Search Documents

By Peter Altounyan

Goedehoop Colliery in the Witbank Coalfield of South Africa produces some 8 million tonnes of coal from fully mechanised room and pillar mining methods, using resin anchored bolts as roof support. Investigation of the quality of the installed bolts resulted in the finding that it was possible to pull out fully encapsulated roofbolts. This led to a drive to improve the quality of installation by making it easier to install a roofbolt correctly and more difficult to install incorrectly, whilst at the same time achieving high bond strength. The method of installation which was investigated, developed and implemented is known as 'spin to stall.' The roofbolt is pushed through the resin capsule to the top of the hole and then spun to mix the resin, until the increasing resistance to rotation exceeds the breakout limit on the bolt torque nut. The nut then runs up the bolt thread and is tightened to the roof as the drill stalls. This procedure is simple and avoids human factors such as non adherence to 'spin' and 'wait' times which contribute to poor installation with conventional methods. However spin to stall installation has been avoided in the past because of concerns over damage to the resin bond. This paper reports on the efforts made to investigate and understand the factors involved, and the progress made in overcoming the problem of resin damage so that the advantages of this installation method can be realised.

Jan 1, 2003

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 Keith D. Koper, Kris L. Pankow, Derrick J. A. Chambers, Michael K. McCarter

"In a mining environment, high quality seismic event catalogs are often useful in interpreting local stress states and identifying areas with elevated ground control risk. Installation, operation, and maintenance of local/in-mine seismic networks, however, may be prohibitively expensive, and mine operators may not anticipate the need for seismic data until unusual mining conditions arise. If regional, generally public, seismic instrumentation could be used to reproduce the results generated by local/in-mine instrumentation to an acceptable degree of fidelity, it would be a valuable and inexpensive tool for mine planners and ground control engineers.In this study we apply subspace detection—a non-traditional seismic event detection technique—to data from a sparse, regional network. The process is employed to identify mining induced seismicity (MIS) from an underground coal district. The results are compared to a seismic event catalog produced by a local seismic array operating within the permit boundaries. Additionally, we analyze the performance of two different stations of the same sparse, regional network in identifying blasts at a surface coal mine for which we have a detailed blasting log. In both cases data from stations between 10 and 60 km away from mining activity are used. We also explore the trade-offs between the number of detections and the number of false positives, which is influenced heavily by detection thresholds and the number of stations used in the process.For the surface mine we are able to identify more than 90% of the production blasts documented in the blasting log. We also find that the detected blasts from each of the four active pits produce waveforms similar to one another. The results are not dependent on source-receiver distance, and by requiring detections to occur on both stations the number of sure false positives is reduced to zero. In the underground mining district we identify between 30% and 75% of the events detected by the local array, depending on the acceptable number of false positives and the source-receiver distance. We also find many events that were missed by the local array, showing that regional subspace detection can usefully augment traditional local catalogs. Moreover, subspace detection can provide an estimate on event location and classification using data from as little as one seismic station."

Jan 1, 2015

The challenge of planning to minimize interaction effects in multi-seam mining is compounded by the difficulties inherent in extrapolating essential geological and spatial data between sampling points. To predict the effects of ultra-close mining on lower seam entry stability, simulated mine openings were studied using finite element analysis and body loaded photoelastic models. Both symmetrical and unsymmetrical loading was used to represent stress fields generated under multi-seam conditions. Results were correlated with field data to determine stress levels at which failure could be expected to occur. Stability predictions require precise definitions of geologic and spatial data, which could not be accurately defined by interpolation between sampling points. To overcome this problem an expanded roof stability model, SESAME2, was developed to incorporate reliability concepts based on Monte Carlo sampling. The model was demonstrated in terms of variations of innerburden thickness using a case study.

Jan 1, 1994

By J. S. Oram

Maltby Colliery, operated by RJB Mining (UK) Ltd is successfully mining the Parkgate seam in Yorkshire at a depth of 1000m using longwall retreat. Extraction in the Parkgate seam is influenced by interaction from previous workings in the Swallow Wood Seam 160m above. The paper describes in-situ stress measurements and simple gate road convergence measurements carried out to assess the extent of the interactive influence. The stress measurements, obtained using the stress relief overcore technique, were carried out from a maingate development roadway in an area where the stress redistribution under an overlying pillar and adjacent panel goat could be measured. The measured vertical stress distribution confirmed a significant interactive influence with high imposed vertical stresses under the overlying panel edges. Simple roadway convergence monitoring stations established in the gateroads of a retreating panel and in the development gateroads of the adjacent panel, confirmed higher rates of roadway deformation relating to overlying panel edges and pillars, particularly in the areas where a vertical stress window developed during panel retreat. In addition to highlighting a close relationship between closure rate and the measured vertical stresses, the convergence monitoring proved valuable in establishing characteristic deformation behaviour under specific interactive influences and also in defining the optimum location, extent and time of installation u£ additional roadway support and reinforcement. The information from the measurement programme has enabled the Mine Management to gain a better understanding of the interactive influences on roadway behaviour and was instrumental in designing the layout of panels in an area of the North East district of the mine where previous experience had indicated the combined influence of high interactive stresses and weak roof lithology resulted in difficult strata conditions both at development and on panel retreat. The planned location of panels and gateroads took into account both mining operational considerations and the need to avoid potentially high risk interaction zones as highlighted from analysis of the monitoring results. To obtain additional data on parameters influencing roadway deformation, extended roadway convergence monitoring has been established.

