Quantifying the effects of freeze-thaw cycles on mine cover system design and performance

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Soil cover systems are used to isolate reactive mine wastes from the environment and limit water and oxygen ingress into the tailings and waste rock below. Typically, cover systems are designed to function like natural hillslopes and to isolate waste material from the atmosphere and biosphere, thereby protecting environmental resources and public health. The current approach to cover design includes laboratory testing of the physical and hydraulic properties of waste and cover materials (at the core- and column-scale), followed by computer-based 2D finite element modeling. But in Canada and other cold regions, freeze thaw cycles complicate the design process because they change the surface infiltration and lateral diversion properties of the cover. Such effects are very poorly understood and rarely include in predictive models used for cover design and environmental performance testing. Here we use the newly constructed Mine Overlay Soil Testing facility (MOST) at the University of Saskatchewan to explore a set of applied questions focused on new understanding of freeze thaw effects on mine cover storage and release. These questions are fundamental to the business model of M.A. O'Kane Consultants Inc., our industry partner, for managing and informing unforeseen liabilities with their customers and their mine closure problems. The MOST facility provides a unique setting to examine hillslope-scale processes (a scale not before possible in a controlled setting) within our 90 m2 indoor high bay facility with 15-20 m2 hillslopes. Beyond testing hillslope-scale freeze-thaw effects on water storage and release, we will test new design approaches for 'seasonally frozen capillary break diversion' (a way of using subsurface frozen layers to aid in melt water diversion) as a proactive solution to add new functionality to Northern cover systems.