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One of the most important parameters in rock/resin/bolt load transfer mechanism is the surface property of the bolt. Although there are various bolt surface configurations available in the market, very little work is reported on the bolt/resin interface failure mechanism. This paper examines the behaviour of bolt surface roughness under constant normal stiffness conditions which is considered as being a realistic way of evaluating bolt surface roughness. A series of shear tests have been conducted on the flattened bolt surface to study the shear behaviour of bolt/resin interface. Based on the experimental results, a mathematical model has been developed to predict the shear resistance of the bolt/resin interface at various normal stress levels for the bolt types used in the study.

Jan 1, 1999

Numerical simulation for microseismicity due to mining at one of the collieries in Australia was carried out and the results were compared to the observed microscismicity. 3-D Stress analysis showed stress concentration on the edges of the mined areas and on the coal pillars- The stress concentration ahead of the coal face was biased to the tailgate. This is similar to the observed distribution of microseismic events. Stress reduction above and below the mined area was seen. Tensile stress was observed mainly above the mined area. It was realized that compressive failure due to nearly vertical maximum principal stress and nearly horizontal minimum principal stress in retreat direction (NS) might occur ahead of the face. Tensile failure due to nearly vertical minimum principal stress above the mined area was expected. Compressive failure due to nearly horizontal maximum principal stress in EW direction and nearly vertical minimum principal stress above and below the mined area were also expected.

Jan 1, 2001

By Keith Heasley, Christopher Newman, Zach Agioutantis

"Previously, in 2013, a laboratory version of the computer code ARMPS-LAM, introduced at the 32""d International Conference of Ground Control in Mining, successfully integrated the laminated overburden model of LaModel into an ARMPS-style pillar stability analysis. The ARMPS-LAM analysis has now been fully integrated into the ARMPS program allowing users to more accurately classify the stability of a given mine design utilizing a laminated overburden model for the determination of pillar loading within theAMZ. ,This paper introduces the new Windows-based ARMPS-LAM program. The program's ease of use, output result generation, and limitations are highlighted through the parametric analysis of three hypothetical case studies where traditional ARMPS output is compared to output generated by LaModel. As mining operations continue to produce at greater depths and in more complex geometric and geological conditions, flexible and efficient analyses of mine stability for underground room and pillar mining has become more and more essential. The ARMPS-LAM program provides the mining industry with an empirically backed, numerical design tool for the evaluation of underground room and pillar mine plans.INTRODUCTIONIn the Southern Appalachian coal fields of the United States, retreat room-and-pillar methods have allowed mining operations to maintain high rates of production in the face of adverse geologic conditions and shrinking coal reserves. Over the years, research has been dedicated to understanding and mitigating mining-related dangers due to second mining practices, such as: pillar squeezes, floor heave, roof falls, pillar bumps, etc. However, as mining operations continue at deeper depths and with more complex geometric and geologic conditions, there is an inherent industry need for more accurate, flexible, and faster evaluations of stability for underground room-and-pillar mining."

Jan 1, 2016

By Jamal Rostami, Asok Ray, Samer S. Saab Jr., Wenpeng Liu

Ground instability, such as roof or rib failures, is one of the most serious and frequent safety hazards that occur in underground mining, tunneling, and underground construction. The ground-related parameters and features of interest, in assessing roof or rib failures, are location, frequency, and orientation of the joints, voids, as well as rock-strength. These parameters are the main components of rock mass characterization that offers effective strategies for ground support, which, in turn, allow one to mitigate the risks related to ground instability. The main objective of this study is to determine the location of joints and classify rock-strengths by analyzing the drilling data recorded from an instrumented roof bolter while drilling for rock bolt installation during the operational cycle. For this purpose, computer programs based on updated pattern recognition algorithms were developed for joint-detection and classification of rock types to offer an estimated strength. This paper briefly introduces ongoing research on joint detection, especially for joints with an aperture less than 0.125in (3.175mm), by employing an instrumented roof bolter in controlled environments. To improve the capability and precision of joint detection programs in detecting the joints from the drilling data and reducing the number of false alarms, many laboratory tests with various simulated joints and rock-strengths were carried out at a J.H. Fletcher & Co. facility. This paper reviews testing procedures, data analysis, updated algorithms used for joint detection, and discusses the latest round of testing in samples with simulated joints at various angles along the borehole.

