of the aquifer become warped,This is a typical symbol in identification of pollution.(3)Pollutants degradation process, underground water level drops, pollution area was significantly high isolation of the anomaly characteristics of the low frequency. With growth time, the oil pollutant degradation, the anomaly characteristics of the contaminated area.Use energy amplitude slice method can realize the pollution area described in three dimensional space.Comparing to the results of different stages of the research, we can determine that it is difficult to describe the area of polluted unsaturated zone by using ground penetrating radar technology, but we can effectively describe the distribution of the free fluid or the evolution of oil polluted area in the degradation process. We can establish polluted dielectric model using the method of reflection wave. However, the analysis method of pollutant content is not feasible in the practical application to determine the mixture permittivity. Exploring a new and effective hybrid permittivity method is the key to realize pollutant content analysis basing on GPR data. This thesis is to study in the future.