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| Titel |
Evidence of non-Darcy flow and non-Fickian transport in fractured media at laboratory scale |
| VerfasserIn |
C. Cherubini, C. I. Giasi, N. Pastore |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 17, no. 7 ; Nr. 17, no. 7 (2013-07-09), S.2599-2611 |
| Datensatznummer |
250018926
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| Publikation (Nr.) |
 copernicus.org/hess-17-2599-2013.pdf |
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| Zusammenfassung |
During a risk assessment procedure as well as
when dealing with cleanup and monitoring strategies, accurate predictions of solute propagation in fractured rocks are of
particular importance when assessing exposure pathways through which
contaminants reach receptors.
Experimental data obtained under controlled conditions such as in a
laboratory allow to increase the understanding of the fundamental physics of
fluid flow and solute transport in fractures.
In this study, laboratory hydraulic and tracer tests have been carried out on
an artificially created fractured rock sample. The tests regard the analysis
of the hydraulic loss and the measurement of breakthrough curves for saline
tracer pulse inside a rock sample of parallelepiped shape (0.60 × 0.40 × 0.08 m).
The convolution theory has been applied in order to
remove the effect of the acquisition apparatus on tracer experiments.
The experimental results have shown evidence of a non-Darcy relationship
between flow rate and hydraulic loss that is best described by Forchheimer's
law. Furthermore, in the flow experiments both inertial and viscous flow
terms are not negligible.
The observed experimental breakthrough curves of solute transport have been
modeled by the classical one-dimensional analytical solution for
the advection–dispersion equation (ADE) and the single rate mobile–immobile
model (MIM). The former model does not properly fit the first
arrival and the tail while the latter, which recognizes the existence of
mobile and immobile domains for transport, provides a very decent fit.
The carried out experiments show that there exists a pronounced mobile–immobile
zone interaction that cannot be neglected and that leads to a non-equilibrium
behavior of solute transport. The existence of a non-Darcian flow regime
has showed to influence the velocity field in that it
gives rise to a delay in solute migration with respect to the predicted
value assuming linear flow. Furthermore, the presence of inertial effects
enhance non-equilibrium behavior. Instead, the presence of a transitional
flow regime seems not to exert influence on the behavior of dispersion. The
linear-type relationship found between velocity and dispersion
demonstrates that for the range of imposed flow rates and for the selected
path the geometrical dispersion dominates the mixing processes along the
fracture network. |
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