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By Russell C. Frith

This paper examines the design of longwall shields, focusing on those aspects that are critical to either their successful application or contribution to failure during longwall extraction. In many instances, longwall shields are assessed and designed along lines similar to that of roadway ground support systems, namely according to typical or normal geotechnical conditions. However it will be contended that for longwall shields, this is inappropriate because unlike roadway ground support systems, longwall shields cannot be supplemented with additional or secondary support in localised areas of adverse geotechnical conditions. In other words, the longwall shield needs to be designed according to what are judged to be worst case or adverse geotechnical conditions?the outcome being that a well-designed shield will be significantly over-rated for the majority of its working life. Therefore, it will be argued that the additional capital cost of such shield design can be readily justified as a prudent riskbased outcome that is essential to minimising future business risks due to strata instability on the longwall face. Shield geometry will be discussed, including such relevant factors as leg angle, inclination of the top caving shield, canopy ratio, operating height range, and tip to face distance. These are all well-established longwall shield design considerations and, most importantly, areas whereby inadequate design can render a longwall shield as highly ineffective. The issue of tip to face distance will be considered in detail, in particular, the extent by which it is an important geotechnical design consideration, the conclusion being reached that, in fact, it is not. The critical importance of maximising set to yield ratio within practical operating limits will be justified, the wisdom of this having been subject to questioning in more recent technical literature. Overall, the aim is to provide the industry with a set of suggested guidelines for future use when designing longwall shields and, hopefully, to initiate discussion on a subject that, unlike roadway ground support design, is not well covered in its entirety in the published technical literature.

Jan 1, 2013

By Yuanping Cheng, Jingyu Jiang, Qiang Zhang

"With the increase of mining depths, deep-seated coal seams face threats from high ground stresses, high gas pressures, high gas content, and low seam permeability, which significantly increase the likelihood of coal and gas outbursts. Challenges continue to grow in coalbed methane (CBM) extraction fields, especially for short-distance gassy multiple-seams. Research has proved that the most effective way to increase coal seam permeability is to decrease the ground stress. Protective seam mining technology is a surrounding rock control technology, which can effectively reduce the ground stress and increase the permeability of the protected coal seam. In this paper, we try to use upper protective seam mining technology to simultaneously extract coal and gas. Findings are based on a FLAC3D simulation of stress variation during the mining of the No. 12 coal seam in the Daxing coal mine, Tiefa Coalfield, China. Results indicate that, after mining the upper protective seam, the pressure-relief effects of the rock mass generated three belts and five zones below the protective seam, providing the space and time for gas pre-extraction engineering. Within the protected area, the numerical simulation indicates that the stress of the No. 13/14 coal seam reduces 95.84% and 88.25% respectively, while the expansion deformation of the protective seams reach 6.87 ‰ and 6.70 ‰ respectively, which demonstrate that the protective mining technology can provide a significant pressure-relief effect to the outburst-prone coal seam. Combining stress relief in this manner with pressure-relief from engineered gas drainage (performed by crossing boreholes from the floor rock roadway) applied before the mining of the protective seam, it would not only be beneficial to CBM drainage but also can reduce the gas outburst risk of the protected seams.INTRODUCTION Internationally, since France used protective seam mining technology to control coal and gas outburst in 1939, it has been promoted and applied in many countries (?????, 1966). Since 1958, China has taken the mining test and engineering practice of protective seam mining technology in the Beipiao, Tianfu, Nantong, Zhongliangshan, Songzao, Huainan, Huaibei, and other coalfields (Yu, 1992). Long-term theoretical research and mining practice of outbursts and dangerous coal seams show that protective seam mining technology is the most effective, safest, and most economical outburst prevention measure (Cheng, Fu, and Yu, 2009; Hu et al., 2008; Cheng and Yu, 2007). Under the condition of high gas content coal seams, the safety and efficiency of simultaneous extraction of coal and gas can be realized through a reasonable mining sequence and an effective gas extraction method (Cheng and Yu, 2003). The in situ stress distribution of the protective seam (No. 1 coal seam) and protected seam (No. 2 coal seam) during protective seam mining in the Haishiwan coalfield formation (Figure 1) (Li et al., 2014). A comparison of the stress and displacement (five zones and three belts) of the rock mass below the protective seam, and in a multiple-seam context in the Dalong Mine, is shown in Figure 2 (Jiang et al., 2015). After mining protection coal in a close-distance seam group, the small spacing between the coal seams causes the protective coal and the protected coal between part of the rock to crack through each other until the protective layer of gob is through the area. This provides a desorption of gas to the protective layer of the mining space channel, making the coal seam permeability increase to several hundred times and improving the gas discharge capacity (Zhai, 2008)."

