The behavior of inclined covers used as oxygen barriers

Covers with capillary barrier effects (CCBE) have been recently proposed as a viable option for gas migration barriers. However, the effect of geometry on CCBE performance has not been clearly demonstrated. In this paper, the results of a laboratory study performed with an original apparatus called the inclined box are presented. The results obtained show that the hydraulic behavior of layered covers is influenced by the inclination of the slope. Generally, the upper part of the slope contains less water than the lower part. This means that the upper part is less efficient than the lower part for limiting gas migration. The authors have also studied an existing site where a CCBE was built on a sloping surface. After validation of the numerical model with in situ measured data, the model was used to perform a parametric study to quantify the influence of the main CCBE parameters on its performance. The results obtained confirm those measured in the lab and clearly show how geometry influences the performance of the CCBE. Based on these results, a simple relationship is proposed for a preliminary estimation of sloping covers performance to limit oxygen migration by diffusion.Key words: cover with capillary barrier effects, acid mine drainage, slope effects, laboratory investigation, in situ measurements, design criteria.