Search Documents

By Yongjie Yang

Experimental study on the strength and deformation characteristics of coal under cyclic loading provides guidance for designing coal pillar which is subjected to repeated mining influence during mining. This paper studies the strength, deformation and fatigue process of No.3 coal from Xinhe Colliery under cyclic loading by the MTS815.03 servo-controlled rock mechanics test system. The results indicate that coal is more susceptible to fatigue damage than other hard rocks. Under uniaxial cyclic loading, the fatigue failure ?threshold value? of coal is smaller than 78% of its uniaxial strength, and there is also some fatigue damage when cyclic loading and unloading experiment is carried out below the fatigue failure ?threshold value?. Axial deformation can be divided into three stages: Initial deformation, steady-state deformation and accelerating deformation. Transverse deformation can be divided into two stages: Stable deformation and accelerating deformation. When the transverse deformation begins to increase rapidly and the deformation recovers only slightly upon unloading, it?s a precursor to failure of coal. Under cyclic loading, fatigue failure develops through a process of compaction, strain hardening, and strain softening.

Jan 1, 2006

By Juan J. Monsalve, Nino Ripepi, Richard Bishop, Jon Baggett

"Terrestrial laser scanning (TLS) is a useful technology for rock mass characterization. A laser scanner produces a massive point cloud of a scanned area, such as an exposed rock surface in an underground tunnel, with millimeter precision. The density of the point cloud depends on several parameters from both the TLS operational conditions and the specifications of the project, such as the resolution and the quality of the laser scan, the section of the tunnel, the distance between scanning stations, and the purpose of the scans. One purpose of the scan can be to characterize the rock mass and statistically analyze the discontinuities that compose it for further discontinuous modeling. In these instances, additional data processing and a detailed analysis should be performed on the point cloud to extract the parameters to define a discrete fracture network (DFN) for each discontinuity set. I-Site Studio is a point cloud processing software that allows users to edit and process laser scans. This software contains a set of geotechnical analysis tools that assist engineers during the structural mapping process, allowing for greater and more representative data regarding the structural information of the rock mass, which may be used for generating DFNs. This paper presents the procedures used during a laser scan for characterizing discontinuities in an underground limestone mine and the results of the scan as applied to the generation of DFNs for further discontinuous modeling.INTRODUCTIONAccording to the Mine Health and Safety Administration (MSHA), between 2006 and 2016, the underground stone mining industry had the highest fatality rate in 4 out of 10 years, compared to any other kind of mining (MSHA, 2016). Additionally, during that same time, 40% of the fatalities were due to ground control issues, such as roof and rib collapses and pillar bursts. The National Institute for Occupational Safety and Health (NIOSH) developed guidelines for designing underground stone mines (Esterhuizen, Dolinar, Ellenberger, and Prosser, 2011). However, these guidelines do not apply to all underground stone mines.Monsalve, Baggett, Bishop, and Ripepi (2018) present a case study of an underground limestone mine experiencing a structurally controlled mode of failure. The authors analyze different methods to study that type of instability. They conclude that the integration of terrestrial laser scanning (TLS) with discrete element modelling (DEM) can be used to prevent rock falls in underground excavations to enhance worker safety. However, an adequate rock mass characterization and structural mapping must be performed in order to generate reliable models that allow the engineer to have a better understanding of the rock mass behavior."

