The objective of this research is to develop analytical approaches for assessment and prediction of the availability of longwall mining systems. After a functional analysis of longwall mining operations, the longwall production system is divided into four subsystems: coal—cutting, face—conveying, roof—support, and outby—haulage. The operating characteristics of the longwall system are then investigated based on the system configuration, component failure and repair processes, and rules of operation. Through use of the techniques of reliability assessment and stochastic systems analysis, five probability models are formulated and solved with respect to different longwall operating logic. The implementation of these models is demonstrated with a number of case studies. Furthermore, three important applications of the results have been identified for improvement of longwall performance: analysis of component importance, assessment and prediction of productivity, and optimization of system operational effectiveness. This investigation provides a systematic methodology for evaluation of longwall operational effectiveness. A number of system effectiveness measures have been developed for longwall systems with various operating characteristics. Some of the measures include system availability, reliability, failure rate, mean time to failure, mean time to repair, the expected average of the number of system failures, and the limiting probabilities of system failure due to any subsystem. Explicit expressions of system availability are obtained for several practical cases. The methodology developed can be used as both an assessment tool and a design tool for improvement of the operational effectiveness of longwall mining systems. / Ph. D.

Velocity tomography is a noninvasive technology that can be used to determine rock mass response to ore removal. Velocity tomography is accomplished by propagating seismic waves through a rock mass to measure velocity distribution of the rock mass. Tomograms are created by mapping this velocity distribution. From the velocity distribution relative stress in the rock mass can be inferred, and this velocity distribution can be mapped at specific time intervals. Velocity tomography is an appropriate technology for the study of rockbursts. Rockbursts are events that occur in underground mines as a result of excessive strain energy being stored in a rock mass and sometimes culminating in violent failure of the rock. Rockbursts often involve inundation of broken rock into open areas of the mine. They pose a considerable risk to miners and can hinder production substantially. The rock mass under investigation in this research is the strata surrounding an underground coal mine in the western United States, utilizing longwall mining. The mine has experienced rockbursts. Seismic data were collected over a nineteen day period, from July 20th, 1997 to August 7th, 1997, although only eighteen days were recorded. Instrumentation consistsed of sixteen receivers, mounted on the surface, approximately 1,200 feet above the longwall panel of interest. The system recorded and located microseismic events, and utilized them as seismic sources. The data were analyzed and input into a commercial program that uses an algorithm known as simultaneous iterative reconstruction technique to generate tomograms. Eighteen tomograms were generated, one for each day of the study. The tomograms consistently display a high velocity area along the longwall tailgate that redistributes with face advance. Numerical modeling and mine experience confirm that the longwall tailgate is subject to high stress. Additionally, microseismic events are correlated with the velocity tomograms. Velocity tomography proves to be an effective method for the study of stress redistribution and rockburst phenomena at underground longwall coal mines, because it generates images that are consistent with prior information about the stress state at the mine and with numerical models of the stress in the mine. / Master of Science

Mining induced seismicity can lead to bumps which cause problems at many mines within the United States and around the world. This seismicity, often referred to as bumps or bursts, can result in injuries, fatalities, and expensive capital damage and production interruptions. There are many factors that contribute to mining induced seismicity but there is still no concrete method to forecast future seismic activity around a mine. One of the main precursors to large seismic events is an increase in situ stress. One way to find areas within geological strata that are highly stressed is to measure p-wave propagation velocities. High p-wave propagation velocities are associated with high in-situ stress levels. By using tomography programs a three-dimensional velocity model can be constructed. When seismic activity is present the event arrival times at each geophone, the locations of each geophone, and the three dimensional velocity model are used in conjunction with one another to locate the seismic events. This research compares the locations of seismic events from a deep coal mine longwall panel in the western United States with the associated p-wave propagation velocities from the previous 24 hours. The aim of this comparison is to provide a link between high velocities and seismic activity that could potentially be used to forecast future seismic activity. The comparison is completed both qualitatively through the use of a visual analysis, and quantitatively using various numerical and correlation comparisons on the seismic and velocity data. The qualitative comparison is completed using the event locations from the tomography program SIMULPS. The quantitative comparison is completed twice using two different tomography programs, SIMULPS and TomoDD, which use different methods for locating the seismic events. Before these comparisons were completed the stresses around the longwall panel were first modeled using the boundary element modeling program LAMODEL to study the effects of three backfilled cross panel entries which were located ahead of the mining face. The modeling showed similar vertical stress distributions as a panel without cross panel entries but higher stress magnitudes. The qualitative analysis involved comparing tomograms created with SIMULPS with seismicity plots from the following day. One noticeable feature of these tomograms is the presence of a stressed area directly ahead of the face. This stressed area represents the forward abutment. The results of this qualitative analysis illustrate a correlation between high p-wave velocities and seismic activity 24 hours later for several of the days studied. The other days showed little to no correlation. Additionally, not all high p-wave velocity regions resulted in seismic activity. Due to these inconsistencies visually analyzing velocity plots obtained from the program SIMULPS is not a reliable way to forecast the locations of seismic activity 24 hours later. The result of the quantitative comparisons completed with the programs SIMULPS and TomoDD further highlighted inconsistencies in the correlation between high p-wave velocities and associated seismic activity 24 hours later. TomoDD provided better correlation values than SIMULPS and generally showed that as the level of seismicity increased the p-wave propagation velocities 24 hours prior also increased. Although TomoDD provided good correlations for some of the data pairs studied, the overall inconsistencies prompt the need for further study in this area using TomoDD to find the optimal forecasting time period. / Master of Science

