Aspects hydrauliques et géotechniques de la conception de barrières capillaires incluant des matériaux recyclés hautement compressibles
Other titre : Hydraulic and geotechnical aspects of capillary barrier design using a highly compressible recycled material
Low permeability covers, such as covers with capillary barrier effect (CCBE), constitute valid alternative for minimizing leachate production from municipal landfill facilities. The use of recycled materials as part of such cover has the advantages of reducing the amount of waste to bury and the amount of soil---a finite mineral resource---needed for its construction. Deinking by-products (DBP) is a paper recycling by-product whose void ratio varies considerably with suction. The challenge of this thesis is to predict the variation of hydraulic properties with suction of a highly compressible recycled material and, using those properties, incorporate this material for the design of a CCBE. The research program led to the design of an inclined CCBE field test at the Saint-Tite-des-Caps (Québec, Canada) landfill, using DBP as a material constituting a low permeability layer. Typical soils do not undergo significant capillary-induced pore shrinkage for suction values higher than air-entry value (AEV). However, this is not the case for highly compressible materials (HCM), such as expansive clays and DBP. A model capable of describing the suction-induced consolidation curve (void ratio function) and water retention curve (WRC) of HCM was developed and validated using published data for a Saskatchewan silty sand. This silty sand was selected for its large amount of available data. The WRC and the void ratio function obtained for the Saskatchewan silty sand were used to predict its hydraulic conductivity functions ( k -function). The proposed model is then applied to describe the WRC of DBP. Water content, suction and volumetric deformation data necessary to determine the WRC for DBP were obtained by applying an experimental technique developed for the determination of the WRCs of HCMs. The k -function was also obtained using Fredlund et al. 's k -function model. Results showed that volumetric water contents were underestimated if volume change was not taken into account, leading to inaccuracies in the WRCs (and in the models used to describe it) and, consequently, in the associated k -functions. It was shown that the Fredlund et al. (1994]'s k -function model can not be applied for all HCMs. An alternative procedure to determine the k -function based on relationships between saturated hydraulic conductivity and void ratio and between AEV and void ratio was also developed. The procedure was applied to determine the k -function of DBP. The validity of the procedure is verified by comparing the k -function of a compressible soil, a Saskatchewan silty sand, obtained based on the proposed procedure (using published experimental data) with experimentally determined unsaturated hydraulic conductivities for the same soil. A new design procedure based on the materials' k -function is proposed to minimize water infiltration into landfills in optimizing the water diversion length of inclined CCBEs. This design procedure was based on a conceptual, mathematical and numerical approach and aimed at selecting materials and optimizing layer thickness. Selection among candidate materials is made based on their k -functions and by a threshold infiltration rate imposed on the designer. Briefly, the capillary break layer (CBL; bottom layer) is characterized by a low capillary rise, while the moisture retention layer (MRL; upper layer) is characterized by a higher capillary rise. The thickness of the CBL corresponds to the height where suction reaches its maximum value for a given infiltration rate. This height can be computed using the Kisch  model. The optimal thickness of the MRL is determined by applying an adaptation of the Ross  model. The results obtained using the proposed design procedure were compared to those obtained from numerical simulations performed using a finite element unsaturated (or vadose zone) seepage software. The procedure was applied for two cover systems; one where DBP was used as MRL and sand as CBL and another where sand was used as MRL and gravel as CBL. Using this procedure, it has been shown that an infiltration control system composed of thin layers of sand over gravel is highly efficient in terms of diversion length and that its efficiency can be enhanced by placing a hydraulic barrier---such as a layer of DBP---above the MRL. The newly developed capillary barrier design procedure was applied for the design of the Saint-Tite-des-Caps experimental CCBE."--résumé abrégé par UMI.
- Génie – Thèses