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By Hani Mitri

A new monitoring device called SAFEBOLT (Stress And Force Evaluator in Bolts) has been recently developed. The device SAFEBOLT, essentially replaces the load cell, it permits the monitoring of bolt axial load from the time of its installation underground. The SAFEBOLT system consists of a portable readout unit, connecting cable and the SAFEBOLT device, which is installed in the bolt head. SAFEBOLT can be installed on any industry standard rockbolt. No special installation method is required; the conventional method of bolt installation by the stoper or roofbolter remains unchanged. The device is completely encapsulated in the bolt head, which makes it resistant to corrosion, rugged, and free of any electrical wires. Pilot tests at three underground Quebec mines were carried out and helped improve the initial design of the device connector. The paper reports on two of such pilot tests.

Jan 1, 2001

By Cao Shenggen

Experiences in the developed countries have shown that continuous increase of panel width (or face length) is one of the major technical trends for high production high efficiency mines. Increasing the panel width will increase not only the panel output, simplify the gateroad layout, facilitate high concentration of production, but also increase resources recovery and facilitate protection of surface structures. This paper uses the No.4326 super- wide panel, Wangzhuang Coal Mine as an example. This mine employs the fully-mechanized top-coal caving longwall mining method. Through surface subsidence monitoring, the dynamic characteristics of surface movement were obtained. The dynamic surface movement during mining and the final surface movement after mining were predicted using the Mining Subsidence Prediction System. The results indicate that after mining, the surface above the super-wide panel reached a state of full subsidence, So it can ensure the No.309 National Highway above is located in the flat bottom of the subsidence basin, and there is little impact on the national highways when panels on both sides of 4326 Panel are mined.

Jan 1, 2003

By Hideki Shimada

In underground coal mines, grouting method is employed in order to reinforce the floor and to control the movement of groundwater into the roadway. However, the seepage and the reinforcement behavior of the grouting material into the floor are not clearly understood. Therefore, grouting is today normally based on empirical relationships and on the experience of the grouting personnel. To assist grouting projects, it must be acknowledged that many of the flow and the hardening processes occurring during grouting so far defy mathematically analysis. From this point of view. this paper discusses the behavior of grouting material, when it is injected into the roadway floor, by means of 3-D Eulerian-Lagragian seepage analysis. Moreover, the effectiveness of reinforcement grouting on the mechanical properties of slaking-prone mine tunnel floor are studied by means of several laboratory tests. Keywords: Mine tunnel floor, Grout, Seepage, Reinforcement

Jan 1, 2002

By Christopher Mark

Mines with exceptionally low-strength roof (UCS <3,500 psi and CMRR <40) are much more likely to struggle with roof falls than other mines. Weak-roof is a particular problem for many room and pillar mines in the Midwestern and Northern Appalachian coal basins. Traditional roof support techniques are often not up to the challenge at these operations. This paper focuses on two mines, one operating in the Upper Freeport seam and the other in the Herrin No. 6 seam. Together, the two mines had more than 300 roof falls during a recent 5 year period. Each has experimented with a variety of roof bolt types and lengths, and with different supplemental supports. Detailed statistical analysis was conducted to determine which support combinations have proven to be most effective. Geology, horizontal stress, and time are also important at both mines. Successful control techniques have included; ? Identifying particularly troublesome lithologic roof units; ? Installing longer and stronger roof bolts; ? Installing supplemental support in intersections, and; ? Limiting the duration that a panel remains open. The lessons learned from these mines, and others like them, could help improve ground control safety for the entire U.S. mining industry.

Jan 1, 2004

By S. S. Peng

The hydraulic powered supports have been employed in U. S. longwall mining for the past two decades. Yet the sciences of roof control at the powered supported faces remain largely unknown. In order to improve longwall roof control and increase production, a series of questions in longwall roof control should be studied and answered: what is the basic rules of roof behavior in longwall coal faces equipped with the hydraulic powered supports? What is the interaction between the roof, supports, and the floor What is the contact condition of the canopy with the roof, and consequently the load distribution on the canopy? Des the periodic roof weighting really exist in the powered supported face and if so, how does it affect the face area? This paper presents the preliminary analysis of underground observations and instrumentations in a longwall panel with 4-leg shield supports designed to address the questions mentioned above.

