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By F. Ziaie

Line electrical resistivity method using physically infinite distance between current line electrodes is proposed to determine the location of mine workings. In this method at least three line electrodes are used. One of the current electrodes is used as a sinkhole electrode while the other two are used for different activiations of line electrodes when the survey area is between one of the line electrodes and outside the other one. The resistivity profiles perpendicular to the current line electrodes for different activation of electrodes is plotted versus the distance of the midpoint of the measuring potential electrodes. The anomaly due to presence of any locally lateral resistivity variation (e.g. mining cavity) will represent itself as peak or trough depending on resistivity contrast between the source of the anomaly and surrounding medium. Physical simulation of the proposed model was conducted by using a tank model in the laboratory. The results of experiments appear to be consistent with the theoretical model. Experiments for different depths and different spacial locations of the simulated cavities appeared to be successful for locating the depth and size of the cavity.

Jan 1, 1989

By L. R. Stace

Arguably, one of the most significant technological breakthroughs that had been experienced during the period when British Coal was the major coalmine operating company in the UK, the use of rockbolts as principal support in underground roadways brought with it the need to re-assess the technical knowledge, management controls and legislative frameworks associated with the support of mine workings. Following a major roof fall in a roadway supported principally using rockbolts in which fatalities occurred, the process of the design of rockbolted support and the systems and procedures that had been put in place to control its use in the UK were further reviewed. The paper discusses the outcome of these reviews, and how the incident initiated a major new interest in strata control research in the UK against the background of the fragmentation of the ownership of the mines following the sale of the former British Coal assets at the end of 1994, together with the proposed introduction of new strata control legislation in 1996.

Jan 1, 1996

By J. K. Whyatt

The paper presents an approach to design a multi level room and pillar layout in a 40m thick seam overlain by a major aquifer. The design was required to maximise extraction with due consideration of the general stability of the workings, the potential water hazards, and spontaneous combustion risks due to air leakage between horizons. The approach utilised was a combination of empirical pillar sizing for water hazard control with numerical modelling to assess potential interactions between horizons. The numerical modelling allowed the size of interleaves, and the appropriate staggers to be optimised in terms of stress distribution. The stress distribution allows both the general stability of the openings and more importantly the permeability changes around the openings to be determined. The permeability of coal is sensitive to stress, and an empirical stress to permeability relationship, and theoretical permeability to flow leakage relationship has been applied to interpreting the relative spontaneous combustion risk associated with each of the proposed layouts. The final proposed design is a compromise between maximum exploitation of reserves and consideration of water hazards and of spontaneous combustion risk. Further more detailed design will be required as more comprehensive data on the geotechnical properties of the coal and overburden become available.

Jan 1, 1996

By Anthony Iannacchione

Coal mine bursts have represented a major hazard for U.S. mining operations for more than 90 years. During this time, many prevention controls have been developed and tested. This paper reviews 11 prevention control techniques. Although coal mine bursts are not common events in most underground coal mines, their occurrence almost always requires a change in mining practice. Over the many years of dealing with these hazards, specialized requirements for layouts and novel extraction sequences have been developed on a site specific basis. The keys to mitigating risks are to properly assess the coal burst hazards and to possess the knowledge and skills to prevent or remediate their occurrence.

Jan 1, 2008

By Hamid Maleki

In this paper, the authors present a review of data gathering programs and stress analyses for improving mine layout designs at BRL mines located near Paonia, Colorado. BRL and other companies have used both longwall and continuous miner methods for the extraction of the Upper D, Upper B, Lower B and C seams from the multiple-seam reserves in the North Fork Valley. Historic mining in the B and C seams has created stress footprints in the neighboring unmined seams compounded by stress transfer from recent longwall extraction in the Upper D Seam. Thus optimum positioning of workings in the remaining reserves requires careful collection of pertinent data and consideration of load transfer from previous workings through remnant abutment pillars. Based on long-term subsidence monitoring, underground mapping and stress analyses, we have confirmed initial load transfer analyses finding mild interactions between the UD and LB workings, and the mining conditions have proven to be good and manageable during the development stage of the LB Seam. This has been achieved through prudent mine planning, prudent positioning of the gateroads in multiple seam workings and support allocations.

