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The purpose and current practice of cable trusses in underground coal mines is briefly outlined and details of various cable truss designs are presented. The main part of the paper describes the in-situ performance of cable trusses installed as secondary supports in gateroads and recovery roads of longwall coalfaces. The performance analysis is based on the results of in-situ monitoring carried out at a number of sites at two underground coal mines within Australia. Truss performance has been assessed as load developed in relation to roof convergence, face position and time. Additionally, the influence of strata conditions, installation pattern/density, roadway layout and geometry have been taken into account. An analytical model has been developed to predict truss loads. The principal variables are listed and the basis of the model is described. Based upon behaviour observed in the field the model has been progressively upgraded and validated against measured performance. Guidelines on truss performance and factors which influence it are presented and the implications of these to the use of cable trusses is discussed. Possible methods for improving truss performance in certain strata conditions are outlined and some comments are made on the value of cable trussing compared to cable bolting in these situations,

Jan 1, 1992

By Vladimir Adamek

Two existing predictive methods were chosen for evaluation; an influence function (Gals Theory) and a profile function (hyperbolic). These were applied to several field measured subsidence pro¬files over United States coal mines. The effect of homogeneous versus non-homogeneous overburden on surface subsidence is demonstrated and the utilization of Bals Theory as a subsidence predictive method for both types of overburden is examined. The major factor affecting subsidence profile characteristics is the migration of the inflection point toward the centerline of the longwall panel. A computer program was written to aid in the analysis.

Jan 1, 1981

By Eleanor Sonley

In October 2000, temporary seismographic stations were installed above the Trail Mountain Mine, Emery County, Utah, USA to supplement a regional network. Over seven months, 1826 mining-induced seismic events were recorded with a magnitude range of M 0 to M 2.2 (Arabasz et al., 2002, 2005). Routine event locations for this dataset cluster around the longwall mining activity during the recording interval. However, applying a double difference relocation technique to the routine locations significantly improves the correlation between mining activity and event location. The resulting relocations depend greatly on station distribution and the number of arrival time picks. We use this dense temporary array to assess station distribution requirements for applying the double difference technique at other mines by systematically removing data from available stations, thus simulating sparser networks. The insight gained using the Trail Mountain dataset is used to develop a metric for assessing the usefulness of above-mine networks and to develop a tool for expanding seismic network coverage. To verify the appropriateness of these tools for wider application, we examine data from two additional mines located in the western United States. Improving the relative locations of mining-induced seismic events highlights the association of these events with active portions of the mine. Clusters, regions of quiescence and relative timing of events can be used by mine operators to assess hazard, optimize production, and evaluate performance of mine plans. The lessons learned from this study may be used in future network design to improve accuracy of event locations at other mines.

Jan 1, 2009

By Sean Harvey

One of the manifestations of the dynamically induced failures in deep coal mines is the violent ejection of coal from the ribs. A possible protection against such failures is the use of a specifically designed dynamic support system with reinforcement units having the sufficient capacity to absorb the kinetic energy of the dynamic failure and a skin support that can adequately contain the disintegrated coal. With this method of mitigation in mind, a recently introduced yielding rock bolt, trade name Roofex, has been identified (Harvey and Ozbay, 2009) as a possible energy absorbing component of a dynamic support system. According to the manufacturer?s specification, the Roofex bolts can yield 300 mm (or more) displacement while holding 80 kN pull load. In order to assess the performance of this support unit in coal ribs, a series of in situ pull tests performed in two coal mines in Colorado. The results show that, under conventional pull test loading conditions, Roofex yielding bolts perform very close to their claimed specifications, thus showing a potential for their use as the main energy absorbing component of a dynamic support system. Further studies are required to confirm the in situ performance of these bolts under dynamic loading conditions and also to develop a containment component for a dynamic support system for the mitigation of dynamic coal rib failures.

