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The applicability of four empirical strength criteria for rock masses, namely, Hoek and Brown, Bieniawski - Yudhbir et al., Rarnamurthy - Arora and Johnston - Sheorey et al. has been tested against the triaxial test data for jointed plaster of Paris of Arora. The following modified Bieniawski criterion shows best agreement with the triaxial test data for jointed plaster of Paris:- where st = axial compressive stress at failure, MPa; s3 = confining pressure, MPa; scm = uniaxial compressive strength of jointed plaster of Paris, MPa; and B = - 3.988 + 9.674 (scm )-0? 185 The modified Bieniawski strength criterion can be used to estimate the strength of a coal pillar, based on a knowledge of stress distribution in it.

Jan 1, 1992

By L. Mahony

This paper describes the design, construction and commissioning testing program for a laboratory facility at the School of Mining Engineering, UNSW, Australia, aimed at evaluating reinforcement tendon performance when subjected to shear loading. The project has been financially supported through the coal industry ACARP research initiative. The single failure plane design adopted in the test rig has been successful in allowing shear loading to be directly applied to fully installed (and where relevant, pre-tensioned) rock bolts. Initial results are extremely encouraging, and illustrate a significant axial component of load development as shearing takes place - particular in lower strength, softer material types. The paper also outlines future plans for use of this facility.

Jan 1, 2005

By Thomas M. Baraak

This paper evaluates factors which influence longwall support and strata interaction. The longwall system is composed of an immediate and main roof structure and three supporting foundations: 1) longwall panel, 2) powered roof supports, and 3) gob waste. The main roof forms a structure that is generally supported by all three foundations, while the immediate roof acts as a beam that cantilevers from the coal face to the powered support. In most cases, shield loading involves a complex interaction of both main roof and immediate roof behavior and is a combination of loads produced from subsidence of the main roof and displacements of the immediate roof caused by deformations of the cantilevered roof beam. Since the shield stiffness remains constant for all leg pressures and main roof convergence is irresistible in terms of shield capacity, the shield must be able to control the behavior of the immediate roof or floor structure for shield loading to be sensitive to setting pressures. If the goal is to minimize total shield loading, any active setting force must be offset by reduced passive shield loading to justify the active setting loads. Field data suggest that the typical reductions in passive loading do not justify the required increases in setting pressure in some applications.

Jan 1, 1990

By David Bigby

A remote reading dual height telltale system has been developed to provide mine management with early warning of impending roof failure. This system is a logical development from the visual dual height and triple height telltales which are increasingly being used worldwide for routine monitoring of mine roof. The paper describes the principles and history of telltales from their origins in France, their refinement and routine use in the UK and their subsequent spread around the world. They are now being used in various forms in USA, Canada, Germany, Spitzbergen (Norway), Poland, Ukraine, Russia, Australia, South Africa, Mexico, India, Egypt and China. The remote reading telltale system has coal mine intrinsic safety approval in Europe and the United States (MSHA) and the first commercial system was installed in a German colliery at the beginning of the year. Up to 100 dual height telltales can be connected, in a simple "daisy chain" configuration, to each of 4 underground interrogation units. These are connected through a twisted pair link to a surface computer which displays the readings, updates the database, generates warnings and provides the user interface. The paper describes the features and principles of operation of the system which differs considerably from conventional mine-wide monitoring systems. A European Community funded research programme is currently underway with the aim of developing improved alarm generating algorithms including evaluation of interfacing a neural network to the system. The paper concludes by exploring other potential applications of the system for ground control monitoring currently in development, including extensometry, stope closure monitoring and support load measurement.

Jan 1, 2001

By Gregory M. Molinda

The U.S. Bureau of Mines has developed a rock mass classification system for coal mine roof control. The Coal Mine Roof Rating System (CMRR) evaluates the structural competence of mine roof using simple field tests and observations obtained from underground exposures in roof falls or overcasts. The basis of the WRR is a weighing system which converts descriptive geologic roof rock data to a numerical value, facilitating its use in engineering design. A full suite of data collection and hand calculation sheets accompanies the CHRR A data base is currently being collected from all major coal basins in the United States to validate the CMW. To date, CHRR values are available from 96 roof exposures in 59 coal mines representing these basins. The system can be used to help solve many practical ground control problems, including longwall gate road design, roof support selection, and decisions regarding extended cut length.

