Laboratory Evaluation of Crushed Rock-bentonite Hydro-geotechnical Properties

Vincent Boulanger Martel, Bruno Bussière, Jean Côté

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Mining Geotechnics

ABSTRACT: This study focusses on laboratory evaluation of hydrogeological and thermal properties of three crushed rock-bentonite mixtures (5.0%, 6.5 % and 8.0% bentonite) for a potential use as a moisture-retaining layer in a cover with capillary barrier effects (CCBE) to control acid mine drainage (AMD). Measured saturated hydraulic conductivities range from 3.5E-7 cm/s to 4.8E-8 cm/s and can increase up to 169 times the initial value after three freeze-thaw cycles. The water retention curves illustrated air-entry values between 8.0 kPa and 10.0 kPa and a desaturation curve tending towards the behaviour of bentonite alone for high suction. The thermal conductivity increases with water content and is greater at frozen state than unfrozen state. Test results show that crushed rock-bentonite mixtures are interesting construction materials for moisture-retaining layer but more work needs to be done to assess their capacity to act as an efficient oxygen barrier. RÉSUMÉ Cette étude se penche sur l'évaluation des propriétés hydrogéologiques et thermiques de trois mélanges granulats-bentonite (5.0%, 6.5 % et 8.0% bentonite) pour une utilisation potentielle comme couche de rétention d'eau d'un recouvrement avec effets de barrière capillaire (CEBC) pour contrôler la production de drainage minier acide (DMA). Des valeurs de conductivité hydraulique saturée entre 3.5E-7 cm/s et 4.8E-8 cm/s sont mesurées et peuvent augmenter jusqu'à 169 fois la valeur initiale après trois cycles de gel-dégel. Les courbes de rétention d'eau ont illustré des pressions d'entrée d'air entre 8.0 kPa et 10.0 kPa et une courbe de désaturation qui, pour les suctions élevées, tend vers le comportement de la bentonite seule. La conductivité thermique augmente avec la teneur en eau et est supérieure à l'état gelé que non-gelé. Les résultats montrent que les mélanges granulats-bentonite peuvent s'avérer d'intéressants matériaux de construction pour une couche de rétention d'eau de CEBC. Cependant plus de travail doit être fait afin d'évaluer leur capacité d'agir à titre de barrière à l'oxygène efficace. 1 INTRODUCTION Acid mine drainage (AMD) is a well-known environmental problem related to the oxidation of sulfide minerals in mine tailings when exposed to air and water (Aubertin et al., 2002). AMD generation is also encountered in Nordic regions and only few reclamation scenarios have been studied. So far, the main reclamation strategy for tailings storage facilities located in continuous permafrost regions has been their encapsulation under an insulation cover (MEND, 2004). In temperate climate, covers with capillary barrier effects (CCBE) are a practical option to limit AMD generation (e.g. Bussière et al., 2007a; Dagenais et al., 2006). The use of such covers combined with an insulation objective can be viable in Nordic conditions. Cover's insulation properties would reduce the period of time where tailings temperatures are over the freezing point and capillary barrier effects would control the oxygen fluxes when tailings are unfrozen. Therefore, sulfide oxidation can be controlled all year long. This reclamation scenario could be a more robust cover option in the climate changes context. Soil-bentonite mixtures have been used for many years as impervious materials in engineering construction. The use of those mixtures is common in structures such as dams, cover for landfills, impervious liners or buffers for underground isolation of nuclear wastes. Bentonite is usually mixed with sand (Chapuis, 1990; Chapuis, 2002; Guo et al., 2010; Kenney et al., 1992) or with crushed rock (Börgesson et al., 2003; Engelhardt and Finsterle, 2003; Mata et al., 2005; Villar, 2006) to improve the hydraulic and thermal properties of the mixture. Soil-bentonite mixtures offer an interesting alternative when natural fine-grained soils are not available close to the construction site. The use of such improved materials as a moisture-retaining layer (MRL) in a cover with capillary barrier effects (CCBE) in Nordic conditions seems to be a good alternative. However, it is essential to proceed to a detailed characterization (hydraulic and thermal properties) before designing a CCBE cover with that modified material. This paper presents the main results of a hydraulic and thermal characterization of three crushed-rock bentonite mixtures at 5.0%, 6.5%, and 8.0% bentonite content by weight. More specifically, saturated hydraulic conductivities, water retention curves, saturated hydraulic conductivities after freeze-thaw cycles and

RÉSUMÉ: atory Evaluation of Crushed Rock- bentonite Hydro-geotechnical Properties

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Cite this article:
Vincent Boulanger Martel; Bruno Bussière; Jean Côté (2014) Laboratory Evaluation of Crushed Rock-bentonite Hydro-geotechnical Properties in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper329,author = Vincent Boulanger Martel; Bruno Bussière; Jean Côté,title = Laboratory Evaluation of Crushed Rock-bentonite Hydro-geotechnical Properties ,year = 2014}