Étude des recouvrements avec effet de barrière capillaire pour minimiser les infiltrations d'eau dans les sites d'enfouissement de matières résiduelles
This thesis concerns the performance of an alternative low hydraulic conductivity cover for landfills, i.e. covers with capillary barrier effect (CCBE). The use of recycled materials, such as DBP, as parts of such covers has the advantage of reducing the quantity of waste to be disposed of (DBP used to be landfilled as waste), while offering an efficient control to the infiltration of water into the landfill, thereby reducing the amount of leachate produced. Given its water retention characteristics, DBP can also help to control biogas emissions. An experimental cell at Saint-Tite-des-Caps landfill, Québec, was designed to be a low permeability cover and to increase the effectiveness of biogas collection. The design procedure of the cover is based on the capillary barrier principle. As a consequence, the water retention curve (WRC) and the hydraulic conductivity functions (HCF) of materials are fundamental. The design procedure included optimization of the thicknesses of the several layers composing the barrier and determination of the transfer length (TL) using an appropriate model. The latter had to be shorter than the total length of the cell (30 m), in order to allow for verification of the design hypothesis. The objective of this project was to evaluate the performance of the CCBE, infiltration was measured by means of lysimeters. The quantities of water recovered in these lysimeters were frequently obtained. In addition, the temporal evolutions of the matric suction and the volumetric water content of the various layers were monitored using dataloggers. Water content data made it possible to determine both the infiltration rate through the DBP layer, which eventually reached the capillary barrier, and the hydraulic conductivity of the material. The latter varies between 7,0 × 10 -9 m/s and 5,0 × 10-11 m/s, in the field. Another important result of this study was the determination transfer length, that is to say the length beyond which water infiltrates in the waste.This length is about 23 m for the cover at Saint-Tite-des-Capes. The total flow rate that could reach the wastes, 4,7 10 × -10 m/s, was estimated based on lysimeter data from 134 days of monitoring. The DCB of Saint-Tite-des-Caps was modelled using SEEP/W, a saturated/unsaturated flow software.This study made it possible to evaluate the performance of the capillary barrier, and the additional layer forming the DCB. The repercussions of this project are numerous. For example, it made it possible to continue to advance in the study of the behaviour of the capillary barriers, to verify analytical approaches used to evaluate its performance (transfer length, hydraulic conductivity, quantity of water which infiltrates). Moreover, one could evaluate the performance of the lysimeters installed.
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