Longwall Mining Method Research Articles

A Method to Relate the Affecting Parameters and Estimate Dilution in Coal Mines

This study provides an overview of the various issues influencing Out-of-Seam Dilution (OSD) in longwall mining method. The collected data has been statistically analyzed to examine the effect of the some factors causing OSD in front of the longwall mining face. Multiple parameter regression analysis was conducted on affecting parameters and the OSD. The SPSS (Statistics Package for Social Sciences) for Windows software package was used for the statistics analysis. Finally, a relationship between affecting parameters and the OSD is established by using the multiple parameter regression results. Results of this study have revealed that depth of seam, dip of seam, roof quality and variation in seam thickness are the most important influence factors for OSD. The proposed method may be utilized for the estimation of OSD for similar mines since, it was based on actual collected data from the coal mines.

The monitoring and prediction of mining subsidence in the Amaga, Angelopolis, Venecia and Bolombolo Regions, Antioquia, Colombia

Amaga, Angelopolis, Venecia and Bolombolo are small towns located in Antioquia, in the Central Cordillera of the Colombian Andes. Mining has been practised in this region for a period of at least 100 years. This mining has mainly been small-scale, poorly mechanised and restricted to shallow room and pillar workings. Recently, the semi-mechanisation of some mines has enabled coal to be extracted using longwall mining methods. However, this has resulted in subsidence that has caused severe damage to structures, residential property, and agricultural land, and also induced landslides. In the British Isles, there are several reliable methods that can be used to predict the likelihood and magnitude of mining subsidence. The British Coal Corporation and the University of Nottingham have developed one such method, the “Subsidence With Influence Function Technique (SWIFT).” Based on mining subsidence observations undertaken in the coalfields of Britain over a period of approximately 50 years. The SWIFT program was used to predict the magnitude of subsidence, above a longwall panel, at the Industrial Hullera mine in Colombia. The results were then compared with subsidence profiles obtained from precise levelling and field monitoring. In each case, the SWIFT program overestimated the magnitude of mining subsidence by 0.17–0.20m. However, the morphology of the subsidence profile, area-of-influence and location of maximum subsidence were similar. This overestimation of the predicted subsidence was attributed to the occurrence of strong, igneous rocks, such as rhyolite sills, in the Colombian coal measures. These strong, competent horizons act as cantilever beams during subsidence, causing bed separation and therefore reducing the magnitude of subsidence. In spite of these differences, mining subsidence can be predicted with a reasonable degree of accuracy and precision using the SWIFT technique, provided the software is calibrated and used in conjunction with local expertise.

THE EFFECTS OF SHIFTWORK SCHEDULE PRACTICES AND PANEL DIMENSIONS ON INJURY EXPERIENCE IN UNDERGROUND LONGWALL COAL MINES

Over the past two decades, there has been a tremendous growth in the amount of coal produced in the United States by the longwall-mining method. During the early-to-mid 1970s, approximately 120 longwall faces contributed less than 5% of the nations's underground coal output; currently, half as many faces contribute nearly 50% of the nation's underground coal output. All this has taken place during a time period when the total underground production grew less than 20%. In addition to the introduction of new technology, new management, operational, and engineering practices have contributed to this explosive growth. Specifically, changing out at the face, lengthened longwall faces, deeper panels, and longer shifts have increased system availability, thereby resulting in these remarkable production gains. However, longer faces and shifts create a concern for the health and safety of face personnel because of increased exposure to workplace hazards and fatigue. This paper examines the impact of increased face lengths, varying mining heights, and increased shift lengths on the accident and injury experience of U.S. longwall mines. Although no statistical significance was established between the three trends and the nonfatal days lost incidence rate, the no days lost incidence rate, and the severity measure — due to limited or nonexistent data, or widely varying incidence rates — a trend was established between the nonfatal days lost incidence rate and shift length. Specifically, for every hour of shift length above eight hours, the nonfatal days lost incident-rate ratio was 1.185, implying that a 18.5% increase in the number of nonfatal days lost incidents is predicted when a shift is extended one hour in the range from eight to nine, or nine to ten hours.

A case study of undermining impoundment embankments by the longwall mining method

Abstract Undermining of impoundment embankments over coal mines has been strictly regulated by state and federal agencies since the failure of the Buffalo Creek dams in West Virginia in 1972. This paper will discuss the safe and successful undermining of one coal fines refuse impoundment and three freshwater supply impoundments and their associated embankments. In cooperation with regulatory authorities, the embankments were undermined with both room-and-pillar development and subsequent longwall mining methodologies at a single mine in the Northern Appalachian coalfield. The mine overburden thickness ranges from 225 to 260 meters and consists of typical upper Pennsylvanian and lower Permian sedimentary deposits. Before the embankments were undermined, the impoundments were drained. After undermining was complete and the embankment integrity was verified, the impoundments were refilled. All embankment crests were monitored for horizontal displacement and tilt using an automated recording system. These measurements were augmented with frequent manual recordings of both vertical surface subsidence and borehole inclination as well as water levels within the embankments.

