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By Bingjie Huo

"China is a major coal producer and consumer. It is necessary to mine the steeply pitching coal seams due to development of the coal industry to meet the increasing needs for coal. Flexible shield supports mining is a safe and efficient mining method for steeply pitching coal seam that was first applied in HuaiNan mining area in the 1970s. The coal seams are steeply pitching in DaAnShan Colliery, so mining is mainly done by the flexible shield supports method. The roadway lay-out and extraction technology are researched in order to improve the safety, yield and work efficiency in the flexible shield supports working face. Optimization of the flexible shield supports mining method is discussed. The main optimization aspects are as follows: (1) the angle of working face and mining track roadways are increased from 23° to 28°, and (2) the technology and parameters of coal breaking are optimized. Applicable conditions, as well as advantages and disadvantages are also discussed. Finally, a comparison is made of the two different flexible shield supports mining methods, namely ""bench blasting . technology"" and ""piecewise blasting technology"".INTRODUCTIONChina is the largest producer and consumer of coal in the world and relies heavily on coal for energy production. At present, Chinese production is about 42% of the worldwide production, and coal has accounted for 76% of primary energy production. Coal plays a dominant role in the structure of energy production and consumption, which is fuel and an important industrial raw material but it is non-renewable. In recent years, the high inclined seams (35°< angle of coal seam < 45°) and steeply pitching coal seams (angle of coal seam >45°) have drawn increasing attention in the mining sector along with the growth of coal mining. There are two reasons. First, there are abundant reserves of high inclined and steeply pitching coal seams in China, which account for 15- 20% of total reserves (Xie, Dong-hai, 2007). Highly inclined and the steeply pitching coal seams are mined in more than 50% of the western mining provinces such as Sichuan, ChongQing, YunNan, GuiZhou, XinJiang, GanSu, NingXia, etc. As the mining of mineral resources continues west in the 21st century, the study of coal mining in high inclined seams and steeply pitching coal seams will be of great importance. Secondly, better quality coal has become scarcer in the eastern mining areas after years of exploitation, so steeply pitching seam mmmg is growing more prevalent. In short, carrying out research on steeply pitching seam mining technology plays an important role in sustaining the development of the Chinese coal industry."

Jan 1, 2010

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 Gary Buchan

"Mine-wide ground control stability is essential to any mining operation to prevent catastrophic failure of underground structures. The ability to recognize or indicate the potential for ground control hazards in underground mine operations is highly desirable to reduce or eliminate ground-control-related injuries and fatalities. The acoustic emissions (AE) form of non-destructive testing has been used for decades to determine material or machine deterioration or potential failure. This paper presents the findings of research in AE with the results of laboratory bolt pull tests and comparisons to field experimentation, including AE sensors and bolt load data in an underground stone mine. The goal of the project is to compare laboratory results of AE sensors on roof bolt pull tests with field experimentation to determine the capability of predicting bolt failure or roof deterioration.INTRODUCTIONMine-wide ground control stability is essential to any mining operation to prevent catastrophic failure of underground structures. The ability to recognize or indicate the potential for ground control hazards in underground mining operations is highly desirable to reduce or eliminate ground-control-related injuries and fatalities. Typical ground control monitoring devices involve drilling into roof or rib, grouting or gluing of sensors, and dedicated cabling for data collection. One of the original goals of this research was to develop a methodology for a simple wireless device that could provide an indication or warning of potential roof bolt or roof failure. Various types of nondestructive testing (NDT) have been used for decades to determine material or machine deterioration or the potential failure of either. One type of NDT is acoustic emission (AE) monitoring, which has been studied for use in mining to predict rock bursts and mine failures since the 1940s (Obert, 1941; Obert and Duvall, 1942). The primary goal of the work was to compare laboratory results of AE sensors on roof bolt pull tests with field experimentation to determine the capability of evaluating bolt loading or roof deterioration in an underground stone mine. Bolt pull tests were conducted in the laboratory to establish a repeatable trend of AE activity versus bolt load. The second part of the project was to then install bolt load cells in an underground stone mine and monitor AE activity in the vicinity of mining."

