Wild, Katrin M.
In 2013, the results from the laboratory test series conducted in 2012/2013 to establish the water retention characteristics and relationship between suction and mechanical properties of the clayey facies of Opalinus Clay were integrated and re-evaluated. Water retention characteristics for wetting and drying conditions were established. Results of p-wave velocity measurements showed that the p-wave velocity normal to bedding (vp,n) dropped sharply upon desaturation until suction approached the air-entry value. The sharp decrease was associated with desiccation cracks solely oriented parallel to bedding. For suction in excess of the air-entry value, vp,n was constant, indicating no further desiccation damage. The suction at the shrinkage limit and at the air-entry point are similar in magnitude. The p-wave velocity parallel to bedding (vp,p) remained constant in the entire range of suction investigated. An almost linear increase in stress at the onset of dilation, Young’s modulus, unconfined compressive strength, and Brazilian tensile strength with increasing suction was observed up to a suction of 56.6 MPa. For suction larger than 56.6 MPa, relatively constant strength and stiffness was observed. The increase is associated with the net contribution of suction to strength/stiffness, which decreases non-linearly with decreasing volumetric water content. A comparison between strength values (Brazilian tensile and uniaxial compressive strength) obtained from specimens loaded parallel and perpendicular to bedding suggests a state dependent strength anisotropy. Additionally, two different laboratory test series were initiated in 2013. A first series of 20 confined compressive strength tests on fully saturated P- and S-specimens aims to derive drained and undrained poroelastic and mechanical properties. A second experimental program deals with the investigation of viscoelastic effects and local pore pressure evolution. Conceptual HM-coupled three-dimensional models revealed that pore pressure evolution around an excavation in a transversal isotropic media is strongly dependent on the sensor location with respect to bedding. Elastic volumetric strain may cause a significant drop in pore pressure when the tunnel face passes. This drop is similar to the pore pressure drop associated with dilatancy accompanying failure. To investigate the combined effect of dilatancy and stress-path dependent elastic volumetric straining, improvements of commercially available constitutive laws will be necessary Show more
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Book titleErfahrungs- und Forschungsbericht 2013. Entwicklungen im Bereich der Grundlagen der nuklearen Aufsicht
Journal / seriesErfahrungs- und Forschungsbericht
PublisherEidgenössisches Nuklearsicherheitsinspektorat ENSI
Organisational unit03465 - Löw, Simon
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