Strain Partitioning and Frictional Behavior of Opalinus Clay During Fault Reactivation

Abstract The Opalinus Clay (OPA) formation is considered a suitable host rock candidate for nuclear waste storage. However, the sealing integrity and long-term safety of OPA are potentially compromised by pre-existing natural or artificially induced faults. Therefore, characterizing mechanical behavior microscale deformation mechanisms faults surrounding relevant predicting repository damage evolution. In this study, we performed triaxial tests using saw-cut samples shaly sandy facies to investigate influence pressure mineral composition on during fault reactivation. Dried were hydrostatically pre-compacted at 50 MPa then deformed constant strain rate, drained conditions confining pressures ( p c ) 5–35 MPa. Mechanical data from was complemented local measurements determine relative contribution bulk slip, as well acoustic emission (AE) monitoring, elastic P-wave velocity ultrasonic transmissions. With increasing , observe transition brittle with highly localized slip semi-brittle characterized non-linear hardening delocalization deformation. We find that localization limited which strength exceeds matrix yield strength. AEs only detected in samples, activity decreased . Microstructural analysis revealed positive correlation between gouge layer thickness. This goes along change fragmentation frictional sliding development shear zones higher cataclastic granular flow. Friction coefficient reactivation slightly µ ~ 0.48) compared 0.4). Slide-hold-slide after 6 mm axial shortening suggest stable creeping weakness applied conditions. Our results demonstrate mode depends present stress field burial history.