Jan 1, 2007

By C. Dinis da Cama

In order to reduce the complexity of mechanisms influencing rock- fragmentation by blasting a simulation approach is proposed, using the capabilities of micro-computer interactive graphics. Situations involving cratering and bench blasting are simulated, and both jointed and intact rocks can be subjected to explosive action, taking into consideration its breakage mechanisms. Size analysis curves relating rock distribution before and after the blasts are determined and compared with field data.

Jan 1, 1984

By Hamid Maleki

A geotechnical monitoring program has been implemented at Energy West Mining Company for enhancing site-specific evaluation of longwall stress conditions. This program consists of underground measurements at five locations in two neighboring mining districts located in the Hiawatha and Blind Canyon Coal Seams under moderate to deep cover. Within the last five years, additional measurements, including data on recorded seismic events and face conditions, have been incorporated into the data collection program together with detailed geologic mapping of longwall gateroads. In conjunction with the measurement program, the authors have completed detailed boundary-element stress analyses of the mine plans. Models have been calibrated using the data from in-mine instrumentations and then routinely used for evaluation of mine plans at depths approaching 2,600-ft. The work has improved our understanding of load transfer, seismicity and yield pillar performance. It has identified areas of potential increased stress levels at certain longwall face positions and provided guidance to measures that could be considered to mitigate the potential for these increased stress levels.

Jan 1, 2009

By Najdat I. Aziz

There are different schools of thoughts about the influence of gas pressure on coal strength. Researchers have reached contradictory results with regard to the effect of confining gas pressure on tensile strength of coal. Accordingly, this paper re-examines the influence of gas pressure on the strength of coal. A specially designed precision drill capable of drilling in a pressurised chamber was used to drill coal samples under both atmospheric and increased gas pressure environment. The drill cuttings were examined for particle size distribution using a laser controlled Malvern Mastersizer S particle size analyser. Petrographic analysis of the sample examined the effect of gas pressures on the maceral structure and the composition of coal. The paper demonstrates that there is a definite variation in the range of particle size distribution with particles obtained from drilling coal samples not subjected to gas pressures, in comparison with those obtained from samples drilled under confined gas pressure. Also observed were the changes in the rate of drilling in soft coal obtained from geologically-disturbed zones compared with other coal samples. Some variation on the maceral compostion of coals were also observed in relation to increased gas pressures and gas type.

Jan 1, 1996

By Raymond A. Mazzoni

Over the last twenty years, roof support technology has made numerous advances since the original wedge and slotted bolts of the 1950's. By comparison, the roof supports used today are more complex and specialized than the supports used in the past, providing mines with a varied selection of supports from which to choose. As a result, when problems with supports are encountered, it is more difficult to determine whether it is the result of geological changes, poor installation practices, or malfunctioning supports. Recognizing this problem, MSHA's Roof Control Division of the Pittsburgh Safety and Health Technology Center, has undertaken the task of publishing a guide for trouble¬shooting problems encountered with roof support systems. The purpose of this guide is to provide a logical sequence to resolving the most common problems encountered with roof supports. The objective of this paper is to introduce this guide to the mining industry as well as provide insight into the evolution of the guide from its beginnings as rudimentary charts to its more comprehensive present format as a practical guide for use by the mining commu¬nity.

Jan 1, 1997

A model was developed to facilitate secondary tailgate support selection based on analysis of over 100 case studies, compiled from two different surveys of operating longwall coal mines in the United States. The ALPS (Analysis of Longwall Pillar Stability) program was used to determine adequacy of pillar design for the successful longwall case histories. A relationship was developed between the secondary support density necessary to maintain a stable tailgate entry during mining and the CMRR (Coal Mine Roof Rating). This relationship defines the lower bound of secondary support density currently used in longwall mines. The model used only successful tailgate case history data, with adequate ALPS SF according to the CMRR for each case. This model facilitates mine design by predicting secondary support density required for a tailgate entry depending on the ALPS SF and CMRR, which can result in significant economic benefits.