Jan 1, 2018

By Thomas A. Bailey

Since the advent of longwall mining, various methods and materials have been used during relocation to control the intrusion of the gob in the shield/panline area. (figure 1) Controlling this gob is critical to ensuring a safe, speedy, and productive longwall move. An uncontrolled gob can cause a number of problems, from increased worker exposure to entrapment of equipment to lost production. With an eye toward worker safety and increased productivity, several different methods have been developed to minimize gob intrusion. This presentation will take a look at the history and development of longwall ?screens? and ?mesh?, from chain-link fencing to high-modulus polyester geogrids. The benefits and advantages of these developments will be defined. Since 1994, longwall coal mines have used polymer geogrids during longwall recovery to control intrusion of gob material into the shield/pan line area. As described by Brandon and Collins (1996) in their paper presented at the 15th Ground Control Conference in Golden, CO., mines had used various forms of support, such as welded wire mesh, chain-link fencing, wooden cribbing, props, and steel cable to accomplish this. These methods worked, but were labor-intensive, slow, and provided varying degrees of gob stoppage. Although a few mines still use chain-ink fencing to control the gob, longwall coal mines have generally settled on polyester geogrids to control gob and roof and these mines have been instrumental in providing input in order to develop and improve these geogrids products. he trend during the past twelve years has been to incorporate stronger grids and to eliminate auxiliary reinforcements, such as steel cables and nylon or polyester webbing. A job that once required heavy steel cables, props, and fencing is now accomplished with strong, lightweight, high-modulus polyester grids. When we discuss high-modulus grids, we refer to the ratio between load and strain, as illustrated in figure 2. These grids are woven or knitted from yarns that have been pre-stressed. When these grids come under load, they pick up the load more quickly. This allows less deformation in, in this case, the mine roof. The same principle applies when these grids are used to control the ribs. With less elongation, the grids will hold rib material tighter, thereby keeping travel ways more open.

Jan 1, 2006

By John E. Feddock

Retreat mining plays an important role in the coal production within Kentucky and the Appalachian Coal Basin. In Kentucky, the majority of retreat mining is performed in the Eastern coal field. However, since September 2004, Kentucky has suffered four mining fatalities during retreat mining operations, and the coal industry has focused attention on the safety concerns associated with retreat mining practices. The Kentucky Department of Natural Resources (KYDNR) engaged Marshall Miller & Associates, Inc. (MM&A) to conduct a study to ensure that retreat mining is utilizing the best technology currently available and that the current available employee training programs afford maximum safety to miners. MM&A studied 34 coal mines that were conducting active retreat mining operations and represent about one third of all the mines with approved retreat mining plans in Kentucky. This paper summarizes the major research work conducted (Feddock and Ma, 2006) and recommends the practical methods for improving safety during retreat mining operations.

Jan 1, 2006

By Dakota Faulkner

Unexpected roof falls often occur in the entries or intersections of active mining sections in underground mines. For large roof falls (greater than 20 ft in height), it becomes dangerous and impractical to clean up the rock debris and re-bolt the newly exposed roof strata. To help mine operators rehabilitate the roof fall areas in a quick, safe, and economic manner, Jennmar Corporation and Keystone Mining Services, LLC (KMS) designed, tested, and developed various impact-resistant (IR) steel set designs, as initially detailed in the proceedings of the 30th International Conference on Ground Control in Mining (ICGCM). Since then, the IR steel sets have been successfully installed in more than 100 roof falls in 43 different coal mines. Significant data has been obtained from these installations, enabling further refinement to and improvement on the design. This paper (1) updates drop test results of the IR lagging panel, (2) presents a case study of the performance of IR arch sets installed 56 months ago at a roof fall rehabilitation site, (3) demonstrates capacity evaluation of the IR steel set, and (4) outlines a preliminary applicability evaluation guideline of the IR steel set for a given roof fall condition. Field evaluation and structural numerical analysis indicate that impact capacity of the system is significantly higher than that of the IR lagging panel, as originally determined. It is concluded that, when evaluating the applicability of an IR steel set, ground control engineers should consider the IR lagging and steel set as an entire system and make a reasonable engineering decision based on actual roof fall geotechnical conditions.