Jan 1, 2017

By Peter Cain

The Phalen Colliery in the Sydney Coalfield is extracting the 2.6 m thick Phalen Seam by the panel and pillar longwall retreat method. Abandoned workings occur in the Harbour Seam 140 m above and overlie the Phalen Colliery. Parts of these workings are flooded, and pose a number of questions relating to the safety of operations in the Phalen Colliery. In order to answer some of these questions, the Cape Breton Development Corporation re-entered an abandoned non-flooded roadway in the Harbour Seam directly above a retreat panel in the Phalen Seam to allow the deployment of instrumentation to monitor interaction effects. Fifteen monitoring sites, each 4.5 m apart, were installed in the 5 East Top Level after it had been re-entered and made safe. Each monitoring station included a vibrating wire strain gauge piezometer and a potentiometric extensometer. The piezometers were attached to rock bolts anchored into the floor and were connected by a flexible standpipe to a constant head apparatus. Variations in hydraulic head due to subsidence were monitored to determine subsidence. The extensometer units were mounted on rock bolts anchored into the floor of the roadway beneath the ribside and monitored ground strains. The instrumentation was capable of remote reading in the event that access to the site was restricted after installation. This paper describes the instrumentation, the installation programme, and some preliminary results.

Jan 1, 1993

By R. F. Valene

This paper is not available for inclusion in the Proceedings at the time of printing. but it will be included as an insert

Jan 1, 1984

By Donovan J. Benton

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

Jan 1, 2014

By Freddie Hunter

An underground mining method for extracting an eight metre (26') coal horizon, containing a sandstone layer. A decrease in the thickness of the rock strata between the number two and number three seams of the Sasolburg Coal Field, has resulted in a total mining horizon approximately eight metres (26') thick. This parting varies in thickness and competency and in some areas is impractical to cut with a continuous miner. In addition, the general mining area is highly jointed. The top seam is first mined to a normal bord and pillar plan with a continuous miner. The bottom seam is then mined by selectively undercutting the stone parting constituting the floor of the top seam. In areas where this parting is between 0.75 - 2.50 metres (29.5" - 98") thick, it is suspended from the primary roof support installed when mining the top seam. Secondary, high extraction retreat mining is then undertaken in the coal pillars adjacent to the suspension supported headings in the bottom seam. Left in-situ, the parting provides lateral support to the pillar sidewalls in both the top and bottom seams, enabling high percentage extraction rates in what was previously thought an uneconomically mineable area. The paper proposed, presents the challenges and practical implications of executing the mining method, including the primary roof control of the top seam and the stone parting between scams.

Jan 1, 2003

By R. Fraher

Hazard analysis utilizes interaction mechanisms in combination with geologic, structural and mining conditions to delineate areas of potential damage in seams subject to interaction. Using characterizations of conditions peculiar to multi-seam mining, such as innerburden thickness, geology and structures, initial interaction contour maps can be constructed. Geologic hazard analysis is then carried out on roof, pillar and floor conditions in the affected seam using lower seam rock properties and layout geometries in the overlying seam. Either safety factors or damage ratings can then be developed representing degree of hazard in the lower seam. The final hazard map shows both the aerial extent and magnitude of potential damage from interaction.

Jan 1, 1992

By E. Yasar

This paper describes the use of the sand and plaster physical modelling technique to investigate the deformation around mine roadways using a variety of support methods in a particular form of stress field. The characteristics and conditions of coal measures rock were considered prior to the preparation of the models and the insertion of support The investigation has clearly shown how floor lift, roof failure and sidewall movements of mine roadways in laminated weak rock conditions gradually develops as a result of the increase in the stress and, also, how it is related to the level of support used.

