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By Robert Anderson

Advance knowledge of roof conditions can lead to improvement in roof control strategies that will reduce roof falls and ultimately will reduce injuries to mine workers. J.H. Fletcher and Company, in cooperation with West Virginia University, has been developing a system to meet these needs by collecting torque, thrust, and rotation speed data during drilling operations. Recent improvements in analysis algorithms to detect anomalies in the roof structure as well as various display enhancements for real time mapping and evaluation of roof structures have been incorporated into current Fletcher Information Display system. The unit has also been housed in an explosion-proof container to allow use in coal mine applications. Recently, the system has undergone extensive field trials in several limestone mines and one coal mine. During these trials, the National Institute for Occupational Safety and Health assisted Fletcher in verifying the accuracy of the roof mapping capability of the system by comparing the display information to bore hole scoping observations and drill corings. It was concluded from this assessment that the intelligent drilling system can complement scoping and core analysis to provide a more complete picture of roof strata and is capable of seeing features or conditions that are not always obvious in these more traditional methods.

Jan 1, 2007

By Andrew P. Schissler

The Citronen Zinc-Lead Project is one of the world?s largest undeveloped zinc-lead resources, containing more than 13 billion pounds of zinc and lead metal. The project is located in northern Greenland, a self-governed region of the Kingdom of Denmark (Figure 1). Citronen is the northern-most mine in the world, operating at a latitude of 83o 3? N. In excess of 67,000 meters of diamond drilling have been completed to delineate the resource. As of January 2012, the measured, indicated, and inferred reserves for the Citronen project totaled 70.8 million tonnes, consisting of 5.7% zinc + lead (3.5% zinc cut-off) (Ironbark, 2012). For the underground mine plan, room-and-pillar and long holestoping mining methods were selected. The beneficial application of structural fill was considered for increased recovery, efficient tailings disposal, and ground control. Three types of fill were compared - paste fill, cemented rock fill, and iced tailings. An environmental and economic feasibility study concluded that iced tailings was the preferred alternative provided it met the ground control requirements. The purpose of this paper is to explain the investigatory steps that led to the possibility for the use of iced tailings as structural fi

Jan 1, 2012

By Yi Luo

Subsidence events occurred over inactive room and pillar (R&P) mines, including abandoned mines or sealed portions of active mines, are classified as unplanned subsidence because of their timing and distribution are unpredictable. When investigating such subsidence cases, many uncertainties exist and disputes often focused on whether the observed structural damages are caused by mine subsidence or other natural or artificial causes. However, solid evidences to identify the causes are often lacking. In order to conduct a thorough and impartial investigation, good knowledge in subsidence theories and other ground control subjects and broad experience are required.

Jan 1, 2009

By Alexander Garcia

Roof and rib falls are the basic ground control hazards associated with underground roadways during development, stand up and, if applicable, retreat. Falls of ground can happen following the deterioration of supports or rock conditions over time, and particularly as a consequence of continuing rock deformation and/ or failure to install adequate support. Once developed, the risk of a failure is increased due to the effects of time as well as to front abutment stresses through retreat mining. The measurement of strata displacement using monitoring equipment is a form of ground control risk assessment. These monitoring systems are active, or ?live?, in a sense that risk is assessed real-time. However, there are circumstances in which falls of ground can occur without the prior recording of excessive movement. In addition, monitoring equipment is typically placed at set intervals, and strata conditions could vary between these points. Consequently, a visual assessment of other factors contributing to the risk of a fall should be made in order to complete a ground control risk assessment. Such surveys are usually one-off, thus capturing roadway conditions at one particular point in time. Ongoing deterioration is not documented through such one-time surveys, and there is a requirement for real-time or live assessment where a system is in place so that observation data can be updated on an ongoing basis, and a useful summary of prevailing roadway states produced on demand. To address the shortfalls of one-time assessments, a ?live? computerbased quantitative ground control risk assessment process has been developed. It combines visual observations processed in a quantitative manner with existing monitoring data into an interpretable output which indicates zones of roadway where there is an increased risk of a fall of ground from the roof or sides, so that remedial action can be carried out to mitigate that risk. Through improved procedures, it is now possible to generate a ground control risk assessment for each roadway, and one which can be updated frequently. This paper aims to outline and describe the assessment process.

Jan 1, 2012

By J. M. Krese

This paper gives an overview of the National REAP program emphasizing the program's current status and future plans. A brief historical review of the program will be given containing roof-fall accident trends and statistics. The latest developments in roof control technology and training as it affects the REAP program will be presented. A brief discussion concerning some effects of the implementation of the amendments to Part 75, CFR, concerning roof support is included.

