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By Brian E. Travis

Recent Developments in the utilization of polymer grid structures for Longwall Shield Recovery operations are discussed. Specifically: various Longwall screen designs and the numerous methods employed during installation. Also discussed is the role of polymer grid structures in head and tailgate mf and rib control and their role in controlling soft bottom often associated in shield recovery operations.

Jan 1, 1993

By Kenneth E. Hay

Researchers from the U.S. Bureau of Mines conducted a field study to assess the safety of remotely controlled mobile roof supports (MRS) in a retreat pillar mining operation, Data were collected to provide the Mine Health and Safety Administration with criteria needed to develop guidelines for MRS use and to determine if precursors could be identified that would alert miners to imminent roof falls. Two test sites at which two different support methods-MRS's and posts were used and were monitored to obtain information on entry stability. Pressure transducers and string pots were installed on all four MRS's to obtain loading and displacement information. and roof bolt load cells. sonic probes, extensometers, and survey targets were installed in the surrounding entries to obtain information on ground behavior. Results showed a larger increase in roof bolt loading and roof movement when MRS's were used, especially in the intersection area. Roof bolt loads in the entries showed decreases in load when the MRS's were set and increases up to 11,1 kN (2,500 lbf) when the MRS's were unloaded. Unloading of one MRS in a pair did not significantly increase load on the other. MRS's I and 2 usually had the higher loads, with these loads increasing as the pillars on each side were being mined. MRS 3 normally had lower loads than I and 2: however, it also experienced some very high loads when in the last position near the pushout. MRS 4 usually had the lowest loads, primarily because it was located near the solid pillar that was not being mined.

Jan 1, 1995

By Wenbing Guo

The stability of strip pillar is the key to successful strip pillar mining. In analyzing the stability of the strip pillar, the width of yield zone must be determined. The determination of the width of yield zone has been an important subject for researchers. In this paper, the numerical method was used to study the relationship between the width of yield zone in strip pillar and coal recovery ratio. The results showed that as the recovery ratio increases, the width of yield zone increases exponentially. Accordingly, the formula for determining the width of yield zone was updated and the effect of changing coal recovery ratio on strip pillar deformation is presented.

Jan 1, 2006

By Lou Gaozhong, Guo Wenbing, Zhao Gaobo, Wang Shuren

"The height of a fractured zone due to high-intensity mining (HIM) plays a vital role in the safety analysis of coal mining under bodies of water. This paper described the characteristics of HIM. The processes of overburden failure transfer (OFT) are analyzed. The state of destruction transfers from a certain stratum to the upper stratum as face advance distance increases, and the processes of OFT are divided into two stages: transmission development stage and transmission termination stage. Through theoretical analysis, the limited suspension-distance and limited overhanging distance of each stratum are proposed to judge the damage of each layer. Based on this, the OFT criteria of fractured zone development are obtained. The mechanical model of strata suspended integrity and overhanging stability are established. Finally, a new method to predict the height of fractured zone due to HIM is put forward based on the processes of OFT, the limited suspension-distance, and the limited overhanging distance. Further, a HIM panel in the Datong coal mine is taken as an example. Theoretical methods are proposed, and engineering analogy is used to predict the height of the fractured zone, which is compared with in-situ measurements reported in the literature. The results show that the in-situ measurements for the height of the fractured zone are in close agreement with the theoretical calculation result. Therefore, the rationality and reliability of the theoretical method proposed to predict the height of fractured zone is verified.INTRODUCTIONThe height of the fractured zone (HFZ) due to the exploitation of coal is a key parameter for the safety analysis of coal mining under a body of water (Wenbing, Youfeng, and Hou, 2012). Accordingly, it is necessary to predict HFZ under the corresponding mining conditions before coal mining."

