Direct Shear Strength Test on Opalinus Clay, a Possible Host Rock for Radioactive Waste

Abstract

In the past decades the long term safe storage of highly active radioactive waste has been one of the greatest challenges for engineers and scientists to be solved. It is internationally agreed that the radioactive waste should be placed into deep geological formations, namely into granite, salt or clay stone. The latter type, in particular the Opalinus Clay stone, is the potential host rock for such repository in Switzerland. The aim of the paper is to broaden the knowledge on this rock type. Direct shear strength tests were carried out, to provide data on the maximal shear strength, friction coefficient and the connection between the plane of the bedding and the plane of the natural fault. The samples were derived from the major fault zone. The specimens were sheared along natural open joints under 1 MPa constant normal load (CNL) condition. Another set of experiments were carried out on intact samples disturbed by a soft clay vein. The shear plane was the same as the plane of the intrusion. On these specimens different normal stresses were applied, between 0.5 and 2 MPa. Apart from the maximal shear strength and the friction coefficient, the cohesion and the consolidation settlement (vertical displacement during the application of the initial normal stress, before the shear test started) were determined as well.