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By Christopher Newman, Zach Agioutantis, Gabriel S. Esterhuizen

"As conventional underground deposits are continuing to be depleted, mining operations have been forced to produce at greater depths and in more geologically and geometrically challenging conditions. Over the past decade, there has been a global increase in the application of cemented paste backfill (CPB) material as a means of ground support in open stope mining operations. Although CPB has been extensively used within the industry, there are many fundamental factors affecting the design of safe and economical fill structures that are still not well understood. A critical design issue with respect to backfilled stopes is determining the stress state within the fill material as well as the surrounding rock.This paper details the development of a reliable numerical model for the simulation of stress distributions around the excavated stope area, as well as through the backfill material. Through discussions on modeling parameters and output results, one is provided with insights into the mechanisms of stress redistribution allowing for further accuracies in simulating the behavior of the CPB material as well as its interaction with the surrounding rockmass.INTRODUCTION AND BACKGROUNDModern technological innovations with respect to material processing, cementitious composition and chemical additives, and material transportation have provided the mining industry with a ground support material that greatly reduces mine waste costs, while, when used appropriately, increases reserve production and mine stability. As mining operations continue to produce in more complex geologic and geometric conditions, cemented paste backfill (CPB) has become commonly employed within primary-secondary excavation-support sequencing allowing for total extraction of the mining reserve. As shown in Figure 1, primary stopes are initially excavated and then backfilled in a two-staged pour: plug and final pours. The plug (initial pour), is initially placed at the bottom of the stope with a CPB material of heightened cementitious material. While the plug provides a strong foundation on which to build the rest of the CPB structure, it also provides protection against barricade breakthroughs (Li and Aubertin, 2009), as well as providing operations a means of underhand stope-and-fill mining through the use of an artificial sill pillar (Hughes, et al., 2011). Following placement, the plug is allowed to cure to a designated design strength. Upon completion of the plug, a less cementitious “final” pour material is used to backfill the rest of the excavated area."

Jan 1, 2018

By Donovan J. Benton

Photogrammetric methods are advancing rapidly and show considerable promise as a ground control research tool. The ability to quickly capture three-dimensional geometry, especially changes in geometry, in underground and laboratory settings is a significant advance from point distance measurements. Photogrammetry is being applied in both of these settings as part of the NIOSH ground control research. This paper describes these applications and the equipment and software being employed. It also describes tests conducted to quantify the accuracy of these systems. Accuracy varied with system specifics and procedures. A factory-calibrated camera produced results within 1/32 of an inch, plus 0.04%. A user-calibrated camera was found to be less accurate, at 1/20 of an inch, plus 0.24%. These calibrations demonstrate that photo grammetry can produce research quality measurements in laboratory and mine settings.

Jan 1, 2014

By Kourosh Shahriar, Kazem Oraee, Ezzeddin Bakhtavar

"In this paper, a relationship between dependant parameters and the crown pillar thickness is first introduced. This relationship defines geotechnical problems caused by thin pillars and economic considerations created by pillars that are thicker than the optimum size. For this purpose, a dimensional analysis as an effective physico-mathematical tool was used. This technique restructures the original dimensional variables of a problem into a set of dimensionless products using the constraints imposed upon them by their dimensions. A model is hence introduced that calculates the optimum pillar thickness. The relationship introduced here and the method applied can be used by mining engineers in all situations where a combined open-pit and block caving method is deemed to be the most appropriate mining method.INTRODUCTIONMany deposits can be mined entirely with the open-pit method; others must be worked underground from the very beginning. In addition, there are the near-surface deposits with considerable vertical extent. Although they are initially exploited by the open pit method, there is often a ""transition depth"" where decision has to be made about changing to underground methods.Some of the biggest open-pit mines worldwide will reach their final pit limits in the next 10 to 15 years. Furthermore, there are many mines planning to change from open-pit to underground mining due to increasing extraction depths and environmental requirements. In this way, it is likely that block and/or panel caving will enable the operations to continue achieving a high production rate at low costs as an underground method (Bakhtavar et al., 2009).In these cases, it is often necessary to consider a crown pillar beneath the transition depth (open-pit floor) before starting an underground caving stope method (Figure 1).There are generally two kinds of crown pillar: a ""surface crown pillar"" and ""crown pillar between open-pit and underground mining."" In general, they both play the similar role in mining. Since the primary purpose of a surface crown pillar is to protect surface land users, the mine, and those working in it from inflows of water, soil, and rock; it is vital that the surface crown pillars remain stable throughout their life. When a crown pillar could potentially remain between open-pit and underground mining it is specially proposed to prevent water entering from the open-pit floor into the stope, as well as to reduce open-pit wall and floor caving."

