Publication Date:
2023-11-15
Description:
The mechanical behavior of the sandy facies of Opalinus Clay (OPA) was investigated in 42 triaxial tests performed on dry samples at unconsolidated, undrained conditions at confining pressures (pc) of 50–100 MPa, temperatures (T) between 25 and 200 °C and strain rates (ε˙) of 1 × 10〈sup〉–3〈/sup〉–5 × 10〈sup〉–6〈/sup〉 s〈sup〉−1〈/sup〉. Using a Paterson-type deformation apparatus, samples oriented at 0°, 45° and 90° to bedding were deformed up to about 15% axial strain. Additionally, the influence of water content, drainage condition and pre-consolidation was investigated at fixed p〈sub〉c〈/sub〉–T conditions, using dry and re-saturated samples. Deformed samples display brittle to semi-brittle deformation behavior, characterized by cataclastic flow in quartz-rich sandy layers and granular flow in phyllosilicate-rich layers. Samples loaded parallel to bedding are less compliant compared to the other loading directions. With the exception of samples deformed 45° and 90° to bedding at p〈sub〉c〈/sub〉 = 100 MPa, strain is localized in discrete shear zones. Compressive strength (σ〈sub〉max〈/sub〉) increases with increasing p〈sub〉c〈/sub〉, resulting in an internal friction coefficient of ≈ 0.31 for samples deformed at 45° and 90° to bedding, and ≈ 0.44 for samples deformed parallel to bedding. In contrast, pre-consolidation, drainage condition, T and ε˙ do not significantly affect deformation behavior of dried samples. However, σ〈sub〉max〈/sub〉 and Young’s modulus (E) decrease substantially with increasing water saturation. Compared to the clay-rich shaly facies of OPA, sandy facies specimens display higher strength σmax and Young’s modulus E at similar deformation conditions. Strength and Young’s modulus of samples deformed 90° and 45° to bedding are close to the iso-stress Reuss bound, suggesting a strong influence of weak clay-rich layers on the deformation behavior.
Description:
Bundesministerium für Bildung und Forschung
http://dx.doi.org/10.13039/501100002347
Description:
Helmholtz-Gemeinschaft
http://dx.doi.org/10.13039/501100001656
Description:
Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum - GFZ (4217)
Keywords:
ddc:550.78
;
Clay rock
;
Sandy facies of Opalinus Clay
;
Triaxial deformation experiments
;
Microstructural deformation mechanisms
;
Pressure-, temperature- and strain rate-dependent mechanical behaviour
;
Anisotropy
Language:
English
Type:
doc-type:article
Permalink
