Etude experimentale des proprietes hydrogeologiques des roches steriles a une echelle intermediaire de laboratoire

The mining industry produces large quantities of waste rock which are usually stored in piles on the surface. Waste rocks often contain reactive minerals that may give rise to a contaminated effluent. It is essential to define the hydrogeological properties of these wastes to assess the environmental risks associated with surface disposal.;The main purpose of this project was to assess the hydrogeological properties of waste rocks by means of intermediate scale laboratory tests. More specifically, the project aimed to determine the saturated hydraulic conductivity ( ksat) and the water retention curve (WRC) of waste rock samples. The effect of fine particles displacement that may occur when water percolates through widely graded materials was also evaluated. The tests were conducted on samples taken from one of the waste rock piles at the Lac Tio mine (RTFT, Havre-Saint-Pierre, Quebec). The samples (diameter ≤ 50 mm) correspond to widely graded sand with diverse proportions of fine particles, gravel and pebbles.;The hydrogeological properties of the waste rocks were determined by means of permeability, tracer, infiltration and drainage tests in large instrumented columns. The tests were conducted on samples having a particle size that was truncated to the preselected maximum sizes (from 5 to 50 mm). The results of the tests showed that the saturated hydraulic conductivity k sat of the waste rocks, measured in the laboratory, is not significantly influenced by the presence of various percentages of gravels and pebbles. The value of ksat varies around 10-1 cm/s for the samples with different particle size distributions. At the laboratory scale, the experimental values of ksat is not significantly influenced by the movement of fine particles, which often occurs at high hydraulic gradients (i = 2-3).;The comparison of the test results with ksat values obtained from predictive models showed significant differences; the measured values are much larger than the latter. The saturated hydraulic conductivity of waste rocks seems to be controlled by a system of interconnected macropores, which act as preferential water flow paths. The presence of such preferential paths in the waste rocks was partially confirmed by the results of tracer and infiltration tests. Alternative models are proposed to predict the value of ksat for these waste rocks.;The water retention curves obtained experimentally show low air entry values (AEV < 10 cm) and a relatively high value for the residual volumetric water content (&thetas;r = 0,06 - 0,08). The obtained results have lead to modifications of the predictive MK model (Aubertin et al., 2003) that enable the model to better reflect the effect of the finer fraction on the residual water content. Data taken from the literature were used to demonstrate that the modifications of the MK model work well with other waste rocks and with other widely graded materials.;The presence of macropores suggests that waste rocks may behave as a double porosity medium. Under water-saturated conditions, the hydraulic conductivity of the waste rock appears to be controlled by macroporosity. Under unsaturated conditions, the hydraulic conductivity decreases rapidly with an increase in matrix suction. As soon as macropores are empty, they do not contribute to water flow. This behavior can be represented by a bimodal water retention curve. The permeability function can also be characterized by a two-phase water flow.;The results of this investigation can be used in numerical modelling studies of water flow through waste rocks piles. These can be useful in developing optimal pile configurations to reduce the geo-environmental risks related to surface disposal of waste rocks.