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By Pinnaduwa H. S. W. Kulatilake

A new formulation is given to conduct a probabilistic block theory analysis. A new computer code (BTAC) has been developed to perform both deterministic and probabilistic block theory analyses. The variability of the discontinuity orientation and shear strength is incorporated in the probabilistic block theory analysis. Discontinuity orientation is treated as a bivariate random variable including the correlation that exists between the dip angle and dip direction. BTAC code was applied to perform both deterministic and probabilistic block theory analyses for a part of an open pit mine in the U.S. Needed geological and geotechnical data for the analyses were obtained from field and laboratory investigations. The variability of the discontinuity orientations resulted in important differences between the probabilistic and deterministic block theory analyses results. The results confirmed that the design value selected for the Maximum Safe Slope Angle (MSSA) for a particular region in the open pit mine based on the deterministic block theory analysis can be on the unsafe side. In summary, the results showed clearly the superiority of probabilistic block theory analysis over the deterministic block theory analysis in obtaining additional important information with respect to designing rock slopes.

Jan 1, 2014

By Elizabeth Holley, Meriel Young, Gabriel Walton

"The coal mine roof rating (CMRR) was developed by Chris Mark and Greg Molinda to bridge the gap between geological variation in underground coal mines and engineering design. The CMRR accounts for the compressive strength of the immediate roof, the shear strength and intensity of any discontinuities present, and the moisture sensitivity of the immediate roof. The CMRR has been widely used and validated in Eastern US coal mines, but it has seen limited application in the Western US.This study focuses on roof behavior at a Western coal mine. Mine A shows significant lateral geological variation, along with localized faulting and a laterally extensive sandstone channel network. The CMRR is not used to predict roof instability at the mine.It is, therefore, hypothesized that there are other factors that are correlated with roof instability in underground coal mines that could potentially also be included in the CMRR.This hypothesis was tested by collecting 30 CMRR measurements at Mine A. At each measurement location, a binary record of the roof condition (stable or unstable) was made along with parameters, such as depth of cover, thought to also correlate with roof stability. A statistical analysis of the data was performed to determine the parameters in addition to those included in the CMRR, which can be correlated to roof stability.INTRODUCTION AND BACKGROUNDRoof fall is one of the greatest hazards facing underground coal miners (Barczak et al., 2000). In 2017, 91 lost-time injuries occurred due to roof fall in US underground coal mines. A further 48 roof falls occurred with no lost days (MSHA, 2018).The coal mine roof rating (CMRR) classification was developed by Molinda and Mark (1994) to quantify the geological description of mine roof into a single value that could indicate mine roof stability and be used in engineering design. It is widely used in the Eastern US as an input for the analysis of longwall pillar stability (ALPS) in underground coal mines. It provides an excellent start; however, it is arguably not fully comprehensive, nor is it widely used in the Western US."

Jan 1, 2018

By Yongjie Yang

Experimental study on the strength and deformation characteristics of coal under cyclic loading provides guidance for designing coal pillar which is subjected to repeated mining influence during mining. This paper studies the strength, deformation and fatigue process of No.3 coal from Xinhe Colliery under cyclic loading by the MTS815.03 servo-controlled rock mechanics test system. The results indicate that coal is more susceptible to fatigue damage than other hard rocks. Under uniaxial cyclic loading, the fatigue failure ?threshold value? of coal is smaller than 78% of its uniaxial strength, and there is also some fatigue damage when cyclic loading and unloading experiment is carried out below the fatigue failure ?threshold value?. Axial deformation can be divided into three stages: Initial deformation, steady-state deformation and accelerating deformation. Transverse deformation can be divided into two stages: Stable deformation and accelerating deformation. When the transverse deformation begins to increase rapidly and the deformation recovers only slightly upon unloading, it?s a precursor to failure of coal. Under cyclic loading, fatigue failure develops through a process of compaction, strain hardening, and strain softening.