Jan 1, 2014

By Gennaro G. Marino

As part of the development of a shopping center in West Virginia, a significant bench had to be cut into a mountainside that was over 700 ft. high. As a result, a steeply stepped, over 400-ft.- high wall was created. The high wall exposed old abandoned room-and-pillar coal workings at the toe of the cut. Because of exposure to the elements, the mine openings began to severely deteriorate with significant potential of undermining of the rock cut face and causing a large rock fall(s). Exacerbating this wall problem was a set of fairly planar sub-parallel and sub-vertical joints creating, in essence, thin rock slabs. Also present were stress relief fractures that were observed in the exposed pillars. Given the proximity of the project building to this high rock face, mitigation of the rock fall potential was deemed necessary. In order to prevent continued damage and deterioration of these exposed mine entries, the rubblized openings were filled with bulkhead grout and pressure injected with grout. The total amount of grout installed in these openings was about 3,945 CY. Also, a rock drape was attached to the entire face to mitigate small rock falls from natural causes. There also existed another level of mining below the ground surface and under an existing building at a depth of about 160 ft. Under a portion of the building, the pillars in these old works were second mined, and the building seemed to have been already affected by limited subsidence above this area. Also, calculated pillar safety factors in this high extraction section of the mine were too low. Consequently, these old works were stabilized by saturation grouting. An indication of overall roof distress was the significant fracturing encountered in the bedrock overburden during the drilling of the injection holes and the volume of grout placed in these holes. The total grout installed in the high extraction section of the lower mine was about 6,660 CY. This paper describes the investigation and the grouting techniques employed at the rock cut face and under the existing building to mitigate continued damage to avoid future subsidence problems at the face and the building premises.

Jan 1, 2013

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

By Morgan M. Sears, Gamal Rashed, Jim Winfield, Brent Slaker

"Over the past decade, ground falls have resulted in five fatalities, representing over 40% of all fatalities occurring in underground stone mines in the United States. In conjunction with recent high-profile pillar collapses, the need for further ground control research in the nation’s stone mines is evident. Ground conditions are growing more difficult. Therefore, this research is focused on deep cover, steeply dipping, and multi-level underground nonmetal mines. The objective of this paper is to introduce a geomechanical study of pillar development in a steeply dipping limestone deposit. To accomplish this, a numerical model was developed using input from modified laboratory test data and in situ stress measurements provided by the mine to simulate the development of a pillar under these conditions. The model was then verified against field observations and stress mapping. The calibrated model was then used to calculate the estimated stresses in the pillar and immediate roof as development progresses around an instrumented pillar.INTRODUCTIONGround falls represent a significant hazard in the nation’s underground stone mines. In response to recent large-scale pillar collapses, as well as stakeholder interactions, researchers from the National Institute for Occupational Safety and Health (NIOSH) are currently conducting detailed investigations into the complex loading conditions at mines operating in challenging operational environments. These include deep-cover, steeply dipping, and multi-level mines where there is the potential for an increased risk of ground failure. The Pleasant Gap Mine, shown in Figure 1, operates in the Valentine Formation, which is typically light grey, extremely fine-grained limestone, and approximately 21.3 m (70 ft.) thick. The Centre Hall Formation makes up the immediate and main roof members and is approximately 9.1 m (30 ft.) thick, consisting of medium-dark-gray limestone (Murphy et al., 2018). Situated in a syncline, the top of the Valentine Formation dips at approximately 19° with a strike of approximately N54E in the area of interest (see Figure 2)."