Jan 1, 1988

By Roland C. Walker

Traditional headed rebar has existed in the mining industry as a ground support product for many years. The head of a rebar bolt is most commonly produced by hot upset die forging. Upset die forging produces a rugged, simple head that performs well. Certain elements of the head must comply with regulatory standards, such as ASTM F432-95, which offers a standard test procedure to ensure quality of the product. The head style produced by all major manufacturers has been optimized to reduce manufacturing costs, provide greater miner safety and provide an excellent performing product. Observations were made in some mines of heads failing under in-situ loading. These observations could not be replicated according to the ASTM testing method. This paper highlights the problem and how a solution was developed. The development includes pictures of in-situ failures from the underground operations, laboratory replication tests indicating how this loading occurs, and then the use of this calibrated test method to validate the new design created.

Jan 1, 2009

By Wenquan Zhang

Based on the mining and geological conditions of Wadong Mine, Longkou City, Shandong Province, China, a viscoelastic model with proper creep parameters was established. The 3-D ANSYS was used to simulate surface subsidence, analyze overburden subsidence characteristics, and propose the rational mining and pillar widths for mining in weak rocks and under special mining conditions, and provide the policy makers scientific data for decision making on mining activities.

Jan 1, 2006

As the surface reserves are being depleted, more and more stone operators are seeking underground mining options. Stability of underground openings is a major concern for the safety and productivity. This paper relates to a field study conducted at a large underground limestone mine in Central Pennsylvania. Identification of hazards leading to ground failures and assessment of roof fall risks are important in mitigating injuries. Field observations at this mine were integrated with Roof Fall Risk Index (RFRI) mapping software recently developed by West Virginia University. The system is designed to combine field study data related to geologic factors, mining-induced damages, roof profile, and ground water influx to generate RFRI maps. The mine has adopted a proactive ground control program consisting of comprehensive examination of drilling and bolting logs; precision surveying of roof and rib; accurate mapping of cutters, falls, and geologic structures; and installation of extensometers and microseismic monitoring systems. Investment of time and resources has eliminated fatalities and lost-time injuries due to ground fall. This paper presents the geologic settings, mining conditions, ground control issues along with risk management and control techniques adopted at the study mine.

Jan 1, 2009

By Naj Aziz

The shear behaviour of reinforced rock joints is investigated for the bolt-grout-rock interaction and for failure mechanism. The effectiveness of the bolt application under lateral and axial loading conditions within surrounding materials is investigated in different medium strength. Double shearing testing of bolts were studied in concrete blocks of 20, 40, 50 and 100 MPa strengths, subjected to different pretension loads of 0, 5, 10, 20, 50 and 80 KN respectively. The experimental study was complemented with three-dimensional numerical analysis. Parameters examined include: shear resistance, shear displacement, induced strains and stresses during bolt bending process and its ultimate failure across the sheared joint planes. The conclusions drawn from the study were; the level of bolt resistance to shearing was influenced by the bolt profile configuration, the strength of the rock or medium influenced the level of load generated on the bolt, and the increase in bolt pretension has contributed to the increased shearing load of the bolted medium.

Jan 1, 2007

By Srinivasulu Tadisetty

The productivity and safety of Indian longwall operations are insignificant because of complex geomechanical conditions. Therefore, the continuous monitoring and forecasting of abnormalities is imperative. Authors developed an innovative real time system and implemented in one of the Indian longwall mines. The real time system was successfully acquired data from underground chock shields and classified the behaviour in real time as per the standard norms. Furthermore, it forecasted the abnormal behaviour of chock shields promptly. The management was implemented appropriate precautionary measures based on real time forecast. Subsequently, the longwall operations were successfully completed with enhanced productivity and safety. This paper discuss the impact of the innovative system on productivity of experimental longwall mine.

Jan 1, 2006

By André C. Zingano

The coal pillars in room-and-pillar mining method are subjected to vertical stress due to overburden rock mass and horizontal stress relieve due to entries excavation around them. Some coal mining companies are applying rock bolts and steel straps to improve the pillar strength, consequently to reducing the pillar size and increasing coal recovery. This kind of approach deserves some discussion, whether it is pillar reinforcement or just rib support. The efficiency of pillar reinforcement (or rib support) is directly related to the initial load capacity of coal pillar, the type of excavation, and the width to high ratio of the pillar. The objective of this paper is to understand the mechanism of pillar reinforcement (or rib support) using rock bolts and steel straps on pillar ribs. Numerical simulation taking into account the relations listed above. The results showed that the increase of coal pillar strength is very short, and there is no influence on improvement of load capacity of pillar. However, the rib support avoids block falling, rib failure, and displacement, reducing the pillar failure propagation into the pillar center. Keywords: coal, pillar reinforcement, room and pillar.

