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By G. Skybey

The Directional Drill Monitor (DDM) is an advanced instrument for real time in hole surveying. It was developed by Du Pont (Australia) to suit Australian gassy coal mining conditions. The instrument consists of three units: i. Down hole transmitter ii. Acoustic transducer iii. Data receiver processor unit (i.e. up hole unit). This paper describes the function of each unit in detail and highlights the importance of the DDM in long hole drilling efficiency. Surveying is carried out independent of hole depth. Each survey takes 2-3 minutes to complete, the frequency of surveying to control borehole trajectory is determined by the accuracy required for a particular hole. The DDM is currently being used successfully for long hole drilling in a number of collieries. A high degree of directional control has been achieved. Borehole trajectories were controlled to within +l¬2m of the planned path with intersurvey distances varying between 6 to 18 metres over distances up to 700 metres.

Jan 1, 1992

By Hanjie Chen

Mining experiences have shown that in a pitching seam, roof behavior is significantly different from a flat seam. Uphill mining usually experiences more roof problems than downhill mining. Based on a case study at RAG American Coal Company, Willow Creek Mine, this paper presents the roof control problems experienced in a high pitching seam. Then, finite element modeling is conducted to analyze the roof stress distribution for an entry developed in different directions relative to the seam strike. The results shows that seam inclination has a significant effect on roof stability in terms of tensile stress. Uphill mining experiences higher tensile stress than downhill mining. The modeling technique utilized in this analysis presents a first of kind methodology.

Jan 1, 2000

By M. V. Kurlenya

The experience of application of geomechanical investigations for substantiation of extraction of undermined ore deposit in the north of Siberia is discussed. The finite element method was used for forecasting the state of massif during the development of mining works. The results of calculations were compared with the experimental data of observations in situ for evaluation of authenticity of numerical modelling.

Jan 1, 1990

By Michael A. Berdine

In early 1997, Twentymile Coal Company took a dramatic departure from traditional longwall recovery methods. Previously, Twentymile's standard longwall meshing procedure included the use of chain link fencing material. Beginning with the 9-Right to 8-Right longwall recovery operation, Twentymile incorporated a polyester geogrid mesh system supplied by DYWIDAG-Systems International. This paper discusses the subsequent utilization of the polyester geogrid mesh system at Twentymile.

Jan 1, 2001

By André C. Zingano

The domino effect in a violent pillar collapse occurs due to the redistribution of stress in the remaining pillars near the collapse, and this stress transfer occurs in the immediate and main roofs. The remaining pillars do not have enough load capacity to support this overstress and also fail, and the domino effect propagates further to the entire panel. The domino effect does not occur only due to low load capacity of the pillars, but also the roof rock mass quality, because the stress is transferred by the roof. In high competent roof without discontinuity (fault), like massive sandstone seam, the deformation of the roof is the cause of pillar collapse extension and propagation. Depending on how close it is approaching the collapse limit; the immediate and main roofs behave differently. When it is close to the collapse limit roof convergence and pillars compression occur. Conversely when it is far from the collapse limit divergence and pillars decompression occur. This is called the arc-effect. This paper studies this behavior of the roof (immediate and main roofs) using numerical modeling to simulate the roof deformation and stress distribution in the roof and pillars. This simulation represents the progression of pillar collapse and shows the zone of convergence and divergence of the roof, and also the effect of this behavior on pillar confinement. Two-dimensional plain strain model was applied to simulate the arc-effect. The simulation results were compared to those of the instrumentation that was installed before the collapse. Keywords: pillar collapse, room and pillar, numerical modeling

Jan 1, 2005

By Xianxin Shi

In surface electrical exploration the high resolution earth resistivity method (HRRM) is a very effective method for detecting abandoned drift mines workings. When the abandoned mines are more than 500 ft (150 m) deep, its detection capability reduces greatly and requires more effort to implement. In Yan Quan coal mine, Shanxi province, we tried to adapt this method for underground application. Two survey lines were designed with the spacing of current and potential poles 20 m and 10 m, respectively and measuring points at 2m. The measurement radius of I line and I1 line were 140 m and 60 m, respectively, and the infinitely far pole was 1200~2000 m from the survey line. (Note the I and II lines are located on the north and south ribs of main tunnel, respectively). The survey results showed that abandoned workings were located at 25-70m, Survey Line I and at 80-1 10m, Survey line 11. Based on this finding, the longwall panel gateroads and set up entry were properly located thereby providing safe mining of the No. 15 Coal seam. Key Words: Abandoned coal mine, High resolution earth resistivity, Underground electrical exploration

