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

Abstract

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.

Inducing Tensile Failure of Claystone Through Thermal Pressurization in a Novel Triaxial Device

“…Avoiding the desaturation and mechanical damage of cores is an important concern, since the claystone mechanical properties should be kept as close as possible to the natural ones. Shales and claystones are known to be particularly sensitive to changes in water content (Chiarelli et al, 2003;Valès et al, 2004;Zhang and Rothfuchs, 2004;Pham et al, 2007;Zhang et al, 2012), that may occur during the successive processes of coring, storage, transportation and trimming of laboratory specimens (Chiu et al, 1983;Monfared et al, 2011a;Ewy, 2015;Wild et al, 2017). Great attention has hence to be paid to preserve the initial water content of the cored specimens.…”