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By Richard Campbell

Effective strata control, utilising fully encapsulated resin grouted roof bolts is dependent on the installed quality of the reinforcement elements. Resin based grouts are the main form of rock bolt anchorage in the underground coal industry in Australia and New Zealand. To be effective the system requires the mixing of the catalyst and mastic components of the resin as well as shredding of the cartridge that contains the resin. Over the past six years Solid Energy New Zealand Ltd (SENZ) has pioneered an extensive work programme quantifying the effects and extent of poor installation quality due to gloving, poor mixing and loss of encapsulation (Pastars 2003, Campbell et al 2003, Mould et al 2004, Campbell et al 2005 and Pastars & MacGregor, 2005). The One-Step Bolt (OSB), an innovative bolting solution designed and manufactured by Hilti Pty Ltd offers a self drilling, single pass bolting method that eliminates gloving, guarantees mixing quality and encapsulation performance of the installed product while not jeopardising the mechanical performance of the bolt. This paper details recent work undertaken by SENZ designed to understand and quantify the system performance of the Hilti OSB in New Zealand?s thick coal seam mining environments.

Jan 1, 2006

By G. J. Hasenfus

There are no known published methods of estimating the degradation of coal measure rocks by water that are simple and efficient, yet still provide a quantitative, meaningful value for assessing the stability of coal mine floor, roof, and rib. The slake durability test, the standard index method for estimating the durability of rock subject to wetting, can provide misleading results for floor stability assessment. Additionally, slake durability testing is time consuming and requires specialty equipment. Methods based on humidity cycling have been demonstrated to be very effective for assessing coal mine roof, but require specialty equipment and do not address floor stability concerns. Visual observation techniques, such as that developed for the Coal Mine Roof Rating (CMRR) method, adequately qualify rock degradation, but lack quantitative rigor. This paper will describe an alternative method, coined the water sensitivity test, originally developed for floor stability analyses, but also found applicable for roof and rib stability assessment. The test was developed by CONSOL in the early 1990's, and in its current form, has been in use for approximately twelve years. The method is based on the basic slake durability principle of measuring the mass of the rock retained on a screen after submersion in water. The new test employs two screens of different sizes, and also uses modified submersion, drying, and data processing procedures. The method is relatively efficient and can be geared toward batched testing. As with the slake durability test, the resulting index value provides a quantitative measure of the susceptibility of rock to water degradation. In addition to discussing the test method and its development, this paper provides a comparison of results with those fiom standard slake durability tests, and tabulated results for various types of coal measure rocks. Examples of the technique's utility are provided, including assessment of longwall and development floor conditions, roof and rib rock weathering and stability, and drum-bit cutability.

Jan 1, 2005

By Yi Luo

The efforts to mitigate longwall subsidence influences on various residential and farming structures by many coal mining companies have been successful in the recent years (Luo, et al, 2003). The successes were largely dependent on the accurate subsidence predictions, correct assessments of potential influences, appropriate design and implementation of the mitigation measures. However, such efforts for protecting large industrial structures are still very rare. In this paper, the successful assessment and mitigation of the subsidence influences associated with a very intensive dynamic longwall subsidence process on a large workshop are presented.

Jan 1, 2005

By Mikhail P. Nesterov

The paper presents the results of the research that can forecast the development of subsidences and deformations of the earth surface with time in the permanent marginal areas of the movement troughs arising when mining sylvinite beds in the Upper Kama deposit of potash ores where the rock formation support is made by means of interchamber (rib) pillars of various yieldability.

Jan 1, 1997

By David H. Tang

Massive pillar failures were observed at two underground coal mines. The results of stability analysis using traditional pillar design formulae did not agree with the underground observations. Finite element models were used to analyze the causes and mechanisms of the pillar failures. The results were confirmed by the underground observations. Finally, the improved mine plan for each case was derived to ensure the stability of the underground structure.

