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A study was performed to investigate the factors that affect the accuracy of the procedures used by the Virginia Department of Transportation for design of drilled shaft sound wall foundations. Field load tests were performed on eight inch and nine inch diameter drilled shafts, and the results were compared to theoretical solutions for ultimate lateral load capacity. Standard Penetration Tests were run in the field and laboratory strength tests were performed on the soils from the test sites. It was found that published correlations between blow count and friction angle for sands and gravels can be used to estimate friction angles for the partly saturated silty and clayey soils encountered at the test sites. A spreadsheet program was developed to automate the process of determining design lengths for drilled shaft sound wall foundations. The spreadsheet was used to investigate the effects of different analysis procedures and parameter values on the design lengths of drilled shaft sound wall foundation. / Master of Science

A research report submitted to the Faculty of Engineering and the Build Environment, University of the Witwatersrand, in partial fulfillment of the requirements for the degree of Master of Science in Engineering Johannesburg, 2014 / The South African power crisis and corresponding rising costs experienced since 2008, created a paradigm shift in terms of electricity use. The mining sector is the second highest consumer of electricity with metalliferous mines being accountable for 80% of the total power. Recent studies revealed that underground ventilation and cooling accounts for 30% to 40% of total electricity costs in an underground metalliferous mine. Hence the need to look at ways to reduce electricity consumption in ventilation and cooling. Work has been done on optimising efficiencies of ventilation and refrigeration systems of underground mines. Currently, the high energy consumption is driven by efforts to achieve a thermally acceptable environment for workers (manned) in deep metalliferous mines which is currently between 27ºC (wb) and 29ºC (wb). However, no detailed study has been done looking at increasing thermally acceptable environments for deep level metalliferous mine. In this study the impact of increasing rejection temperature to 40ºC (db) was assessed in the automated (unmanned) scenario at a maximum depth of 2811 metres. Then the power demand was compared with the manned scenario. The results proved that automation in an underground mine has the potential of reducing electricity cost of ventilation and cooling by more than 50%. For example, the production rate of about 200 kilo-tons per month yield an annual cost saving of R71 million on electricity. These cost savings can be used to justify automation systems. Automation removes workers from the hazardous environment and replaces them with equipment which can withstand harsher conditions. The introduction of an automation system in underground mines would not come risk-free. Currently, automation systems have not yet reached a level of removing workers completely from underground.There are instances that would require workers to enter production zones. A Bow-Tie risk analysis was used to show the hazards that workers would be exposed to and prevention controls and responses to mitigate the impact the risks. / MT2017

Selection of steels for industrial purposes usually means choosing a type of steel to make a part or a product. The steel that is chosen must meet all the designer requirements. A quantitative selection procedure has been used to analyze the large amount of data involved in this selection process so that a complete and systematic evaluation can be made. The designer is responsible for the selection of steel, and this selection requires the designer to find data and information on the mechanical properties required, and also learns ways to improve these properties through different heat treatment processes. When a large number of steels and a large number of specified mechanical properties are being evaluated for selection, the weighed properties method can require a large number of tedious and time-consuming calculations. In such cases a computer program could greatly facilitate the selection process. This thesis reports the selection of steels for gears, shafts, fasteners and springs where the steps involved in the weighted properties method which is written in the form of a simple computer program to select steels from a data bank. This program also includes the digital logic method to help in determining weighing factors. The steels are ranked according to standard designation; BS, AISI, and DIN. It has been found that alloyed steels hardened and tempered at 2050C are most suitable for gears, shafts, fasteners, and springs when higher mechanical properties required, and carbon and low alloyed steels when cost is the main consideration.