Jan 1, 1996

By D. J. Reddish

An understanding of the mechanisms that cause large seismic events in a deep mine provides a foundation for designing effective measures to reduce the incidence of these events, as well as reduce the potential for damage arising from these events. The work described in this paper focuses analytical efforts on major recognizable and controllable factors that influence mining-induced seismicity and serves to screen out many of the more random aspects of individual events. Information used in this study was developed in the course of a long-standing rock burst research program conducted by the U. S. Bureau of Mines in cooperation with mines in the Coeur d'Alene Mining District and regional universities. Information was collected on 39 seismic events having local magnitudes greater than 2.5 that occurred between 1989 and 1994. Five major types of events were developed from these data that describe all but two of the 39 large events. The characteristic mechanisms, tint-motion pattern, damage pattern, and relationships to mining and major geologic structures were defined for each type of event. This information provides a foundation for assessing whether or not changes in mining activity aimed at reducing one type of rock burst will increase the incidence of other types.

Jan 1, 1996

By D. Su

This paper presents the details and results of a preliminary investigation into the response of borehole pressure cells (BPCs) in soft coal. Two parallel approaches, laboratory calibration and nonlinear finite element simulation, were adopted for deter- mining the BPC K-factor, which was defined as the ratio of cell pressure change to the corresponding change in external pressure. Results from both the laboratory calibration and the nonlinear finite element simulation revealed a nonlinear response of cell internal fluid pressure to external loading. The K-fact& also is shown to increase with increasing setting pressure and decreasing medium modulus. -Depending on the setting pressure, the K-factor for coal having a Young's modulus of 1.6 x lo5 psi ranges from nearly 1.2 at 2,000 psi of external pressure to 1.485 at 8,400 psi of external pressure. The improved under- standing of BPC behavior leads to the more accurate calculation of BPC K-factor in coal which significantly improves the correlation between pillar pressures measured in underground coal mines and those predicted by nonlinear finite element simulations of these pillars.

Jan 1, 1990

By A. T. Iannacchione

Numerical simulation of coal pi1lar loading has traditionally been a difficult task due to the unique and highly variable properties of coal and the inability of numerical procedures to duplicate these properties. This simulation was based upon material properties developed from laboratory tests of coal cubes and examined against coal pillar strength data developed from actual underground measurements. The coal cube measurements indicated the coal followed a nonlinear Mohr- Coulomb failure criterion. The in situ measurements showed that a pillar yield zone developed similar to Wilson's hypothesis and, at high confinements, the pillar core seemed to followed a pseudo-ductile behavior. The strain-softening material model, based on a 1inear Mohr- Coulomb failure criterion, simulated coal cube and pillar behavior at moderate load conditions. However, at high loads the models were inaccurate, due to an inadequate failure mechanism and/or to changes in the pillar constraints at the coalbed interface.

Jan 1, 1989

By P. Gaskell

The paper examines the development of rock movement between a longwall extraction horizon and the surface for a fully caved mining situation. Physical modelling has been used to examine the mechanics of ground movement and the propagation of fractures around the longwall working. The paper discusses dimensional analysis, model construction and measurement technique and data processing of the results into effective graphical forms for further study.

Jan 1, 1988

Historically, the selection of mining sequence for multiple seam conditions has been based on many factors other than ground control considerations and minimization of interaction effects. Today, numerous operations are finding themselves mining above existing or abandoned operations, some of which exhibit large scale caving, pressure arches and subsidence troughs. Development of design criteria for the upper seam that would alleviate damage due to lower seam interaction effects can contribute substantially to the safety and productivity of many mining operations. The primary objective of this re search has been to identify methods of improving ground control conditions in the upper seam when mining through either passive or active subsidence waves. These methods concentrate on improved ground control practices for the upper seam, rather than reducing the amount of subsidence in the upper seams by improved practices in the lower seam. Design factors such as pillar size, pillar and opening orientation relative to the subsidence trough, offsetting intersections, and different support methods have been studied for the upper seam in a variety of typical geologic environments. Analysis has demonstrated criteria for ameliorating negative interaction effects and facillitating design in the superincumbent seam.

Jan 1, 1986

By Jun Han

Coal has been mined in the Kailuan mining area for more than 130 years. The remaining reserves consist of, in large part, coals that would have been considered economically unminable or technically not feasible by the previous generations. Some of the current operations have to resort to overmining because the lower seams had been extracted in the past. This paper deals with the feasibility and proper layout of mining roadways of overmining carried out in the No. 5 seam of Qianjiaying coal mine of Kailuan mining area using numerical and physical simulation. FLAC2D was used to investigate the characteristics of stress and displacement in the overburden after extraction of the lower seams. It also analyzed the proper layouts of gateroads in the upper seams, i.e. locating them in the stress-relief zone of the gob so that their stability can be easily maintained. In addition, a two-dimensional physical model was constructed for investigation of damages to the upper seams due to mining of the lower seams. Finally, based on the results of investigations, proper gateroads layout was designed and successful extraction was implemented for panel 1357 in the No.5 seam.

