Search Documents

By Robert W. Bruhn

A 125 foot high steel lattice frame tower supporting a 500 kV EHV transmission line and located over the gateroads of a longwall mining operation was subjected to ground movements from the mining of adjacent longwall panels. Under an agreement with the owner of the powerline, the mine operator was required to minimize mining impacts on the transmission line. In view of this requirement, the mine operator prepared a forecast of the expected subsidence ground movements prior to the onset of mining. These forecasts, in conjunction with finite element analyses of the tower superstructure under the imposed ground movements and wind loadings. suggested that the structural capacity of the tower would probably be diminished little, if at all, by mining. Ground movements determined by survey during mining of the two longwall panels were found to be in close agreement with predictions. Strains measured in selected tower members during mining generally agreed with values calculated by the finite element analyses. The study confirmed a methodology to predict subsidence and to assess its effects on steel lattice transmission towers.

Jan 1, 1990

By Thomas L. Hutchinson

The mechanical design of a roof support is basically a matter of a statics and dynamics problem, assuming of course, that the imposed loads and mining conditions are known. Here in the Appalachian coal fields the general conditions are known well enough to allow the majority of the proposed new faces of longwall to be furnished with standard commercially available supports equipped with suitable variants and options. While not trying to negate the primary importance of thoroughly investigating a potential face and the selection of the correct equipment for that face, it still becomes clear that an equally important aspect of the design of an adequate ground control program has in the past too of ten been overlooked, having been overshadowed by the ?endless? selection process of the roof supports proper. The equally important aspect which this paper discusses is the overall design of a mining system, which design incorporates not only the size and capacity of the equipment but the following points as well, namely: Equipment adaptability to mining scheme, Equipment va. human constraints, Operation at the designed levels, and Coordination of operation, maintenance and support design. Unless the coordination of these factors is considered in the design and selection of the equipment, a lopsided and inefficient operation is possible. How can we afford to put an 8-10 million dollar investment up to chance as to whether it will yield optimum results or not?

Jan 1, 1981

By Lance R. Barron

The U.S. Bureau of Mines, in cooperation with a central Utah coal .mine operator, began a study in July 1988 into longwall gateroad designs applicable to deep, bump- prone mine conditions. Prior to the study, four adjacent longwall panels, incorporating a variety of panel entry configurations using "yielding' chain pi liars, experienced severe bumps and coal outbursts at the face and in the tailgate pillars during panel extraction, resulting in several lost-time accidents and a fatality. To quantify those factors primari1y responsible for bump occurrences during panel retreat, a field investigation was initiated to confirm the anticipated performance of a two-entry gateroad system employing a large, nonyielding chain pillar design. Hydraulic borehole pressure cells and roof-to-floor closure [convergence) measurement stations were installed to monitor gateroad abutment loading and entry closure during panel extraction. Study results indicate that very high confinement of the coal seam by strong roof and floor members existing across the entire property, in conjunction with overburden depths in excess of 1.600 feet, provides for bump-scale energy storage in not only gate pillars, but along the entire periphery of the active mining area. Insufficient gate pillar designs were also identified as possibly enhancing the occurrence of bumps in the tailgate and adjacent face areas.

Jan 1, 1990

By Axel Preusse

In the Ruhr district, pipelines of public and private infrastructure are made of cast iron, steel, plastics or asbestos cement. Legal framework, technical regulations and normative standards define which pipeline materials may be used for the transmission of which kind of product Thus ground water endangering substances as well as inflammable or explosive products are only permitted to be transported in steel-made pipelines. Ground movements, due to underground mining, are transmitted via the soil to the pipeline and cause extra strain within the steel pipeline (Figure I). In extreme cases durable deformations may occur, characterized by an oval profile or a fold in the pipeline. To avoid or minimize damages, balancing elements are installed into the concerning pipeline, reducing the ground movements which might otherwise cause damages. [ ] The distance between the balancing elements is not arranged by random, but by a calculation method developed in a doctoral thesis [Spielberg, 1999] which represents the actual available standards in science and technology. The calculation method considers all relevant influencing variables with impacts on the movement behaviour of steel pipelines in mining areas, such as technical data of pipeline design (e.g. steel grade, wall thickness, weld seam quality), soil conditions (e.g. friction), laying depths of the pipelines, the operational impacts (working pressure, corrosion) and the mining impacts. As of today, mining has caused no damages to steel pipelines protected by this calculation method.