Spectacular production rates have been achieved by certain U.S. longwalls, and yet a large number of longwall operations have failed to meet anticipated production targets. This study attempts to identify the primary factors which contribute to the production shortcomings of many marginal longwall operations. This study presents details of the classification and analysis of delay data for a group of thirty-nine longwall sections located in the eastern and mid-eastern United States. Downtime data correspondIng to over fourteen-thousand shifts were collected and classified according to equipment type, delay type, and specific delay event. A dBase IV-based database was constructed to allow flexible interrogation of the data. The relative downtime contributions of the various equipment components and of the delay types have been determined. Machine availabilities and system availabilities are presented. Probability density functions have been flit to the time-to-failure and to the time-to-repair data sets, both for the principal equipment types and for the longwall system as a whole. Recommendations are made for increasing the availability of longwall systems. / Master of Science

Devido ao esgotamento de jazidas economicamente lavráveis a céu aberto, migrou-se para a lavra subterrânea. Porém, como isso é uma prática antiga, alguns métodos de lavra subterrânea deixaram de ser economicamente viáveis devido ao aprofundamento da lavra. Um exemplo disso é a lavra de carvão no sul do Brasil, onde jazidas exploradas a céu aberto ou mesmo pelo método de Câmaras e Pilares, começam a vislumbrar seu exaurimento técnico de lavra, por altos custos e baixa produtividade, o que norteia a busca por alternativas econômicas mais lucrativas. Uma destas alternativas é o método Longwall, praticamente desconhecido no Brasil, porém com crescente e não nova intenção de implementação no país. Isso já se refletiu em tentativas de operações e em novos estudos conceituais de viabilidade para o estado do Rio Grande do Sul. Estes fatores justificaram este estudo que teve por objetivo lançar luz sobre a lavra de carvão pelo método de Longwall, de modo a respaldar a sua implementação no Brasil. Sendo assim, o método foi descrito com enfoque em seus principais pontos, tais como, geomecânica e planejamento; além de apresentar estudos conceituais de lavra em dois cenários. O primeiro projeto conceitual apresenta um cenário tradicional objetivando implementação no Rio Grande do Sul; o segundo, tem por objetivo apresentar relativa flexibilidade do método, adaptando-o a um cenário não tradicional. Concluiu-se com este trabalho que fatores como geomecânica e correto planejamento de lavra são imprescindíveis para o sucesso da implementação do método. A partir dos resultados do estudo conceitual I e da versatilidade proposta no estudo II se justifica o aprofundamento nos estudos de operações por Longwall no país. / Due to the exhaustion of economically mining deposits, migrated to the underground mining. However, as this is an ancient practice, some underground mining methods are no longer economically viable due to the deepening of the mining. An example of this is the mining of coal in southern Brazil, where deposits exploited opencast or even by the Room and Pillars, begin to envision your fatigue, mining technical high costs and low productivity, which guides the search for more profitable economic alternatives. One of these alternatives is the Longwall method, virtually unknown in Brazil, but with growing and not new intention of implementation in the country. It already was reflected in attempts to operations and on new conceptual studies of feasibility for the state of Rio Grande do Sul. These factors justify this study that aimed to shed light on the mining of coal by Longwall method, in order to support its implementation in Brazil. Therefore, the method has been described with focus on its key points, such as, geomechanics and planning; In addition to presenting conceptual studies of raging in two scenarios. The first conceptual design features a traditional setting with the objective of implementation in the Rio Grande do Sul; the second aims to introduce on the flexibility method, adapting it to a non-traditional setting. This work concluded that factors like geomechanics and correct planning of mining are indispensable for the successful implementation of the method. From the results of the study and conceptual versatility proposal in study II justification the deepening in the studies of Longwall operations in the country.