Jan 1, 2009

By Steve P. Signer

A study of rock support interaction mechanics was conducted by the U.S. Bureau of Mines at the Jim Walter Resources No. 7 Mine, Brookwood, AL. Bolt loads and entry deformation were monitored at four sites in a tailgate roadway. Two sites were areas supported by fully grouted resin bolts, and two sites were supported by tensioned bolts that used resin-assisted mechanical anchors. The yield capacity of the tensioned bolts was 37 pct higher than that of the grouted bolts. To monitor loads, instruments were mounted on 16 bolts, which were installed during entry development in the standard bolt pattern. Additional instrumented bolts were installed as supplemental support just prior to the headgate pass of the first longwall. Instruments to measure roof movements included three-point roof extensometers and convergence stations. Readings were taken during section development and as each longwall panel passed the test area. The fully grouted bolts showed localized loads that were higher than loads on the tensioned bolts; however, overall loading magnitudes were similar. Many sections of the fully grouted bolts passed the yield point of the bolt steel (98 kN or 22,000 lb). However, the maximum strain measured at any loca¬tion was 50 pct of the ultimate strain, and there was adequate bolt length to transfer the high loads into the rock. Significant bending was detected at many points along the length of the bolts and seemed to be the most significant mechanism in support-rock interaction. Loads on the tensioned bolts did not exceed the yield point of 160 kN (35,000 lb). Entry deforma¬tion, supplemental bolt loading, and general entry degradation appeared to be slightly less at the tensioned bolt sites. Local geology and in situ horizontal stress were also observed to affect con¬ditions at the test sites.

Jan 1, 1993

By B. Singh

The use of wire ropes has already been tried in a few countries for roof support In mines. But the use of scrap wire ropes, as a method of support on extensive scale has not been reported from anywhere except India. Extensive trials using freshly discarded wire ropes for roof support were undertaken both in the laboratory and field. In laboratory, model beams supported with different reinforcing techniques were tested to evaluate their comparative load bearing capacity vis-a-vis reinforcing factor. Among all the tests, the model supported with wire rope system at 60° angle in combination with two supplementary vertical bolts offered the best result 1.e. about 95% reinforcement. It also accepted post fracture loading of the beam. In statical analysis too, the best result could be obtained with the rope installed across the gallery at 60° angle. All these findings are in conformity with the field observations obtained during roof stitching practices in coal mines. Of late, roof stitching, an effective and economical method of roof support developed at CMRS, India in 1972, found wide application in over 200 coal mines. In this method, a freshly discarded wire rope is grouted across a gallery in two inclined drill holes supplemented with two middle vertical roof bolts at every 1.0 to 1.2 m interval along the gallery. It is tensioned against the roof using wooden sleepers and thus, the whole system functions like a roof truss.

Jan 1, 1990

By Bill Stormes

This paper will discuss implementation of the Hilti OneStep rock anchor technology to improve face bolting operations during the May 2008 longwall move; increase rock anchor installation capacity; and improve safety by reducing employee exposure periods by utilizing the Hilti OneStep rock anchors.

Jan 1, 2008

By Kenny D. Basnett

An analysis of the Roof Falls Data Base (RFDB) for underground coal mines in Illinois for the period 2004?2008 indicated that about 80% of the roof falls occur at intersections and are associated with geologic anomalies or a rapidly changing geologic environment. Most falls are associated with anomalies such as clay dikes, differential compaction faults, shear zones, joints and fractures, and geologic structure. Therefore, a better analysis of the geology with emphasis on mapping anomalies such as joints and fractures and their application is necessary to improve ground conditions and safety. Such studies within Illinois Coal Basin are limited. This paper presents a mapping study of the joint orientations with documentation of dip of the several lithological units that lie directly above the Herrin No. 6 Coal seam around southern Illinois. These units include the Energy Shale, Anna Shale, and Brereton Limestone. The mapping was done in three mines and the data were plotted on a stereographic projection to determine the average characteristics of joint planes. The study mines included two deep underground mines and one shallow highwall mine. This study has helped identify favorable mining and support orientations in areas of highly variable geology. These are currently under review by the cooperating coal company for experimental roof control studies.