Jan 1, 2006

By Kot F. Unrug

Since the introduction of longwall systems, the prediction of roof behavior and support requirements have become the major issue referring directly to safety as well as productivity. In more recent times, and especially in the USA where longwalls are exclusively equipped with costly hydraulic self- propelled support systems, a decision whether a longwall is applicable in a given condition, and when so, what kind of equipment should be selected, is of primary importance. There are numerous examples where lack of experience, and subsequently wrong selection of supports or winning machines, resulted in considerable losses. It should be emphasized that careful studies of prevailing geological and mining conditions, especially in a new area, are required to assure a successful operation. An evaluation of the conditions can be carried out in different ways utilizing such methods as: - Theoretical approach. applicable when geological conditions comply with the theoretical assumptions. - Empirical relationship which gives satisfactory results where the coefficients could be adequately determined. - Structural geological studies which must be undertaken in all cases, since the frequency of fractures and their orientation have a prevailing influence on roof behavior. - Scale model study on equivalent material for determination of failure conditions in the roof and mechanism of movement (flow) of broken rock matter. Coefficients for empirical formulas can be determined by these types of studies, as can boundary limits for mathematical modeling. - Mathematical modeling, e.g., finite element analysis. - Measurements and observations taken underground during the development period end utilization of experience for previous longwall panels in the area. Usually it is the most practical method where mining and geological conditions are comparable. An application of me or more of the above approaches remains to be a matter of judgement for particular conditions, however, the utilization of a practical experience, when available, is usually the safest way for planning a successful longwall operation.

Jan 1, 1982

By D. Minney

The quality of resin used in South African collieries is currently controlled according to South African Bureau of Standards, "SABS-1534:2002". It has however been found that resin which passed the SABS tests failed in underground short encapsulation pull tests. An investigation was therefore conducted to determine the characteristics of resins that are currently being used in collieries. A series of in situ short encapsulated pull tests was conducted to determine the effect of expired resin on support performance. The results showed that the longer the time after the expiry date the poorer the resin performance. A series of resin-torque tests has been performed using Anglo Coal's testing facility. The following parameters were investigated on different resins: Spinning speed, Mixing time, and Setting time. An attempt was also made to develop a new quality control procedure for resin. This procedure enables mining personnel to make sure that the quality of resin can provide the required support performance. The effect of spinning speed on resin performance was also investigated. The results showed the resin gelling times of resin decreases as the spinning speed increases. It is found that over-spinning with slow speed roofbolters may result in decreased bond strengths. It was found that a 30-second resin (10-second spin, 30-second hold) should never be spun more than 20 seconds, even with very slow roofbolters (100 rpm).

Jan 1, 2005

By Robert M. Cox

The successful application of the science of rock mechanics to the practical problems of coal mine design requires the acquisition and reduction to useable form of large amounts of field and laboratory data, and the construction and analyses of numerous geostructural models containing a wide variety of geometric and physical strength variables. Typically, the rime constraints placed on a new mine design project coupled with the inherent complexities of a good rock mechanics study combine to limit the applications of rock mechanics to the most rudimentary level. To facilitate a better application of rock mechanics to mine design problems, an interactive software package has been developed for use on a graphic mini-computer system that serves to aid the engineer in the timely and efficient analyses of rock mechanics data and geostructural models. The first phase of the rock mechanics package solicits the input of the raw geologic and rock strength data, analyzes and arranges this data in a logical manner, produces complete listings and statisitical summaries of the various rock properties, and stores the data on magnetic tapes and disks to serve as a future Rock Mechanics Data Base. The second phase of the software package provides for the analyses of a variety of geostructural models using a wide variety of geometric variables coupled with the rock strength data stored in the Rock Mechanics Data Base. This software package allows for the evaluation of numerous geostructural mine models for the design and selection of mine roof support and pillar systems (see Table l).