Jan 1, 2017

By Sandin Phillipson

During the course of ground control evaluations conducted by the Mine Safety and Health Administration's Roof Control Division, a number of surface and underground coal mines were visited that exhibited instances of ground failure associated with joints. The evaluations were conducted over a broad geographic area, including the Appalachian Basin from Pennsylvania to Tennessee, and they documented that joints occur in a wide variety of mining conditions and exhibit a wide variety of characteristics. Despite minor local variability in orientations, the joints fit into a cohesive pattern when evaluated on a regional scale in context with the system of thrust faults that define the Alleghany Front. Joints documented for this study, together with joints in sandstone and coal and the trends of drag folds compiled from other studies, were plotted on regional maps using GIS software. The trends of joints, including those that could be described colloquially as "hill seams," were not only parallel to regional fault systems and local trends of drag folds, but were also parallel to the regional patterns of previously mapped joints in sandstone and coal. These observations indicate that the features referred to informally as "hill seams" are in fact joints formed in response to tectonic processes associated with regional deformation of the Cumberland-Allegheny Plateau. The 286-266 million-year-old age of regional deformation significantly pre-dates the time when the Cumberland-Allegheny Plateau was subjected to deeply incised stream valley erosion, which began 25 million years ago. This challenges an existing interpretation that "hill seams" represent local ·stress relief joints that formed when stream valley erosion removed confinement and allowed tensile failure of the rock. Although relaxation of confining stress can reasonably be expected to occur near outcrop, observations indicate that this results in the dilation of existing joints. This paper presents instances of ground failure associated with joints, discusses methods of mitigation, and recommends that the term "hill seam" be abandoned in technical communication because it simply refers to a kind of joint that may exhibit certain weathering and aperture characteristics.

Jan 1, 2010

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 Jimin Su, Enguang Zhu, Kangning Zhang, Yang Li

"The effect of interburden on overlying strata movement during the mining of a lower group coal seam is still a challenge in China. Based on the multiple coal seams in western China, numerical simulation and field tests are applied to study the interburden and overburden movement during the undermining process. This study focuses on the impact of the thickness and structure of the interburden, the proportion of hard rock, and the ratio of the overburden thickness to interburden thickness (OB/IB). In this paper, four typical underground coal mines are simulated for lower seam longwall mining with different interburden parameters. The results indicate that the ratio of the overburden thickness to the interburden thickness is not the dominant actor for multiple seam longwall mining, especially in the mines in western China,which feature shallow depth. The thick and hard interburden could strongly affect the lower coal seam mining process. INTRODUCTION The project background is based on four typical underground coal mines in western China.The information on the overburden and interburden is shown in Table 1. Different overburden to interburden thickness (OB/IB) (Ellenberger, 2009) values of the four coal mines are also studied: 6.2 in Bulianta coal mine, 7.2 in Kaida coal mine, 8.2 in Shigetai coal mine, and 9.4 in Halagou coal mine. The proportions of hard rock in the interburden of the four coal mines are also different: 0% in Kaida coal mine, 70% in Shigetai coal mine, 80% in Bulianta coal mine, and 100% in Halagou coal mine. To be specific: the thickness of interburden are listed as follows: 7m in Halagou coal mine, 6m in Kaida coal mine, 10m in Shigetai coal mine, 28m in Bulianta coal mine. The depth of the upper coal seam are: 66m in Halagou coal mine, 54m in Kaida coal mine, 79m in Shigetai coal mine, 182m in Bulianta coal mine. NUMERICAL SIMULATION UDEC 4.0 is applied in this paper to analyse the overlying strata movement and the interburden failure.(Liu, 2007) This is based on mining in the lower coal seam under the mined-out upper coal seam (Majdi, 2012, Morsy, 2006)."