Jan 1, 2011

By Keith Heasley, Christopher Newman, Zach Agioutantis

"Previously, in 2013, a laboratory version of the computer code ARMPS-LAM, introduced at the 32""d International Conference of Ground Control in Mining, successfully integrated the laminated overburden model of LaModel into an ARMPS-style pillar stability analysis. The ARMPS-LAM analysis has now been fully integrated into the ARMPS program allowing users to more accurately classify the stability of a given mine design utilizing a laminated overburden model for the determination of pillar loading within theAMZ. ,This paper introduces the new Windows-based ARMPS-LAM program. The program's ease of use, output result generation, and limitations are highlighted through the parametric analysis of three hypothetical case studies where traditional ARMPS output is compared to output generated by LaModel. As mining operations continue to produce at greater depths and in more complex geometric and geological conditions, flexible and efficient analyses of mine stability for underground room and pillar mining has become more and more essential. The ARMPS-LAM program provides the mining industry with an empirically backed, numerical design tool for the evaluation of underground room and pillar mine plans.INTRODUCTIONIn the Southern Appalachian coal fields of the United States, retreat room-and-pillar methods have allowed mining operations to maintain high rates of production in the face of adverse geologic conditions and shrinking coal reserves. Over the years, research has been dedicated to understanding and mitigating mining-related dangers due to second mining practices, such as: pillar squeezes, floor heave, roof falls, pillar bumps, etc. However, as mining operations continue at deeper depths and with more complex geometric and geologic conditions, there is an inherent industry need for more accurate, flexible, and faster evaluations of stability for underground room-and-pillar mining."

Jan 1, 2016

By Hamid Maleki

Mining in the Book Cliffs Coal Field of Utah has historically been associated with seismicity because of high-stress environments and the presence of stiff, competent rocks. Recognizing the geotechnical risks in this coal field, mine engineers have dedicated considerable resources to the study of mine seismicity. In spite of these efforts, there are no engineering procedures for assessing mine seismicity for a new property and in developing mine designs. This paper presents the results of ongoing geotechnical monitoring and stress analyses at a western U.S. coal mine. The intent is to demonstrate the application of geotechnical methodologies in evaluating mine seismicity and stress-control technologies including evolutions in yield pillar designs for variable topographic conditions of the Book Cliffs Coal Field. We show that narrow yield pillars are quite effective in limiting strain energy accumulation along the gateroads and thus the potential for pillar seismicity. At the same time, the pillars provide sufficient resistance to control roof-floor convergence at the headgate, gradually unloading to residual strength inby the face position. Lagging, nonuniform caving of overburden rocks results in periodic stress concentrations at the tailgate comer. The sudden release of strain energy triggers sudden failure of critically loaded coal in this area of the high stress gradient. The three-entry gate pillar configuration promotes formation of long cantilevers and load transfer to the tailgate, contributing to formation of cutters and coal bumps. The source of seismicity is investigated while simulating slip along three sets of joints in two stiff stratigraphic units during multipanel extraction.

Jan 1, 2003

By N. P. Kripakov

The U.S. Bureau of Mines (USBM) is conducting research to develop a practical computer-based tool that will allow coal mine planners to anticipate rock mass behavior surrounding mine entries prior to actual mining. More specifically, this tool estimates to what degree and extent the immediate roof and floor strata and the coal pillar ribs surrounding an opening will weaken or fail for a given set of mining parameters. The technical approach couples together two numerical techniques: the boundary-element method and the finite-element method to allow for an approximate three-dimensional simulation of actual mining situations. Outputs from plan-view, linear-elastic, boundary-element models executed at different mining stages are used as input to a detailed, section-view, finite-element model to estimate the degree and extent of failure expected to occur around the periphery of an entry system. Using a pseudo-elastic approach. elastic rock mass properties are continually updated as different zones are predicted to fail. The procedure is relatively easy to use and is being set up to work interactively with the user who will not be expected to be a computer expert. Inputs include easily understood parameters obtainable from the field and rock mechanics laboratories. Examples of computer-generated output from generic sample models representing typical mining situations are presented and results discussed.

