Laboratory Column Experiment to Evaluate Oxygen Diffusion through Covers with Capillary Barrier Effects Subjected to Freeze-Thaw Cycles

摘要

Environmental reclamation of mine waste disposal facilities often requires their confinement under engineered soil covers to control gas migration and water infiltration. In temperate climates, covers with capillary barrier effects (CCBE) are successfully used to control oxygen flux; these covers require a fine-grained material that acts as a moisture-retaining layer. In Nordic environments, where such natural fine-grained soils are not always available, soil or crushed rock-bentonite mixtures could be used instead. A key parameter in the design and performance evaluation of CCBE is the effective diffusion coefficient of oxygen (D_e) of the moisture-retaining layer. This paper aims at presenting the development of a laboratory column testing and interpretation method to evaluate the D_e of a crushed rock-bentonite moisture-retaining layer in a CCBE and the effect of freeze-thaw cycles on D_e. The numerical approach used to analyze the experimental diffusion test results allowed obtaining D_e for various saturation conditions observed in the moisture-retaining layer. Preliminary results show that the initial measured value of D_e increased by two orders of magnitude after 3 freeze-thaw cycles. Steady-state flux calculations based on the obtained D_e showed that despite a good initial cover performance, the capacity of the tested cover to act as an oxygen barrier is reduced in the longer term. This study demonstrates that the proposed laboratory column oxygen diffusion test could be an effective tool to assess the performance of CCBE to control oxygen migration when exposed to cold climate conditions.