Jan 1, 1982

By Ihsan Berk Tulu, Keith A. Heasley, Chris Mark

"The Analysis of Retreat l\.fining Pillar Stability (ARJ\1PS) and the Lal\.fodel programs have been used successfully in the U.S. for designing safe pillar recovery operations for many years. However, the recent Crandall Canyon l\.fine collapse showed that further research is required to improve the pillar design for recovery under deep cover. To this end, the National Institute for Occupational Safety and Health (NIOSH) and the West Virginia University (WVU) l\.fining Engineering Department have been working together to improve both the ARJ\1PS and the Lal\.fodel programs.This paper compares and analyzes the overburden loads calculated by ARJ\1PS 2002, the new ARJ\1PS 2010, and the Lal\.fodel program with regard to the retreat pillar line, the gob, and the barrier pillars. The analysis shows a number of distinct differences between the ARJ\1PS and Lal\.fodel loading distributions. Ultimately, the programs, with their distinctive load distributions, are used to analyze a database of 52 deep cover pillar retreat case studies, and the ability of each program to discriminate between successful and unsuccessful retreat pillar plans is evaluated.INTRODUCTIONThe Analysis of Retreat l\.fining Pillar Stability (ARJ\.f PS) and the Lal\.fodel programs have been used successfully in the U.S. for designing safe pillar recovery operations for many years. However, the recent Crandall Canyon l\.fine collapse showed that further research is required to improve the pillar design for recovery under deep cover.Pillar recovery accounts for less than 10% of the coal produced from underground coal mines; however, in the period between 1989 and 1996, it accounted for more than 25% of all ground fatalities (l\.fark et al., 2003). In the past 15 years, the safety of retreat mining operations has greatly improved. l\.fark (2009) explains three steps promoted by l\1SHA and NIOSH for safer pillar recovery:1) Global stability through proper pillar design2) Local stability through proper roof support3) Worker safety through proper section managementThe ARJ\1PS and Lal\.fodel (Heasley, 1998) programs have been playing an important role in guiding mine operators in designing pillars to ensure the global stability of a retreat panel."

Jan 1, 2010

By Dennis R. Barratt

Rockbolting is now used extensively as a method of primary support in UK coalmines. Over the past fifteen years an optimum bolting system has evolved, based on a high grade steel bolt and a very strong stiff resin. Where necessary, cablebolts are used in conjunction with rockbolts as a supplementary means of support. The rockbolting system, as currently used, is based on a maximum bolt length of 2.4 m whilst cablebolts are generally 6 or 8 m long. Based on the UK experience, there are situations where it is necessary to extend the bolted horizon above that normally achieved with a 2.4 m long rockbolt. Until recently the only options available were coupled rockbolts or cablebolts, both of which have inherent problems in terms of installation. Flexible Strand Rockbolts (FSR), in lengths of 4 to 6 m, provide the means of being able to extend the normal bolted horizon Other advantages include increased strength characteristics (tensile and shear), able to be installed in the UK standard hole size (26-28 mm), encapsulation using resin capsules, thus offering immediate support, high bond strength compared to conventional strand, and able to be installed using existing drilling and bolting equipment. The FSR is considered to be a new concept in terms of strata control and one that compliments the rockbolting system currently in use.

Jan 1, 1997

By Tim Miller, Michael M. Murphy, John L. Ellenberger, Gabriel S. Esterhuizen

"A limestone mine in Ohio has had instability problems that have led to massive roof falls extending to the surface. This study focuses on the role that weak, moisture-sensitive floor has in the instability issues. Previous NIOSH research related to this subject did not include analysis for weak floor or weak bands and recommended that when such issues arise they should be investigated further using a more advanced analysis. Therefore, to further investigate the observed instability occurring on a large scale at the Ohio mine, FLAC3D numerical models were employed to demonstrate the effect that a weak floor has on roof and pillar stability. This case study will provide important information to limestone mine operators regarding the impact of weak floor causing the potential for roof collapse, pillar failure, and subsequent subsidence of the ground surface.IntroductionMassive roof falls extending to the surface at a limestone mine in Ohio have been studied collaboratively by the National Institute for Occupational Safety and Health (NIOSH) and the mine owners. This paper provides a summary of the sequence of events leading to observed instability and presents a numerical modeling analysis that investigates the role a weak floor can have on roof and pillar stability.This study builds upon previous NIOSH research in underground limestone mines undertaken by way of a survey that analyzed performance of pillars in 34 different stone mines in the Eastern and Midwestern United States between 2005 and 2009 (Esterhuizen et al., 2011). This survey led to the development of underground stone mine pillar design guidelines based upon a “stability factor” for the pillar system. The factor is compared to operational experience to determine ranges of values that are typical of stable pillar systems. A software package titled Stone Mine Pillar Design (S-Pillar) was developed for easy application of these guidelines (Esterhuizen and Murphy, 2011).Weak floor in the present case study departs significantly from cases included in the previous NIOSH research, in that none of the 34 study mines had weak floor issues. Moreover, this case study is the first in which a weak floor has been monitored routinely as roof falls are occurring. A detailed report on the observations and measurements taken at the mine has been published (Murphy et al., 2015). The previous observations led to the conclusion that although there were weak bands in the pillar, the weak floor was the significant defect that led to the instability issues. The pillars were initially mined in 2004, approximately 10 years before the instability issues began to occur. The objective of this study is to use numerical models to analyze a variety of floor strengths and the impact of moisture content to find the critical point at which the floor becomes unstable, leading to long-term instability issues."

