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By Clifford McCartney

The PropsetterTM System has been designed and developed to cost effectively solve problems experienced with conventional underground supports used in tailgates, headgates, bleeder entries and as supplemental supports. The PropsetterTM System utilizes the strength and orthotropic properties of timber to achieve initial stiffness and controlled yield as the roof and floor converge. Utilizing a prestressing system developed in South Africa by our parent company, the PropsetterTM prestresses/preloads the roof and floor on installation. The PropsetterTM System consists of five integrated elements which are easily assembled to achieve the objectives of ? Improved support. ? Improved safety, ? Reduced cost, ? Reduced material handling, ? Improved installation productivity, and ? Improved ventilation.

Jan 1, 1995

By John P. Dunford

U.S. Bureau of Mines researchers are investigating the ability of mine-wide monitoring systems already in place at many coal operations to provide a direct link between geotechnical instruments and the mine-wide monitoring console on the surface. This paper describes a number of field tests using instruments such as-string potentiometers to measure roof-to-floor closure and bed separation and pressure transducers to monitor pillar loading. The advantages of using existing systems include on-site data collection and analysis, real-time understanding of geological conditions, and long-term data recovery from areas that have become inaccessible to mine personnel. However, because data are generated constantly, large files develop very quickly. In many cases, the data are redundant, such as during times of reduced mining activity or in areas not yet in the vicinity of active mining. To reduce the volume of data, a software program was written that eliminates unnecessary readings and generates a more concise file that can be output to a mine-wide monitoring system, personal computer, or as hard copy.

Jan 1, 1993

By Mietek Rataj

Installation of pre-tensioned Strand Bolts i.e. resin grouted cable bolts is very common now in Australian coal mines. A short historical development of this type of rock reinforcement is outlined Various systems have been developed to apply 20 to 25 tonnes of pre-load to these bolts but there are still some technical problems which have to be overcome. One of the major problems encountered is bleed off tension which is highly undesirable as required "over loading" rocks the immediate roof thus inducing fractures iii weak strata. The major reason for the loss of tension apart from the design of the tensioning jack, is the design of the conventionally used barrels and wedges. Due to a roof plate tilting during tensioning the cable moves out of the barrel centre which impedes proper positioning of the wedges and subsequent excessive return of the cable once load of the jack is released. This problem has been largely resolved by the design of a special barrel having a centralizing rim allowing for significant reduction of the toss of tension. KEYWORDS: Pre-tensioned Strand Bolts, Cable Bolts, Bleed off Tension, Tensioning Jack, Loss of Tension

Jan 1, 2002

By William D. Gallant

This paper describes a joint cooperative project between the CANMET Cape Breton Coal Research Laboratory and the Cape Breton Development Corporation to conduct a trial of split set cable slings for remedial support in longwall gateroads. Slings were installed in two test sections of the 2 West panel, Phalen Mine which exhibited deformation and the potential for excessive deterioration when subjected to the front abutment of the wallface. Roadway support behaviour was monitored at the trial sites, including lengths of roadway with the standard support of steel sets without remedial support. Observations were made on convergence, loading of the steel supports, loading of the slings, and wallface performance. Comparisons are made of the results obtained from the areas with remedial support to that without, which demonstrates that the slings provided effective remedial support limiting further deterioration of the roof. Improved face end conditions have contributed to increases in safety and productivity of the longwall panel.

Jan 1, 1990

By Liu Changyou

This paper analyzes experimentally the stress-strain relationship and the characteristics and variation trends of acoustic emission signals of the medium- and high-burst-prone coal/rock fracture process. The precursor and sensitive characteristics of the acoustic emissions when the burst-prone coal/rock fracture occurs were obtained. The characteristic index and the feasibility for predicting rock bursts using acoustic emissions technology were proposed. Keywords: burst-prone coal/rock, acoustic emissions, energy, prediction index

