ETD Collection

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Now showing 1 - 6 of 6
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    Influence of pit wall stability on underground planning and design when transitioning from open pit to sublevel caving
    (2019) Mapuranga, Amos
    This research sought to address the influence posed by the pit wall stability and instability on underground planning and design when transitioning from open pit to underground. Conventionally, empirical methods are used and they sometimes lack consideration of rock mass behaviour, groundwater effects, structures as well as geological considerations. This can potentially result in massive failures of pit slopes and subsequent loss of infrastructure, excavations, loss of machinery and human lives. It was against this background that this research sought to reduce mining exposure to the above mentioned hazards. In line with the aims and objectives of the study, this research investigated stress changes around the pit slopes with progression of mining and also the influence of geological and geotechnical conditions on mine planning. This was done so as to determine the zone of geotechnical influence from which planning of the underground mine would be done. Elastic 3D numerical modelling approach was used to determine the expected underground back break and its influence on the underground structure, pit slopes as well as the primary access. Different Factor of Safety shells were modelled, so that the corresponding zone of influence for each Factor of Safety could be correlated to the mine design. The results suggested that a Factor of Safety of two was ideal for this research for underground infrastructure to be outside the zone of geotechnical influence from start to finish of mining the first slice until the last fourth slice of the sublevel caving. This approach yield better projections of rock mass and slope behaviour since it considers a broad range of parameters that include rock mass strength properties, geology, geo-mechanical parameters, groundwater and rock behaviour.
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    The use of chemical stabilisers in labour intensive road construction
    (1995) Van Steenderen, Willem Pieter Cornelis
    Until recently use of ionic chemical soil stabilisers seemed hit or miss. The paper by paige-Green and Bennett explains that the stabilisers work only on soils containing reactive clays. The author's findings confirm this conclusion. It was shown that a CBR test, which can be done in any road soils laboratory, can be used to measure the chanqe in strength caused by the treatment of the soil with a chosen ionic stabiliser. South Africa is faced with a serious unemployment problem. The World Bank and the International Labour Organisation have shown that employment in construction can be significantly increased by the use of labour instead of machinery. Field trials showed that ionic stabilisers can readily be applied labour intensively. These stabilisers could imprpve marginal materials to road-building standard and this could further reduce the dependence on machinery by reducing the need to transport quantities of high quality gravel.
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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.
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    Effect of internal erosion on the mechanical behaviour of soils
    (2017) MacRobert, Charles John
    The effect of internal erosion on the mechanical behaviour of soils was investigated experimentally, using sodium chloride grains as an analogue for erodible soil grains. With this technique, the loss of controlled quantities of finer particles could be simulated under more realistic hydro-mechanical conditions than in previous research, but within practical experimental time scales. Two experimental programs were undertaken. The first looked at general changes in volume and shear strength using a large diameter oedometer adapted to perform a punch test following salt dissolution. The second program investigated particular changes in volume and shear strength following salt dissolution using an adapted direct shear box Previous studies have shown shear strength reductions following the loss of finer particles representing as little as 5 % of the total mass of the original soil. Findings here show shear strength can be largely unaffected if the erodible finer fraction (F) makes up less than a transition value (Ft) of approximately 10 – 15 % by mass of the original soil. This threshold represents F above which the coarser fabric is looser than at its minimum void ratio. As F increases further, finer particles increasingly hinder the coarser particles from achieving their densest packing, such that the coarser fabric remaining after finer particle loss is in a looser state than the original fabric, the remaining fabric reaching its maximum void ratio at a critical finer fraction (Fc) of approximately 25 – 35 %. For F < Fc, finer particle loss results in limited collapse of the coarser fabric and it was found that the state of this initial coarser fabric determines the shear behaviour of the soil following the loss of finer particles. The shear behaviour of initially dense specimens with F < Ft remained similar to that of a dense soil following finer particle loss, whereas shear behaviour of initially dense specimens with Ft < F < Fc approached that of a loose soil as F increased. Soils with higher internal filter ratios (D15c/D85f) were found to have higher values of Ft and Fc. Soils with F > Fc, settled and weakened significantly following finer particle loss, reflecting the load-bearing role finer particles play in this case. This load bearing nature of the finer particles in soils with F > Fc decreases the risk of internal erosion.