Jan 1, 2004

The purpose and current practice of cable trusses in underground coal mines is briefly outlined and details of various cable truss designs are presented. The main part of the paper describes the in-situ performance of cable trusses installed as secondary supports in gateroads and recovery roads of longwall coalfaces. The performance analysis is based on the results of in-situ monitoring carried out at a number of sites at two underground coal mines within Australia. Truss performance has been assessed as load developed in relation to roof convergence, face position and time. Additionally, the influence of strata conditions, installation pattern/density, roadway layout and geometry have been taken into account. An analytical model has been developed to predict truss loads. The principal variables are listed and the basis of the model is described. Based upon behaviour observed in the field the model has been progressively upgraded and validated against measured performance. Guidelines on truss performance and factors which influence it are presented and the implications of these to the use of cable trusses is discussed. Possible methods for improving truss performance in certain strata conditions are outlined and some comments are made on the value of cable trussing compared to cable bolting in these situations,

Jan 1, 1992

By Ismet Canbulat

The cut out distance in the continuous miner sections in South African collieries is limited to 12 m. However, this distance can be extended to 24 m by the permission of the Department of Mineral and Energy (DME). This paper investigates the risk of roof Calls associated with the extended cut out distances permitted by the DME. Extensive underground experiments have been conducted using sonic probe extensometer under various geological conditions to identify the effect of cutting distance and tinge on the stability of the workings and the performance of the support. The results showed that that the most critical parameter with respect to ground control aspects of extended cut out distance is the bord width, which determines the amount of deformation that will take place in the roof. This was confirmed by the numerical modelling. The results also showed that a significant portion of the maximum deformation in the roof takes place before the ratio of cut out distance to bord width exceeds two. This indicates that once the face is extended more than twice the bord width, the roof will stabilise, assuming that no geological discontinuity is present and that there will be no further geometrical changes in the area as a result of for example the development of an intersection.

Jan 1, 2000

By T. N. Singh

Board and pillar system of mining has beer, practised in India in view of abundant availability of cheap labour force, low investment and quick return. Subsequently, selective mining from thick seems and partial mining under surface features boosted the trend. As s result over 2000 million tonnes of coal is locked up in form of developed pillars inclusive of about 1000 million tonnes of high grade coking coal in Jharia field alone. The trend of pillar formation is still uninterrupted as the estimated pillar reserve in this field in 1974 was only 700 million tonnes which increased to 961 million tonnes in 1983. The trend is not much different in other coalfields end as a rough estimate 100 million tonnes of virgin coal reserve is being transferred to pillar every year. The method of board and pillar mining is likely to remain moat preferred technology for decade9 to come in view of several inherent advantage in Indian mining conditions.

Jan 1, 1984

By D. W. H. Su

A two-year study was conducted by CONSOL in a northern West Virginia coal mine to evaluate pillar design and support requirements to improve roof control in right-hand longwall headgates subject to high in situ horizontal stresses. Horizontal stress measurements conducted within undisturbed areas of the subject mine revealed a pre-existing regional horizontal stress field with a significant difference in magnitude between the east-west maximum and the north-south minimum stresses. Three¬dimensional stress cells installed to monitor horizontal stress concentration in the headgate roof during mining revealed that a narrow (60-foot center) headgate pillar reduces the east-west horizontal stress concentration in the roof ahead of the face such that the headgate is more stable and requires less support. This 60 foot x 140-foot pillar design, which has been employed in subsequent panels, still provides adequate stress attenuation to protect future tailgates under a maximum cover depth of 1000 feet. Roof geology derived from underground roof reconnaissance and underground bolt load and roof displacement measurements confirmed the effectiveness of 12-foot long cable bolts for controlling the headgate roof subject to high horizontal stresses. With the new headgate pillar design and the supplemental cable bolts, headgate roof conditions in the subsequent panels improved significantly, longwall production delay due to adverse headgate roof condition was totally eliminated, and record coal production was achieved by the subject mine in the subsequent years.

Jan 1, 2003

By Alan Peacock

Shield supports have been in use in the USA underground mines since 1975, and their development in the intervening time has been progressive and inovative. Specialized techniques are used to optimize their performance in a particular application and to design the component parts.

