Browsing by Author "Mutede, Tawanda Blessing"

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    Comparison of 2D and 3D slope stability factors of safety considering spatial variability
    (Stellenbosch : Stellenbosch University, 2022-04) Mutede, Tawanda Blessing; MacRobert, Charles; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: Historically, slope stability analyses have relied on two-dimensional (2D) models. This is due to the relative ease of implementing 2D slope stability analysis both from a theoretical and computational stand-point. However, with the emergence of powerful computers, the use of three-dimensional (3D) methods is increasing. While 3D slope stability analysis methods model reality better, site investigation methods often do not provide adequate information to create detailed 3D slope models. As a result, the extrapolation of 2D cross sections to generate 3D models is employed. This simplification gives rise to the question of whether these 3D extrapolated analyses are safe, as this typically results in higher factors of safety compared to the corresponding 2D analyses. Extrapolation may hide the spatial variability along slopes leading to an unsafe analysis. This research aimed to determine whether it was safe to conduct 3D slope stability simulations using extrapolated 2D sections or whether it was safer to analyse slopes using simple 2D methods. This research was done with reference to tailings dams. A total of 816 different slopes were generated and analysed using Rocscience’s Slide 2 and Slide 3 software programs. Three different models were used to conduct slope stability analyses, namely: 2D models, 3D extrapolated models from 2D extrapolated sections and 3D composite models which consisted of three merged 2D extrapolated slope sections. The research found that when analysing slopes, if the weakest slope sections are sampled and analysed using 3D extrapolated models, the results that are obtained are safe. However, if the strongest slope section is unfortunately sampled and analysed using 3D extrapolated models, the results obtained are unsafe. In such instances it is safer to rely on normal 2D modelling for analysis of slopes. The reason for this is that 3D extrapolated models’ factor of safety (FOS) do not consider heterogeneity along a slope. With relation to tailings dams, the research concluded that unless extensive sampling is done during the site investigation phase, it is safer to rely on 2D slope stability results especially when the tailings dam has thin embankment walls and high levels of heterogeneity. If good sampling procedures are done during the soil investigation phase, chances of identifying the weak and critical slope sections are increased. This makes the extrapolation of 2D slopes to conduct 3D slope stability analysis safer.