Articles | Volume 8, issue 2
Solid Earth, 8, 351–360, 2017
Solid Earth, 8, 351–360, 2017

Research article 30 Mar 2017

Research article | 30 Mar 2017

The response of Opalinus Clay when exposed to cyclic relative humidity variations

Katrin M. Wild, Patric Walter, and Florian Amann Katrin M. Wild et al.
  • Department of Earth Sciences, Geological Institute, ETH Zurich, 8092 Zurich, Switzerland

Abstract. Clay shale specimens were exposed to cyclic relative humidity (RH) variations to investigate the response of the material to natural environmental changes. Opalinus Clay, a clay shale chosen as host rock for nuclear waste disposal in Switzerland, was utilized. The specimens were exposed to stepwise relative humidity cycles in which they were alternately allowed to equilibrate at 66 and 93 % relative humidity. Principal strains were monitored throughout the experiments using strain gauges. After each relative humidity cycle, Brazilian tensile strength tests were performed to identify possible changes in tensile strength due to environmental degradation.

Results showed that Opalinus Clay follows a cyclic swelling–shrinkage behaviour with irreversible expansion limited to the direction normal to bedding, suggesting that internal damage is restricted along the bedding planes. The Brazilian tensile strength in direction parallel and normal to bedding as well as the water retention characteristic remained unaffected by the RH variations.