A case study of undermining impoundment embankments by the longwall mining method

A case study of undermining impoundment embankments by the longwall mining method

Design and operation of powered supports for longwall mining : Barczak, T M J Min Metal FuelsV40, N1, Jan 1992, P10–17

Throughout the history of longwall mining, the design of the roof support system has been critical to the success of the mining operation. Early forms of longwall mining used wood props for face support and packwalls made from roof and floor rock to control caving of the immediate roof. These systems were replaced by powered roof supports that could be advanced easily while allowing the strata to cave behind them. The first powered roof supports were simple frame and chock structures. These designs were poor in their ability to resist horizontal displacements and moment loading caused by the strata dynamics during the caving process. They often experienced difficulty and failure. The shield greatly improved kinematic stability by providing a horizontal stiffness by mechanically connecting the canopy to the base in a truss-like fashion. The success of the shield support promoted the application of the longwall mining method in highly faulted and massive strata conditions where caving was difficult to control and where chock and frame supports were inadequate. The purpose of this paper is to provide some insights into optimizing shield design and utilization. Motivations for optimization are to minimize support costs and maximize shield life while providing effective groundmore » control in all mining conditions.« less

Reports on a field trial of an underhand longwall mining method to alleviate rockburst hazards : Williams, T J; Cuvelier, D J Proc 2nd International Symposium on Rockbursts and Seismicity in Mines, Minneapolis, 8–10 June 1988P349–353. Publ Rotterdam: A A Balkema, 1990

Reports on a field trial of an underhand longwall mining method to alleviate rockburst hazards : Williams, T J; Cuvelier, D J Proc 2nd International Symposium on Rockbursts and Seismicity in Mines, Minneapolis, 8–10 June 1988P349–353. Publ Rotterdam: A A Balkema, 1990

Reflection Seismic Sources for Defining Coal Seam Structure

The prime objective of the investigations described in this paper is to improve the reliability of structural information in advance of underground mining. Kembla Coal and Coke extracts high-grade coking coal by longwall mining methods. In 1984 major disruption to mining was caused by an unexpected fault which crossed the longwall panels. The costly consequences of this faulting provided the Company with a strong incentive to obtain accurate structural data in advance of mining.Seismic reflection work carried out in the 1970s using large explosive charges, produced poor data of very low resolution. In 1987, the Mini Sosie technique was used to obtain seismic data. Fair data were obtained with moderate resolution. Work carried out in 1988 established that a small explosive charge at the base of weathering produced still better data. The weathering depth was determined by a continuous seismic refraction survey.In order to reduce the costs of obtaining seismic data, as well as seeking further improvements in data quality and resolution, experiments were carried out in 1990 and 1991 using alternative sources. Data from a Bolt LSS-3B air gun, a Mertz M26 vibrator and 1.5 m deep explosive charges were compared with data from explosives at the base of weathering. Experiments were also carried out using shaped charges and high velocity of detonation explosives (up to 8600 m/s).The results from the various experiments and production work have demonstrated that all the surface and near-surface sources used, generated substantial ground roll, which reduced the dynamic range of the recording instruments and degraded the signal-to-noise ratio. Weathered near-surface layers also significantly attenuated the high frequencies, resulting in lower temporal resolution.A 240-g conventional explosive with 6800 m/s velocity of detonation, placed below the base of weathering, proved to be the best available source for obtaining good quality high-resolution data. Substantial improvements in data quality and resolution were achieved. Further work is still required in other areas of data acquisition, processing and modelling to improve confidence in the interpretation of very small faults.

Occupational Health and Safety Regulation in the Coal Mining Industry: Public Health at the Workplace

The strategy for preventing occupational disease and injury in the coal mining industry employs several elements. Standards are set and enforced; technical assistance, research, and development are provided; and surveillance is conducted. Compensation for black lung is a vivid reminder of the consequences of failure to prevent disease. And, workers are represented by a union that encourages active participation in all aspects of this strategy. There are significant problems in each of these elements. Regulatory reform threatens to weaken many standards, there is a decline in government research budgets, surveillance is not well monitored, and compensation for black lung is significantly more difficult to obtain now than in the past. Moreover, the conservative governments of the past decade are not friendly towards unions. Nevertheless, the fundamental structure of disease and injury prevention remains intact and, more importantly, it has a historical record of success. The Mine Safety and Health Act provided for a wide array of basic public health measures to prevent occupational disease and injury in the mining industry. These measures have been effective in reducing both risk of fatal injury and exposure to respirable coal mine dust. They are also associated with temporary declines in productivity. In recent years, however, productivity has increased, while risk of fatal injury and exposure to respirable dust have declined. At individual mines, productivity with longwall mining methods appear to be associated with increases in exposure to respirable dust. These trends are not inconsistent with similar trends following implementation of regulations by OSHA. When OSHA promulgated regulations to control exposure to vinyl chloride monomer, enforcement of the standard promoted significant efficiencies in vinyl chloride production (5). Similarly, when OSHA promulgated its standard regulating exposure to cotton dust, this effort provoked modernization in the cotton textile industry (14). It is not inevitable that occupational health and safety regulations are associated with negative economic performance. On the contrary, in some instances, public health on the job and productivity are complementary.