Jan 1, 2017

By Pengfei Wang, Guorui Feng

With increase of cover depth, dynamic incidents, such as large gateroad convergences and coal bursts, are frequently encountered when mining deep longwall panels. It would be more adverse due to large inclination of the coal bed. Because of the shearer and armored face conveyor (AFC) sliding downhill, toppling of shields, disconnection of AFC to the stage loader are related to it. Tangshan coal mine is a typical deep, inclined coal mine situated in the east of China. The split-level longwall panel layout is being adopted for mitigating problems above, where tailgate entries of longwall panels are driven below gob edge and along the floor, while headgate entries are driven along the roof. Wire mesh and steel sets have been used empirically for support for tailgates for about a decade, which reduces the tunneling speed. In view of this fact, the paper serves to investigate the proper adjustment of the tailgate locations and to analyze the resulting stress and yield conditions according to support strategy. First, field measurements and observations were carried out. Stress data distributed within surrounding rock mass were obtained, especially within the roof since the roof consists of only a coal sheet with a thickness of 2–4 m. Roof pressure of the tailgate represents the pressure at the gob edge since it is below the gob edge. The convergence data were also collected. Numerical modelling using FLAC3D™ was conducted and validated by side abutment stress data. The double-yield constitutive model was used to simulate the gob. The finalized tailgate layout and design were determined through comparison of three scenarios. The research in this paper can help engineers choose the proper tailgate layout and support strategies for coal mines that are going to adopt a split-level longwall panel layout for mining deep, inclined longwall panels.

Jan 1, 2018

By Alan Bugden

Goedehoop colliery in South Africa has experienced a number of substantial roof falls in roadways and intersections. Many of these have been associated with geological slips and/or horizontal compressive stresses. This paper describes a numerical modelling study conducted after one such fall with the objective of clarifying the roof failure mechanism associated with these falls. The fall was located at an intersection and occurred as the last cut was being made to complete the intersection. One bounding surface of the fall was formed by the geological slip; the others were formed by fresh failure surfaces. The fall took place despite the slip being identified as a hazard and additional bolts being placed by the workforce. In conjunction with the modelling work tests were conducted on samples from the roof in which the fall occurred, these gave a U.C.S. of 80 -100MPa. Several in-situ stress tests had already been conducted at the mine; a further test was conducted close to the fall site. The tests show that the largest stresses are horizontal. However, the maximum stresses of 6-12MPa are small compared to the compressive strength of the root. Computer modelling highlighted a mechanism arising from the conjunction of a geological slip and horizontal compressive stresses that could result in tensile failure of the roof leading to the fall. Sensitivity studies were conducted to identify risk factors associated with this mechanism and the modelling results used to assist in formulating a support strategy to combat falls of this nature.

Jan 1, 2003

By Stephen C. Tadolini, Robert Hawker, Peter Mills, Colin Grubb, Tom Meikle

"In unfavorable strata conditions, it is often necessary to install additional long tendon support as part of a primary support cycle. Although these support systems provide the required additional stability to the roadway installation does have a significant effect on the rate of development. To overcome the slow cure time of Portland cement-type grouts, the use of two component resin systems, such as polyurethanes and urea silicates, have become favorable. However, concerns over low modulus and creep properties has led to the development of a two-component grouting medium that displays the properties of traditional cable grouting materials with the rapid reaction times of pumpable resin systems. This paper describes product testing, application, surface trials, underground trials, and full-scale applications of the Tekthix System in a dynamic underground environment. INTRODUCTION Single-component cement grouts have been used to anchor long tendon supports for many years. They range from high- to low-slump Portland cement and can be slow-setting to fast-setting grouts. However, current cement grouting systems, which includes the grout and equipment, have some disadvantages: 1. Low-slump grouts require pumps that can handle a thick, high-viscosity grout, so choice of pumps is limited. 2. Pumping distance is limited with current cable bolt grout pumps; operators often tend to add water to allow pumping long distance, which adversely impacts the quality and strength of the material. 3. Fast-setting grouts tend to cause issues with pump and line blockages due to the reduced working life of these single-component materials."

