Feasibility of induced magnetic gradient surveying for seepage detection in earth-filled dams: Insights from synthetic and field studies

Seepage is a common hydrogeologic hazard in engineering. Determining the seepage paths is vital for derisking the instability of embankment structures. With the improvement of the acquisition accuracy of magnetic sensors, the magnetometric resistivity method has become an emerging technology for detecting seepage paths through earth-filled dams. This technique is nondestructive and gives prominent signals. However, the resulting magnetic data have seen ambiguity in fully determining the targets. We develop an induced magnetic gradient surveying approach to monitor seepage paths in earth-filled dams. First, we briefly review the electromagnetic theory for the magnetic gradient tensor based on Maxwell’s equations. To match against the measurements, we present an accurate modeling framework using the third-order finite-element method and a novel compact difference scheme. We verify our approach on semianalytical 1D and 3D models. Systematic modeling studies are then carried out to investigate the spatial distribution characteristics and sensitivities of the induced magnetic gradient to the seepage in typical dam scenarios. In addition, we conduct two field experiments in the Zhongmou experimental base and Xixiayuan Reservoir in Henan Province, China, respectively. The induced magnetic field vector and its gradient components are both acquired. Cross-validation with a priori geologic information shows that the seepage path can be spatially identified by the induced magnetic gradient components [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text], whereas the field components failed to locate the seepage pathways. This successful application indicates that our approach could be a promising solution for seepage path discrimination in earth-filled dams with high resolution.