Jan 1, 1990

By Krzysztof Kotwica

The steady demand for rock materials leads not only to on increase in mining but to the need for decreasing the loss of material in the process of exploitation as well. It brings about an increase in using of explosives in open pits and as a result an increase of after blasting gases volume, vibrations, the scattering (dispersion) of stone ect. All these factors affecting the environment lead to the research work for applying the electrohydrodynamic methods both in open casts and underground mines. In the article the authors describe the concept of this method and construction of equipment which recently have been successfully introduced in mining, the results obtained determine the possibilities of using this method and the future directions. The results of combined method with high-pressure water jets cutting and prototype equipment for separating rock blocks from the rock mass using special head with high-pressure water jets are also described.

Jan 1, 2006

By K. Unkug

It is commonly accepted that the tension of roof bolts can be used as a measure of the effectiveness of roof support performance in coal bearing strata. The conceptual base for the assumption originates from beam theory. Roof bolt tension acting across the bedding and other weakness planes increases friction, preventing potential separation and slippage within the roof strata and therefore, increases the stiffness of the roof beam between the open face and the rock-mass enclosed within the anchorage. Thus, it is important to monitor roof bolt tension, especially for research purposes, and consequently many measuring systems were developed based on numerous working principles. Research planned by the Department of Mining Engineering at the University of Kentucky required a large number of tension measuring devices of high precision. These were intended to operate reliably in corrosive mine environment over long periods of time. After evaluating the existing systems, it was decided to develop a new type of roof bolt dynamometer which would fulfill the above requirements at minimal Cost. Nearly one hundred such dynamometers were constructed, calibrated and installed in two underground mines. They remained in service for a period of one Year, producing a valuable database for the Project. In this paper the working principle of this new type of dynamometer will be described and technical considerations and samples of the collected data will be given.

Jan 1, 1986

By B. G. D. Smart

An understanding of the nature of yield zones surrounding coal mine excavations is fundamental to the design of mine support systems. Various methods have been designed for investigation of underground rock masses and an extensometric technique, the Magnetic Rod Extensometer, has been developed to overcome inherent design limitations in existing equipment of this type. This paper refers to the prototype form of the extensometer and details changes designed to overcome a variety of drawbacks indicated by routine use of the equipment. The principal change has been one of manual to computerised data acquisition and presentation in the laboratory phase of the system. This has dramatically reduced the time taken to process underground measurements and produce numerical and graphical results. The revised Magnetic Rod Extensometer represents an integrated instrumentation system that combines speed and accuracy in all areas of data handling.

Jan 1, 1984

By Karl Zipf

In highwall mining, once a sufficient number of web pillars are developed, they can fail catastrophically in a domino-type failure, posing a safety hazard to highwall miners and sterilizing mineable reserves. Three recent case histories of catastrophic web pillar failure in U.S. and Australian mines are documented and analyzed with two design approaches. The conventional design approach uses only a strength criterion, while the postfailure design approach uses both strength and stability criteria to insure an acceptable failure mode should strength failure occur. Catastrophic highwall web pillar failures can cost money through equipment losses, production losses, coal reserve sterilization and lost opportunity costs. Coal recovery may be higher. but the benefits of higher recovery must balance the potential costs of failure. Application of the conventional or postfailure design approach will decrease coal recovery and revenues, but the risk of potentially costly failure is much less.

Jan 1, 1999

By Brian R. A. Wood

Any defect activity resulting from an applied stimulus on a structure will generate a stress wave which travels in the medium under the laws of acoustics, thus the name of acoustic emission (AE). AE techniques can therefore provide information on the deformation of both surface and below ground structures, Two operating coal mines were monitored from the surface, and both mining activity and post mining microseismic activity were detected. The nature of the detected AE signals demonstrated that there were a range of deformation mechanisms in operation and that some predictive capabilities were possible with the technique.

