Laboratory investigations for the evaluation of in situ geophysical measurements in a salt mine

Abstract: Problem zones in a sylvinite mine were explored by underground measurements using a set of geophysical methods (geosonar, seismics, georadar, EM methods and geo-electrics), which yield parameter sets for disturbed and undisturbed rock. Underground geo-electrical methods are most suitable for examining humidity content and structures for the transport of brines, although they have to be constrained by wave-propagation methods. Additional laboratory experiments on rock salt samples were carried out in order to provide quantitative evaluation methods. A titration method was used to determine the amount of water. This was applied simultaneously with a four-electrode r sistivity measuring system for samples with very high resistivity. These measurements were made on samples at different scales, yielding relationships between water content and resistivity, as well as information about the parameter distribution i larger core samples. Together, the field and laboratory esults show that geo-electrics is a suitable method for the detection and evaluation ofproblem zones of the geological barrier of hazardous waste repositories, and a criterion for the risk assessment based upon resistivity measurements is defined. High plasticity, high thermal conductivity, an