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By Rob Thomas

Main gate roof control during longwall retreat is subject to a significant increase in horizontal stress and risk. The implementation and management of an appropriate roof support design is as a result, an imperative requirement for any longwall mine and must in addition to the likely consequences of a roof fall, also consider the variables of the geotechnical environment, associated support costs and practicalities. This paper will therefore summarise a number of recent advances in main gate roof control in the Australian coal industry. Points considered include; (i) the ?Longwall Acceleration? concept, (ii) macro-scale horizontal stress notching, (iii) micro-scale horizontal stress notching, (iv) bedded versus laminated roof types and (v) the type of cable reinforcement used.

Jan 1, 2006

By Yao Yuping

The strength and deformation of more than two hundred coal samples have been tested in the condition of triaxial compression. The regression equation showing the relationship between coal strength and pressure in the pores as well as confining pressure, was obtained. The appropriate calculation for stress-strain curve was carried out. Further, an analysis shows the variation of coal strength and its modulus of elasticity in methane medium.

Jan 1, 1992

By Alan A. Campoli

Fosroc continues as a leader in the development of cementitious technology for the mining industry. The considerable expertise accumulated in the development of the Fm cement line has been employed in the development of two pumpable, supplemental roof support systems. The Tekprop system is a unique combination of steel and concrete, specifically designed as a viable alternative to conventional wooden supplementd support. The second system is the Fosroc mineable mi which is a cost competitive variable yield system designed to support longwall ventilation and predriven recovery room entries. Two, separate, ongoing, full scale applications of these systems will be discussed during the inference presentation

Jan 1, 1997

By Kazem Oraee-Mirzamani, Nikzad Oraee-Mirzamani, Arash Goodarzi

"Unexpected movement of ground can potentially endanger lives, damage equipment or destroy property. Occupational accidents frequently occur with fatal consequences in developing countries with significant economic dependence on industries such as mining. Therefore, there is increasing need for miners' protection against such hazards. Slope stability and roof support accidents are two of the major causes of fatalities at surface and underground mining operations. According to national codes, employers are obligated to protect workers against accidents; however, these rules fall short of the standards in developed countries. National safety regulations should clearly specify support systems. The International Labor Organization (ILO) prepared two codes of practice, aiming to guide those responsible for improving standards of safety and to provide guidelines for drafting of safety regulations for the coal mine industry and quarry open cast mines. The practical recommendations of these codes in the ground control area have been analysed and the advantages and disadvantages of ILO codes concerning ground control are summarized.INTRODUCTIONTwo million people die every year from work-related accidents and diseases. An estimated 160 million people suffer from work-related diseases, and there are an estimated 270 million fatal and non-fatal work-related accidents per year. In economic terms, the ILO has estimated that 4% of the world's annual GDP is lost as a consequence of occupational diseases and accidents (ILO, 2009).Mining has always been dangerous due to many potential risks such as those associated with using machinery in enclosed spaces, rock falls, blasting operations and explosion of flammable gases, which endanger miners' safety and health. However, it is suggested that implementing new laws along with strict adherence would reduce such risks in the workplace.The severity and frequency of accidents are trending downward in developed countries, where the focus is on large private companies who invest heavily in mechanization and developing economies of scale. But in many parts of the world, particularly in developing countries, minerals are extracted by people working with simple tools and equipment; they work on a smaller scale, are more flexible, and can exploit irregular ore bodies and steep, dipping seams."

Jan 1, 2010

By Ray Brandon

The recent introduction of polymer geogrids for ground control purposes in underground mines allows mine operators more flexibility in choosing improved products for several applications. This is evidenced most clearly in longwall recovery operations. Since November, 1994, many mine operators have chosen Fortrac geogrid assemblies for the purpose of securing longwall recovery areas prior to shield removal. Fortrac is a lightweight, strong, and flexible polyester geogrid available in many strengths. Utilizing the "diamond" seaming method, different strengths of Fortrac geogrids are easily fastened together so stronger geogrids may be placed in the most critical areas and lighter geogrids in less critical areas.