Jan 1, 1992

By Bill Kyslinger

In underground mining, machine design is predominantly dictated by mine conditions and individual customer desires. In partnership with Boart Longyear Poland and KGHM, J. H. Fletcher & Company was tasked to design and manufacture a single-boom, single operator drill module for installation of 1.2 meter expansion bolt in a 1.6 meter height mine. The objective was to produce a machine to provide ergonomic improvements for the operator while working in the mine environment. This dictated the requirement for a small easily controlled, maintenance friendly design with a remote operator?s control station. The selected design method was to use starter and finisher drill steels. This combination, requiring a number of mechanized machine motions, provides the ability to drill the required depth in the specified mine height. To accomplish the task from a remote location, a conscious decision was made to employ current technology in the form of small pressure compensated hydraulics and electronic controls. The result of the design method is a modular assembly with each sub-component designed to be replaceable and adjustable independently from other machine components. The low profile remote roof bolting module is made up of six major sub-components. Each major component is painted a different color to help the operator make the visual connection from the drill module to the operator?s control/display monitor. The Stabilizer (White) secures the module between the mine top and floor. The Drillhead (Orange) produces the drilling rotation and torque but also must slide out of position to allow the machine to manipulate the drill consumables. The Drill Steel Carousel (Blue) holds and indexes the starter and finisher steel from position to position. The Manipulator Arm (Green) moves and guides the drill steels and drill consumables from position to position during installation. The Roof Reference Guide (Yellow) locates the mine roof and guides the drill steels and drill consumables into position. The Linear Bolt Carousel (Purple) holds the drill consumables. The low profile remote roof bolting module allows the operator to drill and install a roof bolt manually or automatically with the push of a button. This design substantially reduces the operator?s exposure in the mine environment, as well as inherent pinch points and rotary hazards. Positioning the operator safely in the confines of the air conditioned cab.

Jan 1, 2006

By Hani Mitri

Understanding the interaction between rock bolts and underground rock movement is critical for safe and cost effective underground excavation design. Although early research on this subject involved a balance of theoretical analysis and field measurement, recent work has been heavily focused on analytical and numerical studies. This paper describes technologies that have the potential to redress the balance through instrumentation of rock bolts deployed under routine operating conditions in underground mines. Two new products are presented in this paper. Firstly the U-cell coupler is a load cell device that can be routinely coupled to the threaded end of a bolt prior to installation. It measures the ?series? load at the head of the bolt. Secondly, the d-REBAR involves an array of small-diameter, long-base length displacement sensors recessed into grooves along the entire length of the bolt. Both new instruments are interfaced with on-board digital signal conditioning and telemetry. Methodologies for the deployment of the new instrumentation and guidelines are presented for the interpretation of results based on data obtained from field trials. Successful field installations demonstrate the viability and practicality of these new technologies and, moreover, provide important insight in to rock bolt/rock mass interaction.

Jan 1, 2012

By Takashi Sasaoka

Chain Conveyor Cutter (CCC) is a chainsaw-type machine and originally developed for the construction of underground walls and/or ground improvements. CCC was developed from the accumulated technology of coal mining, combining the cutting technology of a shearer and the fuctions of chain conveyor. The CCC can cut harder soils and soft rocks, and vertically mixes the cut soils/rocks with cementing material selected through the discharging port installed at the bottom of the machine. In Indonesia, highwall mining trials have already been conducted in several coal mines. However, full-scale and regular operations have not been done yet due to the ground and machine control issues from their geological conditions. In order to overcome these problems, the application of CCC to highwall mining systems was proposed, and its applicability and technical issues to be solved were investigated in this research. This paper discribes the characteristics of CCC system and discusses the application of CCC to highwall mining systems.

Jan 1, 2012

By Jeffrey Whyatt

Mining coal in deep, gassy strata is difficult, particularly in deep mines of the west. Dynamic failure (bumps, bounces, etc.) is commonplace, particularly where strong sandstone strata are encountered in the overburden. The disaster potential posed by dynamic failure in these mines is examined and found to be significant. Recent trends in MSHA reportable bumping of deep western coal mines have been increasing. Recent clusters of bumps are explored, a number of which have ended badly. The mechanisms of these bumps and their interactions with geologic structures are explored. Significant progress in controlling these hazards depends on a full understanding of their interaction with geologic conditions. It is apparent that not all MSHA reportable bumps have the same mechanism. These reports describe bumping of pillars, rolling of ribs, outbursts of coal, heaving of floor, shaking-induced roof falls, etc. Progress depends on understanding the underlying mechanisms of these events, and then determining which are potentially active at a particular location. Designs and other protective measures can then be adapted and deployed appropriately. Explicit consideration of mechanisms also supports extrapolation beyond experience as design extends into new mine geometries, geologies, mining methods and increasing depth. Finally, the goal should not be only to design hazard out of mines, but also to provide assurance that this, in fact, has occurred. Pursuit of this goal has been taken up by a major NIOSH research project. The centerpiece of this project is development of a Dynamic Failure Control Program to monitor evolution of dynamic failure hazards with changing geologic conditions to assure that control and protective measures are appropriately deployed.

