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By Victor V. Nazimko

Longwall mining technology without interpanel pillars is feasible from a geomechanical point of view. A set of pillarless longwall layouts are proposed including tailentry pillar recovery, headentry pillar recovery and drivage of a new tailentry, partial headentry pillar recovery and combination mining in which advancing panel entries are used for retreating panels. The following mitigative measures are proposed in order to enhance the stability of entries near the panel: driving crosscuts obliquely to the longwall face line, advance support of entries and crosscuts, localized destressing of the chain pillars by horizontal slotting, and partial stowing of the gobs behind the pillars being recovered. A new technology of recovering barrier pillars on the setup entry side is also proposed. This technology uses the same regular longwall face for interpanel pillars extraction.

Jan 1, 1994

By Rodger Fry

All coal deposits contain anomalous geologic conditions which have an impact on roof control, Run-Of--Mine (ROM) coal quality and production costs. To remain competitive in today's coal market and provide a safe working atmosphere, mine operators need to know in advance of mining the geologic conditions which prevail in the coal deposit. In order to identify geologic anomalies within a coal seam and surrounding roof rock in advance of mining, the Radio Imaging Method (RIM) survey procedure has been developed. This paper describes the RIM procedure and how it is used to predict various geologic conditions within a coal deposit. Figure 1 illustrates the RIM in-mine and surface surveys which can be used in an underground mine. [ ] RIM is an electromagnetic (EM} wave process which consists of in-mine and surface survey techniques. Both techniques are used in underground coal mines to detect faults, interbedding, sandstone channels, and thinning coal. Thesurface survey can also be used to determine seam correlation and continuity in strip and underground mining. In-mine and surface surveys work by propagating EM waves along straight paths through the coal. As the RIM signal travels along a ray path, it interacts with the seam material and surrounding rock. This interaction causes the signal to lose energy thereby decreasing its strength along the path. The amount of energy loss per unit path length depends upon the coal seam height and type of surrounding roof and floor rock. A reading of the signal level is taken at the end of the ray path at the receiver location. This reading is used to determine the loss (attenuation) rate of the signal along the path. The signal level data is compiled and analyzed through computerized algorithms which construct images of any anomaly present. This graphical depiction of the coal provides a basis for further geologic interpretation. By comparing the images reconstructed by the RIM analysis to in-mine geologic mappings made while mining through RIM study zones, it has been confirmed that RIM can help detect the following; Rapidly Thinning Coal Incompetent Roof Rock Poor Floor Lithology

Jan 1, 1984

By Leigh J. Wardle

Significant coal reserves in New South Wales lie under areas with steep topography such as valley slopes and cliffs. Subsidence predictions are difficult to make for these locations as existing empirical databases cannot cover all permutations of topography and mining geometry. Two dimensional numerical model alternatives are of limited applicability. Consequently a novel three-dimensional numerical model is developed including the detailed panel layout, realistic rock mass properties including the full stratigraphy, goat behaviour and actual surface topography. Model results show the same trends as subsidence measurements from Baal Bone Colliery in the Western Coalfield of New South Wales

Jan 1, 1992

By Daniel W. H. Su

"This paper presents results from a recent study conducted to evaluate the effects of longwall-induced stresses and deformations on the mechanical integrity of shale gas wells drilled over a longwall abutment pillar. The primary objective is to demonstrate that a properly constructed gas well in a standard longwall mining abutment pillar can maintain mechanical integrity during and after mining operations. Successful designs would allow for the safe recovery of both coal and gas reserves. Major elements of this comprehensive study include: (1) modeling of rock movements to predict impacts on gas wells, (2) measurements of actual rock movements at the surface and in the subsurface, (3) measurements of actual impacts on test wells designed similarly to real shale gas wells, ( 4) comparison of modeling results to actual rock movements to validate the model, and (5) employing the validated models to evaluate various casing and cementing designs to minimize casing deformations and absorb longwall-induced strains along the intermediate and production casings.A study site was selected over a southwestern Pennsylvania coal mine, which extracts 1,500-ft-wide longwall faces under about 600 feet of cover. Four test wells and four monitoring wells were drilled and installed over an abutment pillar with 125-ft by 275-ft centers. The four test wells were drilled to a depth of 642 ft, or 42 ft below the Pittsburgh seam, and were designed like a real shale gas well, except that only three casings (namely the surface, water protection and coal protection casings) were installed in each well. Casing steel grades, wellbore diameters and annular spaces were purposely varied in each of the four test wells to evaluate the effect of different well designs. The four monitoring wells - one vertical extensometer and three in-place inclinometers (IPI) - were drilled to different depths to measure the vertical settlement and horizontal displacements as a result of longwall mining on both sides of the abutment pillar. In addition to the test wells and monitoring wells, surface subsidence measurements and underground coal pillar pressure measurements were conducted as the 1,500-ft-wide longwall panels on the south and north sides of the abutment pillar mined by."

