[1] Capillary barriers have increased in use for protecting sensitive underground regions from downward infiltration. However, questions and uncertainties remain about conceptualization and parameterization of capillary barriers for design and numerical modeling. In order to identify and to parameterize the relevant flow processes in this fineover-coarse soil layer system, large-scale laboratory experiments were performed. The data revealed that water is predominately diverted laterally in a saturated fringe within the fine layer. Percolation through the system was found to be quite complex. At low infiltration rates, small quantities of water seeped uniformly through the system. At higher fluxes the seepage pattern changed to a more irregular distribution because of the occurrence of preferential flow. Numerical investigations based on the laboratory results demonstrated an extreme sensitivity of the system performance to the hydraulic functions of both layers.
Abstract. Landfills and waste heaps require an engineered surface cover upon closure. The capping system can vary from a simple soil cover to multiple layers of earth and geosynthetic materials. Conventional design features a compacted soil layer, which suffers from drying out and cracking, as well as root and animal intrusion. Capillary barriers consisting of inclined fine-over-coarse soil layers are investigated as an alternative cover system. Under unsaturated conditions, the textural contrast delays vertical drainage by capillary forces. The moisture that builds up above the contact will flow downdip along the interface of the layers. Theoretical studies of capillary barriers have identified the hydraulic properties of the layers, the inclination angle, the length of the field and the infiltration rate as the fundamental characteristics of the system. However, it is unclear how these findings can lead to design criteria for capillary barriers. To assess the uncertainty involved in such approaches, experiments have been carried out in a 8 m long flume and on large scale test sites (40 m x 15 m). In addition, the ability of a numerical model to represent the relevant flow processes in capillary barriers has been examined.
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