The effect of cavity wall irregularities on seepage exclusion from horizontal cylindrical underground openings

Hughson, Debra L.; Dodge, F. T.

doi:10.1016/s0022-1694(00)00148-7

Cited by 7 publications

(13 citation statements)

References 16 publications

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“…Because the physical impact of surface roughness on seepage (Ho and Webb, 1998b;Hughson and Dodge, 2000) is indeed related to the capillary rise needed to divert flow out of a topographic low, capturing this effect in an equivalent 1/a value is appropriate.…”

Section: Discussionmentioning

confidence: 99%

Inverse and predictive modeling of seepage into underground openings

Finsterle

Ahlers

Trautz

et al. 2003

Journal of Contaminant Hydrology

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Abstract. We discuss the development and calibration of a model for predicting seepage into underground openings. Seepage is a key factor affecting the performance of the potential nuclear-waste repository at Yucca Mountain, Nevada. Three-dimensional numerical models were developed to simulate field tests in which water was released from boreholes above excavated niches. Data from air-injection tests were geostatistically analyzed to infer the heterogeneous structure of the fracture permeability field. The heterogeneous continuum model was then calibrated against the measured amount of water that seeped into the opening. This approach resulted in the estimation of model-related, seepage-specific parameters on the scale of interest.The ability of the calibrated model to predict seepage was examined by comparing calculated with measured seepage rates from additional experiments conducted in different portions of the fracture network. We conclude that an effective capillary-strength parameter is suitable to characterize seepage-related features and processes for use in a prediction model of average seepage into potential waste emplacement drifts.Keywords: capillary barrier, unsaturated zone, parameter estimation * Corresponding author: Fax: +1-510-486-5686; e-mail: SAFinsterle@lbl.gov 2 IntroductionSeepage of water into emplacement drifts for nuclear waste is considered a key factor affecting the long-term safety of a potential repository at Yucca Mountain, Nevada. The number of waste packages contacted by water, the corrosion rate of engineered barriers and waste containers, the dissolution and mobilization of radioactive contaminants, and their release and migration towards the accessible environment all depend on the rate, the chemical composition, and the spatial and temporal distribution of water seeping into the waste-emplacement drifts.Accurately estimating seepage into underground openings excavated from an unsaturated fractured formation requires process understanding on a wide range of scales. Processes to be studied include (1) the mountain-scale distribution of percolation flux, (2) the intermediate-scalechanneling, bifurcation, and dispersion of flow in the fracture network, (3) the small-scale capillary-barrier effect in the boundary layer around the opening, and (4) the micro-scale phenomena of film flow, drop formation, and drop detachment at the drift surface. In addition, the thermodynamic environment in the drift (temperature, relative humidity, ventilation regime, etc.) must be known as it impacts the boundary condition at the drift wall.Developing a comprehensive, physically based seepage model that covers all scales discussed above would require a large amount of characterization data that are difficult or practically impossible to measure in the field. Moreover, a suite of model assumptions would have to be made to relate fracture and surface properties to hydrogeologic model parameters.Finally, the spatial and temporal resolution of a numerical model necessary to accurately and explicitly ca...

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Section: Discussionmentioning

confidence: 99%

Inverse and predictive modeling of seepage into underground openings

Finsterle

Ahlers

Trautz

et al. 2003

Journal of Contaminant Hydrology

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“…Seepage into cavities of other shapes has been analyzed by Selker [1997] and Philip [1998], but these studies also address cavities with smooth walls. An extension of the quasi-linear analysis of Philip et al [1989] to irregularly shaped cavities is provided, however, by Hughson and Dodge [2000].…”

Section: Cavity With Asperitymentioning

confidence: 99%

“…[15] The approach used by Hughson and Dodge [2000] is analogous to an approach often used to study noisy physical systems: A single representative perturbation with parameterized dimensions is added to the system. In this case, the perturbation is a triangular protrusion of rock into the circular drift.…”

Section: Cavity With Asperitymentioning

confidence: 99%

“…'' [16] There are several reasons to apply boundary layer analysis to the same problem. First, solutions are calculated by Hughson and Dodge [2000] only for 4 s 16, while values of s on the order of 50 are of greatest interest for Yucca Mountain. Boundary layer analysis, which represents a limit of large s, is relevant here.…”

Section: Cavity With Asperitymentioning

confidence: 99%

“…[17] Figure 2 shows the asperity geometry analyzed by Hughson and Dodge [2000]. The seepage threshold is reached when y = 0 at the tip of the asperity.…”

Section: Cavity With Asperitymentioning

confidence: 99%

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Boundary layer analysis of unsaturated seepage into cylindrical cavities

Ross¹

2007

Water Resources Research

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[1] An analytical solution has previously been published for flat capillary barriers in uniform layered rock with a quasi-linear relative permeability function. This solution can be extended to curved surfaces with a radius of curvature that is much greater than the characteristic length of the relative permeability curve a À1 because water flows around the cavity in a relatively thin boundary layer. A simple formula is obtained for the onset of seepage into cylindrical cavities. Published solutions to the quasi-linear seepage problem, which take the form of infinite sums of Bessel functions, agree with this formula in appropriate limits. Studies of seepage into a proposed radioactive waste repository have used a finite difference model to solve the equations of unsaturated flow explicitly. Using the boundary layer solution, the discretization error in such numerical models is calculated. The numerical estimate of the diversion capacity of a capillary barrier is shifted away from the exact solution by a factor of ad cos f/sinh(ad cos f), where 2d is the grid spacing and f is the slope of the cavity wall.

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2001

Hydrological Processes

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The effect of cavity wall irregularities on seepage exclusion from horizontal cylindrical underground openings

Cited by 7 publications

References 16 publications

Inverse and predictive modeling of seepage into underground openings

Inverse and predictive modeling of seepage into underground openings

Boundary layer analysis of unsaturated seepage into cylindrical cavities

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