Jan 1, 2018

By Stephen C. Tadolini

A joint research program was designed and conducted at Lodestar Energy?s Baker Mine to investigate the performance of a high-capacity tensioned cable supported gateroad. The secondary system consisted of a 4.5 m (14.5 ft) 7 strand cables that were 23 mm (.9 in) and 18 mm (.? in) in diameter with a designed capacity of 515 kN (58 tons) and 355 kN (40 tons), respectively. The cables ware installed with an effective resin column length of 1.25 m (4 ft) and then pre-tensioned using a hydraulic jacking system. Roof separations, caving characteristics, and support performance was monitored and evaluated during the critical extraction of the adjacent panel, complex geological conditions of the west Kentucky No. 13 seam were mapped and the support performance recorded. This paper will describe the theory of tensioned cable systems and present an assessment of the support performance during the longwall retreat mining process.

Jan 1, 2000

By Anthony T. Iannacchione

This study, funded by the Appalachian Research Initiative for Environmental Science (ARIES), examines how mine layout, mining method, and geology interacted to allow water from the Grove No.1 mine pool to discharge into local surface waters. Federal and State regulations prohibit the discharge of acid or iron-producing waters from underground coal mines. Mining companies design barriers around their operations to prevent mine waters from discharging to the surface. The Grove No.1 represents one mine where these designs proved inadequate. Unique geologic conditions at the Grove No.1 mine pool, combined with retreat room-and-pillar mining, contributed to a discharge that required passive water treatment.

Jan 1, 2013

Knowledge of initial ground pressures or in-situ stresses and mechanical properties and geological conditions is of great importance in drivage and maintenance of a mine roadway. Field measurements of the in-situ stresses and the geological and mechanical properties have been carried out. However, these methods are really impractical in using in underground mines. Alternatively, back analysis method using measured displacements during drivage of roadway can be used. The paper presents discussion on some problems in applying inverse formulation of back analysis to a roadway driven in an in- homogeneous rock mass. The back analysis is formulated by 2-0 finite element method. The inverse procedure is carried out using a microcomputer, but for the multi-rock layer, a larger computer or a main-frame computer is used due to an iterative procedure.

Jan 1, 1990

By T. N. Singh

An evaluation was made on the cavability of the roof formation of Dishergarh seam including caving sequence, caving span, and load on powered support.

Jan 1, 1994

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 Thomas M. Barczak

The intent of this paper is to make mine operators and engineers aware of parameters which affect the loading behavior of passive roof support systems. The strength of a passive roof support element alone is not a meaningful measure of support performance. Passive roof support elements and the surrounding strata act as a system, responding to changes in the physical mine environment due to the extraction of coal and associated redistribution of stresses. The load- ing of a passive roof support element is a function of the stiffness of the roof support structure; a stiffer structure will react a higher load to a converging mine roof than will a more flexible structure. If the stiffness if the support structure is not properly designed, excessive loading will result due to the displacement of the mine roof, causing premature failure of the support. Ideally, the yield strength of a passive support needs to be no greater than that required to support the dead weight of the immediate mine roof, providing the post yield characteristics of the support are compatible with the irresistible convergence of the overburden strata and the support system continues to provide this resistance after reaching its yield load. Idealized design considerations for passive roof support systems in terms load-displacement characteristics discussed. The stiffness and yield characteristics of wood concrete cribbing, as determined controlled tests in the Bureau's Roof Simulator, are compared preliminary recommendations passive roof support utilization also provided.

