Étude du comportement cyclique de résidus miniers avec inclusions drainantes par des essais sur table sismique.

The ore of an operating mine is extracted and concentrated to obtain minerals of commercial value. The residual material (tailings) resulting from this milling operation is usually mixed with water to create a slurry that is pumped to an impoundment. Such tailings storage facilities are typically surrounded, in part or totally, by dikes. Over the years, dike failures have occurred in tailings storage facilities because of the large stresses caused by severe mechanical loading which can liquefy tailings. Even though the construction techniques for dikes in tailings impoundments has gradually improved over the last few decades, their rate of failure is still much greater than for water retention dams. During an earthquake or other events that can cause significant cyclic stresses (i.e. vibration caused by blasting or by heavy machinery), some materials react in a way that can lead to their liquefaction. Tailings from hard rock mines (like those found in Abitibi, Quebec) are particularly sensitive to liquefaction because of their physical characteristics, which include: no or low cohesion, silt-like grain size, low density index ID, and a high degree of saturation Sr (≈ 100 %). When subjected to cyclic loadings this type of material tends to contract. This contraction can lead to an increase in the porewater pressures that reduces the effective stresses and can ultimately cause liquefaction. In this case, the stresses applied to the upstream face of the retaining dike can be large enough to cause failure. Many studies were undertaken to better understand the physics of liquefaction and to characterize liquefiable materials. Researchers have also developed methods to prevent liquefaction or to limit its effects. These studies were mostly conducted on naturally occurring soils, such as sands and silts; there has been relatively little work on tailings, and none included shaking table testing (to the knowledge of the Author). The project presented in this Masters' thesis aims to improve our knowledge of the factors that lead to liquefaction of tailings in order to reduce the risks. To do so, tests were completed in the laboratory using a shaking table. Nine tests were conducted using an aluminum box with a plan surface of one square meter, with a height of 75 cm. One test was done on sand, and eight others on tailings. Of the latter, three were completed on tailings only, three were done with a cylindrical inclusion (rigid and/or draining) in the tailings and two were conducted with a continuous draining inclusion across the tailings.