Jan 1, 2003

By G. Skybey

The Directional Drill Monitor (DDM) is an advanced instrument for real time in hole surveying. It was developed by Du Pont (Australia) to suit Australian gassy coal mining conditions. The instrument consists of three units: i. Down hole transmitter ii. Acoustic transducer iii. Data receiver processor unit (i.e. up hole unit). This paper describes the function of each unit in detail and highlights the importance of the DDM in long hole drilling efficiency. Surveying is carried out independent of hole depth. Each survey takes 2-3 minutes to complete, the frequency of surveying to control borehole trajectory is determined by the accuracy required for a particular hole. The DDM is currently being used successfully for long hole drilling in a number of collieries. A high degree of directional control has been achieved. Borehole trajectories were controlled to within +l¬2m of the planned path with intersurvey distances varying between 6 to 18 metres over distances up to 700 metres.

Jan 1, 1992

By Syd S. Peng

Full-face shield leg pressures in a longwall panel for a three-month period were collected and analyzed. The pressure data were presented in the following forms: full- panel full-face shield pressure, individual shield pressure, full-face shield pressure, full-panel time-weighted-average pressure, and relationships among setting pressure, final pressure and pressure increment. Although shield pressure varies from shield to shield and from cycle to cycle, the setting pressure and face advance rate do control the 6nal pressure and time-weighted average pressure.

Jan 1, 1997

By Christopher Phillips

In light of recent events in the mining industry, there has been an increasing demand for technology to detect underground voids and abandoned mine workings. This paper summarizes the use of geophysical methods for this application. Geophysical methods have been successfully employed in the detection of underground voids in several disciplines, including foundation analysis, road and infrastructure analysis, and darn analysis, but is not yet being widely employed by the mining industry. The principal reasons are that the combination of the complex geological setting of a mine, mine design, surface conditions, and improper choice of geophysical method often makes the task of locating abandoned mine workings with geophysics a frustrating, time consuming, and often unsuccessful venture. While there are several geophysical methods that have been demonstrated for the successful detection of abandoned mine workings, there is still no 'silver bullet' to solve the problem in every case. The choice of geophysical method to detect abandoned mine workings should be made on a site specific, and sometimes target specific, level. This paper reviews current methods, and introduces recently developed methods, for the detection of underground voids and abandoned mine workings.

Jan 1, 2003

By Marcel0 Mondring

Transportation and the logistic requirements are set very high for the German coal mining industry. Short transportation resources, crowded quarters, and long transportation distances to destinations are some basic conditions that logistic employees of the mines have to deal with. Therefore, in the context of these processes, human effort and technology are faced with great challenges. There can be a total of 300 transport units, depending on the size of the mine. Every day, they are moved through a nearby 150-km-long transportation network of floor and monorail tracks. Of these transport units, 150 are new, and the other 150 units are split into cross traffic units that are moved only in the underground and return travel units. Beside track-bounded transports, all material transports take place in the shaft. As a result, many involuntary transports and changes in the means of transportation make the daily work more difficult. Typical transports in the shaft include the supply of new materials from above to below, as well as returnable goods from below to above. Cross traffics throughout several levels, which are rather rare, would have to be handled above the shaft. Due to limited shaft capacity, these cross traffics should be avoided when possible. Based on the gas resources in coalmine slopes, track-bounded transports using monorails (powered by diesel or rechargeable means) are preferred. This depends on the road degree, the depth, and track cross section of the shaft/slope. The variety of the material spectrum includes more than 100,000 different types of material.