Jan 1, 2010

By Martin McKinnon, Guy Reed, Russell Frith

"It is arguable that the development of reinforcing roof bolting systems has largely stagnated in recent times, primarily due to the prevailing industry view that few, if any, further improvements can be made to what currently exists. However, this paper contends that reinforcing roof bolting systems can be further refined by considering both the specific manner by which horizontally bedded roof strata loses its natural self-supporting ability and the specific means by which reinforcing roof bolts act to promote or retain this natural self-supporting ability. The Australian coal industry insists on minimising bolt-hole diameter to maximise load transfer and on targeting full-encapsulation by any means necessary. This has led to a significant, albeit unintended, consequence in terms of overall roof bolting effectiveness, namely increased resin pressures during bolt installation and the associated potential for opening bedding planes that may have, otherwise, remained closed during the bolt installation process. Given that the natural self-supporting ability of roof strata is strongly linked to whether bedding planes are open or closed, logically, minimising resin pressures should be a significant benefit. This paper focuses primarily on three key issues that relate directly to the function of the roof bolting system itself: (i) the importance of proper resin mixing in the context of maximising load transfer strength and stiffness, (ii) the importance of minimising resin pressures developed during bolt installation, and (iii) the importance of maximising the effectiveness of the available bolt pre-tension. All mine operators should be invested in improving the individual effectiveness of each installed roof bolt, even by relatively small incremental amounts, so this is an important topic for discussion within the mining community."

Jan 1, 2017

By C. Thomas Blevins

This paper is intended to be a hands on experience account about ground control in a Southern Illinois coal mine. Its aim is to show how a combination of real world mining practices and constraints along with practical engineering theory mesh together to formulate a ground control program in adverse conditions. These conditions - your typical localized slips, splits, rolls, clay intrusions, water, changing types and thicknesses of materials, etc. - being amplified by a very strong horizontal stress field. A review will be made about the formation of the overall ground control plan and to what degree it has been successful. A presentation of the various roof control systems and their component parts, how these systems were developed, and the theory behind them will be made. The pointing out of some of the flaws that we found in the components, installations, and/or theory will be part of this presentation. A brief look at some of the efforts in the following items will be made: quality control of the roof control products; using the computer to help keep track of roof control information and soliciting help from various universities, governmental agencies and consultants to give different perspectives to the problem.

Jan 1, 1984

By Keith A. Heasley, Jian Yang

"LaModel uses a laminated overburden boundary-element model and can calculate not only seam-level stresses and displacements but also surface subsidence for thin tabular deposit such as coal seams (Heasley, 1998). Up to this point in time, the material property wizards in LaModel have primarily been designed for calculating accurate stress distributions in single- and multipleseam situations, and for investigating and optimizing pillar sizes and layouts in relation to overburden, abutment, and multipleseam stresses. However, the critical input parameters that will give the most accurate seam-level stress distribution do not necessarily produce the best surface subsidence prediction. The objective of this paper is to develop a methodology for calibrating the critical input parameters in LaModel to optimize surface subsidence prediction.For optimum surface subsidence prediction, it was found that the gob convergence (as defined by the final gob modulus) and the overburden stiffness (as defined by the lamination thickness) were the two most critical parameters that needed to be calibrated (Heasley, 2016). By calibrating numerous panels with various widths and depths, a formula that provides the optimum final gob modulus to use for subsidence prediction was developed. Also, three different empirical formulas for optimizing the lamination thickness as a function of overburden depth and/or the panel width to- depth ratio were determined for the three cases: supercritical panels, and subcritical panels with and without offsets. Further, if the user has measured data for subsidence factor and angle-of draw, the optimum final gob modulus and lamination thickness can be determined from the measured data. These new subsidence prediction formulas are being implemented into new material wizards in LaModel.INTRODUCTIONIn the past few decades, with the increased need for highly productive mining techniques, full extraction mining methods have been increasingly employed in the U.S. coal mining industry. These total extraction mining methods, which include both longwall mining and room-and-pillar retreat mining, normally cause immediate roof caving and the associated surface subsidence. These methods can be highly productive and cost-effective, but the associated surface subsidence can cause damage to surface structures and negatively impact the surface environment (Peng, 2008). Therefore, a reliable program for predicting the surface subsidence associated with full extraction mining is required for appropriately engineering and managing the surface subsidence impacts of full extraction mining."