Jan 1, 1982

By Peter Zhang

As simpler and easier reserves are exploited to depletion, underground coal mining continues in more complex geologic settings and conditions. Roof bolting for long-term entry stability is always a challenge. For long-term entries of a mine such as belt, track entries and return airways, roof could be under-supported if one uses the same bolting plan as in short-term entries or even seem over-supported with increasing use of longer, stronger bolts along with mesh, pans, straps or trusses. In most underground coal mines, roof deteriorates over time with cutters developing deeper in entry corners; roof sagging and popping out between bolts; entry width increasing due to rib sloughage; and separations developing deeper up into the roof. In deteriorated long-term entries, roof falls could occur at certain locations and re-bolting could be costly or sometimes unfeasible. Therefore, it is important to choose an appropriate bolting plan during development based on mining and geologic conditions if the entries will be used for the long-term. In both short-term and long-term entries, primary roof bolting is critical in building a strong and effective beam. But in long-term entries, supplementary bolting is necessary in certain cases to ensure roof stability can still be maintained even if a roof failure develops beyond the primary bolted horizon. This paper deals with roof bolting for long-term entries based on studying the progressive roof failure and roof falls under different geologic conditions. The paper presents bolting considerations in terms of bolt type, length, diameter and spacing as well as bolting strategy to minimize the risk of roof falls in long-term entries.

Jan 1, 2011

By K. Itakura

Information about geostructure for effective rock bolting must be obtained before setting the bolt into rock in a coal mine roadway. Especially, rock type variation and distribution of discontinuities such as layer boundaries, and separation of strata and cracks all represent indispensable knowledge. To achieve in-situ evaluation of roof rock, we developed an MWD (measurement while drilling) system using mechanical data from a drilling machine for rockbolt. System hardware detects torque, thrust, revolution, and stroke of the machine, and software analyzes the mechanical data log and displays locations of discontinuities using Neural Network techniques. Also, this system is able to estimate roof rock 3-D geostructure for varied rock types and discontinuity distribution in cases of a drill hole array arrangement in roof rock. We conducted a feasibility study for it using hydraulic drilling at roadways of the Taiheiyo Coal Mine, Japan. Simultaneously, some core drillings were also performed to confirm system analysis data. For core samples, distribution of cracks was observed and the borehole wall was investigated by OFS (optical fiber scope). Must discontinuity locations estimated from roof logging were conformed with data obtained from core inspection. However, the core sample contained a number of cracks which were not found in the mechanical data log. This indicates that additional cracks were generated during and/or after core drilling by the influence of rotational force of the machine and water supply. Furthermore, in comparison with the OFS image, resolution of the discontinuity&apos;s log estimated by this system was clarified; that is, it is difficult to detect small size cracks (hairline cracks) from a mechanical data log and the core inspection by OFS. This paper outlines the new hardware system for hydraulic drilling machine and compares the discontinuity map obtained from the software system with drilling core inspection.

Jan 1, 2001

By Peter Hayes

Moonee Colliery operates a longwall extraction system in the Great Northern seam of the Newcastle Coal Measures, approximately 100km north of Sydney, NSW. In the initial mine area of longwall blocks1-4a, the Great Northern seam is overlain by a massive conglomerate approximately 35m in thickness. Unanticipated sudden, blocky caving of this material has produced windblasts with associated velocities of 100m/sec and over-pressures of 35kPa. Although these events have not resulted in fatality, the potential safety risk to face personnel was such that the mine was threatened with closure. The development of a Windblast Management Plan to minimise the exposure to windblasts, a Micro-seismic Management flan to predict caving events, and the use of hydraulic fracturing to generate caving on demand, have all contributed to the salvation of the mine. Prior to the introduction of hydraulic fracturing, falls were highly variable and ranged in goaf area from 2000m2 to 30,000m2 with an average of around 7.000m2. Hydraulic fracturing has introduced consistent and far less variable falls, planned as averaging around 5000m2 and all accompanied by microseismic warning, Moonee Colliery is believed to he the only operation in the world using real-time microseismic warning and using hydrofracturing as a day-to-day operational process. These processes have enabled it to return to financial viability in an environment of strict procedural control, whilst ongoing efforts are made to optimise and enhance these systems. Moonee&apos;s story is a case study of the successful application of research and development work to the economics of a mine.