Jan 1, 1996

By Murali Gadde

Among different types of ground control problems associated with underground coal mining, those related to in situ stresses are the most common ones affecting the safety and economy of a mining operation. As a result, this has been the focus of many ground control research works done in the last three decades. This paper summarizes a recent work done on in situ stress related ground control issues of underground coal mine development workings. The approach used in this study was three¬-dimensional finite element modeling by an implicit code, ABAQUS/Standard. In the models, roof stability evaluations were made using Hoek-Brown rock mass failure criterion. Influence of the in situ maximum horizontal stress angle on the stability of both entry and intersection was examined to help determine the best development layout orientation. Also, the effect of in situ stress ratios on the stability of development openings was studied. To make the work more general, both 'low' and 'high' in situ stress fields were considered In general, the modeling results indicated that entries oriented in the direction of maximum horizontal stress were in the best condition while those oriented at 90° had the least stability. For intersections, the maximum and the minimum stability were seen at 0°/90° and 45°, respectively. However, under some combinations of input conditions, the best or the worst conditions were noticed at same other orientations as well. Based on these findings, layout design charts were prepared for both entries and intersections. It was also found that the change in ground conditions with change in layout orientation was more significant for 'low' in situ stress fields than for the higher ones. Change in the average safety factor with change in the ratio of in situ maximum horizontal to vertical stress resembled a lognormal distribution curve. However, the effect of the ratio of in situ maximum to minimum horizontal stress lacked such a clear trend for different input combinations considered.

Jan 1, 2004

By Uros Bajzelj

When driving mine roadways in the vicinity of tectonic disturbances and fault zones, sudden outbursts of gas, along with ejections of fine coal, occur. Substantial dynamic changes occur around the roadways in the coal and around the support. The problem has several aspects. Studies have been carried out on the technical analyses of the phenomena which occurred in the Velenje Lignite Mine from 1957 to 1988, The second part of the investigation involves systematic laboratory studies of strength and deformability characteristics of lignite samples and "in-situ" measurements of stress changes during the driving of some roadways. Analyses of events (using the model of limit convergence and the finite element method) showed the possibility of gas outbursts, taking into account the deformability conditions when crossing over from compact lignite to the disturbed region. The rate of advance of roadways and the method of support strongly influence the occurrence of the phenomenon. The preventative measures used in driving roadways under such conditions include trial drilling and the use of blasting instead of machine cutting.

Jan 1, 1992

By Marc T. Filigenzi

Two of the major ground control safety issues confronting underground mine operations today are shaft pillar stability and the failure of rock around active mine openings. Failure of a mine shaft can lead to the entrapment of workers. Failure of rock around active underground mine openings can lead to roof falls, which in turn can result in worker injuries and fatalities. Finite-element analysis has proven to he a reliable method for predicting stresses and displacements around underground mine openings. However, this is a complex and time consuming technique and is not used as often as it could be in mine planning. The purpose of this paper is to demonstrate one technique developed at the Spokane Research Center that allows the user to create a finite-element model of a two-dimensional section of an underground mine in a relatively straightforward manner. This model is then used to calculate stresses, displacements, and safety factors around mine openings. With this information, mine planners can evaluate the stability of mine openings as well as the stability of pillars and mine shafts. This analysis will help develop mining sequences and layouts that minimize stresses in that section of the mine. This, in turn, should minimize the occurrence of shaft failure, roof falls, and other hazards associated with underground mining.

Jan 1, 1997

By Kot F. Unrug

The shale response to moisture changes and the major finding of the appropriate research concerning this subject are briefly reported in this paper. Also described are mine ambient atmospheric conditions which are responsible for moisture changes in mines. The need for a quantitative measure of the weathering potential of roof. rock is demonstrated in relation to its influence on safety and the potential for increasing the cost of mine operations. The weatherability test presented in this paper has been developed and used in many mines. It imitates the natural process in a mine by subjecting the rock sample to alternating wet and dry cycles. The natural changes are thus accelerated, but are similar to the natural conditions to which the surrounding excavation rock will be exposed. The measure of the weatherability index is the percentage of the initial sample mass remaining after the test as the largest fragment of the sample. Thus, the index changes, from 100% for rock affected by moisture changes which disintegrates completely, to 0% for rock totally unaffected. In this paper, the apparatus and testing procedures are described. Also presented are examples of test results. with a discussion of the design implication to he considered by mine planners.