Jan 1, 2005

By Russell Frith

Probably the most expensive but least well understood roof falls in underground coal mining, are those that occur ahead of the powered supports in the centre of longwall face. Even small roof cavities result in the dilution of the ROM product and large cavities can stop the face for days if not weeks and the incurred cash flow losses can be catastrophic. Expensive and time-consuming remedial measures (e.g. PUR, cavity filling, removal of stone from the AFC by hand) are required and equipment wear and damage can be significant when the need to blast and convey stone is also considered. Through four major research projects within the Australian coal industry and numerous consulting assignments, the author has spent the best part of fifteen years attempting to identify and defme the various geotechnical and operational factors that determine whether a major roof cavity occurs ahead of the powered supports or a normal goaf fall occurs just behind them, the difference in operational outcome being enormous. The paper presents a condensed summary of the overall technical findings covering such issues as roof fall mechanisms, the measured influence of cover depth, periodic weighting of massive strata units and its quantification, the role of cut-throughs in chain pillars, face width and height, the role of the powered support and the influence (both positive and negative) of mine site operations. The big picture outcome is the view that high production longwall extraction is well-suited to certain geotechnical environments, is marginal in others and under certain conditions is fatally flawed and beyond the control of mine operators, although fortunately the latter category is a relatively rare situation. Various risk-based research findings in this regard will be given as a basis for future discussion.

Jan 1, 2005

By R. Karl Zipf

Multiple seam mining interactions caused by full extraction mining, whether due to undermining or overmining, frequently involve tensile failure of the affected mine roof. The adverse ground control conditions may prevent mining for both safety and economic reasons. Prior researchers have identified the geometric, geologic and mining factors controlling multiple seam mining interactions. This numerical study examines the mechanics of these interactions using a modeling procedure that 1) incorporates the essential constitutive behavior of the rock such as strain- softening of the intact rock and shear and tensile failure along bedding planes and 2) captures the geologic variability of the rock especially the layering of weak and strong rocks and weak bedding planes. Specifically, the numerical study considered the effect of vertical stress, interburden thickness, and the immediate roof quality of the affected seam in both undermining and overmining situations. The models show that for overburden-to-interburden thickness (OBAB) ratios of less than 5, interactions do not occur, and that for OBAB more than 50, extreme interaction is a certainty. In between, the possibility of an interaction was found to depend on gob width-to-interburden thickness ratio, site specific geology and horizontal stress to rock strength ratio in addition to the OBIIB ratio. The models also showed that horizontal stress was profoundly altered well above or below a full extraction area and that these changes are likely to influence the success or failure of multiple seam mining. The role of horizontal stress in multiple seam mining interactions has received little attention in prior investigations. Four factors control the mechanics of multiple seam mining interactions: 1. vertical stress concentration 2. horizontal stress concentration 3. stress re-direction 4. bedding plane slip bands A combination of vertical and horizontal stress increase and high stress gradients in the vicinity of full extraction areas re-orients principal stresses into a very unfavorable direction. This seemingly small stress re-orientation has a profound adverse effect on bedded rock.

Jan 1, 2005

By Peter Zhang, Todd Minoski, Mark Van Dyke, Daniel W. H. Su

"This paper presents the results of a 2017 study conducted by the National Institute for Occupational Safety and Health (NIOSH), Pittsburgh Mining Research Division (PMRD), to evaluate the effects of longwall-induced subsurface deformations within a longwall abutment pillar under deep cover. The 2017 study was conducted in a southwestern Pennsylvania coal mine, which extracts 1,500-foot-wide longwall panels under 1,185 feet of cover. One 650-foot-deep, in-place inclinometer monitoring well was drilled and installed over a 150-foot by 275-foot center abutment pillar. In addition to the monitoring well, surface subsidence measurements and underground coal pillar pressure measurements were conducted as the 1,500-foot-wide longwall panel on the south side of the abutment pillar was being mined.Prior to the first longwall excavation, a number of simulations using FLAC3D™ (Itasca, 2017) were conducted to estimate surface subsidence, increases in underground coal pillar pressure, and subsurface horizontal displacements in the monitoring well. Comparisons of the pre-mining FLAC3D simulation results and the surface, subsurface, and underground instrumentation results show that the measured in-place inclinometer casing deformations are in reasonable agreement with those predicted by the 3D finite difference models. The measured surface subsidence and pillar pressure are in excellent agreement with those predicted by the 3D models. Results from this 2017 research clearly indicate that, under deep cover, the measured horizontal displacements within the abutment pillar are approximately one order of magnitude smaller than those measured in a 2014 study under medium cover.INTRODUCTIONDue to a recent shale gas boom, approximately 1,400 unconventional shale gas wells have been drilled through active and future coal reserves in Pennsylvania, West Virginia, and Ohio over the past 15 years. These shale gas wells have penetrated many coal seams, such as the Sewickley, Pittsburgh, Upper Freeport, and Kittanning seams. These unconventional gas wells, whether tapped into the Marcellus or Utica formations, contain very high gas pressure. Strata deformations associated with longwall and other high extraction techniques could induce high stresses and deformations in the shale gas well casings. This could seriously compromise the mechanical integrity of the production, intermediate, and coal protection casings (Figure 1). Damaged well casings could potentially introduce high-pressure, explosive gas into underground mine workings, particularly during an extended well shut-in period, which could seriously jeopardize underground miners’ safety and health."