Jan 1, 2014

By Rob Robinson

Following a massive rib wall failure along the reclaim belt of the large underground surge bunker at CONSOL?s Bailey Mine, a multifaceted, cleanup and rehabilitation effort was initiated to rapidly stabilize the bunker rib walls and place the bunker back into production. Rehabilitation of the bunker included infilling and re-mining of the failed excavation area, installing a system of horizontal tie-back cable bolts, constructing a large knee wall at the base of the rib, reducing water inflow, and providing drainage for rib water. As a result of the coordinated effort, the bunker was safely placed back into production within 38 days. The 7500-ton surge bunker, an engineering feat in itself, was constructed in 2003 to accommodate production surges from two longwalls. In 2005, 14.8 million raw tons passed through the bunker. The 22-foot wide by 75-foot high surge bunker excavation extends as much a 52 feet below the base of the Pittsburgh seam. The bunker excavation measures 325 feet in length, with feeder and reclaim belt excavations extending the bunker excavation by approximately 500 feet. The massive rib roll, which occurred near the bottom of the reclaim belt slope, measured as much as 45 feet high by 60 feet long. Failure of the rib was attributed to progressive failure of a thick claystone unit present near the slope bottom area. Saturation of the claystone by water inflow, high insitu horizontal stress, and pre-existing rock joints were considered contributing factors. Immediately after rib failure, mine production was temporarily rerouted to a parallel belt. Two bulkheads were then constructed 175 feet apart along the reclaim belt slope, and a customized fly ash-cement mixture was pumped from the surface into the unstable reclaim slope area. A tunnel was then mined through the backfill along the original reclaim slope contour; the new excavation supported by a system of customized steel sets. To assure stability of the adjacent bunker rib wall, a pattern of 70-foot long cable bolts were installed downward from the adjacent entries to effectively tie back the rib. Drainage holes and a 12-foot high knee wall were installed. Adjacent gas wells were also plugged to help reduce inflow. Periodic inspections and continuous monitoring are being used to help assure bunker stability.

Jan 1, 2007

By Axel Preusse

This paper shows basic considerations about the prognosis and prediction of surface subsidence and other ground movements in the German hardcoal industry. The following case studies describe experiences collected in projects between university and industry.

Jan 1, 2000

By M. V. Kurlenya

The experience of application of geomechanical investigations for substantiation of extraction of undermined ore deposit in the north of Siberia is discussed. The finite element method was used for forecasting the state of massif during the development of mining works. The results of calculations were compared with the experimental data of observations in situ for evaluation of authenticity of numerical modelling.

Jan 1, 1990

By Dieter Wittenberg

The successful extension of the applications in which rockbolts can be used in the German coalmining industry is, because of the very great raining depth combined with a high degree of stress in the native rock, only possible on the basis of a comprehensive quality management system. The quality assurance system consists of material tests on the individual component parts of a rockbolt, of test rig trials of installed rockbolts, of suitability tests underground and of measures for quality assurance during roadway drivage. Only on the basis of exact knowledge of the way in which installed rockbolts function in the underground and possible sources of error and faults can quality assurance be guaranteed during roadway drivage.

Jan 1, 2000

By Hamid Maleki

During the last decade, a significant amount of research has been conducted by Energy West Mining Company, government agencies, academia, and consulting companies to develop predictive tools for assessing the stability of the Castlegate Sandstone, which is found approximately 250 m above multiple-scam coal reserves, Energy West Mining uses longwall mining techniques in its operations near Huntington, Utah, and these studies were initiated to satisfy requirements for maintaining the stability of the Castlegate Sandstone and resource recovery. In this study, the authors have used multiple-regression analysis techniques and a wealth of data collected over many years on geology, mining, and escarpment stability. The volume of failed rocks is used as the response variable after several other factors were considered, including measurement of surface deformation and frequency of mining-induced surface fractures. Geologic and geometric variables were obtained along 3.7 km of escarpment exposure at 130 study locations. Regression analysis of data for the first 29 study location, which had been fully' undermined, showed that surface topography played a critical rule in influencing escarpment stability. Preliminary regression analysis results from 70 study loca¬tions identified several other important geologic arid mining factors that influence be stability of the sandstone escarpment These are canyon slope, sandstone thickness, and mining influence ante.

Jan 1, 2000

By Christopher Mark

The demographics and safety record of the pillar retreat segment of the U.S. coal industry was analyzed using statistics collected by the Mine Safety and Health Administration. Pillar recovery is practiced primarily by mines in Appalachia and the Midwest. Using 1993 data, the accident rates and productivity of a large sample of pillar re- mines were found to be similar to other room-and-pillar mines in the same geographic areas. Pillar recovery apparently accounts for about 10% of all U.S. underground production, but has been associated with about 25% of the mf and rib fatalities during 1989-96. However, of the 28 fatalities that were analyzed, only 4 occurred for which no citations were issued for violations of mining law. Nearly one- half of the fatal incidents occurred during the mining of the last lift or pushout. All four no-citation incidents occurred during the removal of the last lift during a "Christmas tree" extraction sequence.

