Design, Construction and Preliminary Results for an Inclined Store-and-Release Cover Experimental Cell Built on an Abandoned Mine Site in Morocco

摘要

In arid and semiarid climates, acid mine drainage (AMD; also called acid rock drainage, ARD) generated by mine tailings can be controlled by reducing water percolation. The use of store-and-release (SR) covers with capillary barrier effect is emerging as the most effective way to prevent water percolation through tailings under these climates. Four instrumented experimental cells made of phosphate wastes, as SR covers, were constructed on top (flat surface) of the abandoned Kettara mine site (near Marrakech, Morocco). Results confirmed the potential of phosphate mine waste as SR cover material to control water percolation. However, significant uncertainties remain about the influence of inclined conditions on the hydrogeological behavior of a SR cover at the mine, as the mine wastes at Kettara mine site are retained by dykes that reach a height of 10 m. Due to the slope inclination, water can accumulate above the tilt interface during extreme precipitation events, which could create a breakthrough of the capillary barrier; at this location, the cover is no longer effective to control water infiltration into the mine wastes. A field investigation was conducted to evaluate the influence of the slope on the Kettara SR cover's performance. An experimental field cell (10 m wide by 8 m long) inclined at an angle of 14.5 degrees was constructed on-site. The SR cover retained is made of 0.8 m of phosphate waste, placed over a capillary break layer made of coarse-grained materials. Cover performance was monitored using lysimeters, Tensiometers, suction and soil moisture sensors installed at four stations and at different depths. The paper presents the design, the construction and the instrumentation of an inclined SR covert. Preliminary results of the monitored parameters under natural conditions are also included. The field test showed that the slope influences water distribution in the cover with more water at the bottom of the slope. The inclined SR cover still effectively limited water percolation under natural conditions.