Jan 1, 2008

By Carl Tom Blevins

Resin was first introduced to U. S. mines in 1971 and first produced in 1973. The original polyester roof bolt resin was very expensive and limited to a single cartridge size and a single slow gel time. Early resin applications were limited to very difficult ground conditions. Today approximately 80% of the over 100 million roof bolts installed in U.S. mines, tunnels, and construction projects employ polyester roof bolt resin. The industry has evolved from hand packing samples for trial testing to producing enough resin, if converted to a .9 inch (22.9mm) diameter cartridge, to encircle the world at the equator approximately three (3) times each year. Manufacturing and design improvements allow for a more consistent product with a wide range of applications at a price that is approximately 30% below our 1974 sales price. An inflation adjusted dollar buys six (6) times more resin in 2006 than in 1974. Modern gel times range from a few seconds to over 15 minutes. Viscosity is matched to bolt type and drilling machine characteristics. Multiple cartridge diameters and a wide range of cartridge lengths are offered by two operating companies. Resin manufacturers have also gone through a period of restructuring and change to meet the challenges of the mining industry. DuPont Fasloc has become Fasloc, Inc., a stand-alone company. Celtite became Fosroc then Minova, as it is known today. During this transformation, several manufacturers have either discontinued production or were absorbed. The industry led the development of the chemical grouting materials specifications contained in ASTM F432-95, Standard Specifications for Roof and Rock Bolts and Accessories. A history of the industry will be presented within a discussion of the evolution of the strength index, speed index, cartridge volume, class designation, and product marking requirements of ASTM F432-95.

Jan 1, 2006

By Wenquan Zhang

Based on the mining and geological conditions of Wadong Mine, Longkou City, Shandong Province, China, a viscoelastic model with proper creep parameters was established. The 3-D ANSYS was used to simulate surface subsidence, analyze overburden subsidence characteristics, and propose the rational mining and pillar widths for mining in weak rocks and under special mining conditions, and provide the policy makers scientific data for decision making on mining activities.

Jan 1, 2006

By Christopher Mark

The first International Conference on Ground Control in Mining opened with the topic of pillar design. Two classic papers were presented, one by Bieniwski and the other by Wilson. Unfortunately, the two methods were so radically different from each other that it was nearly impossible to reconcile them. Adding to the confusion were the many other pillar strength formulas (such as the Salamon-Munro, the Holland-Gaddy, and the Obert-Duvall, just to name a few) that were also available. Little wonder that discussions of pillar design in those days often ended with anguished cries of ?but which formula is the right one?? The past 25 years have seen substantial progress in the science of coal pillar design. Indeed, one testament to the improvement is the relative scarcity of papers on the topic at recent Conferences. Two factors have been largely responsible for the progress that has been made. The first has been the collection of large data bases of actual case histories of pillar performance in a variety of settings, from shallow room-and-pillar mines through deep cover longwalls. These have made possible the development of empirical design procedures that are closely linked to real world experience. The second important factor is the development of sophisticated computer models that can accurately simulate pillar behavior and roof/pillar/floor interactions. Together, these two lines of research have led to a new understanding of pillar mechanics that identifies three modes of pillar failure: ? Sudden, massive collapse, accompanied by airblast, for slender pillars (width/height<4) ? Squeezing, or slow, non-violent failure, for most room and pillar applications (4<w/h<10) ? Entry failure or bumps for deep cover and longwall applications (w/h>10) It is particularly satisfying that the insights gained from numerical models broadly support those obtained from the empirical studies. While far less controversial than in the past, pillar design problems continue to arise. One recent example is pillar design for highwall mining. NIOSH has just released a software package, called ARMPS-HWM, which employs a number of modern pillar design concepts. Since highwall mining web pillars are long and slender, the greatest danger is that of a sudden collapse. ARMPS-HWM suggests two possible prevention strategies, one which concentrates on the SF of the webs, and the other which creates a ?pressure arch? using properly sized barrier pillars. The paper will close with a discussion of some current needs in coal pillar design, including: ? Updating older empirical methods, such as ALPS, where changes in technology (new types of roof support, more demanding ventilation requirements, faster retreat rates) may have made some of the original case histories obsolete. ? Methods for determining site-specific coal strengths, focusing on bedding plane strength and other factors that may effect confinement, as input for both empirical and numerical design. ? Improved methods for evaluating coal pillar performance for environmental issues, such as surface subsidence and hydrologic impacts, which consider such factors as depth, w/h ratio, water immersion/drainage, and time dependent seam strength.