Jan 1, 2000

By Jaco J. van Vuuren

Modikwa Platinum Mine, in the Eastern Bushveld of South Africa&apos;s Limpopo Province, is a new operation employing a hybrid mining method where mechanised methods are used for the main developments and the narrow, 60cm reef is conventionally stoped using a down-dip conventional mining method. Throughout the mine, the hanging wall immediately above the reef comprises 3 jointed and laminated layers of varying thickness, commonly known as the triplets, below a non-cohesive leuconorite parting plane. At North shaft, using pre-stressed standing support and mechanically anchored rockbolts, it was found difficult and hazardous to hold all three triplets in the hanging wall, however bringing them down caused a significant increase in dilution and therefore cost of mining. A novel solution was conceived whereby two of the triplets are kept up using short, stiff resin anchored rockbolts installed systematically within 0.5 m of the face. This resulted in both safety and productivity benefits. The rockbolts create a stable and safe hanging wall and allow the mine to extract UG2 reef more economically. New drilling equipment, developed locally from available drilling technology, can be operated from a safe position, and in situ tests and measurements are made to confirm effective support. The technology and underlying concepts were successfully tested in a trial stope prior to rolling out the new support system across all the stopes at North Shaft. This has involved an extensive training programme to ensure that the rockbolt system is installed correctly and that the conditions are appropriate for this technology. The paper describes the motivation behind the project, the underlying technology and its application to Modikwa, and the benefits now being realised.

Jan 1, 2004

By Eddie Martin

Jim Walter Resources, Mining Division, employs the retreat longwall mining system as the primary method of coal production. The strata control aspects of developing and maintaining roadways for retreat longwall mining have continued to improve and advance at Jim Walter Resources. New and innovative concepts in pillar design, roof and rib support, as well as longwall face support, have been combined to provide better strata control. Control of immediate roof breakup in the headgate and tailgate entries has been a problem at Jim Walter Resources&apos; mines. The application of roof trusses as supplemental roof support failed to provide the desired strata stability. The immediate roof deterioration has been controlled through the installation of increased density of roof bolts in the affected roadways. Control of the rib sides has been a documented problem at Jim Walter Resources&apos; No. 4 Mine since its start-up. The installation of 3/4 inch diameter roof bolts at 2 ft. spacing failed to control rib rolls. The development and application of a yieldable rib support system provided the desired results. Rib rolls have been virtually eliminated where the yieldable system of rib support has been installed. An evaluation of longwall panel development using the total yield pillar mining plan has been completed. Results of the strata stability and other operational data have been compiled. Coal production and gate entry stability were not adversely affected using the total yield pillar mining plan for longwall panel development. Strata Control on the longwall face is provided by the face support system. Excessive convergence and roof breakup along the longwall face have been experienced at several of the Jim Walter mines. In an effort to eliminate this problem, an evaluation of higher setting pressures for longwall face supports is being conducted. Results have been inconclusive to date. Each of the above strata control projects will be presented as case studies. Since Jim Walter Resources business is coal production, emphasis will be directed toward the application rather than the theoretical aspect of the projects.

Jan 1, 1988

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 Yoginder Paul Chugh, Jason E. Tinsley