Jan 1, 2018

By Andre Cezar Zingano

"The empirical approach for pillar design assumes that geological conditions should be perfect, such as horizontal seams, and that pillar strength and behavior will only depend on the coal seam strength and the vertical pressure caused by the overburden thickness on the coal seam; this vertical pressure is based on the tributary area. Empirical methods do not consider the effect of the interface between the roof and pillar or the floor and pillar.The effect of the interface shear strength on final coal pillar strength has been studied since the 1960s. However, few case studies have been generated from that, especially in shallow underground coal mining (less than 100 meters). This case study involves a mining section at the 101 coal mine in the Santa Catarina state of Brazil, which is experiencing pillar rib spalling and yielding because of a 1-to 2-cm-thick clay layer at the area of contact between the coal seam and immediate roof. The depth of the coal seam is 60 m on average and 2.3 m in height. This particular section also has 12-14% (7-8°) of seam inclination. The pillar size varies from l lxll to 13xl2m; thus, the safety factor (SF) based on the ARMPS approach is more than 1.5. The objective of this paper is to determine the cause of the pillar yielding and study the effect of the clay layer at the interface between the roof and pillar, including the inclination of the coal seam. This study conducted empirical and numerical models (2D and 3D) to understand the effect of the thin clay layer. The conclusion is that the clay layer affected the strength of the interface between roof and pillar, causing rib spalling and reducing the pillar strength.INTRODUCTIONPillar stability and deformation depends on the coal seam strength and vertical pressure caused by the overburden thickness on the coal seam, and this vertical pressure is based on the tributary area. The effect of the interface shear strength on the final coal pillar strength has been studied since the 1960s. However, few case studies have been generated from that, especially in shallow underground coal mining (less than 100 m). This interface could be represented by a thin clay layer or an abrupt contact between the coal seam and a rigid sandstone layer of the immediate roof. These two interface conditions are found in the coal mines of Brazil, and the effect of the interface shear strength could increase when the seam's inclination is higher."

Jan 1, 2016

By Naj Aziz, Peter Craig

"Double shearing tests were carried out on the 28 mm (1 in) hollow strand Jennmar TG cable bolt to gain a better understanding of the shearing behavior of the cable. The first test was limited to a 50 mm (2 in) travel on the testing machine and produced a shear load of 900 kN (92 t) at the maximum 50 mm (2 in) displacement. The axial load generated on the cable bolt was 238 kN (24.3 t). In the second test, the machine travel was increased to 75 mm (3 in), and first strand failure of the cable, due to shear loading, occurred at 1,354 kN (138 t) vertical load at a vertical displacement of 59 mm (2.3 in). The cable axial load was in the order of 385 kN (39.3 t). Analysis of the failure mode and loads achieved showed that the cable strands bent and the concrete crushed along the shear plane; the shear loading across the concrete and grouted cable then reached the tensile strength of the steel wires.INTRODUCTIONCable bolts were introduced to the mining industry around 1970, initially to surface mining and underground metalliferous mining and then to coal mining in the early 1980s, mainly for roadway reinforcement as a secondary means of support. Cable bolts have since been used as both primary and secondary supports. As primary support, Fuller et al. (1994) described the application of cable bolts, known as FLEXIBOLT, for strata reinforcement in both Angus Place and Ellalong Collieries, in New South Wales (NSW), Australia. As secondary support, cable bolts have also been used as cable trusses, which act to support the immediate roof in a sling-like manner (Fabjanczyk and Tarrant, 1988; Fuller, et al., 1991; O'Grady and Fuller, 1992), and for reinforcement at higher stratification and beyond the rebar bolt length, mainly for anchoring lower strata layers immediately above the coal seam to the higher, competent bedding formation above. Initially cable bolt anchorage was by cementatious grouting and, since the 1990s, by chemical resin. The dominant type of cable bolts used for secondary support in Australian underground coal mines are 588 kN (60 t) capacity cables which are point anchored, pre-tensioned and post-grouted. Point anchored refers to a cable resin anchor. The cables are tensioned on the resin anchor; then the same cable is grouted by cementatious grout pumped to ·fin the annular gap around the cable from the collar of the hole to the resin anchor. Bulbs are located within the resin anchor section for mixing of the resin chemical components and efficient anchorage. The installation of these typically 8 m long cable bolts involves a lot of manual handling of the cables, lifting of heavy hydraulic tensioners, and exposure to resin grouts. Table 1 shows the specification of various cable bolts currently marketed and installed in Australian underground coal mines."