Jan 1, 2018

By Bob Coutts, Matt Martin, Dan Lynch, Dan Payne

"The Broadmeadow punch longwall coal mine in Central Queensland Australia has experienced significant highwall movement associated with the effect of longwall subsidence when the longwalls approach their final position close to the open-cut highwall. In response to this movement, Broadmeadow employed two types of broadscale highwall monitoring (radar and laser scanners) to provide full coverage measurement throughout three consecutive longwalls approaching the highwall. This was to attain a better understanding of the mechanism causing the movement and potentially enable prediction of instability. Results from the monitoring found the highwall is displaced to magnitudes unlike those typically measured in open-cut mining and in direct contrast with typical longwall subsidence behaviour.This paper discusses the ground movements measured, monitoring methods used, safety measures established, as well as theorising the failure mechanism. Recommendations are made for mine and pit designs for future punch longwall layouts. The paper shows how the movements measured are more aligned to some measurements made during stream valley closure studies previously presented at the ICGCM and challenge the mechanisms suggested by previous literature.BACKGROUNDThe mining of longwalls under or adjacent to large voids (e.g., stream valleys, escarpments, or cliffs) is commonly associated with heavily vegetated or steep surface areas. In areas of extreme topographic variance, access to traditional survey pegs and stations or even new radar or laser technologies is limited. In addition, seldom have the longwall layouts aligned themselves parallel or perpendicular to the surface feature, making interpretation of any available surface movement data more complicated.The punch longwall layout (Figure 1) is also quite uncommon (only undertaken at a small number of longwall mines in Australia) but creates the perfect configuration to enable a somewhat controlled study of the effect of longwall subsidence on a steeply dipping surface feature (an un-vegetated, evenly excavated open-cut highwall). The relatively recently developed radar and laser scanning technology has also enabled near continuous, real-time, sub-millimetre monitoring of a full 500m wide x 100m high highwall. Because the punch longwall enables access and a clear view, the technology could be easily deployed as compared to the highly vegetated and variable topography of stream valleys."

Jan 1, 2018

By Tristan H. Jones

Rib-related accidents in underground coal mines continue to cause injuries and take lives at a rate of 1.3 fatalities per year for the last 17 years. Prevention of these accidents cannot simply be a matter of installing more rib support, though the eventual final solution will undoubtedly include that component. Ultimately, rib safety will be brought about through an understanding of the causes and mechanisms that cause rib fatalities, and by fine-tuning mining methods and procedures that are currently in place. This paper investigates the factors likely to be most influential in the occurrence of rib fatalities. A careful analysis has been conducted of the rib fatality reports documented by the Mine Safety and Health Administration between 1996 and 2013. The primary outcome is the determination of the relative impact of each type of rib fatality factor and a better understanding of the impact each factor has. Among the rib fatality factors considered, the influence of rib profileis considered for the first time. Mining height, rib stratigraphy, mining cycle, and the standing position of a miner next to a pillar are also considered. Questions are also raised about the current interpretation of rib fatalities due to mining depth, with the indication being that mines operating at the greatest depths may actually have the most respectable rib fatality record among all mining depths. Additionally, a new method of considering rib exposure is developed. Based on the results, recommendations are made for future work. By gaining a better understanding of how particular factors contribute to rib fatalities as opposed to rib failure or stability, it is hoped that future efforts can be more precisely directed towards the desired outcome of fatality reduction.

Jan 1, 2014

By David Dye

Good morning, everyone, and thanks Syd for that fine introduction. I am honored to be here to help you celebrate 25 years of advancement and success in the important field of ground control. I would also like to recognize Dr. Peng for his significant contributions in longwall mining and ground control. His contributions have had a major impact on improving safety and reducing fatalities in America?s mines. Thank you, Dr. Peng, for the important work you have carried on throughout the years. Many miners are alive today because of your dedicated work to protect them.