Jan 1, 1997

By Binchuan Zhang

Based on the theory of fracture mechanics and blasting, computer simulations were performed to predict the original rock mass structure and those rock mass structures damaged at different levels uing the properties of joints and fratures obtained in the field.

Jan 1, 2001

By André C. Zingano

The domino effect in a violent pillar collapse occurs due to the redistribution of stress in the remaining pillars near the collapse, and this stress transfer occurs in the immediate and main roofs. The remaining pillars do not have enough load capacity to support this overstress and also fail, and the domino effect propagates further to the entire panel. The domino effect does not occur only due to low load capacity of the pillars, but also the roof rock mass quality, because the stress is transferred by the roof. In high competent roof without discontinuity (fault), like massive sandstone seam, the deformation of the roof is the cause of pillar collapse extension and propagation. Depending on how close it is approaching the collapse limit; the immediate and main roofs behave differently. When it is close to the collapse limit roof convergence and pillars compression occur. Conversely when it is far from the collapse limit divergence and pillars decompression occur. This is called the arc-effect. This paper studies this behavior of the roof (immediate and main roofs) using numerical modeling to simulate the roof deformation and stress distribution in the roof and pillars. This simulation represents the progression of pillar collapse and shows the zone of convergence and divergence of the roof, and also the effect of this behavior on pillar confinement. Two-dimensional plain strain model was applied to simulate the arc-effect. The simulation results were compared to those of the instrumentation that was installed before the collapse. Keywords: pillar collapse, room and pillar, numerical modeling

Jan 1, 2005

By Hamid Maleki

A new failure criteria is proposed for assessment of roof stability in underground sedimentary rocks. Unlike other stability assessment techniques, this method is simple and practical, having improved mine safety and productivity in several mines. It is shown that roof movements accelerate to a critical rate prior to actual roof collapse. Critical rates vary between 0.025 inches per day to 0.2 inches per minute depending on rock mass - pillar mechanical properties. Specific critical rates are determined for three rock mass - pillar categories which are common to mining in sedimentary rocks. Time-to-caving varies from one minute to ten days on rock structural controls and type of primary support utilized.

Jan 1, 1990

By Brian E. Travis

The recent development of polymer grids for the underground coal mining industry has created new alternatives for supplemental ground control practices. The grids utilize strong, lightweight polymers - usually special grades of polypropylene. High tensile strengths and resulting load support characteristics are achieved by molecular orientation of these polymers in the manufacturing process. One of the most important applications of polymer grids as supplemental ground control is in longwall shield recovery. When shields are moved from one face to another, the determining factor in the success of the recovery is the ground control provided by roof support structures along the old face. Whereas primary support is usually provided by roof bolts and cables which run the full width of the panel, supplemental support is often provided by metallic meshes of welded wire or chain-link fence. lightweight, high-strength polymer grids replace these heavy, cumbersome metallic meshes, giving the operation increased productivity by decreasing installation time and reducing injury downtime.

Jan 1, 1990

By Vasundhara

Underground coal mining in soft floor environments has often led to strata control problems ranging from small scale issues such as floor heave which disrupts traffic and ventilation, rib spalling and induced fractures in pillars, through to large scale instability and long term subsidence. Past investigations of the problems encountered in Newcastle Coalfields of New South Wales, Australia, have revealed that the soft floor unit comprises of claystone which is very sensitive to moisture. It is prone to swelling, reduction in stiffness and loss of strength in the presence of moisture. Long term stability of mine panels in such an environment is governed by the extent of deterioration of the floor strata. The paper reports the field investigations conducted at Cooranbong Colliery to assess the extent of softened floor zone in the roadway and under a pillar.

Jan 1, 2001