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    Stockpile life of foam stabilised material and the implications for labour intensive construction
    (1998) Chasi, Brian Takaona
    Various studies have been done to show that labour-based construction can meet the high standards normally required in the construction of roads. The organisational requirements that were needed to ensure the efficient use of labour have also been dealt with in various studies. Tile need for alleviation of poverty, unemployment and the negative social impact thereof by increasing the labour input in construction is understood by all concerned. A further step is however necessary before the idea of increasing the . labour component in any kind of roadwork can be taken seriously. Engineers need to move forward from the policy and organisational issues associated with labour intensive construction and start to provide designers with sound and innovative engineering solutions to overcome the hurdles experienced on the ground. The study looks at the process of foam bitumen stabilisation of soils and gravels with a view of utilising this innovative method for labour intensive construction. The material after having been stabilised can be placed in a stockpile. Actual durations that the material can safely remain in stockpile have been determined in this study to be in excess of six months for recycled asphalt and in excess of four months for the foam stabilised sand. Foam stabilised gravel was also studied and showed that after a year in stockpile the material failed probably due to a weakening of the bitumen and aggregate bond. Covering the stockpiled material did not show any significant difference to that of a similar uncovered stockpile. The position within the stockpile also did not have much effect on the engineering properties of the stoc piled material. The fact that the foam stabilised material can be worked on when cold and that it can be stockpiled for several months implies that the material is labour friendly and can be used in labour intensive construction of road base course layers or wearing course layers.
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    A laboratory investigation into the stabilization of natural soils using two waste materials
    (2014-12-04) Barrett, Andrew John
    Soil stabilization is the generic term for any process which has as its aim the upgrading or improvement of one or more soil properties. In South Africa, stabilization is usually effected using a combination of mechanical densification and the addition of a binder to the soil. Two waste materials, PFA (a power station waste) and phosphogypsum (a waste from the fertilizer industry) have been shown to be useful binders overseas. The purpose of this project was to investigate local samples of these waste materials to establish their potential as soil stabilizers. A limited amount of research into the use of these two materials has been carried out in South Africa. The results of these programmes are discussed. Generally, however, none of these programmes were comprehensive enough to reach categoric conclusions regarding either binder. The soils used in the investigation were taken from various locations in the Johannesburg Municipal area in which it is intended to construct surfaced roads for light traffic in the near future. The soils chosen cover a range of plasticity indices from 0 to 30, but unfortunately, were very similar mineralogically. The phosphogypsum used was supplied by Triomf Fertilizer (Pty) Limited. Two samples of PFA were used. One of them was supplied by Darling and Hodgson, Limited, who are extracting a "selected" ash from Grootvlei power station, and intend to make it commercially available at some stage. The other ash was obtained from Kelvin power station. Tests were done to establish both the short and long term effects of the binders on the soils. The short term effects were investigated by looking at changes in the plasticity and moisture density relationships for the soils immediately after the addition of the binders. The long term effects were investigated by looking at the changes in unconfined compressive strength of moulded soil samples with the addition of the binders. (Samples were moulded at 100% Mod AASHO density and optimum moisture content in a tapered cylindrical mould by static compaction). These effects were looked at from 3 different angles. i) the effect of binder composition (i.e. different ratios of PFA/lime and PFA/cement) ii) the effect of binder content iii) the effect of age on strength gain The results of the testing programme were not very encouraging. For the binder contents used, there were minimum short term effects for both binder types. The addition of phosphogypsum to the soils resulted in only very small strength increases. For the PFA binders, it appears that the lime content of many of the PFA/lime binders fell in a range where only short term reactions could be expected. However, even where sufficient lime was present to satisfy the initial lime demand of the soil, the PFA appeared to act mainly as a diluent to the lime. Similar conclusions apply to the PFA/cement binders. The general nature of PFA/lime stabilization was uncovered in this testing programme, but further tests will have conducted before conclusions regarding the quality of our local materials can be drawn.