Jan 1, 2007

By Andre Cezar Zingano

"The objective of this paper is to estimate the coal seam strength and the pillar safety factor for low coal seams using back analysis and rock mass characterization. The coal seam strength is very important to estimate both pillar capacity and mine section design. There are two approaches to estimating coal seam strength: (i) by geomechanics characterization of the boreholes cores; and (ii) by back analysis from pillars successes and failures, or some in-situ tests. For low coal seams (1.2 m, or 47 in.), the confinement of the center of the pillar is very important to defining global pillar strength because the low seam height increases the confinement of the pillar core, even in small pillars. We used in this case study one underground coal mine in the Parana State where the coal seam thickness is 0.8m the pillar height is 1.3m, the entry width is 5m and seam depth is 130m. A panel test was prepared to study the pillar behavior for use of the retreat mining method. The designed pillar size was 6x5m and 1.3m high with a predicted safety factor of 1.0 based on the Hoek and Brown failure criterion is 5.3 MPa. Once no pillar failure was observed, the pillar safety factor was assumed at 1.0 and the coal seam strength was backcalculated. The back analysis estimated the coal seam strength to be 6.2MPa. The confinement of the pillar center directly affects the coal pillar strength, and also the coal seam strength estimated by back calculation.IntroductionThe coal seam strength is very important to estimating pillar strength and mine section design. There are two approaches to estimating coal seam strength: (i) by geomechanics characterization of the coal seam using borehole cores; and (ii) by back analysis from pillar successes and failures, or some in-situ tests like panel test or ultimate pillar capacity (Salamon and Munro, 1967; Maleki, 1981; Peng and Dutta, 1992). For the first approach, lab tests (mainly triaxial tests) and borehole geomechanics descriptions (quality and quantity of the discontinuities) determine the coal seam strength by the Hoek and Brown failure criterion (Hoek and Brown, 1997). For the second approach, a panel test to study the pillar behavior can be built to define coal seam strength by back calculation. The safety factor for the pillars in the test is 1.0, based on the estimated coal strength from the geomechanics characterization. In this case, the probability of failure is 50%. If some pillar failure occurred, and the real pillar size was measured, the back analysis could be applied to define pillar strength and the coal seam strength."

Jan 1, 2015

By Dennis R. Dolinar

Roof falls, even of supported roof, still constitute a major hazard in underground mines. However, associated with any fall or instability is a pattern of roof movement. Therefore, the National Institute for Occupational Safety and Health, Pittsburgh Research Center, has been conducting research into the development of practical extensometer systems that can be used to measure this displacement and to determine if a roof fall may occur, thus increasing miner safety. For extensometers to be used in the detection of potential roof falls in coal mines, an understanding of the movement and displacement rates that will lead to roof failure is required. Because roof falls are unpredictable, it is often very difficult to obtain this information. Therefore, in a coal mine in the lower Kittanning seam in Pennsylvania, a room widening experiment was conducted to intentionally cause a roof fall while roof movement data was collected. In this experiment, two adjacent rooms 5.5 m (18 ft) wide supported with 1.5 m (5 ft) resin-grouted bolts and instrumented with extensometers were widened to 9 m (30 ft). In one of the rooms, 3.6 m (12 ft) cable bolts were installed as supplemental support. In the room with no additional support, a roof fall occurred 72 h after the room was widened. Much of the 3 cm (1.2 in) of movement in this room resulted from the instantaneous and transient response to mining with displacement rates up to 7.6 cm/d (3 in/d) being measured. This was followed by a steady state displacement phase with a rate of 0.43 cm/d (0.17 in/d). Just 12 h before the fall, movement deeper in the roof caused the rate to accelerate to 1.1 cm/d (0.44 in/d). The roof in the room with the supplemental cable support did not fall even though the total roof deformation was over 7.6 cm (3 in). Significant roof movements and strains in the cabled room were detected to a depth of 3 m (10 ft) while maximum cable loads were over 180 kN (40,000 lbf). Essentially, the roof was in postfailure with the cables maintaining the material, while roof stability was indicated by a steady state displacement rate of only 0.025 cm/d (0.01 in/d) at the end of the test.

