The Influence of Bedding Orientation and Temperature on the Creep Behavior of Opalinus Clay

The time dependency of deformation is of critical concern for assessing the integrity of barriers in nuclear waste repositories. Creep, in particular, is a phenomenon recognized for its potential “self-sealing” properties or, conversely, the potential for delayed failure in the rock mass surrounding an excavation. However, in clay shales, the underlying mechanisms and their stress-dependency are not yet fully understood. To investigate the creep behavior of clay shales, a series of drained multi-stage creep tests was performed on pre-consolidated and saturated specimens of the shaly facies of Opalinus Clay. This study further focuses on the impact of the structural anisotropy by testing specimens loaded parallel or perpendicular to the bedding. The results demonstrate a considerable anisotropic creep behavior concerning both primary and secondary creep. A shift in mechanisms was observed with increasing differential stress, referred to as the long-term strength, which coincided for both loading configurations. Furthermore, considering the tests performed at both 30 and 60 (Formula presented.), there was no statistical evidence to suggest that the creep mechanisms were temperature-dependent.