Jan 1, 1997

By Kazem Oraee-Mirzamani

Blasting operations generate seismic effects in underground mines. These effects apply additional dynamic loads on the support system, which should bear both static and dynamic loads. Static loads are caused by the weight of the superincumbent strata, while dynamic loads occur as a result of blasting in the mining area. Identification of the origin and determination of the support system behavior in natural frequencies is crucial in assessing the stability of underground mines. This is because resonance occurs when a support is vibrated with its natural frequencies, which can cause a vibration with the maximum amplitude and subsequently cause extreme deformations. The mechanism of support system deformation during dynamic load displacement has been studied and numerical simulation for the impact of the dynamic loads on stability of supports is carried out using finite element method. The paper introduces a simple technique for improving stability and safety of mining operations. Results obtained and the methodology adopted in this research can help mining design engineers make decisions on adequate support for active mining operations.

Jan 1, 2011

By G. M. Molinda

Ground Penetrating Radar (GPR) is being investigated for the potential to determine roof hazards in underground mines. GPR surveys were conducted at four field sites with accompanying ground truth in order to determine the value of GPR for roof hazard detection. The resolution of the current system allows detection of gross roof fractures (>63 cm (s1/4 in) zone) or rider beds in coal measure roof. Data quality is not yet sufficient to detect small bed separations or subtle lithologic changes in the roof. Differences in data quality are discussed, as well as suggestions for collecting improved data.

Jan 1, 1996

By Arka Jyoti Das, Prabhat Kumar Mandal

"Coal mining in India has a strategic importance for the energy security of the country. Presently, the majority of coal production is coming from open-cast mining. Due to the fast depletion of reserves amenable to open-cast mining, future coal production will depend primarily on underground production. In conventional bard-and-pillar/room and pillar mining as it is practiced in India, the percentage of extraction is very low. In fact, within most Indian coalfields, a large number of coal seams extract only 15- 20% of coal, but no pillar extraction is done due to the presence of surface or sub-surface structures leading to huge amount of coal being locked-up in underground. Spontaneous heating and fire, the accumulation of poisonous gases, severe stability issues, unsafe workings and environmental hazards are all major problems associated with these developed coal pillars, so there is a pressing need for technology in the mining industry to extract this huge amount of coal locked up under different constraints. In this study, we propose that the locked-up coal be extracted by replacing the developed coal pillars with artificial pillars. The paper briefly discusses the extraction methodology designed for this and its evaluation through numerical modeling for applied suitability underground.INTRODUCTIONDriven by rising populations and urbanization, an expanding economy and also a quest for improved quality of life, energy usage in India is expected to increase manifold in the coming years. As for India's energy scenario and its projected future plans, there is no doubt that coal will remain a prime source of energy, even over the next few decades.The majority of coal production in India comes from open-cast mining because of large-scale mechanization, but the coal reserves amenable to open-cast mining are gradually depleting - which may impose adverse impacts on the energy sector if underground production does not increase. Underground coal extraction, meanwhile, is going to become more complicated in near future due to the fast exhaustion of easily mineable coal reserves."

Jan 1, 2016

Appropriate roof control is the most important requirement in underground coal mining and, in the case of longwall panels or second mining in room and pillar extractions, this can be simply expressed in terms of good and predictable roof caveability. Studies of roof caveability have been undertaken in many coalfields around the world. Most of their conclusions. however, are directly related to the mining and geological conditions experienced in these areas and as a result, may not be applicable to the conditions encountered in the Appalachian coalfield. Furthermore, some of these studies appear to be theoretical and conceptual, ignoring many important parameters of the geological environment, whereas others rely heavily on geological information but lack a rigorous foundations upon which quantitative design guidelines can be built. The objective of this study is to analyze caving and mass deformation characteristics above longwall panels in Appalachia and includes: - Analysis of the effects of the geological and geomechanical characteristics of the strata on the caving height and the bulking of the caved-material. - Testing of the applicability of the various theoretical and empirical models of roof caving. Formulation of a numerical around- deformation model for ion-elastic material behavior.