Jan 1, 1995

By Michael Kelly

Longwall mining is the principal method of underground coal mining in Australia, with 70 million tonnes being produced by longwall mines in 1999. However, the mechanisms that control longwall geomechanics are still not clearly understood resulting in stoppages costing several hundred million dollars per annum The CSIRO has been investigating longwall geomechanics with consultant groups and minesites through several ACARP supported projects since 1994. The research has aimed to improve longwall support design and control methods by defining strata failure mechanisms and their occurrence about underground extraction panels, It also aimed to develop better predictive tools bur a broad range of underground environments. As a result of site studies at more than 8 locations some of the aspects that have been touted to control longwall geomechanics, especially from a 3D aspect are highlighted. These aspects include stress controls, geometry, faulting, depth. longwall width and changes in lithology.

Jan 1, 2000

By Sandin E. Phillipson

"On April 5, 2010 a massive dust-fueled explosion at a longwall mine in southern West Virginia claimed the lives of 29 miners. The mine had experienced large gas inrushes from the floor on two known previous occasions, and natural gas was found emanating from floor fractures behind the longwall shields after the explosion, indicating a likely fuel source for the initial ignition. In succeeding months, another longwall mine operating in the same seam 15 miles away encountered smaller inflows of natural gas that halted production from two different longwall faces. Production was halted at a third longwall mine, 30 miles south of the first, in May 2011, when explosive levels of methane were detected inby the longwall face on the headgate. The same mine was evacuated on March 20, 2014 when a series of floor gas feeders were encountered on the longwall face. A literature review indicated that there has been little documentation or description of these events, and that their size and frequency are unknown. The most significant floor gas inrushes in the United States are believed to have been associated with longwall mining in the Pocahontas No. 3 Seam of western Virginia, in which an estimated 5.8 x 107 ft3 of natural gas was expended from a floor feeder on the longwall face over a two-week period (Aul, pers. comm.).A variety of mechanisms and circumstances are associated with methane emanations from underground mines. Hyman (1987) defined an outburst as a violent, simultaneous release of gas and comminuted rock material into a working face or the interior of a borehole, and indicated that certain soft or fractured coals have a propensity for outburst based on gas desorption rates. In this mechanism, reservoirs of autogenic gas hosted in pockets of soft, crushed coal surrounded by harder coal are released suddenly as confining stress is removed by mining. Hyman (1987) also suggested that highly stressed, relatively gassy coal that is penetrated by mining-induced fractures could be outburst-prone. Clayton et al. (1993) and Ulery (2008) recognized the importance of faults as potential conduits for gas from adjacent strata into coal mines, and suggested that biogenic gas trapped in adjacent strata could migrate into mined coal seams due to a pressure differential. Ulery (2008) distinguished between an outburst and a blower, the latter defined as an event expending a large amount of gas over an extended time period, most often emanating from underlying strata, but without expulsion of coal or rock. Methane feeders are further defined as a subset of blowers that continually expend gas over a long period of time but at a lower rate. Many of the mechanisms discussed by Ulery (2008) relate to geologic features that can impound gas within the seam, releasing a voluminous amount when mining breaches the elastic dike, fault gouge, or other geologic structure that had restricted and compartmentalized coalbed methane migration. Thus, the events discussed in this paper can be described as blowers and feeders. However, detailed geological observations of the three longwall mines discussed in this paper appear to indicate a mechanism that is different from those described by Hyman (1987) or Ulery (2008), in that they did not involve coalbed-sourced gas, and the reservoirs were not hosted by coal seams."