The study of dross in ductile cast iron main shafts was performed at Global Castings Guldsmedshyttan AB and presented in this master thesis. The purpose of the study was to obtain answers to why dross defects were present in some of the foundry's casted main shafts, with the main problem located at the flange of the shaft. The chemical composition of the dross formations and which steps in the casting process that increased the dross formation were of interest. The study only included dross in main shafts manufactured at Global Castings Guldsmedshyttan AB. Dross particles form when elements such as Mg, Ca, Si and Mn react with O. These elements, which are highly reactive to O, are used in ductile cast irons to achieve the spheroidal graphite nodules that regulate the cast materials ductile properties. If a higher amount of dross particles has formed, the particles will start to cluster, resulting in a growing dross formation. Dross formations works as surface crack initiation points and reduces the castings fatigue strength and ductility. During the study it was seen that the cause of dross formations is a combination of many parameters increasing the melts exposure to O resulting in dross defects. The dross formations could be connected to worn out ladles, low melt temperatures, incorrect additions of Mg treatment, lack of an extra slag removal station and finally turbulence as the melt were poured into the mould. At Global Castings Guldsmedshyttan AB a greater part of the main shafts containing dross defects were a result of worn out ladles and low melt temperatures. The types of dross found in the main shaft material were mainly Mg, Ca, Si and Al which had reacted with O. S bonded with Mg and Ca was also detected in the dross formations. It was shown that the dross particles could be derived from charge material, Mg treatment and inoculation. To avoid dross defects the first step would be to set up an extra slag station, shorten the interval of maintenance of the ladles and to better adjust the melt temperature to the condition of the specific ladle. To minimize dross due to excess Mg a better controlled process would be recommended with an increased number of monitored manufacturing parameters. / Studien av dross i axlar tillverkade av segjärn gjordes hos Global Castings Guldsmedshyttan AB och presenteras i denna examensrapport. Syftet med studien var att hitta anledningar till varför drossdefekter bildas i flänsen på vissa av gjuteriets tillverkade axlar. Drossens kemiska komposition likväl de steg i tillverkningsprocessen som inverkade på drossbildning var av intresse. Studien inkluderade endast drossdefekter i axlar tillverkade av Global Castings Guldsmedshyttan AB. Drosspartiklas bildas när till exempel Mg, Ca, Si och Mg reagerar med O. Dessa ämnen, vilka är väldigt reaktiva med syre, används vid framställning av segjärn för att de sfäriska grafitnodulerna som starkt reglerar materialets duktila egenskaper ska bildas. Ett större antal drosspartiklar i en smälta leder till kluster av dross vilka växer i takt med att nya partiklar bildas. Dross fungerar som sprickinitieringspunkter i gjutgodsytor och reducerar godsets utmattningshållfasthet och duktilitet.   Under studien kunde det ses att dross bildas på grund av en kombination av parametrar som ökar smältans exponering av syre vilket resulterar i drossdefekter. Drossdefekter kunde kopplas till slitna skänkar, låga smälttemperaturer, felaktig mängd magnesiumbehandling, brist på en extra slaggstation och slutligen turbulens när smätan hälls i formen. Hos Global Castings Guldsmedshyttan AB är en stor del av axlarna med drossdefekter ett resultat av framför allt slitna skänkar och låga smälttemperaturer. Vid analys sågs det att ett antal olika typer av drosspartiklar kan bildas i det duktila gjutjärn som används till axlarna; främst Mg, Ca, Si och Al som reagerat med O. Mg och Ca som bundit med S kunde också hittas i vissa av de studerade drossformationerna. Det kunde visas att den kemiska kompositionen i drosspartiklarna var härrörande från grundmaterialet, magnesiumbehandlingen och ympmedlet.  Ett första steg Global Castings Guldsmedshyttan AB skulle kunna ta för att undvika drossdefekter är att ha en extra slaggstation, införa tätare underhåll av skänkarna och bättre anpassa smälttemperaturen till skicket på den specifika skänken. För att minimera dross som bildats på grund av ett överskott av Mg skulle en mer kontrollerad process rekommenderas med ett ökat antal bevakade tillverkningsparametrar.

The results of a study to model a circular mine shaft constructed in a time-dependent medium are presented. The construction sequence is considered as well as the time-dependent properties of the media around the shaft. The loads acting on the shaft liner are due to excavation of the shaft material and to the loads relieved from the media onto the liner. The results show the importance of considering the time-dependent behavior of media. The analysis was carried out using the Finite Element Method. Axisymmetric triangular and quadrilateral elements were used to model the medium, and axisymmetric shell elements were used to model the liner. The construction sequence was modeled by analyzing the system under small load increments where each load increment represents a construction step. The time behavior was modeled by using the initial strain method, which assigns a different strain value for each element in the medium. The strains are transferred to stresses and then to forces, and an incremental process is started to cover the time range desired. The results for a 400-foot shaft are shown, and changes in liner stresses were monitored as time passes. Different rock materials were modeled by using different constants in the creep law. Some materials showed significant changes in the results, and others did not. The liner horizontal displacement, and horizontal and vertical stresses increased when material constants for rock salt and anhydrite were used. Stresses in the elements adjacent to the liner decreased as time passed by, and some even went into a tensile stress site. A comparison between two solutions, one representing a multi-step construction sequence and another representing an instantaneous construction of the lined shaft, showed that liner stresses are much higher when the construction sequence is not modeled. This is due to the fact that when the excavation is modeled the forces representing the construction sequence are applied to the medium. In the other case, the forces are directly applied to the liner.

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No description available.

The mechanics of massive interseam failure in a multiple seam mine was investigated using three approaches: case studies, physical models and computer analysis. Specific examples of multi-seam mines with the underlying seam mined first prior to the mining of the overlying seam were studied with some design guidelines drawn from them. A loading frame capable of testing model blocks of 24 inches by 24 inches by 6 inches and also capable of applying up to a maximum of 10,000 psi of pressure on the models was designed and built. In this investigation, factors that affect the stability of the overlying seam when the underlying seam is mined first were studied using the finite element method and the Mohr-Coulomb failure criteria. Critical failure surfaces obtained from the computer analysis were analyzed for columnized and staggered pillars in room and pillar mining with the columnized pillars favored over the staggered ones. / Master of Science

Thesis (M.Eng.(Mining Engineering))--University of Pretoria, 2000. / Abstract in English. Includes bibliographical references.