Experimental and numerical investigations on the effect of fracture geometry and fracture aperture distribution on flow and solute transport in natural fractures

Stoll, Madeleine; Huber, Florian; Trumm, Michael; Enzmann, Frieder; Meinel, Dietmar; Wenka, A.; Schill, Eva; Schäfer, Thorsten

doi:10.1016/j.jconhyd.2018.11.008

Cited by 52 publications

(32 citation statements)

References 39 publications

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“…Variable aperture distributions result in preferential flow channels [5,6,14] and low velocity zones that include nonlinear flow features like eddies [2,3,15]. Therefore, smooth parallel plate models have been rejected as suitable simplification for contaminant transport in real fractures [6,16].…”

Section: Introductionmentioning

confidence: 99%

“…In general, reactive and non-reactive transport processes in single fractures have been studied extensively in laboratory experiments and especially in numerical simulations. Several studies deal with experimental tracer tests in single fractures in different materials including sandstone [23], granite [16], diorite [14], dolomite [6], limestone [41] and replicas of scanned fractures [26,27,37,38]. Focus point of several of those studies is the effect of fracture surface alteration on flow and transport processes, e.g., due to the generation of biofilms [40] or due to sorption processes [23].…”

Section: Introductionmentioning

confidence: 99%

“…Focus point of several of those studies is the effect of fracture surface alteration on flow and transport processes, e.g., due to the generation of biofilms [40] or due to sorption processes [23]. Comparing altered and unaltered fractures suggests different flow-controlling geometrical factors [16].…”

Section: Introductionmentioning

confidence: 99%

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Comparison of Surface Roughness and Transport Processes of Sawed, Split and Natural Sandstone Fractures

Frank

Heinze

Wohnlich

2020

Water

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In single fractures, dispersion is often linked to the roughness of the fracture surfaces and the resulting local aperture distribution. To experimentally investigate the effects of diverse fracture types and surface morphologies in sandstones, three fractures were considered: those generated by sawing and splitting, and a natural sedimentary fracture. The fracture surface morphologies were digitally analyzed and the hydraulic and transport parameters of the fractures were determined from Darcy and the tracer tests using a fit of a continuous time random walk (CTRW) and a classical advection–dispersion equation (ADE). While the sawed specimen with the smoothest surface had the smallest dispersivity, the natural fracture has the largest dispersivity due to strong anisotropy and non-matching fracture surfaces, although its surface roughness is comparable to the split specimen. The parameterization of the CTRW and of the ADE agree well for β > 4 of the truncated power law. For smaller values of β, non-Fickian transport processes are dominant. Channeling effects are observable in the tracer breakthrough curves. The transport behavior in the fractures is controlled by multiple constraints such as several surface roughness parameters and the equivalent hydraulic aperture.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Comparison of Surface Roughness and Transport Processes of Sawed, Split and Natural Sandstone Fractures

Frank

Heinze

Wohnlich

2020

Water

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“…Cracks are ubiquitous structures of rocks, existing in unweathered rock matrices or generated by brittle deformation along faults in a damaged zone (Brace & Bombolakis, 1963;Cox & Scholz, 1988a, 1988bVermilye & Scholz, 1995;White & White, 1983). They strongly control transport properties of rocks by acting as preferential pathways for fluids and solutes (Hakami & Larsson, 1996;Sausse et al, 2001;Stoll et al, 2018). Such circulation inside intact rock induces changes in rock mineralogy and pore space geometry fostering rock weathering (Kranz, 1983;Sausse et al, 2001;Velde & Meunier, 2008).…”

