坑道聚焦双频激电法探测技术

Research on the detection technology of focusing dual-frequency induced polarization method in tunnel

为增加坑道断面前方勘探深度,减小电场全空间效应及干扰因素,发展成为聚焦双频激电法超前探测新技术。根据聚焦双频激电效应探测机理,建立电场线微分方程,分析聚焦双频激电法探测电场空间电流密度分布规律。利用有限单元法求解空间多点电源场异常电位的边值与变分问题,分析空间各节点电位聚焦效应分布特性,数值模拟断面中心两侧测量电极节点处的视电阻率和视幅频率随发射电流变化规律。搭建土槽物理模型试验平台,开展不同规模、不同方位含水异常体聚焦激电效应探测。测试结果表明:随电流的增加,视电阻率逐渐减小,视幅频率逐渐增加,且当激电效应参量达到极值点后,视电阻率增加和视幅频率减小的幅度趋于平缓;与仅有一个含水异常体相比,存在两个含水异常体时具有较为明显的异常激电效应特征;根据不同方位测量电极节点处的激电效应参量差异程度确定异常体存在的具体方向。

According to focusing dual-frequency IP effect detection mechanism, this paper establishes a differential equation of electric field lines and analyzes the electric current density distribution of focusing dual-frequency IP method detecting electric field in order to increase the exploration depth in front of the tunnel section, reduce the full spatial effect and interference factors of the electric field, and develop a new technology for advanced detection. The fi- nite element method is used to solve the boundary value and variation problems of abnormal potential with multi-point power sources in tunnel. Through analyzing the focusing effect distribution characteristics of each measuring electrode node on the both sides of the section center, the variation of apparent resistivity and apparent frequency with the emission current is numerically simulated. The test platform of soil groove physical model is set up to carry out the focusing IP effect detection of water-bearing anomalies with different scales and different orientations. The test results are as fol- lows：with the increase of current, the apparent resistivity decreases gradually while the apparent frequency increases gradually, and this variation amplitude of the apparent resistivity increase and the apparent frequency decrease tends to be slow after the IP effect parameters reach an extreme value point. Only compared with one water-bearing anomaly, two water-bearing anomalies have obvious abnormal IP effect features. The specific direction of anomalies is determined according to the IP effect parameters differences at the measuring electrode nodes along different directions.