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By Morgan Sears

The LaModel program (Heasley, 1998) is a displacement discontinuity, boundary element model (BEM) for analyzing stresses and displacements in single and multiple-seam coal mines. After the Crandall Canyon mine collapse, the need for better design guidelines for LaModel was observed and a new calibration method for deep cover pillar retreat was developed (Heasley et al., 2010). However, the scope of this initial calibration was limited to single-seam mines deeper than 750 ft. This limited application of the initial calibration method lead directly to the research presented in this paper, which attempts to define appropriate LaModel calibration guidelines for pillar design where shallow cover and/ or multiple-seam mining scenarios are encountered. As part of this research, a database of shallow cover case histories has been developed, and this database is used to help validate the shallow cover calibration method. By adding the shallow cover database to the previous deep cover database, the LaModel calibration method has now been extended to the complete range of mining depths, as well as to multiple-seam cases. With this shallow cover calibration, the utility of the LaModel program continues to increase.

Jan 1, 2013

By Monte R. Hieb

Study of moisture-induced swelling strain in Pennsylvanian Period rocks of the Appalachian Plateau in West Virginia shows a 2:1 biaxial horizontal anisotropy which trends NW-SE. Oriented in-situ slabs of coal mine roof rock were collected across West Virginia, dry-sawed to size, air-dried to stability, and then monitored for moisture changes and deformations in the horizontal plane through one wetting cycle and drying cycle. Biaxial swelling strains were exhibited in nearly all rocks tested, with maximum horizontal deformations occurring normally-incident to the strike of regional geologic fold structures. This relationship persists as fold strike varies across the study area. A connection with Alleghanian fold development and/or post-Alleghanian fold relaxation is suggested. Deformations were largest in shales, but occurred in sandstones and siltstones as well. During testing, moisture-induced fractures (MIF) developed parallel to the regional fold structure and ranged in size from hairline cracks to sample-destroying cracks that were orthogonal to the observed biaxial swelling strain direction. Preferential wetting and swelling of clay minerals along NE-trending fractures, related to a fold-parallel fracture fabric of regional extent across West Virginia, is the most likely reason for the observed systematic NW-oriented biaxial swelling strains. The testing methods used in this study are simple and inexpensive and produce robust results that offer insight into a regional, anisotropic mechanical weakness that imparts a dynamic, asymmetrical horizontal stress to moisture-sensitive coal mine roof rocks over time. Because a similar mechanical fabric has been reported in Devonian-age shales, these findings may have implications for shale gas developers in the Appalachian Basin challenged by rapid aperture closure rates along horizontallydrilled induced fracture networks in Devonian rocks like the Marcellus Shale. The paper concludes with an example of how the concept of a preferred swelling strain direction might be applied to improve the effectiveness of roof trusses.

Jan 1, 2013

By Zhang Hongzhen

The fast convergence of boundary is a major problem of probability integral method, especially for the prediction of mining under thick alluvium, abandoned mine goaf, etc. To solve this problem and improve the accuracy of probability integral method, a modified model is constructed for surface movement and deformation based on theoretical analysis. In which, three weighted values i.e. 1, -1/t1, 1/t2 are set for the mining movement and deformation of three different major influence radius i.e. r1, R1, R2, respectively, then the parameters are selected as following: (1) Parameters are inversed based on the observation data, in which the subsidence factor q, deviation of inflection point s, displacement factor b are considered as generic parameters, the tangent of major influence angle tanß is modified as tanß2, that is the major influence radius r is modified as r2. (2) Inversion parameters of tangent of major influenceangle tanß or major influence radius r, based on the observation station edge data which beyond major influenc eradius distance from work-face mining boundary. The inversed tanß and r will be used as tangent of major influence angle tanß1 and major influence radius r1, respectively. (3) Other relevant parameters i.e. t1, t2, R1, R2, are calculated with the algorithm of this paper. A comparison experiment between the traditional and modified models has been conducted using the observation data from a observation station, the results show that in its central area, 58.6 percent of observation points accuracy is improved and 36.6 percent is decreased, while in its edge area, 61.5 percent is improved and 15.4 percent is decreased, totally, 68.6 percent is improved and 30 percent is decreased. Therefore, we can draw the conclusion that our modified model can improve the prediction predication accuracy, in particular, the boundary region.