Jan 1, 2010

By Peter Cain

Longwall extraction in the Phalen Scam in the Sydney Coalfield of Nova Scotia is carried out under flooded abandoned workings in the Harbour Seam 140 m above, and at depth of up to 700 m beneath the Atlantic Ocean. Careful planning of panel and pillar dimensions is necessary to prevent inflows from the overlying workings and to prevent the development of excessive subsidence strains at the seabed. This paper briefly summarises the research undertaken over the past five years by CBDC and CBCRL into the problems associated with mining under water, and then describes the development and application of a design/planning code of practice developed jointly by CBDC, CBCRL and mine regulatory agencies. The design method employed in the Code of Practise is based on empirical data from the coalfield and parameters developed from subsidence modelling and previous water inflow experience. It includes precautionary measures to be adopted during development and mining, and monitoring procedures to be followed. It is flexible enough to allow future developments in the understanding of inflow mechanisms to be incoporated without major modifications, and represents a major step forward in reducing the potential hazards associated with coal extraction in the coalfield.

Jan 1, 1996

By Keith Heasley

In this paper, a state-of-the-art, three-dimensional, full waveform, microseismic system was used to analyze the rock failure around a deep (> 750 in (2500 ft) of cover) bump-prone longwall panel. The microseismic system consisted of both underground and surface geophones coupled through radio telemetry and a fiber-optic network to produce pseudo real-time detection and location of seismic events surrounding the coal seam. This was the first microseismic installation of this scope at a U.S. coal mine, and the system was intended to help determine the exact strata mechanics associated with the redistribution of stress and the associated gob formation at one of the U.S.&apos;s deepest longwall mines. Overall, 5,000 calibrated seismic events were recorded during the mining of one panel, including a Richter magnitude 4.2 event which occurred inside of the array. Analysts of these events provides a number of notable insights into the rock mass behavior. For instance, the longwall panel was widened during the retreat process, and the mining-induced seismicity shows a distinctly different behavior between the start of the panel, the mining of the narrow part of the panel and the mining of the wider part of the panel. Also, in itself, the acquisition of the ML 4.2 event was a major milestone in geomechanical and bump research. This is the first time that such an event has been recorded with this detail and accuracy at a bump-prone coal mine in the U.S. `The analysis of this single event has set distinct new limits on the relationship between mining seismicity and coal bumps.

Jan 1, 2001

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 Jinsheng Chen

The major functions of longwall headgate entries are to provide access ways to the outby submains or mains for coal transportation and to the longwall face for fresh air and for transporting men and material during longwall operations. Any roof control problems such as cutter roofs or roof falls in the outby headgate entries could result in significant production delays to the longwall face and may be a threat to miners&apos; safety Under a thinly laminated immediate roof and a high horizontal stress field, even a longwall headgate entry that has an angle of less than 45 degree to the maximum horizontal stress may experience roof deterioration in the outby headgate if the longwall panel mining sequence and retreat direction are not properly considered. This paper attempts to analyze the causes of the roof control problems experienced in the longwall gate entries at our Cumberland and Emerald mines in Pennsylvania and to determine the optimal longwall panel mining sequence and retreat direction for the future mining area at Cumberland

Jan 1, 1998

By Francis S. Kendorski

Rock reinforcement has been in widespread use and generally has been accepted in underground mining and tunneling since the 1950s. The first rock reinforcement technologies employed were mechanical anchors such as split wedges or expansion shells with 5/8-inch-diameter steel bolts. Failures occurred in weak strata which provided poor anchorage or in ground with corrosive waters. Friction rock fixtures consisting of relatively thin-walled tubes have been in use for about 15 to 20 years. While generally performing adequately, longevity problems have developed from corrosion in water bearing ground Longevity of rock reinforcement is much enhanced with grouted bolts. Portland-cement-grouted rock reinforcement has been in use since the mid-1950s, primarily in funneling and other civil engineering underground construction. Tests of decades-old installations have revealed few problems except in ground with aggressive waters. Polyester-resin-grouted rock reinforcement was introduced in the United states to musing in the late 1960s and to tunneling in the early 1970s. Experience from 30 years of resin-grouted bolt installations and field tests have identified longevity problems associated with degradation of steel reinforcing bars, but in generally unusual situations. Improvements continue in resin chemistries, packaging, corrosion protection, grout quantities, and mixing and distribution in the drilled hole to achieve long-term performance. Specific case histories cited with resin- or Portland-cement-grouted rock reinforcement longevity or performance problems, upon close examination, reveal that the causes of the problems were qualify control procedures being inadequate and not in accordance with good practice. Manufacturers&apos; recommendations and engineering specifications, if followed in the field, and with competent inspection and supervision, would have prevented must, if not all, reported longevity or performance difficulties.

