3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Investigating slope stability in an open pit mine – a case study of the phyllites western wall at sentinel pit(2019) Simataa, EphraimSlope 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.Item Hydrogeological characteristics of Hartbeespoort Dam(2017) Davis, AqueelahHartbeespoort Dam, the source of irrigation and potable water for the local community of Hartbeespoort area is a vulnerable water resource. The aim of this research was to evaluate the interaction between dam water and groundwater as well as characterise the hydrochemical data from metals and tritium. The former was done through the application of environmental isotopes and the implementation of a long term water balance, while the latter used hydrochemical data to define the spatial distribution of metals and tritium. The results indicated that the dam water is separated from the groundwater in winter. Two sources of mixing were recognized to have occurred downstream of the dam in 2015 but not in the Hartbeespoort dam area. These were identified as artificial through the runoff of agricultural water that was abstracted from the dam and through the pumping of water near the fault. Higher than normal tritium concentration indicated that contamination comes through the Crocodile River after the fault connecting the river to Pelindaba, the nuclear power generation plant south of Hartbeespoort Dam in the Broederstroom area. The Crocodile River showed that the contamination of water by lead, 22.11ppb in summer and 3.8 ppb in winter, and cadmium,2.2 ppb in winter. The Magalies River feeds the dam with copper. All metals accumulate at the dam wall and settles in the sediment, diluting the downstream water. Boreholes near the dam and spring along the fault are vulnerable to contamination. The water balance estimation resulted 18 345 472m3, with a 3.9% error, gain of water to the dam from the groundwater greater than the amount exiting the dam to through groundwater. The groundwater entering the dam is estimated to be 32 517 704m3. The groundwater exiting the dam is estimated at 14 172 232m3. The difference in groundwater showed a decrease of 10 000 000m3 over the 15 year period from 1st October 2000 until the 30th September 2015. Consequently, these results show an increased stress placed on the groundwater presumably due to an increase in groundwater abstraction from agriculture and the expanding mining area.Item The use of time-lapse electrical resistivity tomography to determine the footprint of acid mine drainage on groundwater(2017) Zulu, Sbonelo MfezekoThe costs of acid mine drainage (AMD) monitoring result in the quest for alternative noninvasive method that can provide qualitative data on the progression of the pollution plume and ground geophysics was the ideal solution. However, the monitoring of AMD plume progression by ground geophysics (time-lapse electrical resistance) proves to be noninvasive but also time consuming. This study focuses on the modeling of different geophysical anomalies (mainly geoelectrical resistivity response) of the karstic aquifers. The models are generated from field parameters such as the electrical resistivity of the host rock and the target rock, depth to the target, noise level and electrode configuration in order to ensure that the model outcomes represent the actual field data. This process uses Complex Resistivity Model (CRMod) and Complex Resistivity Tomography (CRTomo) to generate geoelectric subsurface models. Different resistivity values are applied to targets in order to assess the difference against the baseline model for each target scenario. The resistivity difference is reduced to smallest possible value between the reference and new models in order to gauge the lowest percentage change in the model at which the background noises start to have impact on the results. The study shows that the behavior of targets (aquifer) could be clearly detected through resistivity difference tomography rather than inversion tomography. The electrode array plays a significant part in the detection of target areas and their differences in resistance because of its sensitivity. This therefore indicates that the electrode array should be chosen according to study requirements. Furthermore, this study shows that the modelling of different target sizes, alignments and shapes plays huge role in the final results. Future studies that can provide a correlation between the field quantitative data from sampling and the model outcomes have the ability to add to the knowledge of geophysical modeling, thus reducing costs associated with field based plume AMD monitoring. Key words: Acid mine drainage, geophysics, karst aquifer, complex resistance, modelling, tomographyItem Investigation of the impact of recharge water with respect to quality into the Khutala Colliery Rehabilitated block I opencast operation(2012-01-19) Repinga, Mandla RalphABSTRACT This study was an investigation of the impact of recharge water with respect to quality and quantity into the Rehabilitated Block I opencast operation, a former opencast coal mine in Mpumalanga, Witbank Coalfields western complex. The rehabilitated areas consisted of three mined mini-pit areas known as Block I, Block I Extension A and B. The area has been rehabilitated by backfilling and leveling of spoil material, subsoil material, placement of approximately 400-mm topsoil layer and grassing. As part of the vegetation maintenance lime is added per annum, in an effort to neutralize the soil cover and further assist in neutralizing the potential acid mine drainage. Additional monitoring boreholes were drilled to increase the monitoring of the water quantity and qualities. Ground and surface water samples were taken, analysed for pH, conductivity, redox potential, sulphates, carbonates and trace metals. The pH of the ground and surface water ranged from moderately acidic to alkaline. One of the monitoring boreholes located on the lowest elevation of the Block I area was observed to be filled up to the collar level of the borehole with water samples showing elevated Fe and Mn concentrations of 216 and 46.2 mg l-1 respectively. The water classification revealed the following facies: Ca-Mg sulphate type for the borehole water and Ca-Mg sulphate-bicarbonate type for the surface waters. Acid base accounting studies on the soil samples showed a negative net neutralising potential of up to -9.8 kg t-1 CaCO3 which indicated the potential of acid mine drainage in the area. The total metal analyses showed that the area was contaminated with heavy metals such as Fe, Cr, Mn, Ni and Zn and the metalloid As was also detected. The highest recorded concentrations of total metals were 78 252; 2 402; 1 959; 1 360 and 15 109 mg kg-1 respectively. The highest concentration of Arsenic was detected at 824 mg kg-1 respectively. The transmissivity of the boreholes in the spoil material was highly variable and ranges from 100 to 5 000 m2 day-1. Pump testing suggests that borehole yields of between 23 and 4 l s-1 can be expected in the spoil areas. The specific yield or the drainage porosity of the spoil material was in the range of 25 to 30 %.