Modeling Coupled Evaporation and Seepage in Ventilated Cavities (original) (raw)

2004, Vadose Zone Journal

conditions that trigger seepage into various idealized cavity geometries excavated in homogeneous forma-Cavities excavated in unsaturated geological formations are importions. Detailed numerical models have been used to tant to activities such as nuclear waste disposal and mining. Such study unsaturated flow in heterogeneous fractured mecavities provide a unique setting for simultaneous occurrence of seepdia and seepage into cavities of various geometries unage and evaporation. Previously, inverse numerical modeling of field der transient conditions (e.g., Birkholzer et al., 1999; liquid-release tests and associated seepage into cavities were used to provide seepage-related large-scale formation properties, ignoring the Finsterle, 2000; Finsterle and Trautz, 2001; Li and Tsang, impact of evaporation. The applicability of such models was limited 2003). Site-specific seepage models for the proposed to the narrow range of ventilation conditions under which the models nuclear waste repository at YM were developed by caliwere calibrated. The objective of this study was to alleviate this limitabrating the effective seepage-related parameters against tion by incorporating evaporation into the seepage models. We modfield seepage test data (Finsterle et al., 2003). eled evaporation as an isothermal vapor diffusion process. The semi-Most of the previous numerical models assumed that physical model accounts for the relative humidity (RH), temperature, liquid water leaking into a cavity drips (seeps) immediand ventilation conditions of the cavities. The evaporation boundary ately from the place of entry. The potential for evaporalayer thickness (BLT) over which diffusion occurs was estimated by tion to compete with seepage has been generally igcalibration against free-water evaporation data collected inside the nored, and its effect was lumped with the effective flow experimental cavities. The estimated values of BLT were 5 to 7 mm parameters of the unsaturated medium (Finsterle et al., for the open underground drifts and 20 mm for niches closed off by 2003). In calibration of the analytical model of Philip bulkheads. Compared with previous models that neglected the effect et al. (1989b) against field seepage data, Trautz and of evaporation, this new approach showed significant improvement Wang (2002) accounted for the effect of evaporation by in capturing seepage fluctuations into open cavities of low RH. At adjusting the field seepage data for evaporation. Behigh relative-humidity values (Ͼ85%), the effect of evaporation on cause the data were obtained from tests conducted in seepage was very small.

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