土壤毛细带内油污染区探地雷达异常特征分析及状态评价

Abnormal features analysis and status evaluation for oil contaminated site in capillary zone based on ground penetrating radar

石油污染发生后,油类物质最终在土壤毛细带富集,污染区随地下水流动而扩散,在相应探地雷达探测剖面上亦应表现为不同异常特征.这种变化会给探测剖面准确解译带来极大困难.为清晰界定不同状态油污染区探地雷达探测剖面特征,在实验室模拟毛细带内柴油汇聚、扩散过程,获得900 MHz雷达天线实时监测剖面;并进一步根据模拟结果构建油污染区介电模型,数值计算得到100 MHz、250 MHz、400 MHz天线理论探测剖面,分析实际探测情形下剖面异常特征,研究量化评价分析方法.研究表明:汇聚初期,毛细带内油污染区呈明显的高幅弧状反射异常,毛细带顶界面反射轴有错断现象;扩散过程中反映污染区的弧状异常反射逐渐减弱,当含油饱和度低于50%时,油污染区演变为明亮的、有相连趋势的斑点状异常,毛细带顶界面反射轴错断现象消失.探测信号振幅比和污染区含油饱和度呈正相关关系,当污染区含油饱和度大于50%时,异常信号易于识别;当含油饱和度低于20%时,信号难以识别.250 MHz天线探测剖面具有良好探测效果.

After the oil pollution occurs,the oil material is finally enriched in the soil capillary zone,the contaminated area spreads with the flow of groundwater,and it shows different abnormalities in the corresponding ground penetrating radar detection profile. This change will bring great difficulties to explain the detection profiles accurately. In order to clarify the characteristics of the detection profiles about oil pollution area in different states,the diesel fuel pooling and diffusion process in the capillary zone were simulated in the lab,and the real-time monitoring profiles of the 900 MHz radar antenna was obtained. Based on the simulation results, the dielectric model builds further,the 100 MHz,250 MHz,400 MHz antenna obtained by numerical calculation is used to analyze the profile anomalies, and the quantitative evaluation method. The results show that the anomalous arc-shaped reflex anomaly is obvious at the initial stage of convergence,and the the reflection axis at the top of the capillary is broken. In the process of diffusion,the arclike anomaly reflection in the contaminated area is weakened gradually. When the oil saturation is low at 50%,the oil pollution area evolved into bright,with the trend of the spot-like anomaly,the broken reflection axis at the top of the capillary disappeared.There is a positive correlation between the amplitude of the detection signal and the oil saturation in the contaminated area. When the oil saturation is greater than 50%,the anomaly signal is easy to be identified. When the oil saturation is less than 20%,the signal is difficult to be identified. 250 MHz antenna detection profile has a good detection effect.