Effet de la granulométrie sur le comportement géotechnique de roches stériles concassées utilisées comme surface de roulement sur des routes minières

Mining operations generate large volume of waste rocks, which are usually disposed of in piles. Management and reclamation of waste rock piles can be a challenge because of their size (h > 100 m and A > 100 ha) and their geochemical and geotechnical stability. The valorization (i.e. reuse) of these materials reduces their footprint while meeting the needs of construction materials for mine infrastructures. Waste rock is commonly used for road construction at mine sites. However, current practice usually consists of using waste rock directly, without any particular preparation or selection, thus resulting frequently in punctures, dust generation and low durability. Optimizing properties of crushed waste rocks used in the surface course of mine haul roads could reduce the occurrence of road defects and provide a more comfortable and safer ride for users. The main objective of this research project was to determine the optimal geotechnical properties for the use of crushed rock as a running surface in mining roads. First, a characterization (particle size distribution analysis, specific density, standard and modified Proctor compaction, permeability) was performed on crushed waste rock from a partner mine of RIME (Canadian Malartic Mine). Stiffness is an important index of the performance of the material used in the surface course. The California bearing ratio test (CBR) was used as an indicator of the stiffness of the material for different particle size distributions, compaction energies and water contents. Densities were measured in the field to confirm whether the compaction studied in the laboratory corresponded to what is observed in situ. The results from the laboratory program were then used in the SIGMA/W (Geo-Slope Intl. 2018) numerical code to evaluate the deformations induced by the traffic of extra-heavy vehicles according to the different characteristics of the running surface. The rolling resistance corresponding to the different rolling surface materials modelled was evaluated using numerical simulations. Laboratory results showed that it was possible to maximize the stiffness and density the mining road surface by modifying the particle size distribution and the compaction energy used for its construction. For the tested material, 10% fine particle content (d <0.08 mm) and a high compaction energy yielded CBR results greater than 250%. The results also showed that the coarser particles of the material contributed significantly to increase its rigidity. Fieldwork has shown that the range of density measured in the laboratory corresponded well to field conditions. Heterogeneity of density distribution and particle size distribution of the crushed sterile rocks used in the surface course was observed in the field. Finally, the numerical simulations have shown that the increase of the stiffness of the studied material could contribute to decreasing the rolling resistance by a maximum of 0.26% for initial rolling resistance of around 3%. The results of this study showed that the optimization of the crushed waste rocks used in the construction of the surface course of mining roads could improve the performance of the material and thus promote its valorization.