Jan 1, 2017

By Douglas C. Peters

Part of the ground control research at the U.S. Bureau of Mines is involved with improving ground control data collection and analysis methods. A geographic information system (GIs) is being used within this research effort to standardize the data collected and provide a common graphical and tabular format and analysis system for researchers to access information on underground coal mines. In addition, GIS's can perform relational analyses on multiple map and tabular data sets which are not possible through map-creation or CAD packages or through data bases alone. In addition to standardizing ground control analyses, there is an increasing need for rapid analysis of ground control data in connection with increasing production rates at longwall mines. The examination of a large number of interrelated parameters and their impact on short-term mine safety and productivity under the time constraints imposed by rapid production requires computer-aided techniques. A GIs provides the means to quickly, quantitatively, and reproducibly evaluate mine-wide conditions. This overview of GI8 techniques for mine data integration and analysis, using a mine in Colorado as an example site, will cover the input of data into a GIs, including mine-wide monitoring system data and general data such as roof control plans and geology. The methods to geographically reference these data sets and retrieve and combine them also will be covered. Automation of such processes briefly will be reviewed to allow future users to automate their mine data analyses.

Jan 1, 1990

By Mark F. Sindelar, Yi Luo, Hua Jiang, Michael T. Shook

"Convergence of roof and floor in underground mine openings is a common occurrence. This convergence not only adversely affects the ability of workers, equipment and supplies to travel through the mine, it also reduces the effectiveness of the mine ventilation system, which is essential for the dilution of methane gas and airborne respirable dust. While installing secondary standing supports to control floor and roof convergence, such supports, by nature, partially obstruct a portion of the airway. These added obstructions inhibit the ability of the ventilation system to operate as efficiently as it could by increasing the resistance in and reducing the cross-sectional area of the airway.This study introduces and demonstrates the benefits of The Eye CAN™ standing roof support, which controls floor and roof convergence and is less obstructive to air flow than conventional wooden cribs. Laboratory findings show that the normal resistance of a supported lined airway is reduced by using this new product from Burrell Mining Products, Inc., while providing the same roof support characteristics of an established product-The CAN®. Load vs. displacement curves generated from laboratory tests demonstrated that this new product behaves with the same roof support characteristics as others in The CAN product family. Ventilation data gathered from a simulated mine entry was then used for computational fluid dynamics (CFD) modeling. The CFD analysis showed an improvement with The Eye CAN versus other accepted forms of standing roof support.This proof-of-concept study suggests that, when using this new product made by Burrell Mining Products, Inc., not only will the convergence from the roof and floor be controlled, but airway resistance will also be reduced.INTRODUCTIONOne of the basic elements of underground mining is the necessity to support the mine roof. It is well-known that easier reserves have been mined so that today's underground mines present challenging conditions. Factors influencing roof support decisions include mine depth, mining method, overburden composition, and agency regulations. Mining engineers, therefore, have to balance three objectives: safety, engineering, and cost. While safety is obviously paramount, and engineering often complements safety, the cost effectiveness of any product, method, or device warrants additional consideration in today's harsh business climate. Avenues for adaptation and improvement are found at the intersection of the three objectives."

Jan 1, 2016

By Daniel W. H. Su

This paper presents the results of an extensive geomechanical testing and monitoring program conducted at a longwall panel. The field program included the monitoring of roof caving sequence and mechanism, surface subsidence, change of pillar stress, roof displacement and entry convergence, and strength characterization of the overburden rocks. The response of eight headgate pillars and the adjacent entries was monitored as the longwall face approached and passed the instrumented locations. Overburden response to longwall mining was monitored using time domain reflectometry (TDR) technology; and, the height of the highly fractured zone above the gob was determined by postmining drilling. Good correlation was found between the height of the highly-fractured zone and the TDR, subsidence, and pillar stress data. The results provide a detailed picture of the response of overburden strata and chain pillars to longwall mining. A preliminary model representing the overburden strata behavior at the test site in response to the longwall mining is proposed.