Jan 1, 1993

By Reha Ozel

The stability in longwall faces depends on the interaction beman the roof strata, face supports and floor strata. The load distribution on the other hand, depends upon relative stiffness of the three supporting elements namely, the coal face, support and gob. Therefore, in defining support requirements, it is particularly important to analyze the strata loading, the face convergence and the controlling mechanism provided by supports. The controlling mechanism however, depends on the type and characteristics of supports used in long- wall faces. The design guidelines presented in this paper have bean developed based on a number of strata control oriented projects carried out in Turkey, load and convergence measurements carried out in 10 longwall faces, in Zonguldak Coal Region, and procedures given in literature. Evaluation of load and convergence measurements, and analyses of face supports were carried out by means of a computer program, called L0NGWAI.L-MEW, developed by the authors. The output of the design analyses include the following: (1) estimation of support capacity for roof supports namely; individual hydraulic props, chock-type power supports and various types of shield supports, and (2) analysis of loading conditions and response of shield support components in terms of stability and structural integrity.

Jan 1, 1990

By Lisa Burke

In underground coal mines, concrete block stoppings are widely used to control mine ventilation. Although stoppings are not intended as roof support, they are subjected to roof to floor convergence, and may fail as a result of this loading. Premature failure of stoppings can significantly affect mine ventilation, limiting the amount of fresh air reaching the working faces and increasing the risk for methane explosions. Softening materials are often used in stoppings to reduce the damaging effects of roof to floor convergence. However, to date, research has not focused on the behavior of stopping construction materials subjected to roof or floor loading, leaving the design process to trial and error. A combination of numerical simulations and large scale physical tests were employed to develop a scientific understanding of stopping performance. The first series of physical models were constructed using standard CMU (concrete masonry unit) blocks and tested in a load frame. The behavior of these walls was simulated with a distinct element model. A key finding was that very small variations in block size and irregularities in block shape significantly affect wall performance. These variations, which are inherent to the type of blocks typically used underground, create stress concentrations that initiate the failure of stopping walls. A second series of models employed concrete stoppings that incorporated woos planks, a shredded wood material, and foam planks like those commonly used underground. Numerical models were again able to match the physical test data. Analysis of the softening layers used in stopping construction indicated that the strength and stiffness of the material relative to that of the wall is crucial in determining the amount of roof to floor convergence the wall can withstand prior to failure. The product of this study is a numerical model that can be used to evaluate the performance of stopping materials and different wall geometries in a controlled environment. Testing was done in a laboratory setting with walls constructed on flat, parallel surfaces and subjected to uniform loading at a constant rate. Parametric studies with the model indicate that in this ideal environment it is possible to control the amount of vertical displacement the stopping can withstand by adjusting the number of softening layers built into the wall and the thickness of the layers. Additionally, under these conditions, the position of softening layers within the wall appears to have little effect on the amount of displacement walls can withstand prior to failure.

Jan 1, 2004

By Brian G. D. Smart

A scheme is presented whereby the complexities of design and operation of a hydraulically powered coalmine support are modelled using the finite element method. This enables predictions to be made of the interaction of the support with its environment in a variety of operating conditions. The model is a two dimensional representation. The modelling scheme was applied in two case studies. In the first, the performance of a four leg support was uprated by increasing the front leg force. The finite element model enabled changes in overall support performance to be verified. In the second case study, the change in lateral force developed by a two leg support was assessed with changes in support operating height and floor foundation stiffness. The modelling scheme is capable of further development with the possibility of extending the model into three dimensions and the addition of control elements that would enable an actual mining sequence to be represented.

Jan 1, 1992

By Peter Altounyan

Goedehoop Colliery in the Witbank Coalfield of South Africa produces some 8 million tonnes of coal from fully mechanised room and pillar mining methods, using resin anchored bolts as roof support. Investigation of the quality of the installed bolts resulted in the finding that it was possible to pull out fully encapsulated roofbolts. This led to a drive to improve the quality of installation by making it easier to install a roofbolt correctly and more difficult to install incorrectly, whilst at the same time achieving high bond strength. The method of installation which was investigated, developed and implemented is known as 'spin to stall.' The roofbolt is pushed through the resin capsule to the top of the hole and then spun to mix the resin, until the increasing resistance to rotation exceeds the breakout limit on the bolt torque nut. The nut then runs up the bolt thread and is tightened to the roof as the drill stalls. This procedure is simple and avoids human factors such as non adherence to 'spin' and 'wait' times which contribute to poor installation with conventional methods. However spin to stall installation has been avoided in the past because of concerns over damage to the resin bond. This paper reports on the efforts made to investigate and understand the factors involved, and the progress made in overcoming the problem of resin damage so that the advantages of this installation method can be realised.

Jan 1, 2003

By Thomas Rymer

Mathematical modelling of mine subsidence measured at 21 locations in Pennsylvania and northern West Virginia allows for the refinement of current methods of predicting maximum land subsidence associated with longwall coal mining. This new method (RYBAD model) is an extension of that provided by Tandanand and Powell (1984; TP Model). The RYBAD model accomplishes more accurate subsidence predictions (error typically less than 10 percent) for a greater range of mining and geological parameters through the recognition of the following: 1) subsidence increases at a decreasing rate (curvilinear relationship) with greater overburden thickness up to a critical value beyond which subsidence decreases; 2) subsidence is strongly influenced by the stratigraphic proximity of strong rocks to the coal (size of potential caving zone); and 3) subsidence index is related to overburden thickness by a family of curves, each for incremental variations in the effective percentage of strong rock in the overburden.