Jan 1, 1987

By Kevin Andrews, Scott Nelson, Terry Hamrick

"In the process of Geologic Hazard Mapping (GHM) for underground coal mining, geologists evaluate the effects of various geologic and geotechnical conditions to assist with optimization of mine productivity and with selection of more favorable areas for future development. The methodology involves correlation of multiple geologic factors (such as overburden depth, proximity to sandstone channels, and areas with weak immediate roof strata) with conditions encountered during mining (roof falls, floor heave, pillar spalling, etc.). Such studies yield maps that identify areas where mining is likely to be difficult and allow mining engineers to foresee favorable and unfavorable mining areas when planning new or expanding mines. To expand the benefits of GHM, work has been done to correlate geologic factors with room-and-pillar mining advance rates. Average mining advance rates are mapped and then correlated to different areas, as characterized by GHM. This process exposes the geological characteristics that have a material impact on mining rates of advance, improving the rates of advance into future mining areas with similar geological conditions. The final result of the work allows mine planners to not only design the mine qualitatively accounting for areas of unfavorable conditions, but also allows the mine planner to more accurately apply rates of advance for mine timing and production sequencing. The use of GHM to predict mining advance rates in unmined areas enhances the benefits of traditional hazard mapping and provides quantitative data that can be incorporated into mine sequencing models.INTRODUCTIONThe role of a geologist in the coal mining industry has evolved significantly over the last 30 to 40 years. Geologic Hazard Mapping (GHM) mapping for coal mines began in the late 1970s and early 1980s (Chase, Newman, and Rusnak, 2006). Since its beginnings, the GHM process has evolved significantly and continues to take on new levels of sophistication. Numerous case studies of GHM application to predict future mining conditions exist in the literature. For example, Artrip, Nelson, and Newman (1993), documents the geotechnical characterization of roof and floor for mining in the Imboden Seam in Virginia where previous mining efforts had been abandoned due to adverse mining conditions. In addition, Keim and Miller (1999) summarize evaluation of geological influences on a longwall mine in West Virginia. In both examples, significant geotechnical and geological information was available, including the opportunity to compare predicted mining conditions against actual conditions as mining progressed."

Jan 1, 2018

By Johann van Wjk

Mandatory Codes of Practice to Combat Rock Fall Accidents came into force on South African Collieries in 1997. These were drawn up in accordance with guidelines issued by the Chief Inspector of Mines, The Codes of Practice (CoP's) are legal documents in terms of the South African Mine Health and Safety Act 1996. One of the main results Of the introduction of the COP'S from a practitioner's point of view is that they formalized much of what would have constituted a typical visit to an underground section previously. Other important requirements were as Billows: Support rules and Strata Control Standard Procedures were to be drawn tip. Identification of Special Areas (areas requiring a higher level of rock engineering input and with, typically, higher order of support and restrictions on mining geometries), Changing conditions underground to he identified timeously. Implementation of the CoP to he monitored. To comply with these requirements on Ingwe Collieries (a division of BHPO Billiton Energy Coal) it was decided to produce too separate forms to be used in conjunction with each other. The first of these, the "Underground Section Physical Risk Rating" measures the physical conditions in each section whereas the second form, the "Section Perfomance Rating" determines how well the section personnel are Coping with the conditions. This form also pleasures compliance with the Support Rules and Strata Control Standards. Both forms are essentially risk matrices but with various scenarios described, each with a certain weighting. The "Risk and Performance Form" system for bord and pillar operations has by now been used for five years in the Ingwe and Eyesizwe Mining Collieries and has achieved a great deal of acceptance. This system has enabled the quantification of previously subjective observations and has improved the strata control awareness and management of underground mining sections. Amongst other initiatives it has assisted ill reducing the severity and frequency of fall of-ground accidents.

Jan 1, 2002

By Kent D. Mctyer

Mining commenced at Tasman Mine in late 2006. The current method of mining is bord and pillar using continuous minerbolters and shuttle cars for first workings and secondary extraction using mobile roof supports. The two stage process was chosen to accommodate irregularly shaped coal deposits, allowing adjustments to be made to extraction ratios for better management of subsidence and to maximize the efficiency of the operation. Following the completion of the first three full/partial extraction panels, the mining method was changed due to variable caving. Another partial extraction method, referred to as the Duncan Method was adopted; it involves stripping the developed square pillars on four-sides on retreat to leave a load-bearing remnant coal pillar. The system of partial extraction has been successful in meeting safety, productivity, and subsidence targets.