"Over the last five years, the authors have compiled a database of Short Encapsulation Pull Test (SEPT) evaluations from Interior Basin (Basin) coal mines. Typically, SEPT data are analyzed to obtain peak load carrying capacity per unit length of resin encapsulation designated as the ""Grip Factor,"" or GF. In a previous paper, ""An Analysis of Short Encapsulation Bolt Pull Test (SEPT) Data From Interior Basin Coal Mines,"" authors analyzed tangent value of the load-displacement curve as Anchorage Stiffness at 50% (AS-50) of the peak load, or GF value, to assess reinforcement potential of an installed bolt system. This paper attempts to correlate the secant AS VALUES (of SEPT on 6 ft (1.8 m) long installed bolts at a lower load of about four tons from several different mines in the Basin with their MSHA-approved primary support requirements. Since the current regulatory environment requires plan changes dynamically to ensure that roof falls are minimized, the authors hypothesize that the practiced roof control plan must meet the minimum requirement of adequately supporting immediate roof strata. The analyses are based on 181 SEPT studies performed by Minova professionals. Analyses indicate a macrolevel correlation for both roof support density and roof support cost that may have the potential to be used by mine operators to compare their performance with other mines in the area. Limitations of the analyses include ignoring mining depth, mining height and required secondary supports as part of the requirements for a roof control plan. The authors recommend additional analyses to develop this concept further to develop guidelines that can be confidently used by coal companies.INTRODUCTIONPartially- and fully-grouted bolts are extensively used in coal mines for roof support as part of MSHA-approved roof control plans. Since grouted bolts have a larger area of contact with the rock, they can develop much greater anchorage capacity than conventional expansion shell (point-anchored) bolts. Load transfer characteristics and interaction mechanics between steel rebar, grout and rock mass around the bolt hole for grouted bolts are generally assessed in the laboratory or field though short-encapsulation pull tests (SEPT), which have been extensively researched by Aziz and Jalalifar (2005), Aziz (2004a), Serbousek and Signer (1987), Signer (1990), and Mark et al. (2002), among others. In a SEPT, about 12 in. (30 cm) of bolt length is typically encapsulated in resin and a pull test is performed to collect load-displacement data prior to failure and, in some cases, post-failure. A typical load-displacement data set for a bolt is shown in Figure 1. SEPT characteristics are designated by peak load carrying capacity, or grip factor, which is the peak load carrying capacity per unit length of resin encapsulation. SEPT is routinely used to assess anchorage performance characteristics of different lithologies overlying a coal seam to identify type of bolt, bolt diameter, length and spacing across and along an excavation. Anchorage stiffness, or AS, at any load may also be calculated as the tangent or secant value of the slope of the load displacement curve at a particular load level. Anchorage Stiffness characteristics of bolts from SEPT data have typically not been considered in any depth until recently (Chugh et al., 2014; Chugh et al., 2015)."

Jan 1, 2016

By Robert C. Garson

The Mine Roof Simulator at the DOE&apos;S Mining Equipment Test Facility is described. Its use in the research and development on the behavior and response of longwall roof supports to simulated mine environment is investigated. Advanced technology analysis methods such as finite element modeling, strain gage instrumentation, and photoelastic techniques are investigated for application in roof support design two case studies are presented of test data and results.

Jan 1, 1982

By Richard R. Wilding

The United States Coal Mining Indus- try had the opportunity to greatly improve their roof control techniques during the nineteen seventies by the use of fully grouted resin roof bolts. This new tool was first approved for underground coal mines by M.S.H.A. ten years ago and during the next decade has been perfected to meet many problems previously thought to be unsolveable. The initial approved cartridge was very similar to the ones used in Europe in the nineteen sixties and since then has undergone a great deal of modification for our mines. These refinements in cartridge construction have been obtained by the close cooperation of resin manufacturers with mining personnel in perfecting pro- ducts customized to particular needs. This type of continuing program naturally necessitates a responsibility upon the resin anchor manufacturer to maintain a competant technical department. These roof control technicians by constant exposure to many of the most demanding underground problems, have developed through the years into leaders in successful applications. Today, Celtite has over twenty technically trained underground technicians with an accumulation of over one hundred years experience in resin anchors. Our documented technical reports are in excess of five thousand, involving over six hundred mines representing every major coal mining area in most mineable seams. This department has been the implement used to work with our research and development people in perfecting a continual line of improved resin anchors. This program has been a significant factor in leading the resin anchor industry into a position where approximately one third of the 1980 under- ground coal production used the fully grouted system. However, as gratifying as this accomplishment is, our experience has lead us to believe that there is an additional demand for a roof control system capable of combining the mechanical bolts ability to apply tension with resins proven superiority in anchoring. A significant number mines visited during the last decade had problems that we believed could be better answered by applying tension rather than the fully grouted approach. In most in- stances, their current mechanical installations were doing an adequate job until anchor slippage occured. Fully grouted systems solved this bleed-off problem. However, an acceptable number of falls still occured. In these some- what unique areas which we believe may amount to as much as fifteen percent of the total bolt installations, the need for improved anchors was a necessity. In developing this program we listed the ultimate requirements necessary for both the bolt and the anchor. These are for the bolt: A. Have one end manufactured so it can be grouted to the mine roof with polyester resin, obtaining a variable length from 12" to 36". B. Have a mechanism which allows the operator to tension the roof from zero to 10,000 psi. This mechanism should indicate if the roof is in compression and the bolt in tension. C. Have a mechanism which allows the operator to thoroughly mix the resin. D. The head of the bolt should not extend below the roof line any more than a normal mechanical bolt. E. Not require any extra tools for installation. F. Be bendable for use in low seam coal. G. Be durable and inexpensive. The ultimate point anchor resin should have the following characteristics: A. Have a mix and gel cycle which would compete with a mechanical bolt for speed of installation. B. Have a pull out strength in excess of a normal 5/8" mechanical bolt.

