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| Home > Publications database > Experimental and numerical analysis of flow through a natural rough fracture subject to normal loading |
| Journal Article | FZJ-2024-01832 |
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2024
Macmillan Publishers Limited, part of Springer Nature
[London]
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Please use a persistent id in citations: doi:10.1038/s41598-024-55751-w doi:10.34734/FZJ-2024-01832
Abstract: Fractured crystalline rocks have been chosen or are under consideration by several countries as hostrock formations for deep geological repositories for spent nuclear fuel. In such geological formations,flow and solute transport are mostly controlled by a network of connected natural fractures, eachof them being characterised by internal heterogeneity, also denoted as roughness. Fractures are, inturn, subject to variable load caused by various factors, such as the presence of thick ice sheets formedduring glaciation periods. Understanding how coupled hydro-mechanical (HM) processes affect flowand transport at the scale of a single natural fracture is crucial for a robust parameterisation of largescalediscrete fracture network models, which are not only used for nuclear waste disposal applicationsbut are also of interest to problems related to geothermics, oil and gas production or groundwaterremediation. In this work, we analyse and model an HM experiment carried out in a single naturalfracture and use the results of both, the experimental and the modelling work, to get insights intofundamental questions such as the applicability of local cubic law or the effect of normal load onchanneling. The initial fracture aperture was obtained from laser scanning of the two fracture surfacesand an equivalent initial aperture was then defined by moving the two fracture surfaces togetherand comparing the results obtained using a Navier–Stokes based computational fluid dynamics (CFD)model with the experimental flowrate obtained for unloaded conditions. The mechanical effect of thedifferent loading stages was simulated using a high-resolution contact model. The different computedfracture apertures were then used to run groundwater flow simulations using a modified Reynoldsequation. The results show that, without correction, local cubic law largely overestimates flowrates.Instead, we show that by explicitly acknowledging the difference between the mechanical apertureand the hydraulic aperture and setting the latter equal to 1/5 of the former, cubic law provides a veryreasonable approximation of the experimental flowrates over the entire loading cycle. A positivecorrelation between fluid flow channeling and normal load is also found.
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