Jan 1, 2014

By William J. Conrad, Ryan J. Molka, Erik C. Westman

"In order to study pillar and overburden response to retreat mining, a ground control program was conducted at a Central Appalachian mine. The program consisted of several monitoring methods including a seismic monitoring system, borehole pressure cells in the pillars, and time-lapse photogrammetry of the pillar ribs. Two parallel geophone arrays were installed, one on each side of the panel with the sensors mounted 3m (IO ft) into the roof. A total of fourteen geophones recorded more than 5,000 events during the panel retreat. A MIDAS datalogger was used to record pressure from borehole pressure cells (BPCs) located in two adjacent pillars that were not mined during retreat. A series of photographs were taken of the pillars that had the BPCs as the face approached so that deformation of the entire rib could be monitored using photogrammetry.Results showed that pillar stability and cave development were as expected. The BPCs showed an increase in loading when the face was 115 m (380 ft) inby and a clear onset of the forward abutment at 30 m (100 ft). The photogrammetry results displayed pillar deformation corresponding to the increased loading. The microseismic monitoring results showed the overburden caving inby the face, again as expected. The significance of these results lies in two points, I) we can quantify the safe manner in which this mine is conducting retreating operations, and 2) we can use volumetric technologies (photogrammetry and microseismic) to monitor entire volumes of the mine in addition to the traditional point-location geotechnical measurements (BPCs).INTRODUCTION AND BACKGROUNDExcavation of underground openings is a difficult job in a challenging environment. The rigor of the process is compounded by the lack of a method that allows quantification of changes within the rock mass as excavation progresses. Statistics kept by the Department of Labor, Mine Safety and Health Administration show that 16% of fatalities and lost time incidents in the underground mining industry are due to unexpected rock mass failure (MSHA, 2015). A recent example is the Crandall Canyon, Utah, coal mine accident caused by the vertical collapse of a longwall coal mine on August 6, 2007 (Dreger, Ford, Walter, 2008)."

Jan 1, 2016

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 Jonathan P. Furniss

The paper describes a range of laboratory tests undertaken on full column resin anchored glass fibre rockbolt systems, to assess all aspects of their performance. Laboratory instrumentation has been developed for the accurate study of strain transferral from the Glass Fibre Reinforced Plastic (GRF') bolt, through the surrounding resin annulus, and into the rock. Experience in laboratory testing to the new British Standard on glass fibre rockbolting is discussed. A critical comparison is made of the influencing parameters affecting . underground rockbolted roadway performance to the parameters assessed by BS 7861 : Part 1 The work has been co-funded by MA1 Systems UK Ltd. who supply GRP rockbolt components to the British coal mining industry, mainly for the reinforcement of coal ribsides. In rockbolting, glass fibre has a number of useful * qualities which are discussed in the paper. These properties, make the product more suitable than steel in certain applications, both in mines, and other engineering structures such as tunnels, soil stabilisation, and coastal defences.

Jan 1, 1997

By L. A. Sandbak, Yan Xing

"The purpose of this study is to evaluate the rock mass stability around the tunnels by three-dimensional (3-D) numerical modeling. Complex geological and tunnel features have been included in the model using the software package 3DEC™. Based on the available information on stratigraphy, geological structures, and mechanical properties of rock masses and discontinuities from the underground mine, 3-D stress analyses were performed on various cases with different K0 (lateral stress ratio) values, constitutive models, as well as support systems. Relations between these factors and the distributions of stress, displacement, and failure zones around the tunnels were obtained and discussed. Finally, comparisons between the field deformation measurements and numerical simulations are used as validations for the simulations, helping to determine the appropriate K0 value and material constitutive models for the underground mine.INTRODUCTIONThe case study site is an underground mine in the USA with a monthly ore production between 20,000 and 30,000 tons. The regional geology of the mine is structurally and stratigraphically complex. Rocks in the area include carbonaceous mudstone and limestone, tuffaceous mudstone and limestone, polylithic megaclastic debris flows, fine-grained debris flows and basalts, all part of the Cambrian-Ordovician Comus formation and related dikes. Both the mineralization and faults have general orientations striking N-S to NW-SE with high dip angles. The ore body in the mine has an incline of about 25---45 degrees located in relatively low quality rock; hence, cut-and-fill mining has been used.This underground mine has two vertical shafts used for ventilation, ore hoisting, and for personnel and material transportation. Development drifts were designed and driven to extract and transport the ore, as shown in Figure I. Bolts, mesh, and shotcrete have been applied in this mine for ground control. In order to reach various locations, the tunnel system is designed with different heading directions and inclines, which will be described in detail later. The area selected for modeling is a cubic region including all the tunnels inside the black square (Figure 1)."