Report on a field trial of an underhand longwall mining method to alleviate rock burst hazards : Williams, T J; Cuvelier, D J Proc 2nd International Symposium of Rockbursts and Seismicity in Mines, Minneapolis, 8–10 June 1988P513–522. Publ Minneapolis: University of Minnesota, 1988

Report on a field trial of an underhand longwall mining method to alleviate rock burst hazards : Williams, T J; Cuvelier, D J Proc 2nd International Symposium of Rockbursts and Seismicity in Mines, Minneapolis, 8–10 June 1988P513–522. Publ Minneapolis: University of Minnesota, 1988

Agricultural Impacts of Coal Mine Subsidence: Effects on Corn Yields

AbstractUndergronnd coal mining methodology is moving toward techniques that cause immediate planned subsidence of the overlying land. Damage done by subsidence to structures has been documented, but the effects on agricultural productivity are undocumented. This study was conducted to (i) determine the extent of measurable subsidence effects associated with planned subsidence mining, (ii) measure the impact of subsidence on corn (Zea mays L.) yield, and (iii) compare the effects of longwall and high extraction retreat mining methods. Five locations in southern Illinois were included in the 3 yr of the study. A total of 4605 ha in 1985, 6747 ha in 1986, and 7764 ha in 1987 were involved. These areas represented unmined control areas as well as longwall (LW) and high extraction retreat (HER) types of mines. Aerial photographs of the study locations were taken in the spring of each year. Subsided areas were identified, classified, and measured on the photos. The average percent of the study urea with measurable subsidence effects was 7.5% for LW mining and 3.3% for HER mining. Corn was harvested each year on selected subsided and nearby unsubsided reference areas. The weighted average reduction in corn yield on land above the mines was calculated by multiplying the affected area by the associated yield reduction. The weighted average yield reduction was 4.7% for LW mining and 1.8% for HER mining. Results for the individual years varied with the weather: the greater the precipitation, the greater the yield reductions. The results also reflect the yearly variation in mining activity, crop sample areas, and overall study areas. In addition, the mitigation of subsidence effects in place at the time of the study also influenced the results, but the potential for mitigation for either mining type was not included in the research.

Faults and Absorption in Coal Seams

At the Centre for Geophysical Exploration Research at Macquarie University, computer programs have been developed to model the propagation of SH and P-SV waves in coal seams. These computer programs are based on the finite element method and include allowance for irregularities in the coal seam and for absorption in the coal and rock. In the longwall mining method, it is of the greatest economic importance to be able to detect faulting and other serious interruptions of the coal seam well ahead of the mining face. Scientists of the Broken Hill Proprietary Co. Ltd have conducted surveys of the transmission of SH and P-SV coal seam waves both by borehole observations and underground roadway observations. At frequencies below 200 Hz, interruptions of the coal seam are not readily detectable by SH and P-SV seam waves. At frequencies above 200 Hz, it is not easy to distinguish the effects on the transmitted SH and P-SV seam waves of interruptions of the seam from the effect of more than usual absorption in the seam. Thus, at a frequency of 400 Hz, for a coal seam offset one seam width by a vertical fault, finite element modelling shows that the effect of the fault is to reduce the amplitude of the SH fundamental mode by 82 percent. Allowance for a Q value of 25 in the coal seam and of 50 in the rock above and below the seam indicates a further decrease of 11 percent in only 24 m. Similar results have been obtained for the P-SV M2 3 mode in the same finite element model and for SH and P-SV modes in a model of a coal seam intersected by a vertical hard dyke. Because interruptions of the seam scatter SH and P-SV energy back and above and below the seam, it is desirable to make both reflection measurements and transmission measurements near the central plane of the seam to distinguish more readily the effect of a seam interruption from that of high absorption.

Underground methods of extraction of thick coal seams—a global survey

Thick coal seams, despite the lack of a precise definition and varying national norms for classification, constitute some 30 percent of the global resource endowment in coal. The exploitation of such thick seams by underground methods offers a challenging task, posing as it does a host of problems related to production concentration, spontaneous heating risk, safety and recovery. The current status of the diverse exploitation techniques in different coal basins worldwide is critically appraised and the available database for thick seam reserves and norms of classification, besides contributions from different methods and roof control techniques, are presented and analysed. The paper sets out to review the highlights of technological developments in room and pillar thick seam mining, single pass longwall, multislice longwall, underwinning and hydraulic mining methods in order to help identify the more promising thick seam methods for the near-term future. The strategy of advancing the state-of-the-art of thick seam technology is also briefly examined.