Jan 1, 2015

By Stephen C. Tadolini, Anthony T. Iannacchione

"Coal burst represented a major hazard for some U.S. mining operations. This paper provides an historical review of the coal burst hazards, identifies the fundamental geological factors associated with these events, and discusses mechanisms that can be used to avoid their occurrences. Coal burst are not common in most underground mines. Their occurrence almost always has such dramatic consequences to a mining operation that changes in practice are required. Fundamental factors influencing coal burst events include strong strata, abnormal strata caving, elevated stresses, critical size pillars and the lack of sufficiently sized barrier pillars during extraction. These factors interact to produce excessive stress, seismic shock and loss of confinement mechanisms. Over the 90 years of dealing with these hazards, many novel prevention controls have been developed including novel mine designs and extraction sequences, most of which are site specific in their application. Without an accurate assessment of the fundamental factors that influence coal burst and knowledge of their mechanisms of occurrence, control techniques may be misapplied and risk inadequately mitigated. INTRODUCTIONCoal burst1are violent failures of ribs, roof or floor in underground mines. They are known to occur in complex ways and often under unique sets of conditions. This has made them extremely difficult to anticipate and control. Assessing coal burst risk requires engineers, managers, and safety professionals to recognize the fundamental factors responsible for these events. This helps practitioners recognize the hazard potential and understand the context in which various controls and barriers should be used. Only then can coal burst events be anticipated andappropriate mitigation techniques deployed.Over the last 90 years, a few coal burst events have been anticipated but most have eluded prediction. The authors examined the historical record (Appendix A) and determined that an inadequate understanding of the initiating geologic factors and their associated mechanisms of occurrence have contributed to the poor predictive capability. The historic record also indicates that control techniques have typically been site specific in their application."

Jan 1, 2015

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 Ismet Canbulat, John Naylor, Jason Emery, Peter Craig, Andy Sykes

"Longwall mining is by far the most common method of underground coal extraction in Australia. The industry trends and expectations are placing increasing emphasis on the reliability and productivity of these operations. The longwalls are becoming wider and longer while retreat rates are continuously increasing due to significant improvements achieved in longwall equipment reliability and automation. This increased longwall productivity is placing significant emphasis on the reliability of longwall panel development.Although there have been significant improvements in the reliability of continuous miners and hydraulic drill rigs, the traditional resin encapsulated bolt installation is still the principal method used in all major coal-producing countries around the world. Anglo American realised an opportunity existed to introduce an alternative roof bolt installation technique called “spin to stall” in Australia. Spin to stall was first introduced in Anglo American Coal in South Africa where it has been successfully used for over a decade, though implementation of South African spin to stall resin in Australia has proven to be near impossible due to a significant difference in geotechnical conditions, mining method, and, subsequently, roof bolting equipment. Therefore, a new spin to stall development project was initiated between Anglo American Coal and Jennmar Australia (SPIN2STALL®). This paper summarises the journey of this project, the results, and the successful implementation of spin to stall achieved at Grasstree Mine.INTRODUCTIONThe Anglo American Coal business unit operates Grasstree and Moranbah North underground longwall mines in the Bowen Basin of Central Queensland, with a third longwall mine, Grosvenor, currently being developed, and two more (Aquila and Moranbah South) in the project pipeline. The vision for Anglo American is to achieve “Zero Harm” through the effective management of safety at all operations, while for the coal business unit, at the same time to achieve industry-leading operational performance. Currently, both Grasstree and Moranbah North longwalls are operating at industry best practice rates. This is placing increased pressure on the development process to allow such high productivity levels to be sustainable."