Jan 1, 1981

By Stephen P. Signer

This paper presents the results of a case study conducted in a two-entry gateroad in a coal mine where excessive roof deformation and bolt loading resulted in failure of many roof supports. The instruments consisted of 16 fully grouted, strain gaged resin bolts, load cells on both full and partially grouted cable bolts, and vertical deflection multipoint extensometers. These instruments were installed on-cycle to measure loading on bolts in an existing support pattern and to determine if cable bolts could be used to improve roof stability. Results showed significant amounts of movement within the bolted zone. In sonic cases, these movements were enough to load the supports past their ultimate strength. Geology appeared to be a significant factor in localized roof degradation; that is, a very weak rock layer in the immediate roof overlain by a very strong rock layer contributed to the development of shear planes. Only one instrumented bolt had a maximum strain of less than 2,000 microstrain, which was the yield point of the steel. The average maximum strain on all bolts was 20.000 microstrain. However, electrical continuity to many gages was lost, and a pattern was noted that would indicate possible bolt failure. Wire mesh and concrete cans installed as secondary support performed very effectively.

Jan 1, 1998

A two-dimensional time-dependent analysis of a overburden-coal pillar-weak floor strata interaction problem is presented as a beam model consisting of a composite roof beam resting on multiple elastic foundations (pillars) underlain by a composite rock mass representing immediate floor strata. Several different material models may be considered for the immediate floor strata. The analysis can include all openings and pillars in a panel and permits bed separations in the roof composite beam. The model has enabled identification of the relative significance of different geometric and mechanical behavior parameters which govern the system. The paper presents the theoretical background for the model as well as its application to a mine in Illinois where surface and underground geotechnical observations have been conducted over the last two years.

Jan 1, 1988

By H. Maleki

Gob pressure measurements were made in a Western U. S. coal mine as part of a long-term program to evaluate cave progress and to determine the influence of geological discontinuities on caving conditions, load transfer, and resulting instabilities. Gloetzl cells were selected for the measurements due to their simple, robust construction and a history of being able to monitor pressures in a broken medium. A methodology was developed for the successful installation and protection of the cells and hydraulic lines in the gob as the face retreated. The measurement indicated a cave progress controlled by the frequency of, major faults. The pressure-mining progress profile was compared to those observed in other parts of the world. It was concluded that the significant differences in profiles was caused by the thick-bedded strata, the existence of high lateral stresses and the spacing between faults. Recommendations are given for future applications of Gloetzl cells for gob pressure measurements.

Jan 1, 1984

By John L. Ellenberger

The National Institute for Occupational Safety and Health (NIOSH) has continued the research role of the former U.S. Bureau of Mines to develop techniques that will reduce the hazards in the mining work place associated with coal bumps. Current research focuses on both analyzing historical seismic data from bump-prone operations and utilizing a mine-wide seismic network to investigate the exact strata failure mechanics associated with bump-prone geology. The anticipated outcome of this research will be reduced bump incidences through advanced engineering concepts and designs which implement the new understanding of strata behavior. The analysis of the historic seismic data consists of correlating observed mining seismicity with the geologic and geometric parameters at the sites. The primary seismic parameters are the timing, location and magnitude of a recorded seismic event. These parameters are correlated with such mining parameters as: the overburden, the size of the immediate gob, the size of the district gob area, etc. This detailed analysis of historical seismic data has provided an informative quantifiable relationship between many of the specific mining parameters and the induced seismicity. The second aspect of the coal bump research is the instrumentation of an appropriate field site to determine the main roof, floor, and gob behavior associated with hump behavior. The chosen field site is a deep-cover longwall mine with competent geology in a historically bump-prone area. The primary field instrumentation is a three-dimensional, full-waveform, seismic array with both surface and underground sensors surrounding an active multi-panel district. The purpose of this seismic array is to determine the timing, the exact location, and the mechanism (tensile fracture, bedding plane slip. etc.) of the failure of the strata surrounding the active and multi¬panel gobs. The preliminary results presented in this paper help to define the strata failure areas around the longwall panel.

Jan 1, 2000

By Mohummad Akram

Statistical analysis of multi-seam mining case studies demonstrated that geologic structure and lithological type and sequencing were predominant factors in entry failures. Finite element analysis was used to evaluate the effects of stress field changes on entry instability under differing geologic conditions. Analysis showed the roof to be particularly vulnerable to shear with the location of the failure site changing to meet loading and geologic conditions. Effects of external support on roof stability were examined. Results were correlated with field data to determine stress levels at which failure could be expected to occur. Based on this research design, criteria were developed for roof stability evaluation under specified interactive loading conditions.