Jan 1, 1986

By Gabriel Esterhuizen

When designing pillars in coal and hard rock mines it is necessary to determine the strength of the rock mass forming the pillars. Empirical strength equations, based on rock mass classification techniques, assume that the rock mass is isotropic, this simplification may result in under estimation of pillar strength. Numerical model studies showed that the effect of jointing on pillar strength diminishes as the width to height ratio of a pillar increases. Therefore, the weakening effect of joints should not be equally applied to all pillars regardless of their width to height ratio. The paper presents equations that were developed from laboratory tests on jointed rock samples and numerical models to account for the effects of joint orientation, friction, frequency, and pillar width to height ratio on pillar strength. The equations were calibrated using field data of actual pillar performance in South African coal mines. The method was applied in two case studies in which the strength of jointed coal pillars was assessed and layouts were designed accordingly.

Jan 1, 2000

By L. A. Sandbak, Yan Xing

"The purpose of this study is to evaluate the rock mass stability around the tunnels by three-dimensional (3-D) numerical modeling. Complex geological and tunnel features have been included in the model using the software package 3DEC™. Based on the available information on stratigraphy, geological structures, and mechanical properties of rock masses and discontinuities from the underground mine, 3-D stress analyses were performed on various cases with different K0 (lateral stress ratio) values, constitutive models, as well as support systems. Relations between these factors and the distributions of stress, displacement, and failure zones around the tunnels were obtained and discussed. Finally, comparisons between the field deformation measurements and numerical simulations are used as validations for the simulations, helping to determine the appropriate K0 value and material constitutive models for the underground mine.INTRODUCTIONThe case study site is an underground mine in the USA with a monthly ore production between 20,000 and 30,000 tons. The regional geology of the mine is structurally and stratigraphically complex. Rocks in the area include carbonaceous mudstone and limestone, tuffaceous mudstone and limestone, polylithic megaclastic debris flows, fine-grained debris flows and basalts, all part of the Cambrian-Ordovician Comus formation and related dikes. Both the mineralization and faults have general orientations striking N-S to NW-SE with high dip angles. The ore body in the mine has an incline of about 25---45 degrees located in relatively low quality rock; hence, cut-and-fill mining has been used.This underground mine has two vertical shafts used for ventilation, ore hoisting, and for personnel and material transportation. Development drifts were designed and driven to extract and transport the ore, as shown in Figure I. Bolts, mesh, and shotcrete have been applied in this mine for ground control. In order to reach various locations, the tunnel system is designed with different heading directions and inclines, which will be described in detail later. The area selected for modeling is a cubic region including all the tunnels inside the black square (Figure 1)."

Jan 1, 2016

By W. Mark Hart

The current Automatic Data Acquisition system developed by some support manufacturers make it possible to monitor and record changes in leg pressure, DA RAM stroke in every shield and shearer position at any moment during mining operation. But how can these massive data (more than 1 MB for every 3 hrs for the current scanning option) be effectively used for improving production and maintenance management as well as providing better roof control at a longwall face? The research currently conducted jointly by WWU and Cyprus Amax Minerals at Emerald Mine and Twentymile Mine attempts to answer this question and make the data, especially leg pressure, more meaningful. A computer software package has been being developed to (1) determine mining cycles, cycle time, face advance rate, production rates, machinery delays, and production delays for each shift; (2) identify defective sensors, check valves, yield valves, by-passing leg and DA RAM cylinders, and other hydraulic and electrical abnormalities; (3) determine the roof weighting period; (4) evaluate the performance of the current shield support design - demand relationships; and (5) predict and overcome ensuing encroaching problems and roof conditions ahead of the face.