Jan 1, 2018

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 D. Bigby

The current British Standard on rock reinforcement components used in coal mining (BS7861:1996) employs the axial double embedment tensile PET) test to determine the main system load transfer performance criteria, in terms of bond strength and stiffbess. This test involves measurement of load/displacement characteristics of a tendon fully grouted into internally threaded thick-walled steel tubes. Part 1 of the Standard covers rock bolting systems and Part 2 covers birdcaged cable bolting systems. Both parts are highly prescriptive, defining a specific design of bar (AT) and cable bolt (birdcaged). In 2000, it was agreed by the UK Rockbolt Research Liaison Committee that Part 1 of the Standard should be revised to allow further industry innovation of bolts and resins. Amongst other aspects, it was recognised that the double embedment test was limited by its inability to examine load transfer between the bolt and the host rock and the UK Health and Safety Executive commissioned an RMT research project to develop a new test to replace the DET test. The new test, the Laboratory Short Encapsulation Pull (LSEP) test has now been incorporated into a draft revision of BS7861 Part1 which has been issued for industry wide consultation. In 2003, it was agreed to begin revision of Part 2 of the Standard to encompass the many types of long tendon reinforcement which were, by then, being used in the UK coal mining industry. These included flexible bolts, deformed strands and tensionable systems encapsulated with resin, cementitious grout and combinations of the two. A second RMT research project was funded by the HSE to examine adapting the Laboratory Short Encapsulation Pull Test for the revised long tendon Standard. This project is nearing completion and a revised Part 2 of the Standard is being drafted. This paper presents some of the results of the two research projects, describes the laboratory tests and acceptance criteria developed and discusses the implications of the research on improving the understanding of reinforcement performance and its characterisation. In particular it shows how the new test can reveal very different load transfer characteristics to the double embedment test, as it takes the load transfer at the holefrock wall into account.

Jan 1, 2005

By J. F. T. Agapito

Overcore measurements at the North Fork Valley (NFV) coal mines in western Colorado have shown that horizontal stresses are highly anisotropic. Measurements have been made in four mines at various depths. In many measurements, the maximum horizontal stress is three to four times higher than the minor horizontal stress. At the West Elk Mine, maximum and minimum horizontal stresses of 24 MPa and 6 MPa, respectively, have been measured at depths of 640 meters (m). Under highly anisotropic stress conditions, ground control problems associated with both high and low horizontal stresses can develop. While high horizontal stresses can produce cutter failures and floor heave, low horizontal stresses can allow block fallouts. This paper summarizes the horizontal stress measurements in NFV mines and, in particular, in the West Elk Mine where their role in roof fall and floor heave failures is discussed. This experience has led to an improved use of ground support and safer mining operations at depths of 640 to 700 m.

Jan 1, 2005

By Thomas Barczak

Longwall mines typically use some form of standing support for secondary roof support in longwall tailgate entries. Although there have been several new support products developed for this application, there remains no universal design criteria to optimize the application of these support technologies. The requirement for optimization and proper support selection is to understand the degree of control that the support has on the ground behavior. The ground reaction curve and numerical modeling was used to evaluate the impact of standing support on ground behavior. LaModel was used to evaluate the impact of standing support on main roof and floor behavior and pillar yielding. The conclusion drawn from this study was that standing supports do not have sufficient capacity to control main roof or floor loading or prevent the resulting convergence of the tailgate entry. However, it is imperative that this "uncontrollable convergence" be considered in the support design to prevent premature failure of the support. A FLAC model was used to evaluate the near-seam roof and floor behavior in conjunction with the global vertical and horizontal stresses. The model suggests that standing roof supports can have some impact on the ground behavior as the elastic response of the rock is exceeded and rock structure deteriorates from the stress concentrations that develop around the tailgate opening. During this phase, the capacity and stiffhess of the standing support can be critical to the stability of the opening, as eventually the rock mass will be transformed into a partially detached structure whose weight must be supported by the standing support. This work is part of a ground control program of research at the National Institute for Occupational Safety and Health (NIOSH) aimed at improving mine safety by reducing roof fall injuries and fatalities.