Jan 1, 1987

By Tobias U. Papst

The German Ruhrgebiet is slowly transitioning into a post-mining state. It has been subjected to industrial-grade hard coal mining operations for more than 150 years. Due to a political decision, German hard coal mining will come to an end in 2018. By then the surface will have subsided up to 20 meters. After all mining activities in the area have ended, there will be no need to maintain the current mine water level. Accordingly, the company operating the last remaining coal mines has decided to let the water level rise to an as yet undetermined level. Alongside other issues that may be caused by rising groundwater levels, the protection of the area?s drinking water supply is of utmost importance. This notion is also represented by European and German law. The primary intent of the applicable laws is to protect the health of the citizenship. This means protecting ground water that may be used by humans from being contaminated by the mine water. This paper outlines the consequences of European and German legislature on mining aftercare using the example of one of Europe?s largest agglomerations.

Jan 1, 2014

By Andre Zingano

The coal seam strength and the failure criteria that represent the behavior of the coal seam are very important for mine section and pillar design. Additionally, mine section and pillar design take into account roof and floor layers, which form the roof-pillar-floor system. Therefore, underground ground control design begins, most importantly, with rock mass characterization. Another issue is the distribution or behavior of the coal seam strength for the whole mine area. Sometimes, the coal seam strength is assumed to be the same for an entire area, but this is not true because the coal seam is heterogenic and anisotropic, and also the coal strength is affected by faults and spacing between fractures. The objective of this paper is to demonstrate the use of the methodology for geomechanics characterization to determine the strength for the Bonito coal seam, and discuss the coal seam strength distribution around the entire mine area. The intact coal strength was determined by laboratory tests that were completed during the last 17 years, including triaxial and uniaxial strength tests. It was noted that there is a strong correlation between all laboratory strength tests with 90% confidence interval. The explanation for this coal seam strength variation is the presence of the discontinuities and their variation in quantity and quality at each location in the mine area, because the coal seam rock classification and its behavior will be affected by the quantity and quality of fractures.

Jan 1, 2014

By Ali Naeimipour

Availability of accurate geological information about the rock mass surrounding a tunnel or mine working is the key to enhance and optimize the required ground support measures. Various approaches have been used to obtain data on ground conditions, including the possibility of characterizing the ground while drilling for roof bolts, by the Measurement While Drilling (MWD) system, via optical, sonic and acoustic televiewers, and using various types of gamma probes. While there are many different systems for characterizing the ground in longer, larger-diameter holes drilled downward, the options for using probes and logging systems in short, small-diameter holes drilled in horizontal or an upward direction are very limited. This paper will present the results of recent field tests using optical televiewer (OPTV) to analyze the joints and voids in boreholes drilled in different directions. The studies show that OPTV is a promising tool; however, getting a good quality image from the upward drill holes still need to be studied. Meanwhile, estimated in-situ strength of the intact rock is needed to complement the jointing pattern for rock mass classification. For this purpose, preliminary steps for the development of a borehole scratcher to estimate rock strength will be discussed in this paper.

Jan 1, 2014

By Stephen C. Tadolini, Peter A. Gray, Robert Hawker, Andrew Sykes

"Self-drilling rock bolts (SDRBs) that use pumpable cement grout to anchor bolts have been used successfully in the tunnelling and civil engineering industries for many years. Pumpable cement grout offers a considerable advantage in that the SDRB can be fully encapsulated right down to the bearing plate, including filling cracks and cavities in the borehole. However, cement grout cannot provide the immediate rock support required for the coal industry. This paper describes a new SDRB system that uses pumpable resin to anchor the SDRB in a borehole, which not only provides all the advantages of a pumpable grout anchoring system, but also provides immediate roof and rib support as required in the coal industry. This paper further outlines the latest developments in SDRB technology including (1) extendable self-drilling rock bolts, which can almost double in length during the installation process and are particularly suited to low seam heights and rib support and (2) pre-tensioned SDRBs, where a pre-tensioned load can be applied during the installation process. These new SDRB systems offer both considerable advantages in rock support and improvements in mining productivity.INTRODUCTIONThe mining industry is continually striving to develop more efficient methods to support the roof and walls of roadways and tunnels, and rock bolting has proven to be one of the most significant improvements in ground support over the last 50 years. Rock bolting is now almost universally used in the underground mining industry worldwide, and there are many different rock bolts available.Rock bolts are traditionally made from steel or fiberglass and are anchored into a borehole with a friction-anchoring device, such as an expansion shell mechanism; cement grout; or chemical resin. Friction-anchored bolts are widely used in the Australian metal mining industry, predominantly as short-term support. They are used in conjunction with resin-anchored bolts where there is a requirement for longer life. Resin-anchored bolts are used in the coal mining industry.Friction-anchored bolts provide immediate rock support, but their load transfer capacity is poor compared to resin or cement anchored bolts. In addition, friction-anchored bolts are more susceptible to corrosion than resin or cement anchored bolts."