Jan 1, 1981

By Alan A. Campoli

Fosroc continues as a leader in the development of cementitious technology for the mining industry. The considerable expertise accumulated in the development of the Fm cement line has been employed in the development of two pumpable, supplemental roof support systems. The Tekprop system is a unique combination of steel and concrete, specifically designed as a viable alternative to conventional wooden supplementd support. The second system is the Fosroc mineable mi which is a cost competitive variable yield system designed to support longwall ventilation and predriven recovery room entries. Two, separate, ongoing, full scale applications of these systems will be discussed during the inference presentation

Jan 1, 1997

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 Thomas M. Barczak

Wood cribs have been the dominant form of supplemental support in coal mining for many years. Recently, there has been a renewed interest in prop supports as a replacement for wood cribbing due to the increasing cost of mine timber and engineering advancements in prop design to improve their stability and yield capability. Prop supports generally consume less material, can be installed in less time with less labor, and provide less restriction to mine ventilation than wood crib supports. Several prop supports are now available or under development&apos;. These include: (1) Strata Products Propsetter? Support System; (2) Heintzmann ACS and Super Prop; (3) MBK-Hydraulik MEGA prop; (4) Advanced Mining Technology Inc. (AMTI) BTS Mortar prop; (5) Dywidag Coal Post; (6) Western Support Systems YIPPI support; and (7) "The Can" support by Burrell Mining Products. A comparison of the performance and cost of these support systems to wood cribs is made to provide mine operators with information needed to assess their application potential. Examples of current underground installations are discussed. Included in this assessment are full scale tests of these supports conducted in the U.S. Bureau of Mines&apos; Mine Roof Simulator.

Jan 1, 1995

By J. R. M. Hill

The U.S. Bureau of Mines is involved in research to improve geological sensing (or geo-sensing) techniques. This paper presents results from field trials of two research projects concerned with new technologies for geosensing. The goal of the first project was to develop a "smart" roof bolter drill so that it could probe into roof rock to evaluate rock conditions. The goal of the second project was to modify an existing mine-wide monitoring system in a continuous mining operation so that the system could interface with geotechnical instruments to provide near real-time geosensing. Integration of this mine-wide monitoring system with the smart roof drill to collect, reduce, and analyze geotechnical data and the potential applications of the resulting technology in mining, are described.

Jan 1, 1992

By Ken Barish

Jane Mine of the Keystone Coal Mining Corporation was started in 1962 and is in the Lower Freeport seas located in Armstrong County, Pennsylvania, approximately 45 miles northeast of Pittsburgh. The mine is a slope/shaft complex with the cover ranging from 100 feet at the slope to 450 feet near the back end of the property. The seam height ranges from 48 to 72 inches. A variety of roof conditions have been en¬countered, and an equal variety of roof control systems have been tried with varying degrees of success. Initially, places could be mined as deep as 100 feet without any permanent roof support. After several problems and the advent of the Health and Safety Act of 1969, roof control became more and more prevalent and predominant at the Jane Mine. It started with 4 foot conventional oolts. As the mine progressed in the northeasterly direction, roof conditions changed from the extremely good roof that was encountered initially, to bad roof; and other types of roof support were required. Sixty pound rails and 6 inch 25 pound to the foot steel I-beams were used for supplemental support in long life headings such as belt and track. Resin bolting was done in many areas for long life support due to the deterioration of the shale roof over time. Several areas had to be abandoned because of uncontrollable top.

Jan 1, 1984

By John Bullock

Limestone and dolomite quarries were mapped to determine specific failure mechanisms for the various geologic and structural conditions. Algorithms for analyzing these mechanisms were incorporated into a software package together with ranges of physical properties such as joint shear strength, angle of internal friction, and cohesion for specified lithologic units. Reliability options using Monte Carlo sampling and sensitivity studies are included to evaluate alternative highwall designs. The package is designed to facilitate progressive stability evaluation of quarry highwalls as mining continues. This package includes an optimum design protocol that can be followed to avoid the potential of massive failure. The program was developed in conjunction with the quarry industry and is demonstrated using case studies.

Jan 1, 1993