Jan 1, 1994

By Keith A. Heasley

Pillar recovery in deep coal mines with competent roof and floor can concentrate stresses and generate hazardous bumps. Actual calculation of the geologic strain energy released in association with these coal bumps has been rare, although energy release values have been utilized successfully for indicating burst potential in numerous hard- rock mines. This paper advances the current knowledge of energy release calculations as applied to coal bumps through an extensive analysis of an actual bump occurrence. The U.S.B.M, displacement- discontinuity code, MULSIM/NL, is used to produce a numerical model which generates stress, displacements and energy values associated with a pillar retreat section. This model is calibrated with actual field data, and then dissipated energy values from the model are examined as to their suit- ability for indicating bump potential. Ultimately, it is determined that prudent application of dissipated energy calculations can be used as a tool to investigate the coal bump potential of a mining plan or cut sequence.

Jan 1, 1990

By Peter B. Lilly

Thank you, Syd, for the kind introduction and for inviting me to give the Keynote Address at this very prestigious gathering of some of the finest intellect and talent in the domestic and international coal industry. CONSOL Energy has been a part of this conference for its entire 24-year existence. We have presented 27 papers over that time. CONSOL employees have also been members of the planning committee for the conference, and we have been pleased to support the event both financially and with many participants. So I am honored to be here with all of you this morning, especially during such a positive period for coal. You can just feel the enthusiasm in this room for our industry, and for this conference. I can tell you, there?s also a lot of enthusiasm and excitement in CONSOL Energy?s boardroom. And our enthusiasm is mirrored on Wall Street. But there remains an ironic twist to all of this attention. Even when times are good, the coal industry seems to go largely unnoticed by the mainstream. Outside of West Virginia and other coal-producing regions, the industry still seems to lack influence and support, at least here in America. As an example, last month, an ABC News crew visited our Blacksville 2 Mine, near here, to do a feature story on increased employment in the coal industry.

Jan 1, 2006

By Kristine L. Pankow, Keith D. Koper, Michael K. McCarter, Jared R. Stein

"The Wasatch Plateau region of central Utah contains a number of active underground coal mines in an area of well-documented natural seismicity. As a result, there are several hundred seismic events recorded in this region every year that may or may not be attributed directly to mining activity. Previous studies have linked the majority of this seismicity to mining activity through various means, but have not attempted to develop a method for categorizing individual events within a seismicity catalog. This study uses both relative relocation and waveform cross-correlation to separate events based on hypocentral depth and waveform similarity, respectively, in the area surrounding a single longwall coal mine within the Wasatch Plateau. We conclude that relative relocation can help with depth discrimination, but there are some unavoidable limitations caused by sparse seismic network coverage. The cross-correlation technique is more promising, with the ability to group events by waveform similarity and track mining progress over both space and time. With cross-correlation based clustering, we confirm that the vast majority (97.6%) of events in the study area are directly related to mining activity, but that a small population of natural seismicity is present as well. Eliminating this natural seismicity from the catalog of seismic events, leaving only those events related to mining, can give operators valuable information about the changing conditions as mining progresses and eliminate concern over events unrelated to mining activity.INTRODUCTIONA number of underground coal mines are located in the Wasatch Plateau region of central Utah, and have been in operation since the late 1800s. This activity has resulted in a well-known history of mining induced seismicity (MIS) (Wong, 1985). Additionally, this area is situated near the border of the Basin and Range and Colorado Plateau physiographic provinces, where naturally occurring tectonic earthquakes also occur (Arabasz et al, 1980). Seismicity separating these physiographic provinces is part of a larger band of seismic activity known as the Intermountain Seismic Belt (ISB) that runs from Montana to Arizona and cuts through the western boundary of the central Utah coalfields (Smith and Arabasz, 1991) (Figure 1)."

Jan 1, 2015

By Joachim Leonhardt

Hundreds ofbolt-indicators were already used successfully in the German deep hard coal-mines to increase the safety and economy. The bolt-indicator offers the simple possibility to show roof-bolt (anchor-) loads. to indicate weak points as well as to optimize the anchor density and the dimension: The bolt-indicator is mushroom shaped and consists of coated metal. It is inserted between the anchor plate and the flanged nut. The loads appearing at the anchor are transferred to the bolt- indicator and can be recognized visually at the cylindrical part by the amount of the surface coating. Examples are used to clarify the application aims, operation and usage of the bolt-indicator and its yielding advantages in practice.

Jan 1, 2001