Jan 1, 2016

By Satyendra K. Singh

If the extraction is beneath massive roof strata, the roof tends to 'bridge' across large spans without failing, the caving behaviour is complex and irregular. Understandably, these give rise to many geotechnical problems with safety implications and involving sometime huge direct and indirect costs. Only two important problems, 'feather-edging' in pillar mining and `severe periodic weighting' in longwalling, are discussed in this paper in the background of geomechanics investigations in Australia at Blue Mountain Colliery and in South Bulga Colliery respectively. `Feather edging'- a major source of injury and fatal accidents in Australia and South Africa in such situations, refers to a phenomenon where the roof, at the goat edge, falls as a thin wafer of rock often suddenly, over-riding conventional timber breakerlines. The results of the first comprehensive, monitored trial in an Australian pillar extraction coal mine, suggests how the roof falls into feather-edging caving (generally) because of multiple shear-planes (interpreted) and how it may be alleviated. Because of complex fracturing behaviour of massive roof strata, periodic weighting at a longwall face is certain to manifest itself as 'yielding supports', heavy conditions', rapid convergence and in the worst case, as a cause of face stoppage. After briefly discussing the programme of instrumentation (in a chain-pillar and over the would-be goal) and results, this paper attempts to improve mechanistic understanding of the related geotechnical issues associated with the weighting behaviour and aims at establishing a 'threshold' value of weighting severity index (suggesting intensity of periodic weighting) with an objective to optimise operational controls before mining through potential (future) weighting areas.

Jan 1, 2000

By Tony Iannacchione

A close look at the Loyalhanna Limestone of southwestern Pennsylvania reveals a complex structural environment. Most exposures of the Loyalhanna occur along Chestnut Ridge and Laurel Hill within the Allegheny Mountain Section of the Appalachian Plateaus Province. Because the Loyalhanna is rated as a super pavement aggregate by the Pennsylvania Department of Transportation and because of its proximity to the population centers of southwestern Pennsylvania, the Loyalhanna has been extensively mined along these prominent anticlinal structures. Geologic and engineering analyses were performed using gas well and core logs, outcrop examinations, underground observations, and mine maps. Strata exposures from both outcrops and quarries were used to construct geologic maps, stereonet, and rose diagram projections so that the Loyalhanna's structural environment could be understood better. Many of these structural conditions cause ground control problems at local quarries. These problems ranged from small-to-moderate sized rock falls associated with roof jointing to pillar failures associated with dipping discontinuities. Stresses ranged from tensional on structural domes where weathering dominates, to high levels of compression within structural saddles. A greater understanding of these characteristics is a prerequisite to develop engineering controls, such as improved mine layouts. pillar sizes, etc., that lessen miner exposure to these hazards.

Jan 1, 2002

By Dongsheng Zhang, Xufeng Wang, Wei Zhang, Gangwei Fan

"Large-scale longwall mining of shallow coal seams could cause mining-induced fractures to communicate with the surface immediately in Northwest China, leading to a series of mine safety and environmental issues, including crack formation, water loss, vegetation deterioration, land desertification, and spontaneous coal combustion. Therefore, an accurate and effective understanding of the spatiotemporal evolution law of mining-induced fractures in overlying strata and its relationship to upper aquifers is critical. In this paper, the application of the geophysical-chemical properties of radon in mining engineering is explored as a potential solution to the shortcomings of existing surveying methods. A radioactive measurement method is proposed for the detection of the development of mining-induced fractures in overlying strata in the Baoshan Coal Mine (BCM). The on-site trial indicated that the first weighting step is approximately 60 m, the average periodic weighting step is approximately 20 m, and the influence coverage of the advanced abutment pressure is approximately 30 m. The presented method could be used as an indirect technical support to increase the safety of coal mining by acting as a simple, fast, and reliable method of detecting mining-induced fractures in overlying strata.INTRODUCTIONAccording to the latest coalfield prediction results provided by China’s National Administration of Coal Geology (CNACG) (Zhou et al., 2013), China’s coal resources are mainly distributed throughout the West, e.g., Inner Mongolia, Xinjiang, Shaanxi, Shanxi, Ningxia, and Guizhou. Two major coal mining areas have been established in the Northwest and the Southwest, and are typically represented by Inner Mongolia and Guizhou (Zhang et al., 2010). Northwest China is an arid to semi-arid area, where the coal seams are typically shallow and covered by a thin layer of bedrock. In its natural state, the surface’s ecological environment is fragile. Large-scale longwall mining of shallow coal seams could cause mining-induced fractures to communicate with the surface immediately, leading to a series of mine safety and environmental issues, including crack formation, water loss, vegetation deterioration, land desertification, and spontaneous coal combustion. This can propel any potential ecological fragility into a state of actual destruction (Zhang et al., 2011). Therefore, an accurate and effective understanding of the spatiotemporal evolution law of mininginduced fractures in overlying strata has become the theoretical basis of solving the above issues."

