Application of electrical resistivity techniques to detect weak and fracture zones during underground construction

The scope of the electrical resistivity survey has recently been extended to various fields beyond groundwater and underground resource exploration. Electrical resistivity techniques were evaluated in two case studies to substantiate their applicability to geotechnical and environmental problems. First, electrical resistivity imaging (ERI) was used to map the fractured zone ahead of the tunnel face during construction using the new Australian tunneling method (NATM). The ERI technique could adequately modify tunnel support patterns in quasi-real time, on the basis of the field test results, and could subsequently improve the stability of tunnel excavation. Second, electrical resistivity tomography (ERT) was used between two test boreholes in a research tunnel site to monitor the movement of brine after it was injected in one of the two boreholes. A pair of low-conductivity zones that were regarded as the pathway of groundwater flow between the two boreholes was clearly imaged because of enhancement of conductivity caused by diffusion of the brine. The applicability of electrical resistivity techniques to geotechnical and environmental problems was successfully substantiated.