Jan 1, 1994

By Kevin Beauchamp

In many cases traditional support designs cover the many variations in ground conditions and bolt performance by a conservative factor of safety. The result is that most bolts are ineffectual most of the time and yet the response to occasional roof collapses is an even more conservative design. The probabilistic analysis presented in this paper takes several important parameters of a support design into account such as span, bolt strength, bolt length, water pressure, seismic accelerations, joint orientation, bed thickness and joint strength and allows the effect of variations in these parameters to be evaluated simultaneously. The analysis demonstrates the application of the probabilistic approach to both blocky, wedge-dominated conditions and bedded deposits dominated by laminations. All mine excavations have a designed stand-up time. By taking into account of the possible variations in the design parameters explicitly, it is possible to produce a support system designed to ensure stability over a given period of time. Rather than use a factor of safety criterion, the approach uses a percentage reliability or probability of failure. By understanding the probability of failure of the support system, it is possible to improve the performance of ground support without any increase in cost or conversely to decrease the cost while maintaining the performance of ground support. This approach reduces reliance on empirical experience and leads to a better understanding of the key factors that influence stability and can provide a much more accurate and optimized assessment of support design and performance. The result is a more cost-effective support system and we hope that a broader application of this approach to ground support in underground mines will lead to a greater acceptance in the industry of probabilistic analyses and of terms such as Probability of Failure and Reliability of Support.

Jan 1, 2003

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 Ding Xu Chu

There are many methods developed for measuring the crustal stress in China. Among them only two methods have been adopted in practice, i.e., overcoring method (for which the sensors include: Piezo-magnetic stress gauge, steel-ring strain cell, 3-dimensional hollow-inclusion stress ,gauge, and Leeman's-like stress gauge) and hydraulic fracturing method. For the former method, one of those sensors is installed in a borehole, 36 mm in diameter, then prestressed, and finally overcored with a drill bit of 130 mm in diameter. After that the deformation of the borehole wall is measured, from which the in-situ stresses are determined. In order to avoid the errors resulting from the difference in elastic modulus for various kinds of rocks as well as from the installment of the cells, we have developed a technique to calibrate the sensor on-spot using a confining pressure calibrator and produced a very good result. For the later method, the measurements are achieved by isolating a certain section of a borehole and then injecting water to pressurize it till a tensile break is induced. It is identical to the typical technology used internationally. For many years, through field observations and a large number of laboratory experiments, we believe that the most efficient way of stress measurement for engineering purposes is the overcoring method using Piezo-magnetic stress gauge. It is characterized by stable and reliable measurement values, high accuracy and high adaptability. Taking the measurements in the intact rock mass as an example, the measured stress magnitudes are within accuracies of 8% and the errors in orientation are about 5 degrees. It can even be used perfectly in deep water. Up to now, we have performed in-situ stress measurements in more than 70 sites and obtain more than one thousand sets of data. The deepest depth used in the overcoring method is 80 m in vertical borehole and 780 m in tunnels.

Jan 1, 1987

By Duk-Won Park

A vast majority of the operating longwall sections use shield-type face supports to provide ground control in the United States. As a co-operative research program between the University of Alabama (UA) and Jim Walter Resources, Inc.(JWR), a joint research program is underway to study interaction of shields with surrounding rock masses. A series of analyses on the response of shields are performed using monitored data at a longwall face in a deep coal mine. In this paper, various effects of parameters, such as leg pressure, setting load, developing load, maximum loading rate, pressure in capsule, and convergence between canopy and base, are discussed and recommended as stability indices. A microcomputer program is being developed for instantaneous interpretation of the shield monitored data, and for giving warnings of potential problems. The preliminary results define the effects of the setting load, developing load, and rate of developing load or leg closure rate. The objective of the study is to understand the shield characteristics and their interaction with surrounding strata in real time, then develop a reliable program for maintaining longwall stability.

Jan 1, 1992

By Dr. Daniel W. H. Su

t is both an honor and privilege for me to nominate Dr. Daniel W. H. Su for the inaugural Syd S. Peng Ground Control in Mining Award. I can think of no better candidate than Daniel that is deserving of this award ? an award to recognize technical excellence in advancing ground control technologies [and] approaches. Daniel?s education and career spans over three decades. Having graduated from National Cheng Kung University in Taiwan in 1972 with a B.S. degree in Mining and Petroleum Engineering, he spent the next four years in the Taiwanese military and mining industry, before moving to the United States, where he enrolled in West Virginia University?s Mining Engineering Department. He received his M.S degree in Mining Engineering from WVU in 1978; then in 1982 became the first person to ever receive a Ph.D. in Mining from WVU. His thesis was titled, ?Development of Ultrasonic Techniques for the Measurement of In Situ Stresses?.