Jan 1, 2016

By Uwe Wyink, Guenther Thiele, Isabel Gollnick, Klaus Thyrock

"The application of a thin spray on liner was implemented in longwall T-junction sections in 2009 for the first time. The development of the material and the application is based on a technical cooperation between RAG Deutsche Steinkohle AG and BASF Corporation. The report gives an overview of the first trials. The underground test occurred in a seam with a height of 1.5 m (5 ft) in a depth of 1,100 m (3,609 ft). The roadway is dual-use entry and the roof strata is composed of shale and sandy clay. In some sections geological faults impact the surrounding strata. The poor conditions induce separating and loosening of roof rock. Several remedial actions have to be implemented for decreasing deformations at the face entrance.The application of thin spray on liner (TSL) provides simplification and cost reduction of supporting work at longwall T-junction. The installation of TSL to avoid roof and coal fall operations for lagging are omitted.INTRODUCTIONFor safe operation of face retreat in dual-use roadways, the processes of securing and stabilizing the face end area are very important in order to minimize deformation and stress. Avoiding roof and coal fall are the main concerns for safe operation. For that reason different methods of reinforcement are tested in underground operation. In this paper the application of TSL is presented.The specifications of TSL are described, followed by the case study results. The underground study is located in one mine of RAG Deutsche Steinkohle. The extraction of the hard coal in this mine is characterized by great depth and high stress. There are poor geological and geotechnical conditions. The roadway used for the underground application was headed with the support system combination type A, which will be described later in the paper. After the first face retreat, deformation of steel arch support and bagging destroyed the roadway, so for the second face retreat remedial actions had to be undertaken. For this a new system of reinforcement, simplifying the supporting work at the longwall T-junction was tested. The reinforcement consisted of different parts that are described in the following report. Furthermore two different versions were applied. One method is the operation with TSL and the other one is the use of concrete for sealing. Both methods are compared in the text."

Jan 1, 2010

By Tex M. Kubacki

On August 6, 2007, the Crandall Canyon Mine experienced a collapse which trapped six mine-workers. An MW 4.1 seismic event was recorded in conjunction with this collapse. An additional 54 seismic events were detected and located in the vicinity via routine processing techniques during the month of the collapse. Waveformbased cross-correlation detection techniques have been used to uncover 1,328 small, previously undetected seismic events which occurred near the collapse area between July 26 and August 9, 2007. This work has resulted in lowering the magnitude threshold of completeness from ML 1.6 to ML -0.5, a 2.1 order-of-magnitude improvement over standard processing techniques. Event locations have been computed using a double-difference inversion. The spatial pattern of events ultimately helps to delineate the extent of the collapsed area. It is shown that many of the large catalogued events (>ML1.6) tend to be closely followed by numerous (often 20 or more) smaller aftershocks. Cluster analysis of the known catalog reinforces prior work indicating the existence of seismic clustering on the east and west sides of the collapse. Research now demonstrates that it is possible to differentiate events related to the main collapse from those related to the rescue attempt following the collapse. The cross-correlation techniques described herein greatly improve the ability to detect small mining-induced seismic events. These methods may lead to improvements in assessing seismic hazards for conditions similar to those observed at Crandall Canyon preceding the collapse.

Jan 1, 2013

By Peng-Fei He

CT scanning tests were used to detect the pre-existing fracture systems of 36 cubical coal blocks. Systematic procedures were developed to construct the pre-existing fracture geometry of the cubical coal blocks from the CT images. Based on the constructed fracture systems, the fracture tensor components were calculated to capture the directional effects of the fracture system of the cubical coal blocks. The effect of the pre-existing fracture system and different combinations of confining stresses on the strength and deformability of coal masses was investigated at a preliminary level using some true triaxial test results and the computed fracture tensor components. The strength of the cubical coal blocks in the loading direction was found to be closely related to the summation of the fracture tensor components in the two perpendicular directions to the loading direction and the level of the confining stress system. The deformability of cubic coal blocks in the loading direction was found to be correlated to the fracture tensor component in the same direction.

