THEORETICAL AND EXPERIMENTAL INVESTIGATIONS FOR CAVITY RESEARCH WITH GEOELECTRICAL RESISTIVITY METHODS*

Abstract

A bstract The exact localization of subterranean cavities and the determination of their dimensions is very important for the planning of geotechnical and mining activities. It is a complicated geophysical task often at the limit of detection. Nevertheless geophysical investigation is the only alternative to a dense and expensive grid of boreholes. This report tests the usefulness of geoelectrical resistivity methods for cavity detection under some new aspects. The basis for evaluation was a theoretical analysis of different conventional and focussing measuring arrays and of special arrays for a geoelectrical research between two boreholes. The limit of detectability of a cylindrical cavity of defined cross‐section and depth was calculated for the different measuring arrays on the basis of computation of the apparent resistivity ρ a. Furthermore, the influence of possible errors (current supply of the electrodes and the distance between the electrodes) is discussed for focussed systems. The second part of the article is directed at the behaviour of the apparent resistivity ρ a , the disturbing potential δV d caused by the cavity and the normal potential δV 0 of the measuring array all in relation to a homogeneous earth. Some new results are presented. In the last part of the article theoretical results are compared with some field measurements.