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The detection of metallic particles in the subsurface, e.g. for ore exploration or investigation of landfills, has been an important field in applied geophysics for several decades. Because of the high conductivity and high polarizability of metallic particles, geophysical methods using electrical properties, especially induced polarization, are highly relevant.
To correctly interpret the field measurements, a deep understanding of the underlying processes is necessary. Both, lab experiments and theoretical models help to achieve that kind of understanding. However, existing models usually consider idealized situations and are therefore not suitable to directly be compared to experimental results. To overcome this gap, we present a theoretical model of laboratory measurements carried out on cm-scale metallic spheres embedded in a water-saturated sand-column.
We first focus on the spectral IP response of one single sphere in a cylindrical measurement cell. We investigate the influence of the position of the potential electrodes, the position of the sphere inside the cell, and the effect of cell size compared to the sphere's radius. To distinguish the signal of the sphere from the effects of the measurement setup, we compare the results to existing analytical models of one polarizing metallic particle in a medium of infinite size.
We then add a second sphere to study the interaction between the two spheres and the influence of this interaction on the IP signal. We begin with two overlapping spheres and then gradually increase the distance between the centres of both spheres. Comparing the results to the IP response of one single sphere, we can observe the influence of the interaction between the spheres.
Based on these results it is possible to understand the effects caused by the measuring setup and also to get an impression of the effects arising from the interaction of particles in close packings.
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