Jan 1, 2014

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 Nicholas P. Kripakov

The unpredictable massive collapse of roof in openings developed under apparently safe and stable roof conditions in coal mines of the United States has been of much concern for many years. One type of massive caving phenomenon is often attributed to cutter roof, a failure that initiates at one and/or both upper corners of an entry and propagates nearly vertically resulting in overall failure with little or no warning. This paper reviews current methods being used to control cutter roof and suggests new alternatives. The impact of basic parameters that include mine geometry, overburden geology, rock properties, and in situ stress conditions is discussed in the context of their relationship to this problem. The effects of various stress control measures are investigated with model analysis to gain insight into means of reducing the high level of stress known to exist at the entry corners of a West Virginia coal mine prone to cutter roof. The results are presented in the paper and the feasibility of their practical implementation is discussed.

Jan 1, 1982

By Jay Hilary Kelley

This paper proposes a modification of longwall roof support to meet new difficult mining conditions that are anticipated in the future. A gob canopy is a movable appendage attached on the rear of a longwall shield to counterbalance the troublesome forward downward force couple (FDFC). The gob canopy can be swung in both vertical and horizontal directions, powered by hydraulic cylinders. Several functions and applications are de- scribed

Jan 1, 1997

By Kyle A. Perry

Pillar design formulae have existed for decades, and the guidelines for design stability factors are generally accepted by regulatory agencies and broadly used within the coal industry. Nearly all design pillar formulae are based on geometrical parameters of pillars resulting from empirical investigations, with primary focus on the pillar width-to-height (W/H) ratio and associated shaping constants from regression. The most widely used modern pillar design formula in the coal industry, the Mark- Bieniawski equation, also adheres to this principle. Common practice when applying Mark-Bieniawski equation is to use a coal compressive strength of 900 psi. This reduces the design equation to sole dependence upon geometry. However, recent studies have shown that pillar strength is highly dependent on roof and floor properties, particularly the interfaces between the roof-pillar and pillar-floor. This study utilized numerical modeling using FLAC3D to evaluate the relative effects of varying roof and floor interface and mechanical properties. The results confirm that pillar strength is significantly influenced by the properties of the coal pillar interfaces with roof and floor. The mechanical properties of the roof and floor material have only a minor impact on pillar strength when compared with interface effects. These results were used to formulate design recommendations for existing pillar design methods.

Jan 1, 2013

By Ihsan Berk Tulu, Michael Sloan, Ted Klemetti, Michael M. Murphy, Gabriel S. Esterhuizen, Jame Sumner

"In this paper, the advantage of using numerical models with the strength reduction method (SRM) to evaluate entry stability in complex multiple-seam conditions is demonstrated. A coal mine under variable topography from the central Appalachian region is used as a case study. At this mine, unexpected roof conditions were encountered during development below previously mined panels. Stress mapping and observation of ground conditions were used to quantify the success of entry support systems in three room-andpillar panels. Numerical model analyses were initially conducted to estimate the stresses induced by the multiple-seam mining at the locations of the affected entries. The SRM was used to quantify the stability factor of the supported roof of the entries at selected locations. The SRM-calculated stability factors were compared with observations made during the site visits, and the results demonstrate that the SRM adequately identifies the unexpected roof conditions in this complex case. It is concluded that the SRM can be used to effectively evaluate the likely success of roof supports and the stability condition of entries in coal mines.INTRODUCTIONSince the introduction of roof bolts in the coal mines during the late 1940s and 1950s, roof bolts promised to dramatically reduce roof fall accidents (Mark, 2002). However, ground falls still remain a significant factor in underground coal mine injuries and fatalities. In 2013, ground falls accounted for 4 of the 14 fatalities and 166 of the 1577 reported lost-time injuries in underground coal mines (MSHA, 2015).The design of appropriate support systems requires the understanding of: 1) the variable nature of the rock mass, 2) the performance and characteristics of the roof support, 3) the interaction between the rock mass and the installed support system, and 4) the in-situ and mine-induced stress distribution around the excavation. Over the past 25 years, multiple design approaches have been used in coal mine ground control. The approaches include empirical mechanistic methods, empirical statistical analysis, rules of thumb, and numerical methods (Hebblewhite 2006). In the U.S., Analysis of Roof Bolt Systems (ARBS) can be given as an example of an empirical method. ARBS uses relatively simple equations to calculate the intensity of support provided by a roof bolt system and compares it with a suggested ARBS value (Mark et al., 2001). The suggested ARBS design equation is derived from an analysis of 100 case histories. The ARBS design equation is dependent on two parameters: depth of cover and Coal Mine Roof Rating (CMRR). More recently, a probabilistic design approach was developed by Canbulat and van der Merwe (2009) in South Africa. In this method, the variability of the rock mass, the mining geometry, and support characteristics are included in the analytical models. The major advantages of these two methods are: 1) they can be applied rapidly and easily, 2) complex rock mass/ roof support interaction mechanisms are represented with simple equations, and 3) they are supported by large databases. However, both methods generally ignore mining-induced stress distribution, details of the roof support system, details of the geological setting, and the interaction between the support system and the rock mass."

