Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1988. / Vita. Abstract. Includes bibliographical references (leaves 132-145). Also available via the Internet.

A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy, Johannesburg, September 2017 / Rockburst occurrences and their consequent damage remain a problem in modern mining, particularly at great depth. The problem of rockbursts has also escalated in deepcivilengineeringtunnelsduetohighlevelsofin-situstressatsuchdepths. Key advancementshavebeenmadetodatetohelpmitigatethedrasticimpactscausedby rockburstdamage,withrocksupportremainingalineofdefensetoprovidestability in rockbursting situations. There is, however, an ongoing inability of support to contain severe rockburst damage, especially conventional support systems. More than two decades ago, a support concept termed “sacrificial support” was proposed as a potential additional method to help inhibit rockburst damage. The philosophy behind a sacrificial support system is that, under dynamic loading conditions, support, in the form of a liner must fail (i.e. be ejected from rock surface), leaving behind, undamaged, what was once supported rock mass. It is because of this reason that this support is referred to as a sacrificial support due to its ability to protect the rock from damage whilst the support itself fails. Since the inception of this support idea, it was only recently that the behaviour of support in real rockburst events manifested the sacrificial behaviour in rockbursting, which warranted the need for further research. The sacrificial support concept stated here is applicable in situations where the source (i.e. seismic event) of the rockburst is located remote from where rockburst damage is likely to occur. To investigate the behaviour of sacrificial support, controlled laboratory experimentsbasedonthesplitHopkinsonpressurebar(SHPB)techniquewereconducted to study some aspects of dynamic rock fracturing in tension at high strain rates, and also the role a sacrificial layer plays in combating dynamic rock failure (i.e. rockburst damage). To achieve this, a single Hopkinson pressure bar configured for spalling tests, comprised of a relatively long cylindrical intact rock specimen attached at the bar free end, was impacted by a striker on the opposite free end of the bar in order to generate a dynamic stress pulse responsible for spall failure upon reflection from the specimen free end. Different liners and/or liner combinations were then introduced at the specimen free end as sacrificial support. This experimental arrangement allowed the role of, and failure mechanisms associated with, sacrificial support under dynamic loading to be demonstrated, and comparisons were made with “sacrificial support” behaviour observed in real rockburst events in a mine. Analysis of experimental results revealed that varying liner thickness and mechanical impedance between rock and support liner plays a significant role in helping to limit rockburst damage. Apart from experimental investigations, numerical simulations were undertaken to further probe the behaviour of sacrificial support under dynamic loading. Elastic models subjected to p-wave propagation indicated failure of the sacrificial layer, manifested by ejection of the liner due to reflection of compressive wave at the free surface. This failure mechanism was noticed for all the liners, independent of variation in liner thickness, and wavelength characteristic of the applied wave to the model. The sacrificial support method presented in this thesis presents an opportunity to further enhance safety in seismically active mines. / XL2018

Sudden rock failure in the form of rockbursting has long been a problem in underground mines. The basic mechanism of this phenomenon is still unresolved. This thesis describes the research work on this problem conducted by the doctoral candidate Daihua Zou in the Department of Mining and Mineral Process Engineering at The University of British Columbia, under the supervision of Professor Hamish D.S. Miller. This research project was undertaken in order to investigate the process of violent rock failure and was achieved by examining various aspects of the rock failure mechanism. The assumption that acoustic emission can be used as a reliable means of predicting rock failure was investigated, as well as the possibility that violent rock failure could occur in any mine rock. As part of the research, a rock failure mechanism was postulated. A process analogous to shearing is postulated to be important at the post-failure stage. The stick-slip phenomenon has been analyzed using a numerical model under a variety of conditions. The conditions which could give rise to possible violent rock failure were determined. At the same time, acoustic emissions were tested from rock specimens under different loading conditions. The experimental results obtained show a correlation with field measurements made in a mine. In order to verify the testing results from limited experiments, a numerical acoustic model was developed, which is unique in that it is entirely based on the stick-slip process not on any acoustic theory. This model allows rock tests and their associated acoustic emission to be realistically simulated. With this model, acoustic emissions were simulated under various loading conditions for different kinds of rocks. The case of a hard or a soft intercalation was also modelled. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

Thesis (M.S.)--Ohio State University. / Includes bibliographical references (leaves 111-115). Available online via OhioLINK's ETD Center

Thesis (M.S.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains xiii, 82 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 65-66).

