Analyse numerique des ecoulements et du transport de contaminants dans les rejets miniers entreposes dans les massifs rocheux fractures.

摘要

Environment quality control and natural resources conservation are essentials for humanities' future. Water is one of the most important resources of our planet. The increase of soil and groundwater pollution incite to use powerful and adapted numerical codes for studying and predict water flow and contaminant transport around waste storage sites. Mining industry, despite its important role in the Canadian economy, produce contaminated water and a great quantity of mining wastes that must be managed. Mining wastes can sometimes be disposed into open pit or into underground excavations. In nature, rock is composed of assembled minerals forming the solid matrix, and voids enhancing fluid transfer. These voids are usually pores or fractures. Fractures are produced when local stress exceeds the local strength. In fractured media, characterized by very low matrix permeability, water flow is focalized in fractures.Numerical simulations realized for an axisymmetric open pit under non saturated and transient flow conditions showed that water flow and transport of contaminants depend on filling material, initial and boundary conditions and also nature of roc mass (homogeneous roc or fractured roc). Presence of fractures has a great effect on water flow and transport of contaminants. Contaminant migration is more pronounced when roc is fractured.Results of numerical simulations realized in chapter 5 highlights the effect of hydraulic regional gradient when mining wastes are disposed into a symmetric open pit. Regional gradient effect is more pronounced in presence of fractures. Contaminant migration was more significant with fractures than for homogeneous roc and contaminants could reach more important distance.In chapter 6 of this thesis we showed that when mining wastes are disposed into underground excavations, backfilling a stope modifies water flow and hydraulic heads distribution. Also, presence of a single fracture in the vicinity of excavation has affected results of water flow and contaminant transport, especially when it is localized near excavation surface.The principal aim of this project is numerical analysis of water flow and contaminant transport through mining wastes disposed into fractured rock mass. Different cases were considered depending on the mode of mining wastes disposal and the type of filling material. Numerical simulations using HydroGeosphere code were realized. This code allows simulation of saturated -- non saturated water flow and contaminant transport through fractures and fractured media. An indirect hydromechanical coupling methodology was developed between HydroGeosphere, Phase2 and CSDS model. This methodology allows us to study the effect of water pressure and applied stresses on fracture behaviour and change of its aperture.Finally, results obtained with indirect hydromechanical coupling methodology highlighted stress and water pressure effects around fracture on its aperture change. This aperture variability along fracture could influence water flow and contaminant transport.All simulations realized with HydroGeosphere code highlighted fracture key role on control of water flow and transport of contaminants through mining wastes. Thus, it is very important to consider discretely fractures of system of fractures present in the roc to avoid contaminant migration underestimation.