Jan 1, 2016

By David R. Burkhard

"Comparative roof beam performance, as measured by delamination within the bolted horizon, was used to evaluate two types of roof bolt drill hole geometries in a development setting. Short encapsulation pull tests had demonstrated a higher grip factor in drill holes featuring helical grooves in the side walls in comparison to drill holes featuring continuous smooth to slightly rough walls. The study incorporated the two geometries during development mining in which fully grouted mechanically anchored bolts were installed as primary roof support.bolts were installed as primary roof support.The study site, in an entry adjacent to a longwall panel, was instrumented with extensometers and data collected during longwall retreat. Statistical analysis was conducted to validate null and alternative hypotheses used to compare drill hole geometries. Analysis yielded no statistically significant difference between drill hole geometries. Inspection of the data does reveal less delamination within the smooth walled site in comparison to the site containing grooved hole geometry.INTRODUCTIONFrom their introduction as a means of ground control over sixty years ago, roof bolts today are the primary mechanism of roof support utilized throughout mining. Whether through suspension, keying, or beam building, roof bolts are employed to reinforce the inherent strength of the strata comprising the immediate roof with the goal of creating a competent bolted horizon of sufficient load bearing capacity to be self-supporting for a given mine's design life, stress regime, and geomechanical properties.For grouted bolts in sedimentary strata, axial loading due to vertical rock movement and bending due to horizontal rock movement are the principal means of loading (Signer, 2000). Regardless of the type of bolt and extent of grouting employed, the success of any roof bolting design is determined, to a large extent, by the effectiveness of load transfer between the rock, grout, and bolt.At San Juan Mine, an underground longwall mine located in the northwestern corner of New Mexico, a number of different roof bolt types, grades, and lengths have been used over the years in an effort to optimize primary roof support. One common denominator shared throughout has been the use of full length grout. Load transfer for full length grout is achieved primarily through mechanical bonding between the grout and rock. It is this interaction that is the focus of the study described in this paper. The study assessed and compared two types of bolt hole geometries employed during gate road development at San Juan. Underground instrumentation and evaluation of the bolted roof provided the means of assessment and comparison."

Jan 1, 2016

By Joe E. Bryan, John P. McDonnell

"Underground mine rib stability is an ongoing safety issue in all mining applications. Rib-related accidents present at least as many problems as roof-related ground control. Underground coal mine rib safety is continually emphasized as a primary safety concern at every mining operation. The application of rib support materials is increasing as more difficult mining conditions are experienced due to deeper cover, more variable depositional environments, thicker seam heights, and multi-seam mining effects. As the coal seams become thicker, the need for rib control increases. A variety of rib control methodologies has been documented and research continues on mine design methods and support techniques to reduce or eliminate rib-related accidents.This paper presents an alternative rib bolting technology using proven conventional rib support systems that allows mine personnel to more efficiently install rib support during development operations. This alternative rib bolting method allows for additional rib support with a single support installation.INTRODUCTIONRib control continues to garner the watchful eye of both concerned operators and government officials due to many factors: inherent safety within entries and crosscuts, actual rib stability history, safety improvement, cost control, improved mining methods, and maintaining production goals. As demonstrated through many years of actual practice, desired outcomes can be achieved by scrutiny, innovation, and combining improved practice methodologies.Rib surface control continues to be a necessary part of the production process. However, production and safety issues persist at the point of installation using current control apparatuses and methods to install rib controls. Among others, current issues of rib control are quantity of bolts required, overall time required for installation, ease of apparatus installation, flexibility of the system for appendage installation and operator exposure. A need exists to decrease the time miners spend installing rib control apparatuses, while increasing the safety of such installation processes. At present, installing rib control devices (primary rib bolts, plates, mesh, and, in most cases, secondary rib bolts and plates) is performed in a very congested area and is time-consuming process at the primary coal-winning area: the face. The MatLok system addresses these problems."