Jan 1, 1993

By Brad Seymour

In cooperation with Cyprus Twentymile Coal Co., researchers from the National Institute for Occupational Safety and Health (NIOSI-I), Spokane Research Laboratory, conducted a study at the Foidel Creek Mine, an underground coal mine near Oak Creek, CO, to evaluate the stability of underground working conditions as a longwall advanced through a series of backfilled cross-panel entries. Instruments installed in the cross-panel entry pillars, backfill, longwall panel, and adjacent headgate entry were continuously monitored by a computerized data acquisition system as the longwall approached and advanced through the backfilled section of the panel. Data collected from these instruments were analyzed to determine the magnitude and direction of the secondary principal stress changes ahead of the longwall face, deformation and closure of the headgate entry, and stability of the cross-panel entry pillars and backfill. A three-dimensional, boundary element model was calibrated to accurately predict mining-induced stress changes and the distance they occurred ahead of the longwall face. As the longwall advanced through the backfilled entries, most of the mining-induced load was supported by the cross-panel entry pillars. The backfill provided stability for the root and Moor of the in-panel entries and also confined the entry pillars significantly improving their load-carrying capacity. Comprehensive information derived from backfill material property tests, instrument data, underground observations, and numeric modeling results document the safety and stability of the 8-Right minethrough and should provide beneficial case study information fur other longwall backfilling applications in the future.

Jan 1, 1998

By Peter Cain

In 1993 an opportunity presented to monitor the effects of undermining an abandoned roadway by a longwall panel in the Sydney. N.S. coal field. Interaction subsidence data was collected by survey leveling to benchmarks in the undermined gateroad as well as by a standpipe system equipped with 15 vibrating wire piezometers measuring changes in elevation in the gateroad relative to an outby header tank. The piezometers were monitored at 30 minute intervals using a datalogger. while the leveling surveys were conducted weekly over the life of the project. The monitoring program resulted in the collection of a very large both of data. relating vertical subsidence to the relative position of the underlying face. The most basic analyses derived a travelling subsidence curve from the leveling data only. which hinted at a relationship between rate of extraction in the panel below and the amount of strain developed in the undermined strata. The complexity of the relationships between the amount of subsidence obtained, the location of' the individual monitoring stations, the rate of face advance below and the potential for "periodic" subsidence due to geological conditions has made analysis difficult. and the amount of data has compounded this problem. Recently. an analytical approach using a commercial neural network analysis package has been applied. which appears to have resulted in the ability to draw sonic meaningful conclusions from the data set. In this paper a short history regarding the collection of the data set is followed by a brief' description of neural networks. This is followed by a description of the several analyses performed. some of the results obtained, and conclusions drawn.

Jan 1, 1998

By Joshua Hescock, Zach Agioutantis

"The Surface Deformation Prediction System (SDPS) has been developed as an engineering tool for the prediction of subsidence deformation indices through the implementation of an influence function. SDPS provides a reliable and fast method for the prediction of mining-induced displacements, strains, tilt, and so forth at any elevation between the seam and the horizontal or varying surface topography. One of the key aspects in obtaining reliable ground deformation prediction results is the determination of the edge effect offset. The value assigned to the edge effect corresponds to a virtual offsetting of boundary lines delineating the extracted panel to allow for roof cantilevering over the mined out area. The objective of this paper is to describe the methods implemented in updating the edge effect offset code within SDPS. Using known geometric equations, the newly developed code provides a more robust calculation of the offset boundary line of the extracted panel for simplistic, as well as more complex, mining geometries. Assuming that an extracted panel is represented by a closed polyline, the new edge offset algorithm calculates a polyline offset into the extracted panel by the user-defined edge effect offset distance. Surface deformations are then calculated using this adjusted panel geometry. The MATLAB® program was used for development and testing of the new edge effect offset feature. In completing rigorous testing regimes, the new offset features will be integrated into SDPS, further increasing the speed and reliability of the programs resulting in a retrospective increase in capability and flexibility. INTRODUCTION Underground operations have been known to cause mining-induced subsidence inside and outside of the mine permit area (Karmis, Agioutantis, and Andrews, 2008). Additionally, subsidence can impact surface water bodies, such as rivers, streams, lakes, and wetlands (Karmis and Agioutantis, 2015; Newman et al., 2016), as well as infrastructure, such as roads, railroads, pipelines, and buildings. With an increase in regulatory focus on mining-induced impacts to local structures, the calculation of mining-induced subsidence indices has become necessary in determining potential damage and mitigation efforts. The accurate prediction and evaluation of mining-induced ground deformations is required to obtain underground mining permits due to potential impacts to nearby structures, as well as hydrogeological sources. The prediction of ground deformation indices is often a complex task due to the number of input parameters required, such as mining geometries, overburden lithology, surface topography, the rate of mining (Karmis, Agioutantis, and Andrews, 2008)."