Jan 1, 1988

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 Li-min Liu

The Semi-Analytical method can be used to solve a variety of problems in geomechanics and civil engineering. When it comes to layered rock strata and rock masses, it is superior to all other analytical methods. This paper presents the application of a 3-D semi- analytical method to 3-D surface subsidence and stress analysis caused by mining. In this semi-analytical method the layered elements and triangular elements ate used alternatively. Their displacement pattern, strain mahix, elastic matrix, stiffiness matrix, load matrix and stress matrix are presented. A numerical simulation program based on the semi-analytical method bas been developed using Fortran 90. This program is suitable for subsidence prediction and stress analysis of mom and pillar mining, strip longwall and mechanized longwall mining methods. It is applicable to all geological conditions and mining methods. Comparing with the finite method, this method reduces significantly the number of simultaneous equations to be solved and the amount of data preparation. It not only reduces the computer memory, but also runs faster and cost less. Key Words Semi-analytical method, surface subsidence, stress analysis, layered element, triangular prism element

Jan 1, 2002

By M. Y. Fisekci

This paper concentrates on subsidence measurements, applied over the thick and steep seam mining in the Rocky Mountains Region of Western Canada. The studies to date indicate that two new subsidence monitoring techniques appear to be the most suitable methods for these conditions. The computerized telemetry and aerial photogrammetry systems are being tested for the reliability of the systems during the winter months within the net- work of laser surveying over the workings of the new hydraulic mine.

Jan 1, 1981

By Yunxin Qiu

A new technology has been introduced - the use of the High-Water Solidifying Material for providing pumped roadside supports to maintain a roadway for re-use in longwall retreating. As a gob edge support, its initial use at Hebi No. I Colliery was successful, providing acceptable performances in support and control of convergences and lateral closures of the gob-edge roadways. This acceptability applied to both first use and re-use when the roadway became a gateroad for the adjoining longwall, remaining stable throughout the associated loadings and convergences. The technology promises economic and social benefits.

Jan 1, 1992

By Kevin J. Ma, John Stankus, Dakota Faulkner

"Expandable rock bolts are widely used in hard rock mines as an efficient ground control product. However, capacity and service life can be significantly reduced if the metallic body is subjected to corrosion. In some hard rock mines in the U.S., highly corrosive ground conditions exist, and it has been reported that inflatable rock bolts have corroded within a few months after installation. To provide mining industry a cost-effective inflatable bolt and combat the corrosion issues, Jennmar Corporation, Inc., and its subsidiary Keystone Mining Services, LLC (KMS), analyzed corroded bolt samples, identified root causes, evaluated properties of various coating materials, and developed a new inflatable rock bolt, Python M3TM, that is protected with an innovative PyFlexU2TM coating. The new generation Python M3 features improved steel chemistry for reliable performance, modified profile for better inflation, and surface preparation and coating application. The PyFlexU2 is impervious to liquid and air, durable, and UV resistant. With a flexible adhesive, and highly corrosion-resistant undercoating, and a very hard sacrificial surface coating, the PyFlexU2 coating system provides the Python M3 superior protection against chemical corrosion and physical scratch damage. The under-coating has exceptional flexibility and adhesion to prevent coating micro-cracks or fractures after bolt inflation and possesses excellent corrosion resistance to acids (pH <3), alkalis (pH >11), fuels, and salt solvents. The corrosion and scratch resistant PyFlexU2 coating offers very effective bolt protection for extra longevity in highly corrosive environments. The Python M3 coated with PyFlexU2 has been tested in the most challenging conditions, including laboratory corrosion tests in extreme acidic and basic solvents, rock slurry, and borehole scratch insertion tests. With demonstrated corrosion and scratch resistance, the product has been greatly welcomed by hard rock mines in the West and is currently installed in large scale. This paper identifies the root causes of the bolt corrosion, discusses the analysis process, and details laboratory and underground tests carried out on the Python M3 coated with PyFlexU2. The Python M3TM and PyFlexU2TM are subjects covered by pending U.S. Patent Applications assigned to FCI Holdings Delaware, LLC."