Jan 1, 2015

By Brent A. Slaker, Khaled M. Mohamed

"Understanding coal mine rib behavior is important for inferring pillar loading conditions as well as ensuring the safety of miners who are regularly exposed to ribs. Due to the variability in the geometry of underground openings and ground behavior, point measurements often fail to capture the true movement of mine workings. Photogrammetry is a potentially fast, cheap, and precise supplemental measurement tool in comparison to extensometers, tape measures, or laser range meters, but its application in underground coal has been limited. The practical use of photogrammetry was tested at the Safety Research Coal Mine, National Institute for Occupational Safety and Health (NIOSH). A commercially available, Digital Single-Lens Reflex (DSLR) camera was used to perform the photogrammetric surveys for the experiment. Several experiments were performed using different lighting conditions, distances to subject, camera settings, and photograph overlaps, with results summarized as follows: The lighting method was found to be insignificant if the scene was appropriately illuminated. It was found that the distance to the subject has a minimal impact on result accuracy, and that camera settings have a significant impact on the photogrammetric quality of images. An increasing photograph resolution was preferable when measuring plane orientations; otherwise a high point cloud density would likely be excessive. Focal Ratio (F-stop) changes affect the depth of field and image quality in situations where multiple angles are necessary to survey cleat orientations. Photograph overlap is very important to proper three-dimensional reconstruction, and at least 60% overlap between photograph pairs is ideal to avoid unnecessary post-processing. The suggestions and guidelines proposed are designed to increase the quality of photogrammetry inputs and outputs as well as minimize processing time, and serve as a starting point for an underground coal photogrammetry study.INTRODUCTIONThe stability of underground mine ribs has been a safety concern for underground coal mines for decades. Unfortunately, the average rib fatality rate has been about 1.3 per year between 1996 and 2013 (Jones et al., 2014). In an effort to better understand coal rib behavior, photogrammetry is being investigated in this study as a measurement tool for surveying ribs in an underground coal mine environment."

Jan 1, 2016

By Thomas A. Cook

The effectiveness of tensioned roof bolt systems has been well researched and documented over the years (Stankus, 1990, 1991, 1997; Guo, 1997; Denton, 2000; Su, 2007). Higher and more consistent installed tension has been shown to improve the beaming effect and associated roof stability especially in highly-stressed, weak, laminated roof strata. To accomplish higher and more consistent bolt-installed tensions, various types of anti-friction washers have been developed and applied to many types of tensioned roof bolt systems. In addition to increasing bolt-installed tension, these washers also provide a lubricating effect that minimizes sparking during the bolt torqueing cycle. The most popular and widely used anti-friction washer configuration consists of a plastic washer that is used in conjunction with a standard hardened steel washer. This washer configuration has performed well in the field in terms of increasing the bolt-installed tension (or plate load) and the related tension/torque ratio (the amount of tension achieved per one ft-lb of applied torque). However, the installed tension does not always maintain consistency. One reason for this inconsistency is that the plastic anti-friction washer sometimes dislodges and shreds or tears before the bolt torqueing cycle is complete. This condition prevents the plastic washer from acting as an anti-friction medium for the entire torqueing cycle. Jennmar Corporation and Keystone Mining Services, LLC, developed the ?TT? washer in early 2012. The ?TT? anti-friction washer is comprised of two zinc-coated (galvanized) hardened steel washers that are joined together with an exclusive polymer. The ?TT? washer has been extensively tested and applied in the Sewickley, Pittsburgh, and Indiana #5 coal seams. The test results indicate an average increase in installed load and tension/torque ratio of 20%. More importantly, the installed load consistency improved, with a significant reduction in the standard deviation of values. This paper will detail the development and testing of the ?TT? anti-friction washer with case studies of actual mine applications.

Jan 1, 2014

By Syd Peng, Gamal Rashed

"Bumps in coal mines have been recognized as a major hazard for many years. These sudden violent failures around mine openings have compromised safety, ventilation and access to mine workings. Previous studies showed that the violence of coal specimen failure depends on both the interface friction and width-to-height (W/H) ratio of a coal specimen. The mode of failure for a uniaxially loaded coal specimen or a coal pillar is a combination of both shear failure along the interface and compressive failure in the coal. Unstable interface failures provide a sudden de-confinement to coal rib, thus triggering uns and compressive failure in the sidewalls. The compressive failure of a coal specimen or a coal pillar can be controlled by changing its W/H ratio. As the W/H ratio increases, the ultimate strength increases. With a proper combination of interface friction and the width-to-height (W/H) ratio of pillar or coal specimen, the mode of failure will change from sudden violent failure, which is brittle failure to non-violent failure, which is ductile failure. The main objective of this paper is to determine at what W/H ratio and interface friction the mode of failure changes from violent to non-violent. In this research, coal specimens of width-to-height ratio ranging from 1 to 10 were uniaxially tested under two interface frictions of 0.10 and 0.25. The results are presented and discussed.INTRODUCTIONCoal mine bumps are sudden, violent bursts of coal from a pillar or pillars or a block of coal, resulting in a section, the whole pillar, or the solid block of coal being thrown into an open entry. These bursts are accompanied by very loud noises (Peng, 2008). Several case histories in mining have long described coal pillars or coal faces failing violently with an accompanying ejection of debris and broken material into the working areas of the mines (Campoli et al., 1987; Osterwald, 1962; Peperakis, 1958; Garvey et al., 2013). Because of the catastrophic nature of these sudden failures, understanding the causes of coal mine bumps is essential to create a safe underground working environment. This phenomenon has motivated many ground control researchers to conduct extensive field investigations throughout the past century. Rashed and Peng (2014) compared the mechanical properties of two kinds of coal, one from bump and the other from non-bump-prone mines. They found that coal itself does not play any significant role in coal bumps and recommended that future research should focus more on the local variation of geological conditions such as the interface friction between pillar and roof and between pillar and floor."

