Numerical study on electrical resistivity tomography for prediction of anomaly in mechanized tunnelling job-sites

Anomalies, mixed grounds and fractured zones which are not detected by the geotechnical investigation performed during the design stage may cause difficulty when a tunnel is excavated. So, it is important to predict the ground condition ahead of a tunnel face during tunnelling to avoid accidents. Various methods to predict the ground condition ahead of the tunnel face have been studied and developed. The prediction methods such as tunnel seismic profiling, ground penetration radar, probe drilling frequently used at conventional tunnelling job sites. However, few studies applicable to mechanized tunnellingare tried because of the limitation of available spaces in Tunnel Boring Machine (TBM). So, this study proposes a prediction method applicable to mechanized tunnelling using the pre-drilled borehole. Numerical simulations were performed to adopt the most suitable electrode array for prediction of anomaly ahead of the tunnel face when electrical resistivity tomography is performed at mechanized tunneling job-sites. The pole-dipole and modified dipole-dipole array was found to be able to predict the location and condition of an anomaly reasonably well. A remote electrode is always needed to use the pole-dipole array, but it is very difficult to find an appropriate place to install a remote electrode. Accordingly, the modified dipole-dipole array does not need a remote electrode that is the most suitable one to be used for mechanized tunnelling job sites.