Jan 1, 2015

By Christopher Mark

Dr. Christopher Mark serves as Team Leader of the Rock Mechanics Section in the Rock Safety Engineering Branch of the NIOSH - Pittsburgh Research Laboratory. In this position he leads a multi-disciplinary team and conducts individual research directed towards fundamental ground control safety issues affecting miners. Dr. Mark is recognized as one of the country?s leading authorities on coal mine ground control. Through his research, he has made numerous important contributions to mine safety that have been widely adopted into mining practice. He is a highly original researcher, and has often developed new and innovative methods to tackle extremely complex problems in his field. In recent years Dr. Mark has also achieved wide international recognition. Five research projects in Canada, Australia, and South Africa have been based largely on his work.

Jan 1, 2007

By Herryal Z. Anwar

In recent years, many both mining and civil engineering projects are developed in the area which may be categorized unstable, such as fractured and jointed rocks or "water sensitive rocks". For example, in underground coal mining, in which the floor strata normally consist of weak shale, the problem that may arise in roadway is floor heaving. In this case cement injection in borehole appears to be an economically effective method in order to make roadway more stable. This method may be also applied in the projects in which the constructions are laid on fractured and jointed rock. Nevertheless, the successful cement injection is much dependent on the water-cement ratio and the injection technique. This paper discusses the application of cement grouting to improve the ground stability in longwall mining, the laboratory experimentation of cement grouting and the method of floor injection.

Jan 1, 2000

Design and selection of support systems for longwall faces call for in-depth knowledge of strata mechanics and in particular of strata-support interactions. The paper presents the results of field investigations and analysis of a difficult-to-cave roof using powered supports under a massive dolerite sill in Central India using a state-of-the-art datalogger system. The mechanised longwall face was equipped with 4/680 tons chockshields operated on the IFS mode using a 300 K W DERD shearer. The datalogger system was capable of storing data simultaneously in 32 channels. The paper describes the monitoring system and the monitoring programme. The system provided useful information on support behaviour, build-up of leg pressures and face convergence during an intense dynamic periodic weighting phenomenon which destroyed the integrity of almost half of the face supports. At this point, the face had advanced by about 197 metres from the barrier. The paper outlines a post-mortem analysis of this dynamic event and provides a critical evaluation of the data collected for understanding strata support interaction and the behaviour of the massive sill in the overburden.

Jan 1, 1992

By J. L. Condon

The Bureau of Mines, through in-house and contract research, monitored mountain bump-prone areas of the Olga #2 Mine, near Welch, WV, using microseismic techniques for 15 months during 1985 and 1986. During this period, two ground failures occurred that were considered "mountain bumps" owing to excessive stress buildups. One failure damaged the roof and 4 pillars around an intersection; the second failure, which released much greater energy, resulted in significant damage to over 100 coal pillars. Analysis of the microseismic data collected provided significant insights into the magnitude and location of each failure. The actual failure zone was clearly delineated prior to the mountain bump occurrences through analysis of source locations of each microseismicevent. Trends in cumulative rate plots indicated the onset of structural instability. Although the data could not be analyzed automatically, the significance of the data interpretation cannot be overemphasized. Microseismic monitoring of bump-prone areas can be successful in providing a means to actually observe the structural stability occurring in underground coal mines. This paper discusses data collection techniques, analysis methods, and implications of the monitoring technique, with special emphasis on actual data from two large mountain bumps in West Virginia.

Jan 1, 1987

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