Jan 1, 2010

By Essie Esterhuizen, Michael M. Murphy, Chris Mark

"The response of the surrounding rock mass to the creation of mining excavations determines the ultimate load on a pillar support system. In conditions where the ground is relatively soft and weak, the full overburden weight can be transferred to the pillar system. However, in stiffer and stronger rocks, a greater portion of the overburden load is transferred to the unmined coal barriers or abutments, and the pillar stress is reduced. This paper makes use of numerical models to examine the interaction between typical pillar systems and the surrounding rock mass for weak and strong geological conditions at various spans and depths of cover. The concepts of structural failure and functional failure of pillars are used to assess pillar performance when pillars are deformed beyond their peak resistance. The results show that the span-to-depth ratio is an important factor in determining the pillar stress and the ultimate deformation of pillars. The ultimate pillar strain appears to be closely related to the functional success of pillar systems.INTRODUCTIONThe National Institute for Occupational Safety and Health (NIOSH) was requested by Congress to study the safety of retreat pillar mining following the Crandall Canyon Mine disaster that took place near Price, Utah in August, 2007. As a part of this study, an investigation was made to better understand how the rock mass responds to the creation of mining excavations and how the loads are distributed among the pillars and the surrounding abutments or barriers. The outcome of these investigations contributed to the development of a modified loading model for the ARMPS-2010 (Mark, 2010) method ofretreat mining pillar design.Structural and Functional Failure of PillarsPillar design is typically conducted by estimating the pillar strength and stress, and then sizing the pillars so that an adequate margin of safety exists between the expected strength and stress. The pillar strength can be defined as the maximum resistance of a pillar to axial compression (Brady and Brown, 1985). If a pillar is loaded beyond its peak strength, load shedding or yielding can occur, and the pillar is considered to have failed as a structure. Structural failure generally refers to a loss of loadcarrying capacity."

Jan 1, 2010

By Christopher Mark

Colombia is 11th largest coal producing nation in the world, and the world?s fifth largest coal exporter. But while most of Colombia?s coal is mined at large modern surface mines located near the Caribbean coast, there are also underground mines that produce high-grade metallurgical coal. These mines employ traditional hand-loading techniques in a variety of geologic environments, and they have some of the highest accident rates of any Colombian industry. The National Institute for Occupational Safety and Health (NIOSH) has been collaborating with POSITIVA, the primary provider of worker?s compensation insurance to the Colombian underground coal industry, to reduce the economic and social cost of rock falls in these mines. The specific goals of the collaboration are to 1) document practices and conditions in Colombian underground coal mines, 2) identify relevant international best practices, and 3) provide recommendations for developing a national campaign to reduce fatalities and injuries associated with roof falls. NIOSH conducted a survey of seven underground coal mines in four separate coalfields. Five of the mines were characterized by steep dips and weak roof and floor rock. The coal was loaded by hand at all seven mines, though two employed partially mechanized longwall techniques. Wood posts were by far the most common ground support. Roof bolts were not observed in use at any of the mines, and they are unlikely to replace timbers any time soon. While long-term entries generally appeared to be adequately supported, the survey found that less attention was paid to the temporary support that is installed right after the coal is removed. This temporary support is critical for protecting the workers from rock falls, however, because with hand-loading mining methods most of the activity takes place between the permanent supports and face. The study concluded that improving the temporary support in the working faces would be the most effective way to reduce the number of rock fall injuries. The key principle should be that every worker is protected by planned roof support at all times. Ground Support Management Plans, consisting of specific rules about when, where, and what roof support is to be installed, should be the focus of the campaign. Each Plan should be tailored to a specific mine based on the geologic conditions and mining methods in use. The Plan provides miners with clear, simple rules that can be easily understood, while management can easily check to see if it is being followed. Ground Support Management Plans will also provide the campaign with a concrete focus for the necessary cultural change.