Jan 1, 2000

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 Robert M. Cox

Abrupt tailgate roadway ground failures, described as floor bumps, sometimes occur in the tailgate entry outby the face during the high-speed extraction of coal from mechanized longwall panels. These floor bumps typically damage the tailgate entry support structures for a distance of from 12.2 to 24.4 m (40 to 80 ft) outby the face. The relative closure of the tailgate entry may be a key indicator of potential tailgate ground control problems. Regression analyses of tailgate entry convergence data conducted by the U.S. Bureau of Mines (USBM) indicate that entry closure may be characterized as an exponential function of the distance outby the longwall face. Assuming that the entry closure is caused by the abutment loads created by the excavation of the longwall panel, the resulting convergence equation can be integrated to locate the centroid of abutment loading. This information can be used to document zones of potential ground failure ahead of the operating face.

Jan 1, 1994

By Phil R. Ames, Anil K. Ray, Murali M. Gadde, John A. Rusnak

"Many factors can be responsible for coal mine roof falls including, mining geometry, stress conditions and local geology. In the Illinois Basin coal mines, roof instability is commonly attributed to the low strength of the immediate roof, which is also moisture sensitive. Recently, in order to understand the mechanisms of roof instability, numerical modeling has often been the preferred ground control analysis tool. Since roof materials can exhibit significant spatial variability, such modeling results may not represent every section of the mine. At the same time, it is not feasible to carry out numerical modeling for the full range of geological and mining conditions possible at a mine. Operationally, it is more convenient and highly practical to have a simple map that depicts the expected roof conditions, determined through either complex numerical models or simple empirical analysis throughout the reserve area. In this paper, a case history is presented that shows how a combination of simple empirical analyses of geologic data and past ground control experiences at a mine can be synthesized into a roof stability map, which can then be used to forecast future ground conditions. The usefulness of such a roof stability map will be examined in terms of the predicted and actual ground conditions encountered over a period of more than a year after the map was created.INTRODUCTIONA roof fall, which can result in fatalities and lost work time, is considered to be one of the most severe ground control hazards in underground coal mines. In general, there are many factors responsible for roof falls, including mining geometry, stress conditions and local geology. In the Illinois Basin, roof falls are commonly attributed to the weak nature of immediate roof rocks, and some superficial falls may be initiated due to moisture sensitivity. Some unstable areas also occur when the immediate roof is highly laminated.Numerical modeling is a useful tool used to understand the mechanism of a roof fall by incorporating site-specific parameters. In the past, numerical modeling has been used to explain the mechanism of roof falls as well as simulate· roof falls and cutter behavior, but such work had been strictly site-specific (Gadde and Peng, 2005; Ray, 2009). Because of the restrictions imposed by the input parameters, numerical modeling results cannot represent the entire mine. In the real world, mining conditions vary from place to place, and even in a single panel, modeling results valid at one site may not apply at another nearby site. At the same time, due to the lack of input data pertaining to rock characteristics and in-situ stress variations, it is not practical to carry out numerical modeling for each local area of the entire mine site. In addition to these difficulties, mine operators prefer simple tools to understand the ground conditions at their mine sites. One simple and commonsense based tool is the roof stability map. A stability map not only synthesizes the geologic and stress analysis data empirically, but it can also be used to predict future ground control issues at that mine. Because of this practical appeal, stability maps are more likely to gain mine operators' acceptance and be used in their planning operations. In this paper, a case study is presented on the development of a 'Roof Stability Map' that was principally used for roof fall prediction for a mine in the Illinois Basin."