Jan 1, 2017

By John Stankus

Accurate evaluation of stress and geological conditions is critical to ground control design in underground openings. For a mine slope entry, the problem becomes more complicated because a slope transverses through many different types of strata. Mine slope ground control has traditionally been practiced based on trial and error and prior experience. There is currently no well-accepted slope and support design methodology available for an economical and technically sound ground control plan. Over the last few years, Keystone Mining Services, LLC (KMS), the engineering affiliate company of Jennmar Cooperation, has developed a ground support design methodology called the ?Stress, Geologic, and Support design system? (SGSSM). This patent pending method enables accurate analysis of actual geo-technical conditions and stress; identifies strong, fair, and weak sections along the slope; formulates primary and supplemental roof bolting systems, designs optimal long-term steel structure support; and verifies the adequacy of the developed support. The method has been successfully utilized on various new slope projects and has been well received by state and federal regulatory agencies during the approval process. This paper details the concepts of the methodology using an actual case study of a slope project in the Midwest.

Jan 1, 2011

By Dale S. Preece

In 1975 Congress passed the Energy Conservation Act to establish a U. S. Strategic Petroleum Reserve (SPR) with a capacity of 750 million barrels of crude oil. The most economic storage medium was determined to be salt caverns leached in salt domes in Louisiana and Texas. Salt caverns existed at several sites when the reserve was created. These were obtained by the U. S. Department of Energy (DOE) and used to initiate SPR oil storage. In order to meet the storage capacity approved by Congress, new caverns also had to be leached. To support the resulting design effort, finite element computer program have been used to determine the creep closure and structural stability of salt caverns. Using site specific material properties including creep models, elastic moduli and fracture data, the finite element analyses have replaced earlier empirical approaches to cavern design. This report presents results of such finite element analyses to determine the best cavern roof shape and the minium pillar to dimeter ratio. , P/D. These numerical predictions indicate that the current cavern design is safe.

Jan 1, 1984

By Donald P. Richards

West Elk Coal Company operates its Mt. Gunnison No. I mine on the western slope of the Rocky Mountains in Western Colorado. The mine is located along the north fork of the Gunnisson River near Somerset, Colorado as shown in Figure 1. The mine is designed for a sustained production of 1.4 million tons per year out of the "F" coal seam in the Mesa Verde formation. The coal seam is nominally 7 feet in thickness and dips at about 3 ½ degrees to the northeast. Mining of the seam is up dip with the entry portals on the north facing slope of Mount Gunnison. The mine is designed as a five entry system with four entries for ventilation and access and one entry for a coal-handling conveyor. The mine entry layout is shown in Figure 2. Initial mine planning began in 1979, with "permitting" complete and construction starting in the fall of 1981. A "turnkey" contract for design and construction of all five parallel mine entry tunnels was awarded by West Elk Coal Company to a Joint Venture of Jenny Engineering Corporation (design and contract management responsibility) and Affholder, Inc. (construction responsibility). The first entry access into the coal seam was completed in the early spring of 1982. The mine has been operating at full service (all five entries) for nearly 3 years.

Jan 1, 1984

By J. D. Cole

In order to reduce the number of longwall face moves and to increase the rate of gateroad construction, super longwall panels, 1000 feet wide and 12000 to 14000 feet long, are planned for Wolf Creek Collieries No. 4 mine. The development of the longwall panels at the mine has evolved from 5-entry, to 4-entry, to 3-entry systems. A three-entry system including pillar size and entry supporting method for the super longwall panels was designed for long-term stability. The design procedures included field observation and studies, laboratory properties tests, in-situ stress measurement, and computer analysis. Three pillar design methods consisting of PILLAR, ALPS, and the Wilson Method, and one entry supporting method, ROOFBOLT, were adopted in this study. The procedures, methods, and results are discussed in detail.

Jan 1, 1990

By Mark Colwell

This paper summarizes the results of a research project whose goal was to provide the Australian coal industry with a chain pillar design methodology readily usable by colliery staff. The project was primarily funded by the Australian Coal Association Research Program and further supported by several Australian longwall operations. The starting point or basis of the project was the Analysis of Longwall Pillar Stability (ALPS) methodology. ALPS was chosen because of its operational focus; it uses tailgate performance as the determining chain pillar design criterion rather than simply pillar stability. Furthermore, ALPS recognizes that several geotechnical and design factors, including (but not limited to) chain pillar stability, affect that performance. There are some geotechnical and mine layout differences between United States and Australian coalfields that required investigation and, therefore, calibration before the full benefits offered by the ALPS methodology could be realized in Australia. Ultimately, case history data were collected from 19 longwall mines representing approximately 60% of all Australian longwall operations. In addition, six monitoring sites incorporated an array of hydraulic stress cells to measure the change in vertical stress throughout the various phases of the longwall extraction cycle. The sites also incorporated extensometers to monitor roof and rib performance in response to the retreating longwall face. The study found strong relationships between the tailgate stability factor, the Coal Mine Roof Rating, and the installed level of primary support. The final outcome of the project is a chain pillar design methodology called Analysis of Longwall Tailgate Serviceability (ALTS). Guidelines for using ALTS are provided.

Jan 1, 1999