Jan 1, 2016

By Stephen C. Tadolini

The U.S. Bureau of Mines (USBM) is conducting research to provide alternatives for traditional secondary support methods. These cost-saving methods are proving to afford safer installation, improve entry stability, eradicate material-handling injuries associated with crib supports, and enhance ventilation. In cooperation with Mountain Coal Company, the USBM replaced timber cribbing with high- strength cable supports to provide stability in a gate road that was used for two longwall panels. The support design consisted of 2.1-m (7-ft) full-column resin-grouted bolts and 4.8-m- (16-ft-) long high-strength resin-grouted cable supports. Three support concepts were evaluated: passive, stiff, and tensioned systems. Cable loading and roof deformations were monitored to evaluate the behavior of the immediate and main roofs during panel extraction. The stress and loading histories for both panels and the abutment and yield pillars were monitored to assist in evaluating the stress transfer and pillar performance in conjunction with the roof behavior. The test results indicated that resin- grouted cable support systems successfully maintained the immediate and main roofs during the extraction of two longwall panels. This paper describes the theory, application, and advantages of resin-grouted cable supports and presents the mine measurements made to assess the cable performance during the retreat process of longwall mining.

Jan 1, 1994

By Winton Gale

"Rock and coal fractures and micro seismic vibration are common occurrences during development mining. It is very uncommon for coal and rock to be propelled into the roadway during normal mining operations. However, such occurrences do occur and appear to require significantly more energy than is available from strain energy release during coal cutting. The sources of energy, which can contribute to the propulsion of coal from the face or ribs, are typically strain energy from the surrounding ground, seismic energy from a rapid rupture of the ground in the vicinity, or rapid expansion of gas from within the burst source area.The aim of this paper is to briefly review the bursts that could be related to strain energy or seismic energy. However, the greatest emphasis is placed on the effect that gas within the coal could play in moderate to gassy mines.It has been found that the bursts related to the expansion of gas can occur in coal and stone. The volume of gas involved in coal bursts is typically lower than in gas outbursts; however, the process is generally similar.INTRODUCTIONA coal burst is defined as a rapid expulsion of coal (and potentially gas) from the boundary of the roadway. The volume of a burst can be variable, but volumes above 10-50m3 are noted and cause significant disruption to operations.Rock and coal fracturing is common about roadways, particularly under the influence of elevated stresses, either tectonic or related to mining abutment stress. Shear fracture is very common; however, it is very uncommon that the coal is propelled from the face or ribs as a result of fracture of the material. The nature of rock fracture about roadways under elevated stress is presented in Figure 1.A burst requires energy to propel the coal or rock from the rib or face of the roadway. The depth of material impacted may vary from 0.5m to greater than 3m inside the roadway boundary. The strength of the ground in this zone is variable depending on the nature of the coal seam (or surrounding material). Typically, this material has significant residual strength as confinement increases into the ribside.The energy required to propel this material is typically in addition to that which is associated with normal fracturing about the roadway."

Jan 1, 2018

By George Mishra

In mid-1979, J&L Steel Corporation experienced rapid failure of pillars after only two weeks' operation with a combination of full retreat and partial mining in the 154 Road Section of its Nemacolin Mine, Greene County. The rate of advance of the "squeeze line" was very rapid for the first 500 feet, but it slowed down considerably as it approached some large coal blocks and gas well barrier pillars. After moving all section equipment out tc a safe distance, all accessible headings and crosscuts were filled with cribs and tri-set posts to prevent further spread of the squeeze. At one time, there was great apprehension by mine management that without implementation of some immediate corrective measures the safety of #3 airshaft and the only haulage and access road to the 8 Road mining area would be in jeopardy. In September, 1979, the U.S. Bureau of Mines established convergence monitoring stations outby the squeeze area. Readings were taken at weekly intervals until January, 1980, and monthly thereafter. Mathematical calculations, plot- ting of contour maps, and graphing of total convergence at different stations were used to follow and analyze the progress of the squeeze and provide guidelines for mining plans in the adjoining areas.

