Abstract

A tailings dam, as part of a tailings storage facility, is typically constructed using waste rock or mine tailings, which are the waste created during extraction of ore from mining or by-products from mineral beneficiation and manufacturing. These dams are often raised continuously, as the tailings facility is expanding. The holding capacity of these facilities is needed to accommodate large volumes of tailings with the increasing demand placed on the mining industry. Thus, the topic of focus in this thesis is to investigate the seepage conditions that can ensure that the embankment can be safely constructed and operated during the raising stage and that it remains safe afterwards, beyond closure of the mine. However, according to statistics, a tailings dam must be protected against failures caused by various reasons even during its construction stage. Structural stability is the most important aspect and it should to be considered when addressing the problem of "safety" for tailings dams, which are threatened by seismic liquefaction, slope instability, overtopping and seepage. The seepage conditions of upstream-type tailings dams are the main topic of this research, which is associated with knowing the position of phreatic surface. The amount of pore water below the phreatic surface affects the stability of a tailings dam by reducing the shear strength of soil. The purpose of this thesis is to develop a seepage analysis model using a numerical modeling technique and to investigate potential means of phreatic surface control. Parameters like beach width, permeability anisotropy, raising rate of embankment and slope inclination will be investigated to identify factors that may have a significant influence on the long-term evolution of phreatic surface within the tailings dam during the mine’s life. This research will develop an uncoupled hydro-mechanical model using finite elements in which the whole process of construction is simulated in stages of embankment raising and filling of the tailings pond. The finite element model will be built using RS2, which is a comprehensive two-dimensional finite element program for soil and rock applications. It can model a wide range of engineering projects including excavation design, slope stability analysis, groundwater seepage, probabilistic analysis, and dynamic analysis. RS2 is able to carry out a finite element groundwater seepage analysis, with due consideration of both saturated and unsaturated soil states, in both steady-state and transient groundwater seepage formulations through both homogeneous and heterogeneous dams, dikes and other embankment types. However, basic finite element analysis principles will also be presented in this thesis, to aid the comprehension of the models developed. Based on the results of modeling, each identified parameter was assessed and guidelines were given regarding its contribution in the development of seepage face breakout on the downstream face of tailings embankment dams. These guidelines can serve practicing engineers in their design and evaluation of tailings dams to ensure safe and economical operation of tailings facilities.