Experimental and Physical Modeling of Bed Load Heterogeneous Sediment Transport

Abstract

The hydraulic deposition process linked to tailings dams normally presents some technical deficiencies mainly because of the lack of control of hydraulic parameters. Problems of instability in tailings dams usually arise from poor management practices, such as poor decant pond control, in addition to the material being placed randomly. Hydraulic parameters, such as the flow rate and concentration of the slurry, play an important role in the formation of hydraulic fills. Grain size, distribution, segregation, and density, and slope inclination are the main characteristics of tailings dams, which are affected by the hydraulic parameters of the slurry. To investigate these factors, an experimental apparatus [hydraulic deposition simulation test (HDST)] was used to simulate the hydraulic deposition process in the laboratory, where all variables that could affect the phenomenon could be controlled carefully. The HDSTs using different flow rates and concentrations were carried out using the iron waste from the Morro Agudo Mine, Minas Gerais, Brazil (operated by Vale). The results presented in this paper are mainly related to the segregation patterns, mean grain sizes, specific gravities, and densities obtained along the small-scale deposited beach in the HDSTs. The main objective of this investigation was to analyze the influence of hydraulic deposition parameters on the formation process of hydraulic fills, focusing on segregation and its importance to density and porosity values. Moreover, a mathematical model was developed to describe and simulate the mechanism of formation of granular tailings dams based on momentum and continuity equations of the fluid and sediments (quartz and iron). The model takes into account the main external variables (slurry concentration and flow rate) and internal variables (such as mean particle size, grain density, and relative percentage of iron and quartz) related to the slurry mixture. The analytical and numerical results of the model were compared with the deposition profiles obtained by the HDST.