Jan 1, 2009

By Dennis Dolinar

Improperly designed support systems have led to unplanned roof falls in longwall tailgates. To prevent such falls requires appropriate support and adequately designed support systems. The National Institute for Occupational Safety and Health (NIOSH) is currently developing a standing support design methodology based on the ground reaction curve. To design the support system with this methodology requires a quantitative assessment of the ground and support interaction, which is developed from instrumented test sites installed in longwall tailgates. To compliment and expand the field data results and to optimize the support design, numerical modeling is also conducted. The models are calibrated from the test site data. In the present study, data was obtained from a longwall tailgate in the Illinois basin. The test site was located in the Herrin No. 6 coal seam at a depth of 500 ft. At the site, the immediate roof was a weak shale overlain by a competent limestone. Above the limestone, sandstone formed the intermediate roof. The floor consisted of a weak underclay. In the study, the performance and interaction with the surrounding rock mass of two different standing supports, an engineered crib and a conventional 4-point wood crib were monitored. The two cribs have similar load-displacement characteristics at least through 6 in of displacement. Beyond 6 in, the engineered crib becomes unstable and begins to strain soften and shed load. The measurements and developed ground reaction curves indicated that the tailgate at the mine was a low convergence environment until well inby the face. Because the convergence was well below their capacity, both supports provide more than adequate levels of support to the tailgate. Significant convergence and support loading did not occur until 90 to 100 ft inby the face. The results of this study were also compared with results from similar studies conducted in the Pittsburgh seam to further advance the development of the ?ground reaction curve? based support system design.

Jan 1, 2009

By Axel Preusse

On the basis of the Law on Financing Hard Coal Mining dated 28 December 2007, the subsidized German hard coal mining industry will be shut down to the end of the year 2018 in a socially acceptable manner; in 2012 this decision will be reassessed. Even after the abandonment of all mining activities subsequent burdens are inevitable. In this paper, the possible long-term effects resulting from a mining industry history, which is spanning more than 200 years, and their possible consequences are pointed out, in particular in connection with the abandonment of mine water drainage measures which is economically meaningful in the long term. According to the decision situation as it presents itself today, this point in time will be far beyond 2018. In preparation for this, an action framework is to be developed in areas possibly affected.

Jan 1, 2008

By Andrew G. Martin

In 1991, Modular Mining Systems began marketing a Slope Monitoring System (SMS) now installed at twelve mines. The SMS uses automated wire line extensometers to monitor field conditions frequently. Every few minutes, the slope displacement values and current temperature are transmitted to a central computer via a packet radio telemetry system. The desktop workstation receiving the data continuously provides updated displays of active slope monitors and generates audible and visual alarms if movement exceeds user specified thresholds. The computer system also generates numerous graphs and reports for quick analysis of slope stability. This work describes the functionality of the SMS, details improvements to the SMS hardware and software developed for several clients, outlines different installation techniques needed for wall rock and spoil monitoring, and interprets slope movement data using illustrations of stable and unstable conditions.

Jan 1, 1996

By Shane McDonald

Australia produces approximately 84 million tonnes of coal per annum from 30 longwalls in New South Wales and Queensland, operating at an average depth of around 300m. Industry trends and expectations place increasing emphasis on the reliability of these operations; for example, the current average face width is 245m and this is expected to increase to approximately 270m by 2010. In recent years, Beltana No.1 Mine has consistently been Australia?s highest longwall producer, with ROM output of 7.2Mt in YEJ2007. Strata management has become a key feature of the operation of Australia?s longwall mines, as a tool to manage variances in the geotechnical environment. This involves an understanding of the impacts of the geotechnical environment on ground behaviour and the implications for mine design, stability and associated support, interaction and horizon selection. The anticipated ground control impacts of these factors form the assumptions that drive the format of plans specifying both triggers and actions, with quantified, monitoring-focussed experience used to refine the plan in a continuous improvement (ie ?plan-do-check-act?) process. This paper summarises the Beltana No.1 Mine strata management methodology and experience to-date.

Jan 1, 2008