Predicting anomalous zone ahead of tunnel face utilizing electrical resistivity: I. Algorithm and measuring system development

This study applies the harmony search (HS) inverse analysis algorithm and develops the tunnel resistivity prediction (TRP) system for predicting the location, thickness, permittivity ratio, and conductivity of the anomalous zone ahead of the tunnel face by utilizing electrical resistivity. The relationship between the four characteristic values of the anomalous zone and the electrical resistance is derived using Gauss’ laws and Ohm's laws. The optimum values of HS algorithm operators (such as the harmony memory considering rate (HMCR) and the pitch adjust rate (PAR)) are proposed that can provide the best inverse analysis that correlates the four characteristic values with the electrical resistance. Also, the prediction accuracy of inverse analysis using the proposed HS algorithm is verified by laboratory tests on the artificially formed ground with an anomaly. An electrical resistance measuring system is devised to obtain the electrical resistance of the ground, and inverse analyses are performed from the measured resistance to estimate the four characteristic values of the artificial anomaly. The test results from laboratory scale experiments show that the characteristics of the anomalies are predicted reasonably well, resulting in less than 3% average error. This paper is part 1 of the companion papers; the second paper will verify the developed system through the field tests.