Section: Introductionmentioning

confidence: 99%

Determining Crack Aperture Distribution in Rocks Using the ¹⁴C‐PMMA Autoradiographic Method: Experiments and Simulations

et al. 2020

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Because cracks control the global mechanical and transport properties of crystalline rocks, it is of a crucial importance to suitably determine their aperture distribution, which evolves through alteration processes and rock weathering. Due to the high variability of crack networks in rocks, a multiscale approach is needed. The 14 C-PMMA (polymethylmethacrylate) method was developed to determine crack apertures using a set of artificial crack samples with different controlled apertures and tilt angles and also using Monte Carlo simulations. The experiments and simulations show the same result: the estimation of apparent aperture w A was successful regardless of tilt angle, even if the estimates are less accurate for low tilt angles (<30°). The uncertainties on the estimation of the real crack aperture w R arise from the unknown tilt angle. The ability of the 14 C-PMMA autoradiography method to estimate crack aperture distributions in rock samples was successfully confirmed on a sample of Grimsel granodiorite.

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“…These experiments aim to demonstrate the retarding effects of matrix diffusion and sorption in cases comparable with groundwater flow in fractured rock. It has been shown that even in well controlled laboratory experiments the advection field may be challenging to resolve and that properties of the fractures affect heavily to the measured breakthrough curves [15,16]. Hence, it is beneficial to simplify the flow channel in order to reliably determine the transport properties of the bedrock.…”

Section: Introductionmentioning

confidence: 99%

Comparison of water phase diffusion experiments in laboratory and in situ conditions

Voutilainen

Kekäläinen

Poteri

et al. 2019

Journal of Hydrology

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In some countries, the spent nuclear fuel produced by nuclear power plants will be deposited in crystalline granitic rock formations. In Finland, such repository is being built at Olkiluoto. The safety assessment of the repository requires a careful determination of transport properties of the bedrock. Porosity of the rock and effective diffusion coefficient and distribution coefficients of different radionuclides for the bedrock are used as the main parameters in safety assessment calculations. It has been questioned if the parameters determined using laboratory experiments can be used to estimate the parameters in the in-situ conditions. Water Phase Diffusion Experiments (WPDE) performed in the laboratory and in-situ conditions were addressed to resolve this questions. In the experiments, transport of HTO, 36 Cl and 22 Na were studied using similar experimental setups in both conditions. Analytic models were constructed and solved to determine the transport parameters from the measured breakthrough curves. The in-situ WPDE resulted from 12 % to 38 % smaller porosities and from 30 % to 60 % smaller effective diffusion coefficients for HTO and 36 Cl than the laboratory WPDE. It was also shown that anion exclusion reduced the transport parameters of 36 Cl compared with the parameters of HTO in veined gneiss that is the most dominant rock type of Olkiluoto bedrock. Furthermore, the distribution coefficients of 22 Na for veined gneiss were found to be about one order of magnitude smaller in the in-situ conditions than in previous laboratory batch sorption experiments. The effects of the results on the safety assessment were evaluated and discussed.

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Experimental and numerical investigations on the effect of fracture geometry and fracture aperture distribution on flow and solute transport in natural fractures

Cited by 52 publications

References 39 publications

Comparison of Surface Roughness and Transport Processes of Sawed, Split and Natural Sandstone Fractures

Comparison of Surface Roughness and Transport Processes of Sawed, Split and Natural Sandstone Fractures

Determining Crack Aperture Distribution in Rocks Using the ¹⁴C‐PMMA Autoradiographic Method: Experiments and Simulations

Comparison of water phase diffusion experiments in laboratory and in situ conditions

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Experimental and numerical investigations on the effect of fracture geometry and fracture aperture distribution on flow and solute transport in natural fractures

Cited by 52 publications

References 39 publications

Comparison of Surface Roughness and Transport Processes of Sawed, Split and Natural Sandstone Fractures

Comparison of Surface Roughness and Transport Processes of Sawed, Split and Natural Sandstone Fractures

Determining Crack Aperture Distribution in Rocks Using the 14C‐PMMA Autoradiographic Method: Experiments and Simulations

Comparison of water phase diffusion experiments in laboratory and in situ conditions

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Product

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Determining Crack Aperture Distribution in Rocks Using the ¹⁴C‐PMMA Autoradiographic Method: Experiments and Simulations