Jan 1, 2015

By Denise Y. Dixon

The objectives of this study were to (1) document the hydrologic impacts of longwall mining on ground water, (2) identify the factors which affect the extent of dewatering, and (3) develop empirical trends to predict the extent of dewatering and recovery in advance of mining. The study was confined to three mine sites in north-central West Virginia. At each site, available ground water supplies were identified and monitored for dewatering effects and recovery. Mine A, located in Upshur County, West Virginia, has relatively thin overburden (approximately 715-280 feet). At this site domestic water supplies and specially constructed monitoring wells were monitored, continuing with an earlier study done by Cifelli arid Rauch. Most such supplies were completely dewatered over the longwall panel. Some of these wells have shown significant recovery, especially near a stream. Extensive monitoring of two nested piezometer wells revealed that dewatering generally started in advance of undermining in the lowermost monitored overburden zones first and then progressed upwards. Most dewatered wells completed in bedrock have shown no recovery, except. for valley drilled wells located within 100 feet of a Stream. Affected dug wells completed in valley alluvium rend located within 200 feet. of the nearest stream have shown significant recovery. Some wells have partially collapsed following mine subsidence. Mine B, having relatively thick overburden (approximately 585 to 900 feet), is located in Monongalia County, West Virginia. Ground water supply surveys have been conducted there in an attempt to study past dewatering effects. Owners reported Chat several wells were dewatered by longwall mining arid vertical air shafts that preceded longwall mining. Dewatered wells over longwall panels hove shown some recovery within 3 ½ years of mining. Mine C also has relatively thick overburden (approximately 585-900 feet), and is located mostly in Greene County, Pennsylvania. In addition to a survey of domestic water supplies at this site, five specially constructed monitoring wells were tested. The shallow monitoring wells suffered drops in water level due to mining but totally recovered within one day to three weeks after dewatering occurred. However, they did occasionally exhibit partial collapse during mine subsidence. Subsidence fracturing was beneficial in increasing the lateral hydraulic conductivity by a factor of about S to 22 for rock strata located within 124 feet of the surface, indicating enhanced shallow aquifer potential. One deep well suffered both partial dewatering and structural damage, with the state of water recovery bring uncertain. Also, two shallow domestic supplies out of five located over the mine were reportedly dewatered, but this claim could not, be substantiated.

Jan 1, 1988

By Ke Yang

"Engineering practices have shown that the skip-fault longwall mining is frequently used when faults with offsets larger than 1 Om are present. Since the skip-fault longwall mining not only reduces the recovery rate of coal reserves, but also increases the cost due to developing another setup room on the opposite side of the fault and moves the longwall into it. The coal pillar so created induced residual stress in and thus affects the safe mining of adjacent coal seams. In order to investigate the influence on panel layout and retreat by a l 6.5m offset normal fault, the similar material simulation model was constructed based on the geological and engineering conditions of No.13 coal seam in the western district of Liuzhuang coal mine employing the down-dip longwall mining. The characteristics of deformation, movement and failure of the overlying strata and abutment pressure when the face cut through the hangingwall and footwall of a normal fault were obtained. There were significant differences between the hangingwall and footwall as conformed by the equilibrium structure model. The results showed that superposition of the tectonic stress from a normal fault of large offset and that induced by mining is one of key factors that lead the severe pressure difficult to control during panel retreating from the hangingwall to footwall. Accordingly, the technical solutions for a fully mechanized mining face directly cutting through the fault are presented and optimized, and the applications of the technical solution in Panels 171301and171303 of Liuzhuang mine enabled them to complete the mining safely and efficiently. INTRODUCTIONFaults have been one of the important technical factors in underground coal mining l1-2i. Engineering practice has shown that the methods of mining through the faults depend on the seam thickness, seam dip angle, offset of fault throw, equipment height, rock strength, and advancing direction l3-5l. In the fully-mechanized longwall mining, the face normally proceeds to cut through the fault directly if the offset of the fault less than 5m, and to skip Uump) the fault if the offset is larger than 5m. In the former case, the most important problem is to efficiently control or avoid roof fall accidents (i.e., crushing, falling, pushover, and rock burst). In the latter case, the most important problem is very expensive to drive a new setup room and move the face equipment to it. The skipped coal pillar may poses problems for mining in adjacent seams."

