Impact of Mineralogical Composition on Geotechnical Properties of Opalinus Clay

Opalinus Clay is the selected host geomaterial for the construction of underground geological disposals for radioactive waste in Switzerland. The formation has been studied in several sites, i.e. the Mont Terri laboratory, and several boreholes in the northeastern part of the Country, and several lithostratigraphic sub-units were identified. In this work, a hydro-mechanical testing campaign was performed on samples from a recently cored shallow borehole (< 70), and the results were compared with previous testing campaigns. The mineralogical compositions of the specimens were analysed and correlated with the geotechnical properties and hydromechanical behaviour. It is shown that the mineralogy (and in particular the clay-mineral content) plays a predominant role on the specimen compaction properties. On the other hand, the burial history is manifested in the porosity of the geomaterial, that is considerably lower for the samples sourced at greater depth with a similar composition.