Jan 1, 2015

By John R. Poland, Benjamin Mirabile

"There are significant ground support hazards to both personnel and equipment when longwall equipment must mine through cross-panel entries. Backfilling support strategies are often cost prohibitive. Additionally, it is often very difficult to install backfill material in full contact with the mine roof in backfilled entries. This paper will demonstrate the use of fiber-reinforced concrete crib material as a method for standing support in longwall cut-through entries. Despite conceptions of poor performance in potentially high convergence environments, fiber-reinforced concrete crib material can be used in longwall support environments subject to high abutment loads and convergence. Central to the proper design of these supports is the use of yield material between crib layers and at the mine roof/crib interface. The placement location of cribs within the cut-through entry has a significant effect on the main roof behavior and associated ground conditions in the longwall abutment zones. It is particularly important to engineer the proper load displacement characteristics of the installed crib to support expected ground conditions. The cost of fiber-reinforced crib supports is less than 50% of backfilling methods.INTRODUCTIONThe design and execution of a longwall cut-through is perhaps one of the most difficult and risky endeavors in the field of ground control. The magnitude of abutment loads and potential for ground failure present a significant safety hazard to underground personnel. In addition, there is significant financial risk, with replacement costs of face equipment exceeding $200 million. Faced with these consequences, it is both advisable and common for an engineer to design ground support with a significant margin of safety. This paper outlines a robust support system that possesses a significant margin of safety along with significantly lower costs than most other support systems employed in similar conditions.SITE PARAMETERSThe mine site described in this study operates in the Herrin No. 6 seam in southern Illinois. The seam height is typically 76- 84 inches. Mining height in gateroads and mains is typically over 96 in, and typical mining height on the longwall face is 82 in. The overburden depth is 950-970 feet in the area of the longwall cutthrough."

Jan 1, 2016

By Morgan M. Sears, Mark Van Dyke, Gamal Rashed, John Rusnak, Khaled Mohamed

"In 2016, room-and-pillar mining provided nearly 40% of underground coal production in the United States. Over the past decade, rib falls have resulted in 12 fatalities, representing 28% of the ground-fall fatalities in U.S. underground coal mines. Nine of these 12 fatalities (75%) have occurred in room-and-pillar mines. The objective of this research is to study the geomechanics of bench room-and-pillar mining and the associated response of high pillar ribs at overburden depths greater than 1,000 ft. This paper provides a definition of the bench technique, the pillar response due to loading, observational data for a case history, a calibrated numerical model of the observed rib response, and application of this calibrated model to a second site. INTRODUCTION Bench mining is a an underground mining technique typically applied to room-and-pillar mines where full seam extraction on development presents an unacceptably high risk of injury from high pillar ribs or where the mining equipment is not designed to extract the full seam thickness. To mitigate the increased risk associated with high ribs and slender pillars, a more modest thickness is extracted from the top of the seam on development. This is followed by grading the floor and recovering the bottom of the seam with or without extraction of the pillars during retreat mining. A mine located in Eastern Kentucky extracts two seams at depths ranging from outcrop to 2,000 ft. In some areas of the mine, Seam A and Seam B are close enough together to be mined simultaneously. Seam A (top) is mined on development 7 to 9 ft. high for the entire length of the panel. On retreat, as each pillar is extracted, the continuous miner is ramped down into the floor (Seam B), two pairs of Mobile Roof Support (MRS) units are set, and the pillars are extracted at the full mining height of 14+ ft. During the pillar recovery process, the floor is extracted in each entry, from a ramp initiated outby the retreat line, sequentially just prior to extracting the lifts from the pillars (see Figure 1)."