Jan 1, 2006

By WenFeng Li

A 3D roof bolt model with the consideration of rebar, resin, bearing plate, and resin/rock interface was developed for studying the bolt/rock interactions of the tensioned and fully-grouted resin bolts. For the tensioned bolts, 2 ft compressive zone above the rooflineis generated by the 10 tons pretension. Since the free portion of the tensioned bolts displays a higher vertical stress, the increase of the bearing capacity of the rocks in such range is much larger. For the fully grouted resin bolts, despite no pretension is generated during installation, the roof sag can indirectly generate a compressive zone near the roof line. In addition, the analysis on the differences in bolt/rock interactions when employing the tensioned or fully-grouted resin bolts indicates that the fully-grouted resin bolts are preferred as the primary support when weak and thinly-bedded immediate-roof is present. Meanwhile, it is found that both the tensioned and fully-grouted resin bolts may have very limited effect in preventing and/or control the cutter roof.

Jan 1, 2014

By Kevin MacPherson

After 34km of roof bolted drivage the first fall of ground occurred at the Phalen Colliery in the maingate of the 8th East longwall panel. The fall occurred over the stage loader as the wall approached an area of poor roof geology. This area had developed a severe cutter since initial drivage and the longwall had yet to mine through 500m of even worse conditions. This paper describes the cause of the poor roof conditions, the use of polyurethane resin injection and cable bolting to re-stabilize the roof outby the fall, and the measurement of roof movement and performance subsequent to the continuation of mining under the rehabilitated roof.

Jan 1, 1999

By Deno Pappas

During the past few years, the Pittsburgh Research Laboratory of the National Institute for Occupational Safety and Health (NIOSH) has been evaluating developments in sealant support systems from a ground control perspective. The proper selection and use of a sealant material can significantly enhance ground control which may result in a decrease in worker related injuries due to ground falls. The purpose of this paper is threefold: to briefly review the current state¬of-the-art technology in shotcrete and membrane developments, to evaluate the preliminary findings of a long-terra underground study of various types of sealant materials, and to examine installation practices that are critical for an effective sealant material. The underground study utilizes NIOSH's Lake Lynn Laboratory Experimental Mine to evaluate the long-term performance of several types of shotcrete and membrane materials. Sealant performance to date have been evaluated on a regular basis over a two year period. Although the study is still ongoing, critical mining practices were identified that may seriously effect the bond of the sealant materials to the mine roof and rib; most notably, the importance of scaling and thorough cleaning of the rib prior to application. Also, results from an extensive series of Schmidt Hammer tests found that the shoterete increased in strength by 70% during the humid summer months.

Jan 1, 2002

By Gary R. Corbett

The federally owned Cape Breton Development Corporation (CBDC) mines approximately 2.5-3.0 Mt of coal per annum from its Phalen Colliery. As part of an ongoing process to become more commercially viable the Corporation has implemented changes in its support method, namely, the transition from traditional steel set inseam supports to roof bolts as primary support in the single entry longwall retreat drivages. During 1991 and 1992, a monitoring program was implemented by the Cape Breton Coal Research Laboratory (CBCRL) to determine the loading on support systems and ground reaction in the gateroads in front of the retreating longwall faces of the 4 East and 5 East panels at Phalen Mine. The 4 East gateroad had been supported by steel sets alone. The 5 East gateroad had been supported by steel sets as well as roof bolting and strapping of the gateroad roof. Steel sets in both gateroads were instrumented with strain gauges and load cells to record support reaction to the retreating face abutment pressure. Multipoint borehole extensometers and multipoint strain gauged roof bolts were installed in the gateroad roof to monitor strata displacement and bolt loading above the gateroad as the longwalls retreated. This paper describes the details of the instrumentation and monitoring techniques utilized during this program and discusses the results, trends and differences observed in the two differently supported access roadways. Work on future data acquisition instrumentation is also briefly described.

Jan 1, 1993