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

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 emis- sion 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 deter- mined according to the IP effect parameters differences at the measuring electrode nodes along different directions.