Uncertainty analysis of UMRS parameters and its application for water detection in the tunnel

Abstract

As a novel geophysical exploration technology, the underground magnetic resonance sounding (UMRS) method has been applied to detect water inrush in underground construction over the past 10 years. Non-invasive UMRS technology has found potential use in preventing water inrush disasters in tunnel due to its direct sensitivity to water molecules. Small water bodies are often the origin of severe water inrush disasters in tunnels. In most cases, UMRS signals have a low SNR, yielding high uncertainties that are important to be correctly estimated for an optimal interpretation of the water distribution. In this paper, we describe a method by which to evaluate the uncertainty of UMRS parameters for advanced water detection in tunnels, calculating for the quasi-whole space model. The key point is that the response caused by water surrounding the tunnel is non-negligible. In addition, we discuss the resolution of water content as the main inverted parameter for UMRS advanced detection. In order to guide the configuration of the acquisition settings, the influences of some parameters, including coil size and turns, tunnel size, water content surrounding the tunnel lane, as well as the noise level, on the uncertainty of the advanced target, are analyzed. Finally, we invert a set of measurement data related to a case of tunnel advanced detection, and analyze the uncertainty of the results.Based on the study results, we have concluded that during the advanced detection the water content surrounding the tunnel may significantly increase the uncertainty of the target. In addition, the increasing coil size and number of turns cause an increase in the amplitude of the signal, and also provide a reduction in the uncertainty of the water content. However, at the same time, these also introduce a higher noise level, which may offset the improvement. For these reasons, it is necessary to conduct the parameter uncertainty analyses according to different tunnel environmental conditions before performing the field test, so as to obtain reliable UMRS results.