Water Interception of Landfill Cover Systems Under Unsaturated Conditions

Abstract

Soil-water characteristic curves for paper sludge (PS) and construction sludge (CS), applied as landfill barrier materials, are examined to estimate the unsaturated infiltration parameters. A prediction of water interception, based on the unsaturated infiltration characteristics of each type of the compacted sludge constituting the cover systems, is made using the UNSAT-H model. The data obtained from soil-water retention tests are identified by representative fitting models such as the van Genuchten and the Brooks-Corey models. From the soil-water characteristic curves and the fitting parameters, the effects of molding water content of the compacted sludge on the soil-water characteristic curves are clarified. It is found that PS compacted at a higher water content retains water greatly, because α and n (fitting parameters for the van Genuchten model) of PS decrease with an increase in the molding water content of the specimen. In the case of CS, macroscopic pore space forms when the compacted CS has a lower level of molding water content, while the CS at a higher water content can be compacted without the formation of clod structures. Such formation of clod structures contributes to the water retentiveness of CS. The results of an evaluation of the water interception performance of the cover systems, using a sludge barrier, show that the cumulative quantity of percolation water through the cover systems is less than 15 cm, which is approximately 1% of the total rainfall during the three- year analyzing period. Although the occurrence of leakage depends on the molding water content and rainfall condition at each site, over 99% of the rainfall can be intercepted by the installation of a cover system, even under a heavy raining condition such as that at Owase, Kyoto, and Tokyo in Japan.