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UBC Theses and Dissertations

Predicting void ratio for surface paste tailings deposited in thin layers Salfate, Eduardo Raul


Surface thin layer deposition of paste tailings has become an increasingly popular method of disposal. One of the reasons for its popularity is the advantages associated with the faster increase in strength and density after placement as a result of enhanced evaporation and drainage. This makes thin layer deposition particularly attractive in dry climates with high evaporation rates. Understanding how density evolves with time is an extremely relevant problem during design stages as both the overall capacity of the tailings impoundment and its stability with time depend on this parameter. Since tailings density is not readily available at early stages of planning, predictive tools are required to estimate it. Density is primarily gained through four different processes; sedimentation-self weight consolidation, drainage, evaporation and consolidation. Although consolidation will likely be the main contributor to the final density of the impoundment, the other three processes are important as the consolidation behaviour of hard rock paste tailings has been observed to depend on the initial density or state achieved during early stages of densification. The primary objective of this thesis is to provide an overview of the processes affecting the early stages of densification and to propose an approach for predicting this parameter. Laboratory testing presented as part of this work is primarily focused on determining the variables affecting the sedimentation-self weight consolidation process whereas the numerical work is focused on targeting some of the issues related to drainage and evaporation. The approach described herein has combined measured data obtained in the lab with results generated by numerical modeling to provide with density estimates as a function of time. Another important goal of this thesis is to give general guidelines for proper material characterization, which is required to overcome some of the difficulties encountered when evaluating the properties of slurries prone to large volume changes. Focus has been given to outline a method to determine hydraulic conductivity functions and soil water characteristic curves (SWCC) that account for both changes in suction and volume.

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