Jan 1, 1997

By Daniel W. H. Su

Current longwall pillar design relies heavily upon past experience and many assumptions about pillar and entry response to longwall abutment pressures. Caving characteristics of the immediate and main roof strata are known to play an important role in the overall pressure redistribution, which determines the maximum abutment pressure, abutment pressure at the T-junction, and the width of influence zone. This paper presents the results of an extensive geomechanical study in a longwall panel at a West Virginia coal mine. The response of eight headgate pillars and the adjacent entries was monitored as the longwall face approached and passed by the instrumented locations. Overburden response to longwall mining was also monitored, and height of the highly fractured zone above the gob was determined by postmining drilling. Good agreement was observed between the measured stress changes and those computed using the known height of the highly fractured zone. The results provide a detailed picture of the response of overburden strata and chain pillars to longwall mining.

Jan 1, 1987

By John P. Dunford

Ground support continues to be the most important safety consideration in underground mining. The Bureau of Mines has developed a yielding steel post with a capacity of 45 tons and b c1osure allowance of 24 inches in a 6 to 7 foot seam height. The post mechanism in a three piece unit consisting of a top and bottom leg made from standard steel pipe and a separate foot bracket. It develops its load carrying ability when the lower pipe, with an attached interference ring, is forced into the larger top leg. The walls of the top leg are deformed radially and along the axis. Yield continues until the unit bottoms out. Other advantages of the post is that due to its simplicity it can be made at the mine shop level and its cost should be about one-hundred dollars. Prototype units were tested in the laboratory. Based on these results, modifications were made that would make the post perform better as a mine support. Two field tests were conducted. The first test used the units as supplemental support for the wood crib rows in a longwall tailgate. The second and larger field teat had 84 posts placed on salvaged track rails. They were installed on two foot centers in the middle of the entry. Overall the supports functioned well during use in the headgate entry, but problems with the quality of some of the pipe caused localized failures. However, these problems can be attributed to one manufacturer of pipe and through tighter specifications can be eliminated. The use of the posts with the rails is showing additional benefits as a ground support system. By providing continuous support between the posts a beam is created that has much more load bearing. The additional support can reduce floor heave and in some cases eliminate the need for the rib side crib line.

Jan 1, 1986

By Shengliyang Yang, Jinghu Yang, Jiachen Wang, Xiaomeng Li

"Safe and efficient mining of extremely inclined thick coal seams less than 20m thick is one of the new challenges in China coal industry. In recent years, the extremely inclined thick coal seams have been encountered in some old mines and western China, and currently the top coal caving longwall mining method has been successfully applied to this kind of coal seams. Accordingly, this paper studies the roof movement and its impact on shield supports of top-coal caving longwall mining in extremely inclined thick coal seams. The structure of main roof before failure was simulated by the fix-ended beam, and provided the solutions for determination of maximum compressive stress of the bottom beam end and maximum tensile stress of the top beam end. The failure mode on the upper end of working face is mainly a combination of compression and shearing, while that for the bottom end is tension and shearing. Roof fracture begins at the upper end of working and propagates downward. The shape of collapsed roof strata can be described as parabolic and divided into three segments from top to bottom, including no filling, uneven filling and densely filling segments. The roof loading conditions of no filling segment is more likely to have dynamic burst impacts.INTRODUCTIONExtremely inclined thick coal seam refers to that the dip angle of coal seam is greater than 45° and the thickness is greater than 3.5m (Wang and Zhang, 2015a; Wang and Zhang, 2015b; Wang, 2005; Xie, Gao, and Shangguan, 2005; Wu, et al., 2014; Deng and Wang, 2014; He, et al., 2015). This type of coal seams can be divided into three categories: 1. The extremely inclined thick coal seam, of which the thickness is less than 5m and the dip angle is less than 60°, is usually mined by fully-mechanized longwall mining method. 2. The extremely inclined thick coal seam, of which the thickness is 5 m-20m, is usually mined by top coal caving longwall method. And 3. When the thickness of extremely inclined thick coal seam is greater than 20m, it is mined by the horizontal section top coal caving longwall method. For example, the average angle ofWudong coal mine in Xinjiang province is 45°, and the thickness is 27m. Wudong coal mine is applying the horizontal section top coal caving longwall mining, producing 3 million tons annually per working face (Figure 1)."