Jan 1, 2016

By Markus Papst, Denise Millier, Daniel Beckers, Axel Preusse

"At an open-pit lignite extraction mine in Germany, groundwater has to be pumped over a large area, which leads to subsidence at the surface. As long as the geology of the area of influence is homogeneous, the subsidence is uniform and has marginal influence on buildings.Since the geology of many regions is characterized by faults, there are different rates of subsidence along those faults, which can lead to considerable consequences. Those different rates of subsidence on both sides of a geological fault are associated with the structure of the geology and soil mechanical properties. Horizons with various thicknesses and types of soil are affected differently by the groundwater pumping because of the offset of the faults, and thus react dissimilarly to dewatering.The smaller the grain of the geological horizon, the stronger the chance of shrinking, which leads to a stronger effect at the surface; therefore, dewatering impacts on clayey soil are different to those on sand and gravel. Regions consisting of meadows with turf inclusions are endangered as well; compared to the surrounding geology, those areas react in an entirely different way to water removal, which leads to immense differences in subsidence.The differences in area and respective subsidence impacts, as well as if it is possible to localize those areas, is an issue which needs to be analyzed. Furthermore, detailed mapping can help in the development of future forecasts about those subsidence differences and can also help with monitoring geological faults. In the context of subsurface spatial planning, this mapping has to be kept under review medium- to long-term.INTRODUCTIONThe utilization of underground mining is of increasing significance and of high interest, both for the common good and for future generations. For decades, humanity has been extracting resources from the subsurface, and salt, coal, lignite and water - just to mention a few resources - have been extracted from underground (Sailer, 2013)."

Jan 1, 2016

By Stephen R. Iverson, Jeffrey C. Johnson, Donovan J. Benton, Michael J. Raffaldi, Lewis A. Martin

"The NIOSH ground control safety research program at Spokane, Washington, is exploring applications of photogrammetry to rock mass and support monitoring. This paper describes two ways photogrammetric techniques are being used. First, photogrammetric data of laboratory testing is being used to correlate energy input and support deformation. This information can be used to infer remaining support toughness after ground deformation events. This technique is also demonstrated in a field application. Second, field photogrammetric data is compared to crackmeter data from a deep underground mine. Accuracies were found to average 8 mm, but have produced results within 0.2 mm of true displacement, as measured by crackmeters. Application of these techniques consists of monitoring overall fault activity by monitoring multiple points around the crackmeter. A case study is provided in which a crackmeter is clearly shown to have provided insufficient information regarding overall fault ground deformation. Photogrammetry is proving to be a useful ground monitoring tool due to its unobtrusiveness and ease of use.INTRODUCTIONNIOSH Mine Safety ResearchPhotogrammetry systems have been implemented by the National Institute for Occupational Safety and Health (NIOSH) as part of its ground control research to improve mine safety. Conventional monitoring of ground movement has typically focused on movement of a few discrete points that are marked or anchored to instruments. Loss of a designated point or anchor, or the ability to identify a stable point in an unstable area, have often frustrated monitoring efforts. NIOSH researchers are using photogrammetry to conduct full-field measurements of rock surfaces underground. Periodic measurements of the entire surface of a ramp allow patterns of displacement to be observed. Full-field measurements provide much more insight into ground behavior than point measurements.BackgroundPrevious work by Benton, et al. (2014) discussed laboratory calibration and verification testing of two photogrammetry systems being used by NIOSH researchers. Both systems utilize stereoscopic image pairing techniques for photogrammetric reconstruction. This paper discusses how a laboratory system was used to conduct volumetric analyses of testing of shotcrete panels with varying types of reinforcement. The laboratory system was found to be accurate to within 2 mm. Additionally, a field photogrammetry system was found to produce linear measurements within 1 mm of known lengths in laboratory conditions. This system is currently being used at a deep underground mine to observe ground support conditions and deformations that have occurred. This paper discusses comparison of preliminary volumetric measurements of rib deformation to laboratory tests, as well as comparison of the field system against a crackmeter installed across a fault surface where it intersects the ramp."

Jan 1, 2015

By Klaus Opolony

The world's most popular method of longwall mining requires multiple entry systems for the panels. In contrast to this mine layout the roadways in German coal mining are used for advanced mining from the rock mechanic point of view or are even re-used by a second panel. This procedure of roadway use is presented within this paper using a 3D visualisation software tool. In the previous conferences in Morgantown several papas had addressed the basics of rock mechanic background, planning tools and variants. This paper gives a practical case study for reuse of a roadway in a German coal mine. The heading and the use of various alternatives are compared under the aspect of efficiency and costs. Within the comparison the specific requirements and benchmarks of German coal mines are taken into consideration. The costs for a multiple entry system and first of all the development rates that can be achieved with common road heading systems are compared with international layout alternatives. A prospect includes a discussion of pro and con for various development methods. Devices are given due to this prospect if and how multiple entry systems are applicable to German coal mines. The paper gives an initial point for international comparison and is a base for further discussion.