Jan 1, 2005

By William Kendall

INTRODUCTION Stillwater Mining Company, with its two underground, hard rock mines in South Central Montana, is the largest primary producer of palladium and platinum in the Western Hemisphere. Platinum Group Metals (PGMs) are mined from a specific zone within the Stillwater Complex, a layered mafic/ultramafic igneous intrusion, named as the J-M Reef. Over much of the J-M Reef, the economically minable, mineralized horizon is contained at typical horizontal widths of 6.5 ft to 8 ft wide. This feature of narrow mining widths has made it challenging to safely and effectively mine these areas of the J-M Reef using mechanized cut and fill and sublevel sill development mining methods. Mechanization of most or all of the steps of the mining process is important to Stillwater in the continuous pursuit of high standards in safety and health. Mechanized bolting within the J-M Reef ore production headings is an important piece of reaching these objectives. In general, metal/non-metal mining requires varied mining techniques, as compared to more traditional bedded mineral/resource deposits. Narrow vein mining is a selective mining technique that generates a minimal amount of waste material while obtaining the more valuable ore deposits. Drilling and bolting in narrow vein mining has traditionally been performed with air-powered, hand-held ?jackleg? equipment because mechanized equipment is, typically, too large for the selective narrow vein techniques. In addition, traditional hand-held pneumatic equipment provides significant flexibility for small-opening, narrow-vein developments, reducing waste rock handling and improving ore recovery management. The hand-held equipment is also relatively inexpensive to purchase. Due to its simplicity, it is also relatively easy to train operators to use hand-held equipment. Hand-held equipment has been routinely used to safely install ground support and to develop production faces in hard rock mines for many years. Although it is effective, the hand-held equipment requires operator exposure to certain inherent hazardous conditions in the active face/development mine areas. These include falling rock, tripping hazards, bending/twisting/lifting hazards, high noise levels, and chemical fumes from the hammer exhaust. Based on health and safety statistics from the Stillwater mines, operation of the rotary-percussive hand-held equipment adversely affects the long-term health of the operator?continual jackleg operation frequently results in long term damage to hearing, shoulders, arm and wrist joints, and back injuries. This reduces the quality of life for the operator and also results in higher personnel turnover rates for the mining company.

Jan 1, 2014

By Quanxi Wang

This paper presents a new stability mapping system which tightly integrates structural and geologic mapping with geo- mechanical stress analysis for use in support design and mine plan- ning. The structural and geologic input can include such local characteristics as: rock strength, layer thickness, faults, stream val- ley effects, etc. The geo-mechanical stress inputs can include overburden stress, multiple-seam stresses, abutment stresses, etc. The mapping system utilizes the popular AutoCAD/SurvCADD platform as a foundation for inputting the geologic characteristics, and then integrates the boundary-element program LaModel for determining the geo-mechanical stress influences. Additional func- tionality in the system allows the user to transform each individual geologic or stress factor into an individual rating and then the user can apply various weighting functions to the individual factors to generate an overall stability index map for the mine property. A sample case study is included in the paper to demonstrate the basic concepts, procedures and utility of the stability mapping system.

Jan 1, 2005

By Andrew Starkey

Ground anchorage systems in the form of rock bolts are used extensively throughout the world as supporting devices for civil engineering structures such as bridges and tunnels. It is widely recognized that non-destructive testing methods for ground anchorages need to be developed as a high priority [1 ], with only a small proportion of anchorages currently being monitored in service [2]. The condition monitoring of anchorages is a relatively new area of research, with the objective being a wholly automated or semi-automated condition monitoring system capable of repeatable and accurate diagnosis of faults and anchorage post tension levels. The GRANIT tm system developed by the University of Aberdeen is capable of measuring the integrity of ground anchorages and has won two major UK Awards - the National John Logic Baird Award for Innovation in 1997 and a Design Council Millennium Product Award in 1999. The normal procedure with the GRANIT tm system [3,4] is to train a neural network on dynamic response data that has been sampled from an anchorage over a range of post-tension levels. Further data is needed in order to test the neural network. The paper presents neural networks that have been trained on data taken from a number of anchorages on different sites, and the results of the diagnosis of these neural networks on new test data is presented. The results show that the cross-diagnosis of anchorages is possible, where a neural network trained on one anchorage is capable of successfully diagnosing the post-tension level for an anchorage of similar construction, and the high level of accuracy that can be attained with the GRANIT tm technique is shown. The paper also introduces a mathematical model of the GRANIT tm process.