Jan 1, 2016

By Peter Zhang, Dan Neilans, Scott Peterson, Scott Wade, Joe Pugh, Ryan Mcgrady

"A coal outburst is a severe safety hazard in room-and-pillar mining under deep cover. It is more likely to occur during pillar retreating. Multi-seam mining dramatically increases the risk of coal outburst within the influence zones created by remnant pillars and gob-solid boundaries. Though coal outburst is generally associated with heavy loading of coal pillars, its occurrence is difficult to predict. Risk management provides a proactive tool to minimize coal outburst in room-and-pillar mining under deep cover. Risk assessment is the first step in identifying and quantifying outburst risk factors. The primary risk factors for coal outburst are overburden depth, roof and floor strength, geological anomalies, mining type, multi-seam mining, and panel width. A risk assessment chart can be used to proactively screen out mining sections with high risk of coal outburst for further analysis. Gob-solid boundaries and remnant pillars are critical factors in evaluation of the coal outburst risk of multi-seam mining. Risk identification, risk assessment, geologic influence mapping, geotechnical evaluation, risk analysis, risk mitigation, and monitoring are essential elements of coal outburst risk management process. Training is an integral part of risk management for risk identification and communication between all the stakeholders including management, technical and safety personnel, and miners.INTRODUCTIONA coal outburst is a sudden violent burst of coal from a pillar with broken coal or blocks of coal forcibly ejected into open entries. A coal outburst is a severe safety hazard as the mining crew is highly exposed at the site when the event occurs. Though deep cover and strong roof and floor are underlying geologic conditions of a potential burst incident, its real occurrence is also the result of additional mining factors. In room-and-pillar mining, a coal outburst could occur during both development and pillar retreating, but the latter greatly increases the risk of outburst. The other risk factors of coal outburst also include mining layout, multi-seam mining, presence of adjacent gob, cutting sequence, and local abnormal geologic conditions. Over the years, the cases of coal outbursts have been studied by many researchers and mining practitioners(Peng, 2008; Newman, 2008; Iannacchione and Tadolini, 2008; Gauna and Phillipson, 2008; Hoelle, 2008; and Newman, 2002). It is commonly believed that the coal outburst is the result of a sudden release of elastic strain energy stored in coal pillars and is highly associated with cutting into heavily loaded coal pillars, but its occurrence is a rare event and is difficult to predict. A number of engineering controls have been recommended to mitigate outburst potential. For room-and-pillar mining, sufficient pillar sizes have been the primary control for coal outburst prevention. The pillar design tools such as ARMPS and AMSS developed by NIOSH have played an important role in the design of stable pillars to prevent pillar collapse and squeezing as well as coal outbursts. In fact, with the implementation of pillar design using proper stability factors, pillar collapse and squeezing have been almost eliminated, and the number of coal outbursts has been greatly reduced in the US over the past decade. However, after a few outbursts occurred during pillar retreating in the US over the past a few years (MSHA, 1996; MSHA, 2014; MSHA, 2013), it has been realized that sufficient pillar size is still not enough to prevent coal outbursts. The investigations of the incidents showed that other factors such as multi-seam mining, panel layout, cutting sequence, and local geologic factors also seemed critical in causing the events. Therefore, it has become imperative that additional proactive measures beyond proper pillar design be implemented to prevent coal outbursts."

