石英砂岩体的地质雷达波频谱特征

经过岩土体介质反射回的地质雷达波特征携带了所穿透的岩土体内部的相关信息,其中地质雷达波频谱主频值可以作为判断岩土体结构特征的一个定量指标. 以围岩为石英砂岩的公路隧道工程为依托,采用MALA地质雷达配100 MHz屏蔽天线,对隧道掌子面前方的石英砂岩体进行超前地质探测试验,分析典型的Ⅴ级、Ⅳ级和Ⅲ级石英砂岩围岩的雷达波形图图像特征和雷达波在岩体介质中传播的傅里叶频谱特征. 通过分析现场试验数据,得出岩体介质的雷达波主频值因自身结构特征和周边环境变化而在一定的敏感频率区间内的规律. 对比分析研究结果与工程开挖实际,表明通过分析超前地质探测获得的雷达波傅里叶频谱主频值特征来反演识别围岩结构特征是切实可行的.

Frequency spectrum characteristic of quartz sandstone rock mass with GPR

Ground penetrating radar ( GPR) electromagnetic waves which penetrate through rock and soil mediums and are reflec-ted back carry internal information about the target objects. The GPR basic frequency values of Fourier spectra can be used as a quan-titative index of judgment for the structure characteristic of rock and soil mediums. Based on a highway tunnel project with the surrounding rock of quartz sandstone, advanced geological exploration test was carried out in front of the tunnel face with MALA GPR and a 100 MHz shielded antenna. Typical Class Ⅴ, Class Ⅳ and Class Ⅲ quartz sandstone surrounding rock mass were chosen to analyze their waveform graph information characteristic and the Fourier spectrum frequency characteristic during electromagnetic wave propagation in rock mass mediums. The regularity of GPR wave basic frequency values corresponding to the quartz sandstone rock mass medium in a certain sensitive frequency range due to its structure and surrounding environment changes was obtained through field test data analysis. A comparison between the research results and engineering excavation practices shows that it is feasible to invert the basic frequency value characteristic of GPR waves derived from advanced geological exploration for determining the structure character-istics of surrounding rock.