Jan 1, 1981

By Bob Thomas

The roof drill operator productivity can be enhanced by the introduction of control technology The operators control station can be improved by considering human factors such as handle forces and control location. The smaller electrical controls can be located much easier than the traditional hands on valves. The operators control can he improved by using processors with programmable subroutines that assist the operator in the decision making process. For example to increase feed rate - to slow rotation - to avoid clogged steels - etc. The overall affect is to improve drilling and bolting consistency. The control system uses a dedicated processor packaged as an intrinsically safe control station. The roof drill operator is assisted in the drilling; arid bolting by a closed loop feedback system. The processor monitors the drilling parameters such as feed force, feed rate, rotation torque, RPM, drill position, and vacuum condition Based on the drilling parameters the processor executes pre-determined condition statements intended to enhance drilling The drill operator has an active display to alert him to the real time machine status. For example if the feed were to slow or delay due to a high vacuum level the display would show "high vacuum". The dedicated processor is available on the arm feed style machines, The prototype machines used programmable logic controllers to develop the feedback relations. The ability to record drilling parameters was extremely helpful in this development project. The extended use of the recording feature will aid operators in mapping the mine roofs Interpreting the recorded drilling parameters can reveal a void in the top or hard competent drilling The prototype machines also showed the importance of vacuum monitoring This feature is extremely valuable in softer materials, The benefits of the control system range from efficient use of the consumable bolting materials to uniform operator performance.

Jan 1, 1999

By Yao Yuping

The strength and deformation of more than two hundred coal samples have been tested in the condition of triaxial compression. The regression equation showing the relationship between coal strength and pressure in the pores as well as confining pressure, was obtained. The appropriate calculation for stress-strain curve was carried out. Further, an analysis shows the variation of coal strength and its modulus of elasticity in methane medium.

Jan 1, 1992

By Syd Peng

In designing a proper roof support system, one must know the features of roof geology in advance of mining. The drilling parameters obtained during normal roof bolt installation cycle can provide a large amount of information on the roof geology when properly interpreted. It is also an economic way for identifying the geological features of the roof. This research develops a method for predicting the roof geology based on the drilling parameters obtained during roof bolting operation. From the results of a series of laboratory and underground tests, feed pressure is found to be a good indicator for identifying the voids/fractures and estimating the roof rock strength. This paper describes the method for determining quantitatively the location and the size of void/fracture and estimating the roof rock strength from the drilling parameters of roof bolter.

Jan 1, 2005

By Michael Kelly

Current research in longwall mining in CSIRO Exploration & Mining is focused within five major projects and several minor projects. The major projects are: 1 3D Aspects of Longwall Geomechanics. This was reported to the conference last year and a final report will be available by mid-2001. 2 Mine Gas Control. This just completed project centred on Dartbrook Colliery which has a longwall gas make of more than 8 cubic metres per second. 3 Rapid Roadway Development This includes the construction of an autonomous conveying and bolting module (ACBM) that sits between the miner and haulage system. 4 Top Coal Caving In conjunction with the YanKuang group in China, CSIRO and the University of NSW are conducting a prefeasibility study of the Top Coal Caving method in Australian conditions. 5 Longwall Automation. In partnership with the Cooperative Research Centre for Mining Technology and Equipment (CMTE), the CSIRO has conducted a scoping study on this issue and will commence an initial three-year demonstration project in July this year. This paper describes these protects in more detail with particular focus on the last three in the above list.