Jan 1, 2017

By John L. Hill

Cutter roof failure is a specific type of ground control problem which frequently results in massive roof failure. It is a cannon occurrence in coal mines of the Northern Appalachian Coal Sasin, causing delays in production and posing a safety hazard to mine personnel. The Bureau of Mines is conducting research on the causes of cutter roof failure togain a basis from which to prevent its occurrence and to support such roof when failure does occur. Research conducted in a coal mine of central Pennsylvania has revealed a correlation between the occurrence of clastic dikes and fonation of cutter roof failure. Inmine mapping of ground conditions showed an increase in roof failure in areas of high frequencies of clastic dikes. Rock pressure monitoring around clastic dires registered the greatest amount of roof loading near the inter- section of dikes with the rib. Load cells measurim horizontal pressure changes in the roof indicated that the greitest pressure changes were occurring perpendicular to entry headings when clastic dikes were present. Analysts of rock pressure nwnitiring shows that the roof behaved as two cantilever beams when severed by a clastic dike. Additional roof supports such as trusses and cribbing were found to effectfvelv suooort the roof in areas of clastic dikes and prevent cutter roof iailure. However, there lnethads were only successful when employed shortly after mining.

Jan 1, 1984

By Kenneth Rigsby

Black Mountain Resources' Highlands Mine No. I is a full extraction room and pillar operation located in Harlan County, Kentucky. Black Mountain extracts the 0.9 to 1.1 meter (36- to 42-inch) thick Owl Scam that is situated 60 to 70 meters (200 to 235 ft) above the longwall panels of the abandoned Arch No. 37 Mine, in the 3.4 meter (I I ft) thick Harlan Scam. In the areas where full extraction has taken place, the overburden above the Owl Seam ranges from 60 to 430 meters (200 to 1,400 ft). A short room and pillar panel was developed above an extracted longwall panel to test the selected pillar size, to evaluate support systems, and to verify the shape of the subsidence profile over the recovery end of the depleted longwall panel. It is over the recovery end that Highlands Mine No. I would access the Owl Seam reserves that exist above the No. 37 Mine. Black Mountain selected pillars sizes to be employed above the longwalls based on the ability to fully extract a pillar employing extended cuts. After a mechanical testing program was completed and mine behavior and top disturbance were observed in the test panel, John T. Boyd Company (BOYD) verified pillar stability and designed support systems. BOYD previously designed No. 37 Mine's gate pillars and studied subsidence and gob formation over its longwall panels; this effort aided the analysis of overburden movement and pillar integrity at Highlands Mine No. 1.

Jan 1, 2003

By Madan M. Singh

Currently longwall coal mining operations require at least 3 entries on both the headgate and tailgate ends because of ventilation and safety requirements. Driving of entries, however, is a slow and costly process. Often it is a bottleneck in longwall development. Single entry gateroads are permitted in Europe and commonly used there. This study entailed ascertaining the feasibility of using a single entry in the United States, without sacrificing safety. This design was conducted for an operating longwall mine in the Black Warrior coalfield in Alabama, An understanding of rock loads and consequent support requirements is prerequisite to the design and successful demonstration of the single entry system. Efforts in this regard were directed at determining center (packwall) support requirements for various single entry widths. Critical to the analysis is knowledge of the nature and extent of side abutment stresses. In collecting geological and geotechnical information relating to the stability of the single entry, Engineers International, Inc. engaged in the following: ? Examination and inspection of the single entry demonstration at the Sunnyside Mine in Utah. Severe ground conditions and unacceptable levels of entry closure were experienced there prior to the tailgate phase. Observations at the mine presented a clear perspective on possible ground control problems for future single entry designs. ? Reconnaissance inspection and classification of roof rock conditions. ? Detailed mapping of roof structure in the areas to be instrumented. ? Installation of convergence stations in the longwall headgate to monitor roof movement during mining. ? Measurement of side abutment stresses in a yield pillar in the area of the convergence measurements. ? Measurements of coal fracture distribution by the detail area method. ? Rock properties determinations of roof, coal, and floor rocks; samples obtained by core drilling. ? Determination of floor bearing capacity by in-situ testing.

Jan 1, 1982