Jan 1, 2017

By Keith A. Heasley, Christopher R. Newman

"Originally developed in 1993, LaModel has aided mining engineers and researchers alike in improving the design and safety of underground single- and multiple-seam mining operations (Heasley, 1998). Through the years (Heasley, 2011), the use and capabilities of the LaModel program have grown immensely while adapting to ground control concerns and problems within the mining industry. Presently, MSHA specifically mentions the use of LaModel for the analysis of, “complex non-typical roof control plans,” defined as either room-and-pillar retreat mining greater than 1000 feet, bump- or bounce-prone mines, or other criteria considered unusual by the District Manager (Stricklin, 2013).With an ever increasing number of users and an increase in available solution options and complex analyses, there is now a significant demand for better education and training in the practical application and detailed analysis using LaModel. This paper presents the development of an electronic user’s manual and comprehensive online training course created in an open online learning environment in order to better inform and train industry professionals as well as engineering students and new users. The development of both the user’s manual and online training course will ultimately increase the ground control design effectiveness of mining engineers, leading to safer and more productive mine designs.INTRODUCTIONOver the past 20 years, mining engineers and researchers have used the LaModel program for improving the design and safety of single- and multiple-seam mining operations. LaModel uses a laminated, displacement-discontinuity, boundary-element method which simplifies the overburden into a stack of frictionless homogeneous laminations and limits the detailed analysis to the seam itself. This approach is fundamentally simpler than either finite-element, finite-difference, or discrete-element approaches; and, therefore, the program provides a significant reduction in computational time and efficiently calculates the displacements, stresses, pillar safety factors, multiple-seam interactions, subsidence, etc. for thin-bedded deposits such as coal, salt, potash, limestone, etc. (Heasley and Salamon, 1996; Heasley and Agioutantis, 2001). The laminated overburden model in LaModel is different than previous homogeneous elastic formulations and more realistically represents the natural flexibilities of the stratified sedimentary overburden typically associated with coal seams (Heasley, 2008)."

Jan 1, 2015

By Khaled M. Mohamed, Michael M. Murphy, Ted M. Klemetti, Heather E. Lawson

"The design of rib support systems in U.S. coal mines is based primarily on local practices and experience. A better understanding of current rib support practices in U.S. coal mines is crucial for developing a sound engineering rib support design tool.The objective of this paper is to analyze the current practices of rib control in US coal mines. Twenty (20) underground coal mines were studied representing various coal basins, coal seams, geology, loading conditions, and rib control strategies.The key findings are: (1) any rib design guideline or tool should take into account external rib support as well as internal bolting; (2) rib bolts on their own cannot contain rib spall, especially in soft ribs subjected to significant load—external rib control devices such as mesh are required in such cases to contain rib sloughing; (3) the majority of the studied mines follow the overburden depth and entry height thresholds recommended by the Program Information Bulletin (PIB) 11-29; (4) potential rib instability occurred when certain geological features prevailed—these include draw slate and/or bone coal near the rib/roof line, claystone partings, and soft coal bench overlain by rock strata; (5) 47% of the studied rib spall was classified as blocky—this could indicate a high potential of rib hazards; and (6) rib injury rates of the studied mines for the last three years emphasize the need for more rib control management for mines operating at overburden depths between 500 ft and 1,000 ft.IntroductionEfforts to improve the stability of underground mine ribs have continued for decades. These efforts by mining professionals around the world persisted throughout the 1990s and 2000s as well, though much of this work focused on rib support methodology and selection of proper support for a specific location. Despite these efforts, it is unfortunate that there has been a continual occurrence of rib-related fatalities in underground coal mines. While overall improvements in rib safety have been achieved, the average fatality rate is still about 1.3 fatalities per year over the last 18 years (Jones, 2014).To manage and control the rib hazard, rib support is used in U.S. coal mines. The current rib support methods for U.S. mines fall into two main categories: rib control based on intrinsic support systems and those based on external support systems. Intrinsic or rib-bolt support requires a roof bolting machine that can install a bolt fixture into the rib. Furthermore, the appropriate level of support needed to control the ribs with an intrinsic-based support system as well as the design parameters for those support systems for various mine conditions have not been established in U.S. coal mines. Furthermore, surface control systems are often an integral part of these support systems and must be considered in the system design."

