Risky Ground Prediction ahead of Mechanized Tunnel Face using Electrical Methods: Laboratory Tests

Abstract

An accurate determination of the ground condition ahead of a tunnel face is key to stable excavation of tunnels using a Tunnel Boring Machine (TBM). This study verifies the effectiveness of using the Induced Polarization (IP) method along with electrical resistivity for identifying hazardous ground conditions ahead of a tunnel face. The advancement of the TBM toward a fault zone, seawater bearing zone, soil-to-rock transition zone, and mixed-ground zone is artificially modeled in laboratory-scale experiments. The IP and resistivity are assumed to be measured at the tunnel face, whenever the excavation is stopped to assemble one ring of a segmental lining. The measured IP showed completely different trends from the measured resistivity and varies with the type of hazardous zone. As the TBM approached the fault zone, transition zone, and mixed ground, the IP values were observed to be constant, increasing, and fluctuating, respectively. Therefore, a more reliable prediction of the ground condition ahead of a tunnel face can be achieved by using the IP and resistivity methods together. A table that can be used to predict the ground conditions based on the afore-mentioned methods is presented in this paper for use in mechanized tunneling job sites.