Tailgate stability within longwall coal mining is critical to longwall productivity and safety of mine personnel. A mechanistic model was developed and tested to explain observed high deformation tailgate behaviour characterised by lateral strata movement. Field investigations were conducted at three Australian longwall mines with an emphasis on the measurement of; horizontal strata movement about gateroads during longwall extraction, and the load/deformation characteristics of standing supports. 3D numerical modelling was used to simulate tailgate deformation, and interaction of various support types and design strategies. The sensitivity of strata and support behaviour to; variations in roof geology, strength of sliding interfaces, depth of cover, pre-mining horizontal stress magnitude and orientation, and strength and stiffness characteristics of standing supports was modelled. Laboratory investigations of a standing support product, the ???Can???, at reduced scale (one third) were conducted. The tests determined the loading mechanics of the product and provided a basis for optimisation of the engineering properties (strength and stiffness). Horizontal strata movement about longwall extraction was found to have a significant impact on strata behaviour at two of the three mines investigated. The term ???skew roof??? was coined to describe the deformation process. Essentially the roof strata was found to ???skew??? towards the approaching goaf. The key geotechnical factors found to control the skew roof mechanism were; magnitude and orientation of the pre-mining horizontal stress, presence of weak interfaces along which sliding could occur, and shear strength of the interfaces. Measurement of the nature and extent of skew roof deformation specific to each mine provided a sound engineering basis for support design. These included; the relative roles of long tendons versus standing support, optimal pattern (position across and along the roadway) of standing supports, and appropriate strength and stiffness characteristics. The findings were successfully implemented at Metropolitan Colliery in particular, where adequate tailgate serviceability has been achieved within a high deformation environment, and whilst maintaining a relatively small chain pillar width. The research has achieved an alternative to empirical and trial and error tailgate support design methods.

Thesis (M.S)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains xi, 104 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 69-70).

This thesis presents the results of research into the potential of underground mining methods applicable to inclined thick seams (thickness greater than 3.5m, and seam dip of 15 - 35 degree) in the Quangninh coalfield, Vietnam. The primary objectives of this research are to investigate the most suitable underground methods applicable to inclined thick seams in the Quangninh coalfield and to improve understanding of the operational and geotechnical issues associated with the application of chosen methods in thick seams with steeply dipping conditions. From a risk and operational assessment, the Longwall Top Coal Caving (LTCC) method is considered most appropriate for inclined thick seams under the current mining conditions in Vietnam. The LTCC method offers great potential for the efficient extraction of thick seams by caving coal from the upper section during the mining of the lower section. This significantly reduces the development cost per tonne. Compared to High reach Single Pass Longwalling, the LTCC method offers a low extraction height, resulting in smaller and less expensive equipment and better face conditions. Results from this study identified that for extracting an inclined thick seam, the face retreating along the strike has better operational advantages and better cavability than the face retreating updip or downdip of the seam. The operational issues of the LTCC method when extracting inclined seams are: the stability of the support, transport in the mine, and the difficulties in roof control at the transition between face ends and the gateroads. In terms of geotechnical issues, better cavability of the top coal is anticipated for flat coal seams compared to inclined seams. In addition, the chain pillar for flat coal seams is subjected to a higher vertical stress distribution than that of inclined ones. An improved cavability assessment method for the categorisation of the cavability of the top coal with four categories, ranging from 1 (excellent cavability) to 4 (very poor cavability), was suggested to assist the feasibility and design stages of the LTCC application. The cavability assessment method was conducted by numerical analysis combined with back analysis from the database obtained from past LTCC practices.

Thesis (Ph. D.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains xviii, 163 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 159-162).

Tailgate stability within longwall coal mining is critical to longwall productivity and safety of mine personnel. A mechanistic model was developed and tested to explain observed high deformation tailgate behaviour characterised by lateral strata movement. Field investigations were conducted at three Australian longwall mines with an emphasis on the measurement of; horizontal strata movement about gateroads during longwall extraction, and the load/deformation characteristics of standing supports. 3D numerical modelling was used to simulate tailgate deformation, and interaction of various support types and design strategies. The sensitivity of strata and support behaviour to; variations in roof geology, strength of sliding interfaces, depth of cover, pre-mining horizontal stress magnitude and orientation, and strength and stiffness characteristics of standing supports was modelled. Laboratory investigations of a standing support product, the ???Can???, at reduced scale (one third) were conducted. The tests determined the loading mechanics of the product and provided a basis for optimisation of the engineering properties (strength and stiffness). Horizontal strata movement about longwall extraction was found to have a significant impact on strata behaviour at two of the three mines investigated. The term ???skew roof??? was coined to describe the deformation process. Essentially the roof strata was found to ???skew??? towards the approaching goaf. The key geotechnical factors found to control the skew roof mechanism were; magnitude and orientation of the pre-mining horizontal stress, presence of weak interfaces along which sliding could occur, and shear strength of the interfaces. Measurement of the nature and extent of skew roof deformation specific to each mine provided a sound engineering basis for support design. These included; the relative roles of long tendons versus standing support, optimal pattern (position across and along the roadway) of standing supports, and appropriate strength and stiffness characteristics. The findings were successfully implemented at Metropolitan Colliery in particular, where adequate tailgate serviceability has been achieved within a high deformation environment, and whilst maintaining a relatively small chain pillar width. The research has achieved an alternative to empirical and trial and error tailgate support design methods.