Jan 1, 2015

By Ben Mirabile

Over the past three decades, the U.S. coal mining industry has widely used cable supports to supplement traditional primary bolting systems, especially in difficult ground conditions. However, increased mining activity in adverse conditions has underscored the limited effectiveness of the non-tensioned, partially grouted cable supports used to supplement primary bolts. Roof failures in conditions such as corrosive environments, highly laminated strata, low overburden depth and water intrusion have demonstrated that the need for cable technology has reached beyond the traditional non-tensioned, partially-grouted cable tendon. Furthermore, declining market conditions and increased competition for coal customers has demanded that new cable bolt technology be costeffective and readily adaptable to the mining cycle. Jennmar Corporation has developed several cable bolt technologies that can be used as stand-alone solutions or in concert with one another to mitigate adverse conditions. These technologies include rapid tensioning of cable supports, structural surface control and polyurethane injection. The case studies presented in this paper use one or more of these technologies to address adverse mining conditions or special ground control problems.

Jan 1, 2013

By Anthony (Sam) J. S. Spearing

Backfilling using coal waste is not a novel means for waste disposal throughout the world; yet, backfilling using a high density (paste) backfill is relatively new, except in Germany and Poland. One of the main benefits of a high density backfill, as opposed to a low density (slurry) backfill, is that, if placed at a low permeability and low moisture content, the risk of water table contamination can be relatively low. In addition, if paste backfill can be placed cost effectively, environmental benefits are huge because the surface impoundment footprint can be greatly reduced or even eliminated. This is especially true in room-and-pillar applications. In its current state, backfilling is considerably more costly than surface disposal. This is mainly because paste, as opposed to slurry, significantly increases backfill placement costs; however, this could be offset by increasing the achievable extraction rate. Overall, such a system could potentially improve the public?s image of coal mining in the US for a myriad of reasons. This paper discusses a proposed backfill system for a typical room-and-pillar coal mine in the Illinois Basin of the US and clearly shows the technical advantages, although costs are still higher with fill. The cost differential will likely reduce over time, in favor of the backfill option, as costs of traditional surface disposal increase, due mainly to ever-restrictive disposal regulations.

Jan 1, 2013

By I. Sedat Buyuksagis, Jamal Rostami, Ali Naeimipour

"Improving the safety of underground openings and optimizing ground support systems requires reliable ground characterization. This includes understanding the joints, discontinuities, and rock strength. Joint information can be obtained from borehole cameras, but measuring in-situ rock strength is very difficult. Use of borehole probes can be an ideal and efficient way to meet this requirement. This paper discusses the development of the Rock Strength Borehole Probe (RSBP) and presents the preliminary laboratory/field test. This device can be an accurate, flexible, quick, non-disruptive, and cost-effective alternative to estimate the rock strength inside boreholes in underground mines and tunnels. In addition, the scratch testing procedure in the laboratory by means of a newly developed miniature linear cutting machine is explained. Based on the results of these tests, two equations are developed to estimate the uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS) of the sedimentary/metamorphic rocks. These equations, are based on testing 27 different sedimentary, igneous, and metamorphic rocks by full-scale scratch tests, including the cutting tests by a miniature disc. The results show a good correlation between the normal force and the compressive strength of sedimentary rock if the depth of the scratch is known. No significant correlation was observed for igneous rocks, due to the impacts of grain size.INTRODUCTIONEstimated rock mass properties are essential input for geomechanical studies and stability analysis for any structure constructed in or with rock. The availability of geological information is the crucial component of rock mass classification. One of the important parameters in evaluating rock mass properties is the intact rock strength. This parameter is usually measured by testing the core samples, obtained from exploration boreholes. These samples are subsequently tested in geomechanics laboratories. The test results offer limited information about the rock at the few boring locations despite all the efforts and costs. In addition, these results may not necessarily be representative of the behavior of the rock in the field as the test cannot provide the insitu condition of the ground."

Jan 1, 2016

By G. P. Neobutov

The near surface inclined gold ore deposit is mined out at freezing temperature. The replacement of ore pillars by artificial freezing rocks during the rock pressures control in this conditions presented no difficulties. At the present, the mining operations are maintained at a depth of more than 300 meters. The exploration of mining conditions showed partial warming of rock mass and unstable ground conditions. Analytical calculations using a mathematical model of heat exchange predicted undesirable duration of freezing of artificial pillars. Practical techniques and recommendations for mining with ice pillars as an artificial support system using a new freezing method are discussed.

Jan 1, 1996