灰岩隧洞围岩结构面空间位置及填充物FDTD正演

地质雷达(GPR)法是以电磁波在岩土体介质中的反射和衰减,通过电磁波回波信号反映灰岩隧洞中岩体结构面空间位置及其填充物。建立单条裂隙、双条裂隙和交叉裂隙及其空间位置的二维地电模型,设置结构面中的填充物为空气、泥土、水;以FDTD法正演模拟并对比分析其图像特征。结论如下:填充物对结构面的判据具有较大影响,水对电磁波的强烈吸收作用导致图像成像特征复杂,多次反射波规律性较强;结构性的探测取决于介质介电常数的差异,且近掌子面的结构面对电磁波的反射和吸收形成多次波干扰深部结构面的成像。FDTD正演结果对地质预报的判断提供科学依据和指导作用。

FDTD Forward Modeling of Structural Face and Filler in Space of Limestone Tunnel Surrounding Rock

Ground Penetrating Radar (GPR)is based on reflection and attenuation of electromagnetic wave in rock tunnel. And we observe the spatial structure and physical properties of the medium through the echo signal. In this article, we build a 2-D geoelectric model of single joint, double joints and intersected joints. Simultaneously, its spatial location and the fillers of air, soil and water are also considered in this model. Therefore, the comparison and analysis of its image characteristics can be reached with FDTD forward modeling. The composition of filler has great influence in estimating the joint. The reflection and absorption of electromagnetic wave in the water is strong and obvious. The image of structure characteristics is distinct, but the regularity of multiple waves is obvious. The detection of structural joints depends on the diversity of dielectric constants. And the joint close to the lining face has reflection and absorption to the electromagnetic wave, which disturb the imaging of the deep structure. The forward analysis results provide scientific basis and guidance for the geology forecast.