Jan 1, 2011

By Jennifer Riefenberg

Research efforts by the U.S. Bureau of Mines include running a series of displacement-discontinuity, boundary-element models to simulate the gateroad design at an underground coal mine in northwestern Colorado. The initial mine design is a yield-abutment chain pillar arrangement in a three-entry, longwall gateroad system. Pressure effects from mining the first and second panel were recorded using borehole pressure cells (BPCs). These field data were then compared directly to the model output. Observed yielding in the field was approximated by reducing material property values and/or removing pillar elements in the model. Model results using this calibration technique mirrored the field measurements consistently. Using the calibrated model parameters, a suite of models was run simulating an experimental entry design: exchanging the yield and abutment pillar locations. These model results reflect a 20¬to 33-percent reduction in core stresses in the yield pillar during mining of the second panel. Improved pillar and entry conditions are suggested by these predictive results. The design modifications were then implemented at the mine along a 150-m (500-ft) test section. Field observations and measurements from the experimental design test site compared favorably with trends of the model predictions.

Jan 1, 1993

By M. G. Schuerger

The United States Steel Mining Company, Inc., (USM) Lynch District, operated the No. 37 Mine in the Harlan coal seam, Harlan County, Kentucky, from 19'2 until its sale to Arch of Kentucky in 1984. Overburden depth varied from 400 to 2000 feet and mining height varied from 8 to 12 feet. In 1981, because of deep overburden, high seam height, and previous pillar stability problems, U. S. Steel Research and the Lynch Mining District entered into a joint project to measure longwall pillar stress. Eight gateroad pillars were instrumented with a total of 86 vibrating-wire stressmeters under overburden depths varying from 500 to 1550 feet. Stress-increase measurements were taken during: (1) pillar development, (2) retreat of longwall panel No. 1, and (3) retreat of longwall panel No. 2. Total average pillar stress was approximately three times the pre-mining stress with total stress at an individual meter reading 5.5 times the pre-mining stress. When maximum, measured average pillar stress was compared to pillar strength predicted by several popular pillar design methods, the pillars were found to be stronger than predicted. This paper will summarize the pillar instrumentation program and present the results. Stress distributions, average measured pillar stress, and comparison of measured pillar stress to predicted pillar strength by several design methods will be given.

Jan 1, 1984

By Steve Tadolini

Underground roof falls can have devastating effects on the safety of operations personnel, and equipment, and seriously impact production. Immediate steps are usually taken to danger off and secure the area while clean-up efforts are designed and implemented. A critical step, often overlooked due to production demand, is the determination of - why the roof fall occurred so that additional occurrences can be avoided in future developments or what measures can be taken to identify areas that have similar ?symptoms?? Forensic engineering includes the investigation of materials, products, structures or components that fail or do not operate/function as intended. The authors define forensics in ground control engineering as the study of evidence discovered while examining underground roof falls by applying expert observational techniques and established mining engineering principles to determine the probable cause, hypothesize solutions, and design engineering safeguards to prevent reoccurrences. Simply stated, the primary steps in the forensics of underground roof fall techniques are: ? Assess regional and local conditions prior to the event. ? Assess post-event conditions. ? Hypothesize plausible ways in which the pre-event conditions ? became the post-event conditions.Search for evidence that either denies or supports the various ? hypotheses.Apply engineering skill to relate the various facts and evidence into a cohesive scenario of how the event may have occurred. This paper details the proposed technique by utilizing a roof fall case study that required the examination of five primary factors: mine design parameters, excavation geology, method of excavation, method of support, and mining cycle times.