Jan 1, 2015

By Claude A. Goode

Large quantities of high grade coal exist in thick seams in the United States. Many of these thick seams are too deep to be surface mined and do not lend themselves readily to underground extraction. To develop the new mining technology required to effectively mine thick seams, the Department of Energy has entered into a Cooperative Agreement with Mid- Continent Resources, Inc. to demonstrate the multilift longwall mining technique in a 28 foot-thick seam at their L.S. Wood No. 3 mine near Redatone, Colorado. The seam will be extracted in two lifts, with a 5-foot natural partition of coal left between the upper and lower lifts. Proper selection of face supports is critical to the success of this project. Specifications were defined for the roof supports, and it was concluded that the supports selected must provide full coverage, yield at the legs, and have a 60-inch push- out cantilever that can be set at any position under full load. A Hemscheidt two-leg shield was judged as the best qualified candidate and was selected for the multi-lift trial.

Jan 1, 1981

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 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 Bill A. Kyslinger

"In underground mining, machine design is predominantly dictated by mine conditions and individual customer desires. In partnership with Foresight Energy, J. H. Fletcher & Company was tasked to design and manufacture a new roof bolting machine with six independent drilling apparatus on board capable of drilling and bolting the roof and ribs with material handling. This is the first Fletcher® six-head machine to be designed and built for the mines in the United States. The machine is intended to work in the Illinois Coal Basin.The objective was to produce a machine capable of drilling and installing six bolts simultaneously with a limited number of operators. The goal of the mine is to decrease the time to bolt a cut to improve the safety level of the current roof bolting method, improve efficiency and to improve the bottom line cost of entry development. The customer wanted four mast feed drills at the front of the machine dedicated to installing roof bolts and then another two mast feed drills behind them dedicated to rib bolts. This dictated the requirement of latched controls, which would allow the operator to start drilling one hole and then latch the controls to be able to move on to the next. To accomplish this, we developed a unique hydraulic latch circuit to maintain operator safety and compliance. Guarding was added to prevent an operator from coming into accidental contact with a latched drill.The result of the design is a machine with a single platform and six independent masts with drillheads: four masts strictly for drilling and installing roof bolts on the front of the platform and two masts on the back of the platform for rib bolts. The feed and rotation controls at each operator's station include a latch control for drilling. The latch control will allow the operator to lock in the feed and rotation once the hole has been collared, allowing the operator to move on to the next hole. The rear of the machine is equipped with material handling. There are two material pods with winch controls as well as a mesh rack that includes mesh lift, mesh tilt, and mesh sump.The six-head roof bolter allows fewer operators to drill and install roof and rib bolts, which in tum lowers the miners' roof exposure per cut. This design reduces the operator's exposure from the inherent pinch points and rotary hazards once he has engaged the latch drilling. Therefore, the machine will help to decrease the time to bolt a cut, improving productivity while enhancing the ability to operate the machine safely."

Jan 1, 2016

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