An evaluation of density dependant convective airflow causing accelerated drying of reclamation soil covers

Bryan Koehler, Lee Barbour, Grant Ferguson

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

Session: Geoenvironmental Engineering

ABSTRACT: ION OF DENSITY DEPENDANT CONVECTIVE AIRFLOW CAUSING ACCELERATED DRYING OF RECLAMATION SOIL COVERS Bryan Koehler, Lee Barbour, Grant Ferguson University of Saskatchewan, Saskatoon, SK, Canada ABSTRACT The most critical element in the design of a soil cover as part of the reclamation of mining waste is an understanding of water balance and the key property of these cover systems is their water holding capacity. Two large scale trial cover systems were built over top of an unsaturated petroleum coke deposit at the crest of a large sand tailings dyke at the Syncrude Canada Ltd. Oil Sands Mining Facility in Fort McMurray, Alberta. These cover systems were instrumented with soil monitoring equipment, and have been monitored since 2004. Since this time, both cover systems have been drier than anticipated, despite success of the cover configuration at other similar sites. It is hypothesized that the enhanced drying of these covers is a result of convective airflow through the unsaturated mine waste underlying the cover systems. This convective airflow would be triggered when the ambient air temperature rises above the temperature within the coke and sand tailings. The higher density air within the unsaturated mine waste would then sink, drawing dry air into the cover along the crest of the dyke. The objective of this project is to determine the presence, or lack there-of, of convective air flow within the vadose zone of the coke/sand deposit. The presence of a convective cell may indicate enhanced evaporation within the deposit resulting in premature drying, and thus failure, of the cover systems. A combination of in situ measurements of differential pressure, temperature, and soil water content will be used to establish the air density and pressure profiles across the covers and within the mine waste. These profiles will be used to quantitatively describe the seasonal direction and volume of airflow across the covers. Changes in water storage will be assessed using a daily water balance for all monitoring years. RESUMÉ est leur -Sands Mining Facility a Fort Mc Murray, Alberta. Ces systèmes de couverture ont été instrumentés avec des appareils de surveillance des sols et ont été observés depuis 2004. Depuis ce temps, les deux systèmes de couverture ont été plus secs que prévu, malgré le succès de ldéchets miniers insaturés en-dessous de ces systèmes de couverconvective pourrait indiquer une évaporation accélérée dans le dépôt avec, comme résultat, un séchage prématuré, et donc la faillite, de ces systèmes de couverture. Une combinaison de mesures in-situ de la pression différentielle, la couvertures ainsi que dans les déchets miniers. Ces profils seront utilisés pour décrire de façon quantitative les directions sai 1 INTRODUCTION The reclamation of mine wastes and mine sites has historically focused on physical stability of the landform and more recently on its ability to minimize the environmental impact of the mine waste (McKenna, 2004). Soil cover systems are a method frequently used to reclaim mine waste, and utilize a combination of local materials and engineered layers to provide water and nutrients for vegetation, control water and/or oxygen ingress into mine waste, and minimize problems associated with contaminated runoff or wind or water erosion of mining waste. A cover system may consist of various natural and manufactured materials, but typically is intended to achieve the following goals Wels, 2003): Erosion/dust control Control of oxygen and water ingress to mine waste;

RÉSUMÉ: ALUATION OF DENSITY DEPENDANT CONVECTIVE AIRFLOW CAUSING ACCELERATED DRYING OF RECLAMATION SOIL COVERS Bryan Koehler, Lee Barbour, Grant Ferguson University of Saskatchewan, Saskatoon, SK, Canada ABSTRACT The most critical element in the design of a soil cover as part of the reclamation of mining waste is an understanding of water balance and the key property of these cover systems is their water holding capacity. Two large scale trial cover systems were built over top of an unsaturated petroleum coke deposit at the crest of a large sand tailings dyke at the Syncrude Canada Ltd. Oil Sands Mining Facility in Fort McMurray, Alberta. These cover systems were instrumented with soil monitoring equipment, and have been monitored since 2004. Since this time, both cover systems have been drier than anticipated, despite success of the cover configuration at other similar sites. It is hypothesized that the enhanced drying of these covers is a result of convective airflow through the unsaturated mine waste underlying the cover systems. This convective airflow would be triggered when the ambient air temperature rises above the temperature within the coke and sand tailings. The higher density air within the unsaturated mine waste would then sink, drawing dry air into the cover along the crest of the dyke. The objective of this project is to determine the presence, or lack there-of, of convective air flow within the vadose zone of the coke/sand deposit. The presence of a convective cell may indicate enhanced evaporation within the deposit resulting in premature drying, and thus failure, of the cover systems. A combination of in situ measurements of differential pressure, temperature, and soil water content will be used to establish the air density and pressure profiles across the covers and within the mine waste. These profiles will be used to quantitatively describe the seasonal direction and volume of airflow across the covers. Changes in water storage will be assessed using a daily water balance for all monitoring years. RESUMÉ

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Cite this article:
Bryan Koehler; Lee Barbour; Grant Ferguson (2014) An evaluation of density dependant convective airflow causing accelerated drying of reclamation soil covers in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper186,author = Bryan Koehler; Lee Barbour; Grant Ferguson,title = An evaluation of density dependant convective airflow causing accelerated drying of reclamation soil covers,year = 2014}