Jan 1, 2006

By John Popovich

The MICON RokLok binder system including component and consolidation processes and safety and its first aide are described. The implementation procedures and selection of injection parameters are discussed. Finally a case example of recovering a 30-ft. long roof fall in mainline haulage entry is used to illustrate the economic potential of preventive measures by RokLok injection.

Jan 1, 2001

By J. Nielen van der Merwe

Rock engineering research and technology development in South Africa only received serious attention in reaction to the Coalbrook disaster in 1960. At the time, a number of gaps in knowledge of rock related matters were identified and in the ensuing years, these were progressively attended to. The paper describes the events that led up to the Coalbrook disaster and reviews the developments that took place afterwards. The effectiveness of the research outcomes are tested by referring back to the disaster. It is concluded that tremendous advances were made but that not all the unknowns were attended to at the same level. The strength of nominally square internal pillars is the one issue that received the most attention, but the strength of barrier pillars, overburden behaviour and loading systems are still largely unknown. Due to the complexity of the remaining unknowns, they can and should be addressed by the application of back calibrated numerical models. There are no readily available simple analytical solutions. The state of mining rock engineering research in South Africa borders on an emergency. More than a 1000 years of aggregate research experience has been lost in the last three years and funding is under severe pressure. There are disturbing parallels between the current positioning of the industry as a whole and the Coalbrook mine in the years preceding the disaster.

Jan 1, 2006

By Kot F. v. Unrug

The present combination of coal market prices and reserves, situated in the Central Appalachian Coal Field, is such that mining of smaller coal reserve blocks has become economically attractive. In above drainage deposits, and particularly under mountain ridges, overburden depth can be changing within a wide range. Mines operating in these deposits are usually developing mains along the center of the ridge, with panels projecting from the mains towards the outcrop. Due to changing topography, proximity of the outcrop, and related cover depth, the panels have various lengths. In this reported case study, a mine in Pike County, Kentucky, along the Kentucky ?West Virginia border, difficult ground conditions were encountered, during the development of the mains, under shallow cover, along a narrow mountain ridge. An area having unusual density of vertical joints was encountered. Mining operations were suspended because of roof stability concerns. The ground conditions were studied, analyzed, and control measures proposed to ensure safe passage through the difficult roof area of the mine. The advancement of the mains, through this area of challenging ground conditions, was successfully completed. In this paper, ground conditions are described, with an explanation of the geologic process contributing to their formation. It is interesting to note that similar locations were predicted by the authors, to be encountered in the same mine, based upon the experience gathered from studying conditions of the case described within this paper. When approaching the predicted locations, stability problems appeared to be even more challenging than those encountered previously. Due to changes in the coal market, mine management chose to move the affected mining section to another area of the mine having better coal quality. The advancement of the mains, through the difficult ground conditions, was temporarily postponed. Based upon the analysis of a probable kinematical mechanism of blocks in the mine roof, ground control measures were proposed. The actual application of these principles proved to be appropriate, ensuring safe passage through the difficult ground conditions encountered in the mine.

Jan 1, 2006

By Thomas M. Barczak

The resultant load vector is the representation of the forces applied to a longwall roof support element by caving strata into a single, quantifiable measure of support resistance. The relatively complex kinematics of the shield support prohibit a determination of support resistance simply by summation of leg forces. A method is being investigated by the Bureau of Nines to determine the resultant load vector by instrumenting supports with pressure transducers and strain gages to measure leg, canopy capsule, and lemnisoate link forces. This concept has been laboratory tested in the Bureau's Nine Roof Simulator. Functional relationships among variables have been assessed, and confidence intervals have been established for prediction of the resultant load vector parameters.