Jan 1, 1997

3-D finite element modeling was performed to study the effect of bedding plane sliding and separation and tensioned bolt in layered root It was found that the major influence zones of a tensioned bolt are restricted to the neighborhood of the anchor points; that bedding plane sliding and separation releases the vertical stress in the roof above entry but greatly increases the horizontal stress within the first layer of the roof, and that there is a triangular zone between the two adjacent bolts at and near the roofline level that is beyond the influence zone of the bolts which is liable to fail if conditions exist. Based on the results, three possible modes of roof failure are proposed for the design of tensioned bolting.

Jan 1, 2001

By Leslie Carver

The effects of longwall mine subsidence on water resources were studied at a West Virginia coal mine (mine Z) by Carver (1994). Data were obtained for 137 domestic supply wells and springs and 12 baseflow streams. Subsidence caused short-term dewatering (of a few days to weeks) of wells located on lower hillslopes and valleys, and long-term dewatering of hillslope and hilltop springs (with no recovery yet). New or increased spring discharge was observed at lower elevations. Unsubsided water supplies experienced no dewatering beyond a nearby panel's 27°-38° angle of dewatering influence zone. Subsidence from longwall mining beneath streams commonly reduced discharge when panel ages were less than two to three years. However, "normal" discharge was typically observed over panels greater than three years in age; such streams exhibited lower baseflow recession constants, moderated winter baseflow, and increased summer baseflow compared to unsubsided streams.

Jan 1, 1994

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

This paper presents a two-dimensional numerical procedure which incorporates concepts related to the mechanics of strata deformation' as well as' empirical indices associated with subsidence engineering. Regional deformation data were employed in order to establish overburden deformation zones, while material properties were kept constant. Scaling of final displacements was based on empirically predicted values for subsidence and strain for the Appalachian coalfield. The model was validated with a number of regional case studies and predicted subsidence and strain curves were compared to those obtained using the semi-empirical influence function formulation developed by VPI&SU.

Jan 1, 1988

By David Hill

Over the last decade, Beltana No.1 Mine has generally been Australia?s most productive longwall operation, with a ROM output of 7.2 Mt in YEJ2007. Characteristically favorable roof conditions and low depths of cover resulted in typically high rates of development drivage and longwall retreat. As a consequence of these high rates of development and extraction, there was a continuing focus on recovering and relocating the longwall face as efficiently as possible to minimize associated production delays and operational costs. This paper presents a comprehensive case study of the conventional longwall recoveries (?take-offs?) at the mine, from Longwall 1 to 14. By examining the take-off monitoring data collected over the life of the mine, the key geotechnical issues are demonstrated, including their relationship to the ground behavior experienced and the issues overcome.

Jan 1, 2011

By Zhang Liandong

Roof control in thick-seam mining has long been a difficult problem in mine design and coal mining. In the early 1980's, through ground control instrumentation and investigation the rules of roof strata movement were determined, based on which the sliding roof bar powered support was properly designed and successfully applied to roof control to thick seam mining with caving. Underground trials in Huating Coal Mine produced satisfying results. The technique is being employed in many Chinese coal mines and won the national price for technical advance.

Jan 1, 1990

By Kevin M. Connor, O&apos

An example application is presented in which Time Domain Reflectometry (TDR) was utilized to monitor roof strata movements during pillar extraction in a potash mine. The study was initiated when Western Ag-Minerals decided to implement secondary mining of pillars in order to extend the life of their Nash Draw Mine. A prototype operation was conducted in one mine panel to assess mining equipment and procedures, and to determine if ground control problems would develop. An instrumentation array was installed by personnel from New Mexico Tech and Western Ag to monitor strata movements, changes in pillar stress and surface subsidence, and these data are being analyzed by the Bureau of Mines. This paper is limited to a discussion of roof-floor convergence and roof strata movement to illustrate the application of TDR to ground control. Plots are presented which demonstrate the capability of distinguishing location, magnitude and mode of rock movement using TDR to interrogate coaxial cables grouted into holes drilled in the roof.

