Tunnel Magnetic Resonance Tomography for 2-D Water-Bearing Structures Using Rotating Coil With Separated Loop Configuration

Abstract

In tunnel construction, to prevent the occurrence of water inrush, the geological conditions of faults and underground rivers must be determined in advance. As a direct detection method of groundwater, magnetic resonance sounding (MRS) has been applied for the advanced detection of water-related hazards in tunnels and mines recently. However, the results of conventional 1-D MRS cannot correctly reflect the spatial distribution characteristics of complicated water-bearing structures. In this article, we propose a measurement scheme using a rotating coil with separated transmitter and receiver loop configuration (SEP) for the 2-D imaging of water-bearing structures, such as faults and conduits. In this scheme, the receiver coil rotates several times, while the transmitter coil, which is separated from the receiver coil by a certain distance, remains stationary. Moreover, all the observed data participate in the inversion to achieve the 2-D magnetic resonance tomography (MRT). Numerical simulations of water-bearing faults are performed, and we compare and analyze the 2-D sensitivity and inversion results of two measurement schemes for a rotating coil, i.e., an overlapping transmitter and receiver loop configuration (OVE) and SEP. The results showed that the imaging results of the SEP are better than those of the OVE because the OVE imaging has a symmetric artifact. Finally, we discuss the influence of the transceiver distance, the resistivity, and the environmental noise on the imaging results. Moreover, the imaging results of the water-bearing conduit at different locations were obtained to validate the effectiveness of the SEP rotating coil measurement scheme.