Jan 1, 1984

By Holger Witthaus

Beside the traditional geomechanical evaluation methods the geotechnical parameters are recognized as important facts of the planning work for multiple seam mining. Standards for applied monitoring and investigation methods for geotechnical determination of drill cores, laboratory rock-tests and observation of roadheadings are the basics for rock mechanics classification and support design. The geomechanical classification is in this context an essential element. The planning procedure, as it is becoming more and more detailed, beginning with the panel layout up to the technical instructions of roadway development and design of roadheading machinery, nowadays uses a lot of geotechnical information that also are expanding to include quantitative determination of more parameters. The current monitoring system includes the description of separation planes using drill cores and roadheading observation as well as laboratory tests of rock-strength and geophysical borehole examinations. This information is analyzed within the geomechanical standard-classification. The re-engineering process of comparison the predicted support success to the actual monitoring results provides the opportunity for continuous optimization of the planning work und support design. This way of empirical analysis is used for basic planning work in Germany for decades. But using the technical standard of information technology and a centralized database now it is possible to reach quick-win effects in implementing research results on the one hand and actual experiences on the other hand.

Jan 1, 2006

By Anil K. Ray

This paper discusses in situ studies conducted at an Illinois Basin room-and-pillar coal mine to evaluate the performances of three different types of bolts under similar geologic conditions. The bolt types considered were the fully grouted passive rebar (FGPR), the resin-assisted mechanical anchor (RMAB), and the fully grouted tension rebar (FGTR). During the evaluations, the three types of bolts were installed in a single entry covering a span of three contiguous pillars with almost identical geologic conditions. The performances of the three types of bolts were investigated by instrumentting the bolts prior to installation as primary supports on cycle. Additional data on roof behavior was collected with extensometers and shear meters placed near the instrumented bolts. Excluding some time lapse right after installation, the performance evaluation of the three bolt systems was based on the data collected for over a year. Based on this study, it was found that the axial loads measured in the different bolt types did not show any identifiable patterns under the prevailing geological conditions at the mine. Therefore, the assumption that active bolts must be superior to passive ones is not always valid. Even though the studied mine did not have any thinly laminated, weak rocks in the immediate roof, the passive bolts performed as well as the active systems.

Jan 1, 2012

By Anthony T. Iannacchione

The Roof Fall Risk Index (RFRI) is a new method introduced by the National Institute for Occupational Safety and Health (NIOSH) to assist the underground stone mine operator in 1) assessing defects the mine strata and 2) rating the relative roof fall risk these defects pose. The RFRI utilizes observational techniques to identify defects in the roof strata caused by local geologic, stress, and mining conditions. Assessment values for ten defined defect categories provides the foundation for estimating a range of risk conditions between 0 and 100 that define the potential for a roof fall. This paper examines how the defect information is collected using two field verification sites and proposes methods to analyze the RFRI data. These examples provide information on how well the method replicates observed conditions and how it might be applied in practice.

Jan 1, 2006

By Kristineq Pankow

The August 2007 Crandall Canyon mine disaster raised national awareness of mining-induced seismicity (MIS) in Utah as well as general interest in how seismic monitoring might improve mine safety in the region. Unlike the situation in most other mining areas in the U.S., local seismographs in Utah?s Wasatch Plateau (WP) and Book Cliffs (BC) coal fields are an integral part of a modern real-time earthquake information system developed by the University of Utah Seismograph Stations (UUSS) as part of an Advanced National Seismic System. The UUSS earthquake catalog contains a continuous record of MIS at all active mine sites in the WP-BC region since 1978 (more than 18,000 seismic events = M 4.2). We describe characteristics of MIS and current seismic monitoring capabilities in the WP-BC region. We then demonstrate, using MIS from an example Utah coal mine, the ability to refine event locations with estimated absolute errors of ~200 m or less using a combination of (1) a double-difference relocation methodology and (2) ground truth information provided by mine operators. This approach enables sufficient spatial resolution to correlate MIS with mining activities, providing a useful tool to help improve mine safety.

Jan 1, 2008

By Peter Fischer

Between 45,000 and 50,000 claims for subsidence are submitted each year to the German hard coal industry. In order to improve the service to claimants a quality management was established in 2005. This paper describes the process now used for handling these claims. A quality check has also been carried out by way of a customer survey, which was performed by an independent research agency. The results of the survey are presented in this paper. In Germany, research into mining subsidence mainly involves the prediction of ground movements caused by deep mining operations. Special areas of research are subsidence reducing aspects of the extraction panel planning, especially from the point of view of mining dynamics, as well as securing and restoration measures. This work seeks to prevent or minimize mining-induced damages close to the surface, for instance, buildings or infrastructure installations (such as pipelines), or underground mine openings (e.g. shafts). Roof collapses and surface fractures caused by shallow mine workings of an earlier era currently constitute a special area of investigation.

Jan 1, 2006