Jan 1, 2006

By Kot Unrug

Mine seals are necessary in nearly every mine to isolate mined-out areas from the ventilation network. There is a large number of seals in active mines and that number continually increases as the development spreads across the reserves. The recent accident caused by the failure of seals in the Sago mine resulted in new regulations. These regulations have been set based on a principle of eliminating the risk of failure, rather than the sound engineering and understanding of the conditions that may cause seal failure during an explosion of methane in sealed areas of the mine including the probability of such occurrences. This paper discusses the following subjects related to mine seals: The potential causes of methane explosions and the dynamic effects of pressure wave propagation. Seal materials and methods of construction in view of the interaction of the seal with the host rock environment as well as requirements for gathering geotechnical data. The design of seal dimensions is based on loading conditions, therefore the probable ranges of such loading is reviewed. There is also discussion of possible methods for shielding of seals from pressure pulses following an explosion. Particular seal?s types are examined in reference to the conditions at the seals location. A novel design is presented that will be a low- cost solution for the sealing of mined out areas. Recommendations are given for further research leading to a rational engineering system for design of new seals in coal mines.

Jan 1, 2008

By Karsten Zimmermann

The paper presents a study on the influence of face retreat rate in longwall coal mining on surface subsidence. It shows possibilities to influence dynamic ground movement by using a specific and controlled winning regime. For this, a dynamic stochastic prediction model used by DMT in Germany will be proved and adjusted on the specific character of geology in the Northern Appalachian coal field. Occurring ground movements such as inclination, curvature and deformation can be analyzed under static and dynamic points of view. It is theoretically shown that the face retreat rate has only a small influence on the static deformation values, but directly affects rate and acceleration of subsidence and deformation processes. The study shows that because of low mining depth and high mined thickness, static deformation values have the largest impact to surface objects. This implies that high face retreat rates don?t affect the impact on surface objects.

Jan 1, 2007

By Holger Witthaus

Beside the traditional geomechanical evaluation methods the geotechnical parameters are recognized as important facts of the planning work for multiple seam mining. Standards for applied monitoring and investigation methods for geotechnical determination of drill cores, laboratory rock-tests and observation of roadheadings are the basics for rock mechanics classification and support design. The geomechanical classification is in this context an essential element. The planning procedure, as it is becoming more and more detailed, beginning with the panel layout up to the technical instructions of roadway development and design of roadheading machinery, nowadays uses a lot of geotechnical information that also are expanding to include quantitative determination of more parameters. The current monitoring system includes the description of separation planes using drill cores and roadheading observation as well as laboratory tests of rock-strength and geophysical borehole examinations. This information is analyzed within the geomechanical standard-classification. The re-engineering process of comparison the predicted support success to the actual monitoring results provides the opportunity for continuous optimization of the planning work und support design. This way of empirical analysis is used for basic planning work in Germany for decades. But using the technical standard of information technology and a centralized database now it is possible to reach quick-win effects in implementing research results on the one hand and actual experiences on the other hand.

Jan 1, 2006