Jan 1, 2009

By T. P. Mucho

Mine roof failure due to excessive horizontal stress has been recognized as a major cause of hazardous roof conditions in some mines. Stress measurements gathered by the U.S. Bureau of Mines (USBM) at 24 different eastern mines show horizontal stress to be typically 2 to 3 times as great as vertical stress. The focus of current Bureau work is to develop detailed design parameters to assess and control the effects of horizontal stress. To facilitate the recognition of horizontal stress effects and to easily determine principal stress direction without resorting to cumbersome, expensive, and time consuming field measurements, the Bureau has developed a stress mapping methodology. Stress recognition and direction determination are required to successfully employ a number of control strategies such as mine layout, mining sequences, and support optimization to control the effects of horizontal stress, thereby increasing the safety of U.S. coal mines. This approach has been used in other major coal producing countries, most notably Australia and the UK, and has greatly enhanced the safety of their mines (1). This paper discusses horizontal stress, directional based control techniques, and provides guidelines for the use of the stress mapping technique. A case study of a mine where the technique has been used is also presented.

Jan 1, 1994

By Shosei Serata

The Stress Control Method improves productivity and safety in underground coal mining. The method stabilizes the roofs and floors of mine openings in both shallow and deep coal beds, regardless of whether or not there are ground stability problems. This paper describes the means by which a tapered pillar experiment is used to collect in situ data, which is then used as input for a computer model. The resulting computer model is then used to optimize Stress Control design for the mine under study. The behavior of any underground coal mine is not elastic, as is generally conceived in the conventional view of rock mechanics, but rather is highly time-dependent and site-specific. Unfortunately, conventional rock mechanics methods based on the elastic principle are not able to capture the highly non-elastic nature of ground behavior which actually occurs. To capture actual behavior, a new method of study is required. In this regard, geomechanical study of an underground coal mine may be compared to studying the behavior of a living fish. Its true behavior zannot be understood by examining it "dead in the laboratory. It Is the "live" nature of the coal mine that is required for design optimization of the Stress Control Method in the given mine. The Stress Control Method is based on a time-dependent theory of the global behavior of the mine ground, which generally contradicts the conventional elastic theory of ground behavior. Therefore, site-specific adaptation of the Stress Control Method required a comprehensive understanding of the global behavior of the mine as a function of time and site-specific ground conditions.

Jan 1, 1986

By Yong-Ming Jiang

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 hackfillcd entries, most of the mining-induced load was supported by the cross-panel entry pillars. The backlill 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 Elizabeth Holley, Meriel Young, Gabriel Walton

"The coal mine roof rating (CMRR) was developed by Chris Mark and Greg Molinda to bridge the gap between geological variation in underground coal mines and engineering design. The CMRR accounts for the compressive strength of the immediate roof, the shear strength and intensity of any discontinuities present, and the moisture sensitivity of the immediate roof. The CMRR has been widely used and validated in Eastern US coal mines, but it has seen limited application in the Western US.This study focuses on roof behavior at a Western coal mine. Mine A shows significant lateral geological variation, along with localized faulting and a laterally extensive sandstone channel network. The CMRR is not used to predict roof instability at the mine.It is, therefore, hypothesized that there are other factors that are correlated with roof instability in underground coal mines that could potentially also be included in the CMRR.This hypothesis was tested by collecting 30 CMRR measurements at Mine A. At each measurement location, a binary record of the roof condition (stable or unstable) was made along with parameters, such as depth of cover, thought to also correlate with roof stability. A statistical analysis of the data was performed to determine the parameters in addition to those included in the CMRR, which can be correlated to roof stability.INTRODUCTION AND BACKGROUNDRoof fall is one of the greatest hazards facing underground coal miners (Barczak et al., 2000). In 2017, 91 lost-time injuries occurred due to roof fall in US underground coal mines. A further 48 roof falls occurred with no lost days (MSHA, 2018).The coal mine roof rating (CMRR) classification was developed by Molinda and Mark (1994) to quantify the geological description of mine roof into a single value that could indicate mine roof stability and be used in engineering design. It is widely used in the Eastern US as an input for the analysis of longwall pillar stability (ALPS) in underground coal mines. It provides an excellent start; however, it is arguably not fully comprehensive, nor is it widely used in the Western US."

Jan 1, 2018