Jan 1, 2014

By Anthony Iannacchionc, Jessica Benner, Harold Miller, Megan Witkowski

"Longwall bituminous coal mining has been practiced in Pennsylvania since the 1970""s. Hundreds of longwall panels have been mined during the last 40 years but only 24 have actually undermined Pennsylvania's Interstate Highway System. The impact to interstate highways are summarized in this paper and the factors that influence the magnitude of these impacts are examined.INTRODUCTIONOver the last 30 years, interstate highways in Pennsylvania have been undermined by portions of 21 bituminous coal mine longwall panels. From 2003 to 2008, three of the panel were extracted by the Emerald Mine and six by the Cumberland Mine both in Greene County and both owned by Alpha Resources. Previous assessments of longwall mining under Pennsylvania’s interstates have identified impacts to the highways but no danger to public safety. In general the magnitude and extent of impacts during the recent undermining of Interstate 79 or 179 appears to be similar as those identified in previous studies. The nine longwall panels are among some of the widest in the U.S. They are supercritical in character with overburdens ranging from greater than 152 m (500 ft) to less than 305 m (1,000 ft).The Pennsylvania Department of Environmental Protection (PA DEP) requested that the University of Pittsburgh summarize observations collected by their staff during the recent undermining of 179. Observations and photographs of impacts to the highway were made by PA DEP staff and entered into reports prepared by California District Mining Office (COMO) staff and statements written into the Bituminous Underground Mining Information System (BUMIS) database. In addition to the observations by the PA DEP, the Pennsylvania Department of Transportation (PennDOT) conducted a series of detailed land surveys along portions of the highway undermined from 2003 to 2008. To characterize the subsidence basin fanned by longwall mining. PennDOT information has been analyzed by another research group within the university (Guticrre7, et al., 20 I 0)."

Jan 1, 2010

By P. Oliver

Rockburst conditions were first encountered at Inco's Sudbury area operations in the mid 1930's when mining advanced to below the 610 m (2000 ft.) horizon. Now, mining is being carried out at depths down to 2130 m (7000 ft.) at Inco'a Creighton Mine. While rockburst potentials have increased with depth. improvements in mine planning, methods, support systems and developments in destressing have alleviated the condition to where it is less of a problem now than it was in the early years. Hang of the improvements were developed, of necessity. through observation and reasoning because these were the only tools available at the time. Now, we are making use of stress - measurements, numerical modelling and microseismic source location technology to - help further reduce rockburat hazards.

Jan 1, 1987

By Behdeen Oraee, Amirhossein Bangian, Kazem Oraee

"Determination of the optimum design of chain pillars has a significant effect on the economics and safety of longwall operations. Most pillar design formulae are based on empirical methods and supplemented by local experience. They therefore lack versatility of application under different geotechnical conditions.In this paper, in order to illustrate the shortcomings of the above, a typical real coal pillar in Tabas coal mine has first been studied and the conventional formulae have been used to determine the optimum dimensions. The results show that a wide difference exists between the predicted and the real field data. The Oraee-Hosseini formula has then been applied to this mine in order to determine the optimum design. The results from this formula demonstrate a close fit between the theoretical VALUES (and those produced by laboratory tests and in practice. It is further demonstrated that the wide discrepancy between the results obtained from the two formulae is attributed to the dissimilarities between geotechnical conditions of Tabas and the original regions whose data were used to devise the empirical formulae.It is finally concluded that the application of numerical simulation methods and experimental equations together with engineering judgment used by the mining design engineer, will provide the most accurate design characteristics.INTRODUCTIONLongwall is an underground mining method which has a high rate of production capacity and mechanization ability. This mining method, which is appropriately applied for soft rock fiatlying bedded ore bodies, gradually became a widespread mining method amongst European coal mines at the beginning of the 19'h century. It was then applied in some of the U.S. coal mines with the development of self advancing support mechanisms in early 1960's (Oraee, 2001).Underground coal production around the world using Longwall mining method doubled during 1990s. The main reasons for this improvement were: the high level of mechanization, increased 10 safety, adequate design of panels, and well designed ventilation systems (Peng, 2006)."

Jan 1, 2010