Jan 1, 2010

By Leslie Carver

The effects of longwall mine subsidence on water resources were studied at a West Virginia coal mine (mine Z) by Carver (1994). Data were obtained for 137 domestic supply wells and springs and 12 baseflow streams. Subsidence caused short-term dewatering (of a few days to weeks) of wells located on lower hillslopes and valleys, and long-term dewatering of hillslope and hilltop springs (with no recovery yet). New or increased spring discharge was observed at lower elevations. Unsubsided water supplies experienced no dewatering beyond a nearby panel&apos;s 27°-38° angle of dewatering influence zone. Subsidence from longwall mining beneath streams commonly reduced discharge when panel ages were less than two to three years. However, "normal" discharge was typically observed over panels greater than three years in age; such streams exhibited lower baseflow recession constants, moderated winter baseflow, and increased summer baseflow compared to unsubsided streams.

Jan 1, 1994

By Yun Zhang, Haijun Jiang, Shenggen Cao, Chen Wang

The distribution of front abutment pressure is closely related to the force, deformation and energy distribution of hard roof before periodic weighting. So it is necessary to carry out research on the relationship between them. According to front abutment pressure distribution feature, using the location of peak front abutment pressure as the dividing point, coal seam is divided into two parts along the direction of mining: the yield zone that is the area between the faceline and the point where the maximum front abutment pressure occurs, and the elastic zone that is the part before the point of peak front abutment pressure. The proposed mechanical model of unit width hard roof at the panel center periodic weighting consists of five parts including the yield zone. All parameters of the deflection equations for each of the five parts that satisfy the continuity conditions and natural boundary conditions are obtained by using the Matlab software. The continuous curves of front abutment pressure, deflection, bending moment and bending strain energy density distribution of hard roof are obtained by iterative approximation method. The following conclusions can be drawn through analyzing those curves: (1) The position of peak front abutment pressure is located at the transition of coal seam foundation from yield zone to elastic zone (elastoyield critical point), the distance of it to the faceline is equal to the width of yield zone. The peak front abutment pressure increases with yield zone with. (2) The peak bending moment in front of the faceline, and the distance of it to the faceline increase with the yield zone width. The deflection of hard roof at the face and midspan also increase with yield zone width. (3) As the yield zone width increases, the accumulated elastic energy of hard roof in front of the faceline increases, and the core zone of energy moves forward away from the face. (4) When the yield zone width is zero, the whole coal foundation is regarded as elastic foundation, and the peak front abutment pressure occurs at the faceline.

Jan 1, 2015

By Renn Oler

Corrosion can often cause significant strength reduction and failure of steel rockbolts, thus demanding continuous rehabilitation and posing challenges to underground mines in maintaining long term ground support. The mining industry has traditionally applied galvanized and epoxy coatings for protection of ground support and reinforcement in corrosive environments due to cost considerations. However, under a harsh and corrosive groundwater condition with extreme pH levels, failure of the existing coated rockbolts often results in failure and falls of the mine roof, especially in long-term mine drifts or entries. To prevent the roof falls induced by corrosive bolt failure, DSI developed a new polymer coating, called ?Obduro AP coating,? to combat harsh and corrosive ground conditions. The new polymer coating was tested in extreme conditions to identify weaknesses and was found to be capable of handling highly corrosive mine water solutions. This paper highlights the challenges faced by underground mines with corrosive bolt failure and shows that the DSI Omega BoltTM can withstand the most corrosive ground conditions when it is coated in the new, economic Obduro AP coating.