Jan 1, 2003

By Long Fan, Shimin Liu, Guijie Sang

"Weak shale roof falls have long been the main cause for fatalities in underground coal mines. Moisture-induced swelling is one of the root causes for the degradation of roof shales. In this study, slake durability tests are conducted on shale samples collected from Illinois basin coal mines, and different levels of durability are analyzed according to Gamble slake durability classification. There are two main mechanisms influencing the shape of retained fragments after two cycles of wetting and drying: mechanical abrasion and swelling pressure. A prototype optically based shale swelling apparatus is designed and manufactured for the shale free-swelling measurement. The experimental results suggest that swelling pressure tends to deteriorate shale laminations. Moisture-induced swelling of the No. 6 roof shale from Bear Run Mine was measured under 100% relative humidity condition. The measured swelling strain normal to beddings is ~5 to 7 times greater than the swelling strain parallel to beddings. This suggests that interlayer expansion plays a key role in moisture-induced swelling. Cracks induced by swelling pressure tend to occur along the bedding plane and lead to shale deterioration. INTRODUCTION Background Ground falls have long been the cause for nearly 50% of all fatalities in underground coal mines and continue to be one of the greatest safety hazards in underground spaces. Among the various ground fall hazards, roof failure takes up 23% of total fatalities in underground coal mines, of which 13% are due to skin failure and 10% are due to massive roof falls (Mark, Pappas, and Barczak, 2011). Roof failures associated with weak shales are summarized in previous studies (Molinda and Mark, 2010; Aughenbaugh and Bruzewski, 1973; Bajpayee, Pappas, and Ellenberger, 2014; Murphy, 2016). For mine roof instability and failure, two aspects can explain the failure mechanism of weak roofs. One is the elevated stress concentration in lateral direction due to the mining-induced excavation and its stress redistribution around the mine opening (Song and Stankus, 1997; Fan and Liu, 2017; Hill, 1986). The other mechanism is the passive stress-relief due to the strength weakening induced by the ambient moisture and temperature fluctuations during a period of time. Shale is moisture sensitive and presents a lower durability if it is exposed to a highly humid environment for a long time, thus leading to roof deterioration and instability in underground coal mines (Aughenbaugh and Bruzewski, 1976; Stateham and Radcliffe, 1978; Chugh and Missavage, 1981; Klemetti, Oyler, and Molinda, 2009). It is well known that shale is a clay-bearing sedimentary rock and that clay minerals are water sensitive. The moisture uptake for shale will induce the micro-deformation of a shale matrix, thus the structure and strength of shale is a function of time and intensity of moisture exposure. All mine engineers notice moisture-induced shale deterioration; however, the underlying mechanism(s) are still not fully understood due to the complexity of geophysical-chemical water-shale interactions (Huang, Aughenbaugh, and Rockaway, 1986; Hensen and Smit, 2002; Diaz-Perez, Cortés-Monroy, and Roegiers, 2007). The coal mining industry is still in the process of finding a technically sound, cost-effective technology to prevent this unexpected and unpredictable shale roof failure. Therefore, understanding how the moisture-sensitive shale responses to various ambient moisture and what role exposure duration plays in shale roof failure is key to prevent unexpected roof incidents, which will lay the foundation for the long-term roof support design and ground control management."

Jan 1, 2017

By Paul L. Tyrna

The Fola Coal Co., LLC No 2 surface mine, located in Nicholas and Clay Counties, WV, exploits up to nine coal seams by contour, highwall, and mountain top removal mining methods. After encountering faults, areas of highly fractured coal, and subsidence failures. the mine requested a lineament analysis from the Mine Safety & Health Administration's (Pittsburgh Safety and Health Technology Center) Roof Control Division. The 31 km2 study area was viewed on a LANDSAT-5 band 4 (near infrared, 0.76-0.90 µm wavelength) satellite image with ERDAS Imagine 8.4 software. The software allows image examination under artificial sun azimuths and elevations, resulting in variable tonal characteristics. The study area image was viewed in 45° azimuthal increments from 000° to 315° at artificial sun angles of 10°, 30°, 50°, and 70°, yielding 32 separate images. The interpretation process developed by MSHA Roof Control personnel identified 16 northeast-striking and one northwest-striking lineament that intersected mine property. Faults and areas of roof instability corresponded well with lineaments identified in the study. Successful lineament identification prompted mine management to incorporate lineament analysis as a mine-planning tool for adjacent property, thereby identifying in advance areas that could adversely affect safety and production.