Jan 1, 2001

By Francis Kendorski

One of the most dangerous events in underground coal mining is unexpectedly encountering water inrushes from undetected abandoned mines in the same seam. The surest and most confident method is probe drilling either from the mine or from the surface. However, drilling is expensive and may even miss the suspected mine voids entirely by drilling through pillars. Many operators rely upon one or more of several remote sensing techniques for detecting mine voids. However, mine "voids" often are not air- or water-filled open cavities, but are collapsed, rubble-filled chimneyed columns in the strata. Geophysical techniques, such as seismic reflection and refraction, electrical resistivity, magnetics, ground-penetrating radar, and others, often assume a continuous or fractured rock mass that has varying properties which provide the signatures that allow discrimination of one strata from another, or of strata from voids. However, a rubble-filled cavity has rock block-to-rock block contact throughout its volume and can still respond as a continuous rock mass with the rock blocks allowing signal transmission or mass detection, rather than a void space. Hydraulically, a rubble-filled cavity is essentially as transmissive to water as an open mine void. Thus, the problem of detecting a mine void with confidence is significantly compounded.

Jan 1, 2004

By Charlie Li

A cut-and-fill mine stope, located at a depth of about 1000 m in a lead-and-zinc mine, was closed down because of large roof convergence and fractures appearing on the hanging wall. The instability problem was owing to the relatively low strength of the rock subjected to high in-situ stresses. Extra reinforcement was required to secure the stope so that the remaining ores in the stope could be mined. Assessment of the fracture mode in the country rock surrounding the stope was carried out and then the reinforcement de- sign was worked out. It was proposed that the unstable section of the stope would be reinforced by bolt-shotcrete ribs as well as selective long bolts. The philosophy of the design was to hold up the fractured country rock by bolts and shotcrete so that a load-bearing arch could be formed in the roof and in the hanging wall. Six shot- Crete ribs were set up in the unstable section of the stope. Displacement measurements showed that the roof convergence reduced from about 2 &day to the ordinary creeping level, about 0.25 &day, immediately after the reinforcement operation. Six month later, the hanging wall collapsed into the stope in a place just outside the reinforced section, which indirectly proved the effectiveness of the bolt-shotcrete ribs in reinforcing the fractured country rock. This case showed that an appropriate rock mechanics assessment would form a solid base for reinforcement/support design. It also provided an evidence for the philosophy of the reinforcement by bolt-shotcrete ribs - establish a load-bearing arch in the rock.

Jan 1, 2005

By Murali Gadde

Numerical simulation of cutter roof failure is a daunting coal mine excavation design issue. The complex progressive failure mechanisms associated with cutter failures are extremely difficult to replicate in computer models. However, this paper shows that with a proper selection of constitute behavior and implementation of cutting sequence, it is possible to realistically reproduce cutter failure using continuum models. Strain-softening material behavior and a systematic step-by-step model solving for a four-entry-and- three-crosscut model produced results that are similar to cutter patterns noticed in field. These results show that traditional modeling with geometries created in one model-step has limited applicability and may even provide misleading conclusions under some circumstances. Most importantly, the proposed modeling methodology provided some insights into the reasons for the inconsistent spatial distribution of cutters often noticed in coal mines. The modeling also revealed the usefulness of cutter mapping to determine the directions of in situ horizontal stresses.

Jan 1, 2005

By A. Bortolussi

The paper discusses the state of the progress reached in the development of the diamond wire tool for cutting hard rocks. To the advances of this relatively new technology a substantial contribution has been provided by the research being carried out at the University of Cagliari on samples of granite rocks from different Sardinian stone quarries. On the basis of field experiments and laboratory test data, the mechanism of diamond wire cutting has been assessed. In particular the influence of the rock features and operational variables an tool performance (cutting rate and bead wear) has been elucidated.

Jan 1, 1992