A dissertation submitted to the Geophysics Department, School of Geosciences, Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Masters of Science. Johannesburg, February 2012 / Impala Platinum Mine (Impala), situated north of the town of Rustenburg in the North West Province of South Africa, has experienced an increase in seismicity from ~841 seismic events in the year 2005 to ~1588 seismic events in 2008. The seismologists and rock engineers need to understand the underlying mechanisms and driving forces responsible for seismicity to develop and design mining layouts and support strategies to lessen the risks posed by rockburts. However, most previous studies of seismicity conducted on Impala and other Bushveld Complex mines in the Rustenburg area provided limited information regarding the source parameters and mechanism due to insufficient data. The study is designed to investigate the seismic hazard on Impala Platinum Mine by means of two approaches: an investigation of seismic source parameters and the mechanism of potentially damaging seismic events, and mapping of the weathered layer of the near surface within the Impala mine lease area. A number of detailed investigations of rockbursts were conducted whereby damage was mapped and photographed. The investigations includes reviews of the seismic history, short-, medium- and long-term seismic hazard assessment methods, and an analysis of the source parameters of the seismic event and associated ground motions. The study has revealed that most of the seismic events occur close to the reef plane, and are the result of the failure of a volume of rock that includes the pillar and the host rock that forms the foundation of the pillar.

A review of coal bumps. their nature. causes. prediction. prevention. and mitigation is presented. The design and construction of a borehole stressmeter is discussed. Laboratory testing. which yielded promising results of the stressmeter (inclusion) is presented along with preliminary field test results. Laboratory testing involved comparison with the results of a two-dimensional finite element model of the physical laboratory test with those of the physical test itself. Results correlated well. The results of the field test indicate the need for further research into the practical application of the solid inclusion method in the field. / Master of Science

A Thesis presented to the Department of Geophysics of the University of the Witwatersrand, Johannesburg / Violent failure of the rock surrounding under ground excavations forms a major hazard and obstacle in deep-level mining. (Abbreviation abstract) / AC 2018

M.Sc. (Geology) / Please refer to full text to view abstract

Three hybrid moment tensor inversion methods were developed for seismic sources originating from a small source region. These techniques attempt to compensate for various types of systematic error (or noise) that influence seismograms recorded in the underground environment in order to achieve an accurate and robust measure of the seismic moment tensor. The term 'hybrid' was used to distinguish between the relative method proposed by Dahm (1995) and the methods developed in this thesis. The hybrid methods were essentially weighting schemes designed to enhance the accuracy of the computed moment tensors by decreasing the influence of any low quality observations, to damp (or amplify) any signals that have been overestimated (or underestimated) due to local site effects, and to correct for raypath focussing or defocussing that results from inhomogeneities in the rockmass. The weighting or correction applied to a particular observation was derived from the residuals determined when observed data were compared with corresponding theoretical data (for a particular geophone site, sensor orientation and wave phase) and were calculated using a cluster of events rather than a single event. The first and second weighting schemes were indirectly related to the mean and the median of the residuals where the residuals were defined as the ratio of the theoretical to observed data. In the third scheme, the residuals were defined as the difference between the observed and theoretical data and the weights were based on the distance of a data point (measured in standard deviations) from the mean residual. In each of the weighting schemes, the correction was applied iteratively until the standard error of the least-squares solution (normalised to the scalar seismic moment) was a minimum. The schemes were non-linear because new weights were calculated for each iteration. A number of stability tests using synthetic data were carried out to quantify the source resolving capabilities of the hybrid methods under various extreme conditions. The synthetic events were pure double-couple sources having identical fault-plane orientations, and differing only in rake. This similarity in the mechanisms was chosen because the waveforms of tightly grouped events recorded underground often show high degrees of similarity. For each test, the results computed using the three hybrid methods were compared with one another and with those computed using the single event, absolute method and two relative methods (with and without a reference mechanism). In the noise-free situation, it was found that the relative method without reference mechanism showed the highest resolution of mechanisms, provided that the coverage of the focal sphere was not too sparse (> 3 stations). The hybrid method using a median correction was found to be the most robust of all the methods tested in the most extreme case of poor coverage (2 stations) of the focal sphere. When increasing levels of pseudo-random noise were applied to the data, the absolute moment tensor inversion method, the hybrid method using a median correction, and the hybrid method using a weighted mean correction all showed similar robustness and stability in extreme configurations concerning network coverage of the focal sphere and noise level. When increasing levels of systematic noise were added to the data, the hybrid methods using a median correction and weighted mean correction were found to exhibit similar robustness and stability in extreme configurations concerning network coverage of the focal sphere and systematic noise. In all situations investigated, these two hybrid methods outperformed the relative and absolute methods. The hybrid moment tensor inversion methods using a median and weighted mean correction were applied to a cluster of 14 events, having remarkably similar waveforms, recorded at Oryx Gold Mine. For comparative purposes, the absolute method was also applied. The inputs to the inversion methods consisted of the spectral plateaus of both P- and S-waves at frequencies below the comer frequency of the time-integrated displacement traces. The polarities of dominant motion were used as an additional constraint and were determined from cross-correlation of observed with synthetic P- or S-waves. The solutions computed using the hybrid moment tensor inversion using a median correction displayed a distinct improvement after the iterative residual correction procedure was applied. The radiation patterns and faultplane solutions showed a high degree of similarity, and are probably more accurate reflections of reality than those computed using the absolute moment tensor inversion methods. These observations are very encouraging and point towards the method's potential for use as a standard processing tool for mine seismicity. The implications of this work are a better understanding of the focal mechanisms of seismic events induced by mining activities, ultimately leading to improved safety underground.