Jan 1, 2001

By Steven Derycke, Stephen C. Tadolini, Anand Bhagwat

"The tensile and shear strength of intrinsic bolting support systems has always been a major concern of designers. A comprehensive laboratory testing program was designed to evaluate the tensile and shear strength of individual wires and completely wound PC-strand cables. PC-strand cables with smooth wires and the recent anchorage enhancement innovation of indentation were evaluated and compared. The testing protocol detailed in ISO Standard 15630 utilizes a mandrel system that was investigated at 3 different diameters which alters the wire to mandrel ratio from 2:1 to 9:1. The results demonstrate that the difference between smooth and indented wires is statistically insignificant when larger diameter mandrels are used, and that indentation does not adversely affect strand properties and performance. Insight into the shearing mechanism and evaluation techniques are discussed with the introduction of triaxial loading to describe the PC-strand tensile and shearing mechanisms. Another important result indicates that the shear strength of PCstrand cable bolting systems has a greater shear strength value than traditional steel bar bolting systems.INTRODUCTIONPC-strand cable bolts have proven to be a global cost effective ground control solution in metal/non-metal and coal mines. The inherent strength to weight ratio of cable supports, combined with flexibility has been used in underground entries that range from 20 to less than 1.2 m in height (65 to 4 ft). In coal mining, the systems are used as primary and secondary support installed both passively or actively with installation tensions that range from 38 to over 178 kN (8,500 to 40,000 lbs) . While cable can be specified in several diameters, the most predominant sizes in the US remain 15.2mm (0.6 in) and 18mm (0.7 in). The capacity of the systems defined in the ASTM 432-13 is 90% of the minimum strand strengths of 260 kN (58,600 lbs) and 320 kN (72,000 lbs), respectively.Cables are not only suitable to support vertical loads, but are also often used to effectively support fractured and jointed materials and can be exposed to shear forces across the wound PC-strand structure. In fact, Goris et al. reported that cable bolts placed across jointed surfaces could more than double the shear resistance. These results were duplicated for both smooth and rough jointed surfaces (Goris et al., 1996). An example of tensioned cable bolts used to support a fractured and sliding roof in a longwall tailgate entry is shown in Figure 1."

Jan 1, 2015

By Joao Felipe Costa, Jair C. Koppe, Andre Zingano, Cleber Gomes

"Run-of-mine Brazilian coal has high ash content and low calorific power. Therefore, the coal must be washed to achieve the power plant specifications for burning coal. A large amount of waste results from the coal preparation, and it must be disposed of in waste piles or waste dams, depending on the material size. These waste disposals are the cause of serious environmental problems, not only in the short and medium terms, but mainly in the long term, due to the risk of provoking acid drainage or spontaneous combustion. Waste disposal requirements also demand large areas. Other problems include the pillar and roof stability in abandoned and mined out areas, building of edifices on the old and active mines, and mining under urban areas. To solve these problems simultaneously, backfilling the entries in mined out areas began with two objectives: to understand the mechanical behavior of the filling material and to model the backfilling of room-and-pillar coal mine entries through numerical simulation. Laboratory tests were performed for different filling material (with and without cement) to determine its mechanical properties and failure criteria. Based on this study, it was possible to conclude that the backfill method is a good strategy to improve the ground stability in room-and-pillar coal mines for the long term, especially for weak coal seams, and to reduce the quantity of material on waste piles on the surface.INTRODUCTIONRun-of-mine (ROM) Brazilian coal has high ash content and low calorific power. Therefore, the coal must be washed to achieve the power plant specifications for burning coal. Two types of waste are associated with power plants that bum coal for energy generation: 1) the waste from the coal preparation plant and 2) the ash from the power plant after coal burning.The Brazilian coal ash content in the ROM coal is between 45 and 55%. The clean coal is 20 to 30% ash for 4,500 kcal/kg (18,000 BTU). The coal preparation plant recovery is only about 35%. Santa Catarina State (SC) produces about 7 million tons/year of ROM coal, which results in a total of 4.5 million tons of waste. This is a large amount of waste that must be disposed of in waste piles or waste dams, depending on the material size. The waste and ash content is represented by silicate materials, such as clay and sand, and by sulfide materials, like pyrite and organic sulfur (between 1and5%)."

Jan 1, 2010