Jan 1, 2001

By Lu Jiam Zhang

Coal and gas outburst is one of the serious natural disasters in the coal mines of China. Since 1950, more than 10,000 coal or gas outbursts have occurred in more than 200 underground coal mines of different types. The outburst prone coal mines are widely spread out. It occurs in different types of coal -ma and is very serious in some areas. Most outbursts occurred at the time of roadway driving in coal seam, serious outbursts occurred mainly when entering the coal seam during the cross-cut driving; of the outbursts, coal and gas outbursts We UP major proportion, while pressing out and pouring out ah account for a large proportion; outburst. occur under different operating conditions, but mostly occur during shotfiring. This paper introduces the prevention and control measures as practiced in China and illustrates the three types of outburst cla8sification. Both technology and management are equally important in outburst prevention and control. Measurement of the volume of drilling cuttings and the initial gas outflow rate fm- boreholes have proven to be effective. A special team and organization must be set up to deal with the problems.

Jan 1, 1987

By P. Tsang

In order to deal with ground control problems such as roof falls, floor heaves and pillar failures in underground coal mines, a new pillar design method based on the "yield pillar" concept is proposed. Using the finite element model simulation, the functions and mechanisms of the "yield pillar" are studied. The important variables that affect the stability of longwall entry-pillar system are identified. To simplify the geological and mining conditions, a new pillar design method classifies the in-situ roof and floor conditions into four categories: 1) strong roof and strong floor, 2) strong roof and weak floor, 3) weak roof and strong floor, and 4) weak roof and weak floor conditions. The design formulae are derived based on the finite element model simulation, stability study and nonlinear regression analysis. The finite element models used consider the plastic failure properties and time-dependent behaviors of rock. To better organize the finite element model simulation, the orthogonal experiment design is used to arrange the finite element models and proved to be very effective. An application example is used to illustrate the basic design procedures involved in the new pillar design method.

Jan 1, 1993

By Saeed Zandi, Kazem Oraee

"Tunnels and galleries are the most important structures in coal mines. They are used for variety of purposes, such as transporting ore and people and for ventilation. A well-designed support system is necessary to stabilize structures and prevent collapse.Using rock bolts increases the strength of the rock in which tunnels are made. Rock bolts are used extensively in most underground mines today, and coal mines are no exception. Almost all galleries in a typical coal mine use some type of rock bolt, at least, as a means of partial or supplementary support.In this research, changing the support system from expensive methods to the use of rock bolts as the primary means of support is discussed, with the focus on a particular gallery in Hejdak coal mine. Visionary design methods, in conjunction with rock mass classification schedules, were used to determine an optimal rock bolt pattern. For this purpose, rock mass rating (RlVIR) and quality index (Q) classification systems were used. Several empirical methods were also used to design an optimal pattern for rock bolt installation in the particular tunnel under analysis.As such, the tunnel support system was designed using both finite element and empirical methods. Finally, the results obtained from both numerical and empirical methods were compared under different load conditions. The methodology prescribed in this paper, together with the comparison, can be a useful tool when selecting a support system. The results can also be used to design a support system in this and any other coal mine with similar conditions.INTRODUCTIONSince the advent of underground excavation techniques, one of the biggest challenges has been stabilizing tunnel walls and preventing roof collapse in tunnels and other underground openings, such as galleries. Loose rocks and layers drop into tunnels and galleries, except in very hard rock. Underground roof collapse and falling rocks can have devastating effects on the safety of operation personnel and equipment and can seriously affect production. When designing an underground coal mine, the stability of tunnels and galleries is an important parameter that should be studied carefully because it has an important role in the production process of the mine. Therefore, an appropriate and well-designed support system is necessary for preventing collapse and helping to stabilize the tunnels and galleries."

Jan 1, 2016

By John L. Edwards

The underground coal mines in the Lake Macquarie area of the Newcastle Coalfield, New South Wales, Australia are constrained by surface subsidence restrictions as low as 150 mm. The mining environment is shallow, generally between 100 m and 200 m, often multi-seam and commonly overlain by residential development or tidal waters. Most mines use partial or panel and pillar extraction techniques to meet the subsidence restrictions and allow maximum resource recovery. This paper gives an overview of the results of a recent two year government funded research project aimed at developing a mechanistic, geomechanically based mine design criteria for subsidence control. Three extraction layouts were monitored in detail to assess the relationship between mining geometry, pillar behaviour and surface subsidence. Pillars at each site were instrumented with stress cells, convergence monitors and extensometers. Field data was used to initially calibrate, and subsequently, verify stress and displacement predictions made by the three-dimensional displacement discontinuity code, SUBSOL. Back-analysis of the modelling results indicate SUBSOL's capability as a tool to satisfactorily predict surface subsidence magnitudes and pillar loads for alternative pillar and panel layouts.