Jan 1, 2015

By Josh Johnson, Stephen Tadolini, Mark Ferster, Curt Jacobs

"Stillwater Mining Company is the only U.S. producer of platinum group metals (PGMs) and the largest producer outside of South Africa and Russia. The Company controls a considerable portion of the J-M Reef and is currently developing the ""Blitz Project,"" which will provide a main haulage level, ore pass systems, backfill plants, and flow-through ventilation to increase production and ensure sustainable extraction of this critical strategic mineral. While driving two sub-parallel footwall laterals to about 8,125 m (26,000 ft) long, one of the development drifts experienced a massive fall in a geologically disturbed area created by a dike intrusion. Combinations of a void fill material (Tekseal), polyurethane injection, fore poling coupled with steel arches, and supplemental bolting allow safe and efficient advance through this geologically disturbed zone. This paper presents the details of this project.INTRODUCTIONStillwater Mining Company is the only U.S. producer of platinum group metals (PGMs) and the largest producer outside of South Africa and Russia. The Company controls a considerable portion of the J-M Reef and is currently developing the ""Blitz Project,"" which will provide a main haulage level, ore pass systems, backfill plants, and flow-through ventilation to increase production and ensure sustainable extraction of this critical strategic mineral.Tunnel Boring Machines (TBMs), shown in Figure 1, have been used extensively at both the Stillwater Mine and the East Boulder Mine to develop access to the J-M Reef. The J-M Reef is a PGMbearing reef deposit located in the Stillwater Complex near NyeMontana. The mining property and location are shown in Figure 2.The Blitz Project is named after the Blitz mining claims and is developing the Eastern extent of the J-M Reef Project., This consists of a 5.5 m (18 ft) diameter TBM drive on the SOE (1,562 m (5,000 ft) above sea level and east of the shaft collar) and a 4.7 x 4.7 m (15 x 15 ft) drill and blast heading on the 5,600E (1,750 m (5,600 ft) above sea level and east of the shaft collar). The Benbow Decline will be completed running perpendicular to the TBM by drilling and blasting methods. The TBM drift will be used for exploration drilling, ventilation, and will serve as the main haulage level. The 56E will be used for ventilation and exploration drilling. The Benbow decline will serve as the exhaust drift."

Jan 1, 2016

By K. Biswas

So far, all pillar design methods or approaches consider the coal seam as a uniform structure From some mine visits in northern Appalachian Region. it is found that some coal seams have binder or parting material within the coal scan with varying thicknesses and numbers- And it has also been found that these kinds of hinder materials tire prone to weathering when exposed to ambient mine moisture In this paper an attempt has been made to study the weathering susceptibility of parting materials and coal when exposed to moisture and a two dimensional finite element analysis has been carried out to study the effect of the presence of partings on the structural integrity of the coal pillar in terms of short-term and long-term stability.

Jan 1, 1995

By Kanchan Mondal, Anthony (Sam) Spearing, Gopi Bylapudi, Joseph C. Hirschi

"The U.S. coal mining industry uses about 100 million rock anchors per year. ASTM F432 specifies the requirements for rock bolts on mines but does not address corrosion. Corrosion has been found to be an issue in Australian coal mines (Hebblewhite et al., 2003 and Villaescusa et al., 2007), where the problem has been researched and stress corrosion has been found to be a significant cause of rock falls. Corrosion is also a major concern for underground civil construction in the U.S. but has not been considered an issue or adequately researched in coal mines. Underground conditions are conducive to corrosion mainly because of water quality and humid conditions. There is a perception, however, that when bolts are fully grouted, adequate corrosion protection is offered to the steel. Research has shown that this is not necessarily the case, due to the formation of micro-cracks as the resin sets and with subsequent rock movement shearing the resin column. This paper outlines a method to determine the corrosion potential of bolts used in long-term excavations and suggests ways to mitigate such effects based on research conducted in the lab and on three mines.INTRODUCTIONResearch on rock anchor corrosion in mines has not been extensive enough in the past, and the effects of several factors in the mine atmosphere and waters are not clearly understood. One probable reason for this lack of research may be attributed to the time required for gathering meaningful data, which makes the study of corrosion quite challenging.Almost all the rock bolts used in coal mines are made from steel, hence the corrosion of iron needs to be understood. The corrosion of iron is an electrochemical phenomenon with the overall equation"

Jan 1, 2010