During tunnel construction, the unexpected occurrence of anomalies ahead of the tunnel face, such as weak zones, fault zones, and cavities, may cause mechanical failures and ultimately result in casualties. For this reason, various methods to predict the geotechnical ground conditions in advance have been proposed and studied, while conventional geophysical characterization methods have been relied upon. However, the application of conventional geophysical characterization methods is quite limited because of their failure to yield reliable prediction, especially for weak zones near the tunnel face.

An enhanced electrical resistivity prospecting system for predicting weak zones ahead of a tunnel face was developed on the basis of electrical resistivity measurements at the tunnel face. First, the analytical solution is considered the characteristics of the electric field in the rock mass. The analytical solution is designed to estimate the resistivity of an anomaly, such as a weak zone and a faults zone ahead of the tunnel face, and the surrounding host medium, as well as the location and size of the anomaly. Based on the derived equation, an inverse analysis can be performed to estimate the unknown parameters using in-situ measurements. Second, a series of experimental tests was performed using a scaled tunnel model for verification of the analytical solution and the inverse analysis.

Analytical solution designed to estimate the resistivity of multiple anomalies, such as parallel pipes running across the excavation area, are being researched.