Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 72-74). Also available via the Internet.

Thesis (PhD.(Mining Engineering)--University of Pretoria, 2008. / Summary in English. On title page: Submitted in partial fulfilment of the requirements for the degree Philosophiae Doctor in the Faculty of Engineering, Built Environment and Information Technology, University of Pretoria. Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains iv, 62 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 59-62).

M.Sc. / The coal-bearing Permian Vryheid Formation of the Ecca Group (Karoo Supergroup) was investigated at New Denmark Colliery, situated in the north east section of the Karoo Basin, South Africa. The lithostratigraphy of the sequence is defined in terms of conventional lithostratigraphic terminology but also by applying detailed genetic stratigraphic schemes that have previously been proposed for the adjacent coalfields. The succession is divided up into depositional sequences named after the underlying and overlying coal seams, the No. 2, 3, 4 and 5 seam sequences. The sedimentary succession was divided up into five facies, namely: conglomerate facies, sandstone facies, interlaminated sandstone-siltstone facies, siltstone facies and coal facies. These were interpreted hydrodynamically. Facies assemblages were then interpreted palaeoenvironmentally. Glacial, fluvial, deltaic and transgressive marine sequences were responsible for forming this sedimentary succession. Attention was then focussed on the main economic No. 4 seam, which is mined underground at the colliery. Detailed subsurface geological cross-sections, core sequences and isopach maps of the No. 4 seam coal and the lithologies above, were used to determine specific aspects of the depositional environment that could contribute to unstable roof conditions above No. 4 seam. Coarsening-upward deltaic cycles, fining-upward bedload fluvial cycles, glauconite sandstone marine transgressions and crevasse-splay deposits are recognized in the overlying strata. Poor roof conditions occur parallel to palaeochannel margins because the interbedded channel sandstone and adjacent flood plain argillites cause collapsing along bedding plane surfaces. Rider coals overlying thin crevasse-splay sequences in close proximity to the No. 4 seam, create one of the most serious roof conditions; complete collapse occurs along the rider coal contact with the underlying splay deposits. Differential compaction of mudrock/shale/siltstone over more competent sandstone causes slickensided surfaces that weaken the roof lithologies. Correct identification of these sedimentological features will enable the prediction of potential poor roof conditions during mining operations and mine planning.

The study that is described in this thesis deals with stope support design from a rockmass stiffness approach. Three models were developed and combined into a single one in the third part of the study in an attempt to describe and quantify the stop support and rockmass interaction. The first model describes stope support with all the factors having an influence on its performance, where this is referred to as the capacity of the stope support. The second model describes rockmass behaviour and is referred to as the rockmass demand. These two models are represented on a common load-deformation graph during the third part of the study. Here the demand of the rockmass is compared to the capacity of the stope support as a whole. In contrast to previous design attempts, both the demand and the capacity for any given situation are considered as variables. The demand varies according to the position relative to the abutments and the capacity varies according to the state of deformation of the support. Each combination of mining configuration, rock type and support type results in a unique base set within which variation is allowed according to position. This is achieved by: (a) comparing the energy released by the rockmass to the energy absorbed by the support system for a given deformation interval; and (b) comparing the rockmass stiffness to that of the support system at any given point of deformation. The methodology is tested by two case studies on Beatrix Gold Mine. In the first study the condition of unstable failure of the support was evaluated where the support failed and the stope collapsed in a relatively short span of time. This is referred to as unstable failure of the stope. The underground observations were confirmed by the outcome of this study. The energy released by the rockmass, that is rockmass demand, exceeded the capacity of the stope support after a given stage of mining. The absolute value of the rockmass stiffness was also less than the absolute value of the load-deformation curve of the stope support for the same mining interval. During the second case study some elements of the stope support failed while the excavation remained open and stable. Underground observations again confirmed the model during this study. Here the Pencil Props failed some distance from the stope face. In this case the absolute value of the rockmass stiffness was less than the magnitude of the negative load-deformation curve of the Pencil Props, while the Matpacks have a positive load-deformation behaviour throughout the deformation process. In the latter case the total energy generated by the rockmass never exceeded the capacity of the permanent stop support. This is referred to as stable failure of the stope support. The study proves that it is possible to evaluate stope support even when a combination of different supports is used as permanent support. The latter is achieved by adding the capacities of the stope support as deformation takes place and comparing that to the rockmass demand for the same mining steps. / Thesis (PhD(Mining Engineering))--University of Pretoria, 2006. / Mining Engineering / unrestricted