Jan 1, 2014

By Hamid Maleki

This study presents a historic overview of the role of mobile roof support (MRS) technologies in improving stability and worker safety and presents the results of recent field evaluations of the MRS load rate monitoring device and other remote deformation-monitoring techniques. Field studies were implemented at two sites in cooperation among researchers from the National Institute for Occupational Safety and Health (NIOSH), Maleki Technologies, Inc., and J. H. Fletcher & Co. The objective of the field programs were to (l) study the interaction between MRS&apos;s and coal mine strata and (2) develop and test suitable monitoring systems for assessing roof and pillar stability. An MRS consists of a roof canopy, four hydraulic cylinders, a caving shield canopy, and associated electromechanical systems mounted on crawler tracks. The machines are controlled by radio from a remote location and operate on self-contained power units. Typically, MRS&apos;s have capacities of 5,340 and 7,120 kN (600 and 800 tons). In comparison to posts, an MRS is capable of maintaining the yield load after significant amounts of roof-floor deformation. Because the mining cycle is accelerated, MRS&apos;s help reduce the potential for time-dependent roof falls. MRS performance has been monitored in the laboratory under controlled static loading conditions and in the field under deep, two-scam mining conditions. Laboratory studies have quantified support capacity and system stiffness as a function of machine height. Field investigations have focused on determination of optimum operating conditions and development of warning systems that indicate excessive load on the machine and/or impending roof-pillar stability problems. Analyses of field data show that roof instabilities are influenced by (1) pillar failure, (2) pillar yielding, (3) mine seismicity, (4) geologic structures, and (5) panel layout designs and mining practice. Pillar yielding and failure (unloading) and seismicity can be conveniently monitored by the load rate monitoring device, but for consistent detection of roof falls, additional deformation measurements directly within the cuts ate needed.

Jan 1, 2001

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 Stankusm John C., Xiaoting Li

"Quantitatively identifying the load on a steel king beam set is a complicated issue in designing the king beam structure at the slope bottom area. From an engineering perspective, understanding the nature and support mechanism of the king beam structure as a standing support is critical in identifying the calculation input parameters for the structure design software. Based on design practices in recent years and successful applications in several slope bottom intersections, the authors present a king beam design methodology, including qualitative analysis, quantitative calculation with a structural design software, and computer Finite Element Analysis (FEA) verification.Especially important is the concept of interaction and the confinement effect between the king beam structure and surrounding rocks, which is essential in designing a proper steel structure in terms of maintaining the roof stability, as well as saving the steel materials and costs of manufacture, labor, and delivery. This paper details the design methodology and applications in several underground slope bottom intersection designs, reaching the goals of improving roof stability and reducing costs.INTRODUCTION AND DESIGN METHODOLOGYCurrently, the load on a square or arch set is typically determined by either past empirical design experiences or known heights of roof falls in current or adjacent mines. These methods work but sometimes are too conservative from an engineering perspective. For example, when designing a king beam structure for an intersection, these methods may lead to a design with extremely large and heavy steel beams, which are not convenient for delivery and installation on-site, not to mention, costly. Therefore, accurately identifying the potential maximum load on the king beam structure is important for designing a safet, effective, and cost-efficient steel structure. Based on past several years’ practices and fundamentals of ground control and structural design engineering, the authors propose a design methodology including the following components:The nature and mechanism of effective roof support (qualitative analysis),Ground reaction curve,Interaction and confinement effect between bolts and steel standing support and surrounding rocks,Factors affecting the load conditions of the king beam set"

Jan 1, 2018

By Murali Gadde

Among different types of ground control problems associated with underground coal mining, those related to in situ stresses are the most common ones affecting the safety and economy of a mining operation. As a result, this has been the focus of many ground control research works done in the last three decades. This paper summarizes a recent work done on in situ stress related ground control issues of underground coal mine development workings. The approach used in this study was three¬-dimensional finite element modeling by an implicit code, ABAQUS/Standard. In the models, roof stability evaluations were made using Hoek-Brown rock mass failure criterion. Influence of the in situ maximum horizontal stress angle on the stability of both entry and intersection was examined to help determine the best development layout orientation. Also, the effect of in situ stress ratios on the stability of development openings was studied. To make the work more general, both &apos;low&apos; and &apos;high&apos; in situ stress fields were considered In general, the modeling results indicated that entries oriented in the direction of maximum horizontal stress were in the best condition while those oriented at 90° had the least stability. For intersections, the maximum and the minimum stability were seen at 0°/90° and 45°, respectively. However, under some combinations of input conditions, the best or the worst conditions were noticed at same other orientations as well. Based on these findings, layout design charts were prepared for both entries and intersections. It was also found that the change in ground conditions with change in layout orientation was more significant for &apos;low&apos; in situ stress fields than for the higher ones. Change in the average safety factor with change in the ratio of in situ maximum horizontal to vertical stress resembled a lognormal distribution curve. However, the effect of the ratio of in situ maximum to minimum horizontal stress lacked such a clear trend for different input combinations considered.

Jan 1, 2004