Capillary barrier performance in heterogeneous porous media

Abstract

Abstract. The effects of heterogeneities on the performance of capillary barriers is investigated by numerically simulating three systems comprised of a fine soil layer overlying a coarse gravel layer with (1) homogeneous, (2) layered heterogeneous, and (3) random heterogeneous property fields. The amount of lateral diversion above the coarse layer under steady state infiltration conditions is compared among the simulations. Results indicate that the performance of capillary barriers can be significantly influenced by the spatial variability of hydraulic properties. In the layered heterogeneous systems, realizations with highly stratified regions within the fine layer performed best and resulted in localized capillary barriers that delayed breakthrough into the coarse layer. In contrast, realizations of the random heterogeneous system performed worst because of channeled flow that produced numerous localized regions of breakthrough into the coarse layer. Results of the homogeneous model were comparable to the mean results of the layered heterogeneous realizations, but homogeneous results underpredicted the frequency and amount of breakthrough for all realizations of the random heterogeneous system. These results indicate that homogeneous models can be used to estimate the average behavior of layered heterogeneous systems with reasonable accuracy. In addition, engineered capillary barriers may be improved through emplacement and packing methods that induce highly stratified features within the fine layer of a capillary barrier system.

Seepage into an underground opening constructed in unsaturated fractured rock under evaporative conditions

“…The primary thrust of these efforts has been the evaluation of sloping capillary barriers and their effectiveness in promoting lateral movement of water downdip along a hydrogeologic contact [ Montazer and Wilson , 1984]. A layered capillary barrier's capacity to funnel water away from a desired area has been the impetus for numerous analytical and numerical studies related to waste isolation and optimum landfill cover design [ Gardner and Hsieh , 1959; Ross , 1990; Steenhuis et al , 1991; Oldenburg and Pruess , 1993; Stormont , 1995; Webb , 1997; Ho and Webb , 1998; Selker , 1997]. However, very few detailed laboratory investigations [ Miyazaki , 1988; Conca et al , 1998; Walter et al , 2000] or field studies [ Wang et al , 1999] pertaining to capillary barriers have been performed and reported in the literature.…”

Inverse and predictive modeling of seepage into underground openings

“…Several analytical and numerical studies were performed in which capillary-barrier performance in engineered or naturally layered systems was investigated (Frind et al, 1977;Ross, 1990;Oldenburg and Pruess, 1993;Warrick et al, 1997;Webb, 1997). Ho and Webb (1998a) and Birkholzer et al (1999) examined the impact of heterogeneity on the distribution and rate of water flow across a capillary barrier. Ho (1997) and Or and Ghezzehei (2000) analyzed drop formation and drop detachment as well as evaporation of droplets forming within rough fractures or emerging from fractured formations.…”

Seepage into an Underground Opening Constructed in Unsaturated Fractured Rock Under Evaporative Conditions

“…The primary thrust of these efforts has been the evaluation of sloping capillary barriers and their effectiveness in promoting lateral movement of water downdip along a hydrogeologic contact [Montazer and Wilson, 19841. A layered capillary barrier's capacity to funnel water away from a desired area has been the impetus for numerous analytical and numerical studies related to waste isolation and optimum landfill cover design [Gardner and Hsieh, 1959;Ross, 1990;Steenhuis et al, 1991;Oldenburg and Pruess, 1993;Stonnont, 1995;Webb, 1997;Ho and Webb, 1998;and Selker, 19971. However, very few detailed laboratory investigations [Miyazaki, 1988;Conca et al, 1998;and Walter et al, 20001 or field studies [Wang et al, 19991 pertaining to capillary barriers have been performed and reported in the literature.…”