M.Ing. / Safety within the mining industry is a primary concern for everyone involved. More specifically, active below-ground stope support for South African Mines is becoming increasingly important due to a renewed emphasis on the safety and well-being of the people actually working underground. It is imperative that all stope support systems are rigorously tested, continuously, both under laboratory conditions and in-situ to prove their performance and manufacturing standards. The Rocprop was initially manufactured in 1995 with the first two hundred props being installed at East Driefontein Consolidated Gold Mine in the Carletonville area. In the three years since the first introduction over three hundred thousand Rocprops have been manufactured and sold to South African Mines with the number steadily increasing. The Rocprop is a tubular support consisting of two tubes — a Ø139mm 'inner' tube and a Ø152mm 'outer' tube. One end of each tube is sealed by dome ends which are welded onto the tube mouths. The two tubes, cut to identical lengths, fit inside one another and extend telescopically during installation. Once the desired height has been reached, leaving enough tube overlapping to ensure the support does not buckle, the wedge is hammered in locking the prop at that height. The water is then removed after which the prop will provide active support of the rock mass above it. One of the components responsible for the Rocprops success is a dome end. This is either a forging or a pressing welded onto each end of the support and allows continual concentric loading throughout the life of the Rocprop. At present the dome ends are pressings, manufactured into hemispheres from 10mm mild steel plate in one action. The reason for the Rocprop's success is its performance characteristics. It's all metal construction, ease of installation, reliability and predictability in both seismic and static conditions, fire resistance, blast resistant, economically viability and versatility have made the prop successful. Reasons for the research were to investigate the dome end forming process in general and to investigate current numerical analysis techniques ability to predict loads during manufacture, the final shape, spring-back and other local deformation areas. Also to investigate alternate manufacturing methods such as cold forming, which provides advantages such as better mechanical properties and higher structural capabilities. The use of alternate materials in the Rocprop manufacture has been an ongoing process for MSP, manufacturer and current licensee holder of the Rocprop. A substitute for the current dome end manufactured from mild steel was investigated. For the substitute to be viable the material should be stronger, weigh less and be cost effective. In depth knowledge about the forming of the dome end at various velocities was gathered, providing information for further optimisation of the component.

Roof and rib failures in underground coal mines are one of the major problems facing the industry today. In addition to safety considerations, the resulting economic impact of such failures is staggering. Uncovering and replacing buried and damaged equipment and clearing entries can account for a large expenditure in lost man-hours and machinery. Yet, because of the complex nature of their formation, geological variability, and structural characteristics, coal mine roof strata are one of the least controllable of all mine design parameters. This is especially true along the leading (southeastern) edge of the Appalachian coalfields where considerable faulting and movement have contributed to hazardous coal mining roof conditions. For this research, a detailed study of several mines, in the southern Appalachian coalfields, was undertaken to determine the most prominent geomechanical factors affecting roof stability and to evaluate their influence in promoting unstable ground conditions. In order to accomplish this task, the major geological and geomechanical features found to be detrimental to the coal mine roof within the Appalachian basin were identified and mapped in four Virginia mines. Statistical processing by chi-square and linear regression analysis as well as analytical analysis by the finite element method were used to determine the influence of geology, mine-layout, and support methods on roof stability. It was found that some easily determined parameters can be successfully used to predict potentially unstable areas. A simplified roof classification system was developed based on the geomechanical parameters, which can be used to assess the stability of a particular roof type. A Roof Rating Index was also devised capable of expressing the probability of failure under a given set of geomechanical conditions. / Ph. D.

A major objective in the design stage of an underground mine is the reliable prediction of roof falls' size, frequency and location. Probabilistic simulation of potential roof control problems allows a designer to test the performance of competing mine layouts against assumed roof conditions. By comparing different roof control plans using the simulation, the option that provides the lowest overall cost can be selected. The program ROCSIM (Roof control Optimization Cost Simulation) was developed to provide a theoretical solution to this problem. The occurrence and frequency of roof falls are related to the type of roof support, support density, geology, structural discontinuities, location in the mine, and elapsed time between mining and the roof fall. Using a Roof Rating System (RRS) developed for this research, a numerical rating can be given to each area of roof. Using this rating, specific parameters can be assigned to these probability distributions to simulate the occurrence of roof falls within a given geologic setting. Once the location of a roof fall is determined, a cost is calculated taking into account the production delay that would result and the direct cost of cleaning up the fall and resupporting the roof. Assigning a cost to a roof fall allows the comparison of competing roof support designs relative to their overall cost. The final decision on the amount of support and room width must be determined based on legal restraints and minimization of mining costs. / Master of Science