Jan 1, 1993

By Joe McQuerrey, William Kendall, Gene Wilson

"Roof bolting is the standard for ground control in underground coal mining. Rib and truss bolting is just as important when conditions are less than desirable. As a manufacturer of roof drills, J.H. Fletcher & Co. (""Fletcher"") promotes a walkthrough design machine to protect the machine operators from rib hazards.When installing rib and brow bolts in high mined heights, the operator's natural desire is to step from under the canopy onto the drill feed mechanism. This is done to allow a better reach to the drilled hole in the rib or brow. This, of course, is not an approved or acceptable practice.The effort to improve the operators' ability to reach the rib and brow has resulted in a new boom design. The design was first shown in September 2008 at the MINExpo in Las Vegas, NV. The design incorporates a step out area towards the rib side of the machine. The step provides improved access to the mine rib and brow.Having a solid concept does not guarantee an accepted design. Operator acceptance is the goal. When the machine was first tried in the underground environment, the machine operators did exactly as requested: run the machine as supplied and suggest improvements.In the fast pace job of roof bolting, any ergonomic improvements are welcome. These improvements usually increase the operator's productivity and safety. Based on operator feedback and final evaluation with Fletcher, machine revisions were generated. When the machine revisions were completed, Fletcher again asked the operators for comments, giving the boom design an evolving path into our industry.INTRODUCTIONIt's human nature to find the most comfortable position in which to do a task, especially for repetitive tasks. Designing a machine that will withstand the rigors of underground mining is a challenge in itself. With stringent safety requirements and limited real estate, there is a constant evolution in design to converge safety with productivity. With the ongoing development of the ""Rib Access Boom,"" one more step in the evolution process has been taken."

Jan 1, 2010

By Michael Gauna

In 2010, the number of fatal rib falls in U.S. underground coal mines exceeded fatal roof falls for the first time ever. While recent trends have seen roof fall fatalities reduced by about 62% since the 1990s (from an average of 9.6 per year in the 1990s to 3.6 per year during the last five years), the incidence of rib fall fatalities has remained approximately constant (about 1.5 per year). In addition, injury incidents associated with pillar rib failure have been steady at approximately 100 per year. The persistence of rib fall injuries, underlined by the recent increase in rib fall fatalities, has led to this investigation of the coal rib failure parameters and methods available to mitigate rib failure in U.S. underground coal mines A detailed study of the 21 fatal rib fall incidents that have occurred since 1995 (excluding coal burst incidents) indicates that the two most important risk factors are the mining height and the depth of cover. The depth of cover was 700 ft (213 m) or greater in 81% of the fatalities, and the mining height was at or exceeded 7 ft (2 m) in every instance but one. Other risk factors included multiple seam interactions, rock partings in the seam, and retreat mining. The accident history reveals that joints or slickenside features within the rib increase the hazard. Approximately threequarters of the rib fatality victims were roof bolting machine operators and continuous mining machine operators. This paper includes a brief overview of techniques for rib control; including bolts, standing support, bent steel straps, and rib strapping. The available mining equipment features for installing rib support and protecting operators from rib falls are also discussed. A proactive approach to rib control using available technologies will lower the risk to miners and is an endeavor that must be pursued to reduce rib fall accidents.

Jan 1, 2011

By R. Karl Zipf

Highwall mining is an important coal mining method. Upwards of 60 highwall miners are presently in operation, and they may account for approximately 4% of total U.S. coal production. A review of the Mine Safety and Health Administration (MSHA) accident data over the 20 year period from 1983 to 2002 identified 9 fatalities attributable to auger and highwall mining of which inadequate ground control accounted for 1/3. In the past 5 years, 1 fatality occurred in highwall mining. Estimates of the manpower requirements in highwall mining suggest that its fatality rate is essentially the same as for surface coal mining, thus highwall mining appears to be a very safe modern mining method. Highwall stability is the major ground control related safety concern, and operators are required to develop and follow an appropriate highwall mining ground control plan. The plans usually specify the following geotechnical parameters: hole width, maximum hole depth, maximum overburden depth, seam thickness, web pillar width, barrier pillar width and number of holes between barriers. Calculated web pillar stability factor exceeded 1.3 for most designs evaluated. This study examined records from 5,289 highwail miner holes with a total completed footage of about 2,560,000 feet to understand the reasons for early pull out. Average lost footage is typically about 20% of planned footage. Only 35% of the holes reached planned depth, and 20% were short due to rockfalls. Water and adverse geology accounted for 15% of the losses. Mechanical/electrical problems, guidance, and slope stability problems accounted for the remaining 30%. Web pillar stability factor for these holes also exceeded 1.3 in 95% of cases. Trapped highwall miners present a safety hazard to workers during their recovery. Best practices to avoid trapped highwall miners include: avoid mining in stream valleys, avoid mining near outside corners, careful alignment of each hole and the use of an onboard guidance system, Several issues in highwall mining ground control require further investigation including highwall mining through old auger workings, highwall mining near old underground mines, multiple-seam and multiple lift highwall mining and finally the size and frequency of barrier pillars.

