ETD Collection

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2018 - 20192

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Has files: YesSubject: search.filters.subject.Slopes (Soil mechanics)

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    Investigating slope stability in an open pit mine – a case study of the phyllites western wall at sentinel pit
    (2019) Simataa, Ephraim
    Slope stability is critical for final wall in open pit mining operations. Not only is slope failure costly to manage, it might also be accompanied by loss of lives. Factor of safety is very critical during the slope design phase, however, the execution of the design is as important as the design phase itself. Among the many factors affecting stability of highwalls, geology, groundwater and blasting are at the top of the list. This research takes a kinematic stability analysis approach and investigates the possible failure mechanisms in the phyllites rock mass. The data collected from the structural geological mapping along with the window mapping classifies the rock as fair to good rock. The induced failures causing reduced catchment berms and consequently longer bench heights are largely influenced by the prevailing geological conditions, presence of groundwater seeping through the highwall and quality of blasting being conducted. Amongst the factors influencing slope stability, blasting is the only controllable one. Therefore, adjustments to the blast designs need to be made as mining progresses keeping in mind that rock is not homogeneous. Wall control blasting techniques should be continuously adjusted depending on the Rock Mass Rating or blastability index of the rock mass in that area. Hydrogeological testing of boreholes including Packer testing was conducted in order to estimate the hydraulic conductivity. Adjustments to blast designs were made taking due cognizance of the geological conditions as well as presence of ground water. Adjustments to the wall control blasting techniques need to be made as mining progresses through the different rock mass zones. A few blasts on the lower levels (mining benches below 1112RL) were conducted which saw an improvement in the quality of the highwall. Further adjustments to blast designs need to be made as the pit gets deeper and as geological conditions vary.
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    Guidelines for the stabilization of banks using the functional traits of roots
    (2018) Van der Haar, Megan Carene
    A decrease in riverbank stability results in accelerated changes in channel morphology, a loss of agricultural and natural lands, reduced water quality, possible movement of sediments and/or contaminants from surrounding lands into the river, and potential damage to property. Vegetation plays a critical role in stabilizing natural slopes. The purpose of this study was to determine the applicability of vegetation roots for the stabilization of South African riverbanks and quantify the effect of root reinforcement, specifically by means of root functional traits. The study focuses on South African riverbanks as there are limited studies on soil bioengineering for the South African environment. Further, there is a growing concern of riverbank failure in South Africa as expressed by the Water Research Commission. Numerical modelling using geotechnical software formed the method of research. A table was developed to provide scoping level guidance on the suitability of vegetation stabilization for various soil types, bank angles and bank heights for various flood conditions. Results from transient finite element seepage analyses show that the input parameters are reliable within realistic ranges, but the saturated volumetric water content should be identified with accuracy in order for the guidelines presented to be used with greater confidence. This report includes a thorough review of existing models that account for the effects of vegetation on bank stability. A limit equilibrium based model that accounts for the enhanced cohesion due to the presence of roots was proposed. A sensitivity analysis together with literature indicated that the most significant root functional traits are: root diameter, root density and root length. Results pertaining to the root functional traits that were able to stabilize appropriate banks were presented and the use demonstrated through hypothetical examples. It was concluded that bank geometry, material permeability and material strength perform a significant role in riverbank stability and as a result loamy sand and gravel riverbanks are more suitable for vegetation stabilization.