Jan 1, 2004

By Robert L. Schmidt

The support of underground openings by water is a natural phenomenon. Surface sinkholes, such as those that occur with some frequency in Florida, are attributed to a lowering of the water table resulting in the draining of existing limestone cavities. This withdraw the natural support and causes the surface subsidence. The role of water as a ground support medium was demonstrated in a mining situation during Bureau of Mines research on borehole mining of phosphate in St. Johns County, Florida. The borehole mining tool (BHT) incorporates a water jet nozzle and slurry eduotor in a single down- hole tool. The tool is lowered through a bore- hole into the ore zone, and an underground cavity is eroded by the motion of the water jet with the slurry simultaneously pumped to the surface. In addition to phosphate, the system has been successfully used in coal, oil sands, and uranium. The Florida phosphate ore is located at a depth of approximately 250 ft in strata that produce high water inflows. These factors preclude extraction by conventional methods, either surface or underground, but they present an ideal setting for borehole mining. Previous borehole mining research had led the researchers to believe that the system would only be effective in a void cavity, that is, a cavity where the water level is maintained below the water jet nozzle, so that the water does not impede the action of the let. It was soon discovered, however, that the void cavity presented ground control problems. The overlying strata started to cave soon after the support provided by the water was removed. This was an unacceptable situation as it adulterated the ore and threatened surface subsidence. Further tests wherein the size of the cavity -as reduced by cutting only a 30° arc also resulted in caving. A new concept, air shielding, was then introduced and tested. With this system, the water jet cutter was surrounded with a shroud of compressed air, thereby gaining the advantages of cutting in air while retaining the roof support afforded by a water-filled cavity. This arrangement proved to be highly successful. The air-shrouded jet was able to cut a cavity radius of about 18 ft, and the system production was 35 tph, which compared favorably to the production previously attained in void cavities. The borehole phosphate experience proves the efficacy of remote mining in a water filled opening. This system neutralises the hazards of heavy ground, and may, as in the case of the phosphate deposits, be the only viable alternative. It opens up the possibility of application in a wide range of deposits not only those amenable to hydraulic mining. Remote mechanical System might be developed using present robotics technology and then operated in water-filled openings.

Jan 1, 1986

Tailgate pillar and tailgate-face corner humps have been a major threat to longwall coal mines where hump-prone conditions exist. The yield pillar design concept, in which the longwall chain pillars are designed in such way that they can yield in a nonviolent or controlled manner during longwall retreat, has been used in many longwall mines to prevent tailgate pillar humps. However, this practice often shifts the side abutment load onto the tailgate-face corner especially when a massive and strong sandstone member is present within the caving zone or in the vicinity of the coal seam. Therefore, the abutment pillar design concept has also been used in some hump-prone coal mines to minimize the stress concentration on the tailgate panel rib for the control of tailgate-race corner humps. The disadvantage of using the abutment pillar design concept is that it is more costly and puts additional pressure on mine operations for gate entry development and significantly reduces the recovery of coal reserve. In addition to pillar size, panel layouts. such as the panel width and panel orientation also play a critical role in pillar or face humps and should he taken into account. Based Upon the Cyprus mine design and operational experiences at Willow Creek and case studies at other bump-prone longwall nines in the U.S., the authors attempt to identify the critical factors causing coal mine bumps and to introduce some guidelines and criteria for the design of both yield and abutment pillar systems and panel layouts.

Jan 1, 1999