Jan 1, 1990

By M. Guana

Island Creek Corporation is predominately an underground mine operator deploying room-and-pillar and retreat longwall mining methods for extracting coal. Wide variations are encountered in overburden depth, stratigraphy, and insitu stress fields. This requires major adjustments in mine design among mines and occasionally within a mine. Simple rock mechanics principles are utilized in mine design to optimize safety and productivity. Physical observations and micro deformation monitoring of roadways are the primary techniques employed. Pillars and artificial support systems are the primary design elements modified. The specific case histories reviewed in this paper include narrow panels with high extraction for conventionally mined rooms, pillar sizing for longwall gate entries at great depths, and bolt type selection for difficult ground conditions.

Jan 1, 1988

By Michael J. Friedel

The fundamental problems associated with ground control reflect the inability of mining personnel to "see" the development of anomalous conditions. Toward this end, the U. S. Bureau of Mines is investigating the application of seismic refraction tomography for imaging the process of pillar yielding, at the Foidel Creek coal mine, near Steamboat Springs, CO. The inherent three-dimensional problem of imaging coal pillar stress is reduced to a single plane by considering only the stress transmitted from the pillar to the adjacent floor rock. This approach exploits the fact that refracted seismic energy is essentially confined to the adjacent higher velocity sandstone strata. The tomographic analysis using ray-tracing based on wavefront migration resulted in a robust P-wave tomogram from which regions of high velocity indicate zones of high stress concentration, whereas low velocity zones indicate regions of stress relief. The interpreted region of high stress concentration occurs at the pillar end nearest to the working face of the adjacent longwall panel. This finding is corroborated by vertical pressure cell measurements recorded in the pillar. The stress diminishes toward the pillar perimeter with local minima correlating to the locations of observed pillar spalling. Time-sequence monitoring, as the longwall face advances, is recommended for evaluating changing stress conditions.

Jan 1, 1993

By Edward S. Custer

Recent investigations of mine roof falls have demonstrated that roof failures are generally associated with geologic conditions. The roof falls can be predicted by using the techniques of depositional modeling for the coal bed and roof rocks, and by lineament analysis. The ability to predict potential roof failure areas will allow the engineer and mine planner to develop a mine plan to avoid the roof failure areas and thus reduce overall mining costs. The ability to avoid roof failure areas also will permit maximum recovery of the coal resources.

Jan 1, 1981

By David A. Newman

Strength and physical property testing of coal is conducted regularly by the Arch Mineral Corporation as part of reserve exploration. Pillar design and mine layout are the primary applications for the coal strength data. Distinct differences in pillar behavior were observed during longwall mining at a mine in Southeastern Kentucky. Horizontal and vertical variation in both triaxial and uniaxial compressive strength was observed within the four (4) benches of the Harlan seam. Similarly, geographical variations in coal strength were noted across the Harlan seam reserve. During the past three decades substantial research efforts have been focused upon coal pillar behavior and the refinement of pillar design methodologies. Ironically, little attention was directed to integrating the variability of coal strength into pillar design. The authors examine, through the presentation of case history data, i) typical industrial practice with respect to establishing a database of coal strength for use in pillar design and stability analysis, ii) approaches in which the observed variation in strength in the Harlan seam is integrated into pillar design and stability analyses, and to iii) propose standards for coal cube testing

Jan 1, 1993

By Deren Zhu

The principle of roof control in longwall mining is to control main roof fractures so as to reduce roof weighting, plus reasonable and effective design of supports to reduce the convergence and premature caving of the immediate roof. This paper introduces a comprehensive test for better roof control based on the geological conditions of coal seam No. 16 in Zaozhuan Colliery, China.

Jan 1, 1990

By Joachim Leonhardt

Hundreds ofbolt-indicators were already used successfully in the German deep hard coal-mines to increase the safety and economy. The bolt-indicator offers the simple possibility to show roof-bolt (anchor-) loads. to indicate weak points as well as to optimize the anchor density and the dimension: The bolt-indicator is mushroom shaped and consists of coated metal. It is inserted between the anchor plate and the flanged nut. The loads appearing at the anchor are transferred to the bolt- indicator and can be recognized visually at the cylindrical part by the amount of the surface coating. Examples are used to clarify the application aims, operation and usage of the bolt-indicator and its yielding advantages in practice.

Jan 1, 2001

By Hamid Maleki

A novel ground control program has been developed at Plateau Mining Company through five years of geotechnical investigations. The study was initiated to determine the causes for roof stability problems and to develop alternative support and monitoring systems for increased safety and productivity. From systematic roof fall observations, extensive geologic mapping, roof drilling and monitoring ground movements along gate entries of four longwall panels, a sand- stone channel system was detected and shown to impact roof stability. In particular, underlying mudstones up to seven feet thick experienced instability due to differential compaction and load transfer from the gob. Roof bolter operators were trained to report roof lithology for mapping channel positions into the roof and for selective use of longer bolts. This boosted operator morale, and improved ground conditions. Monitoring rates of roof movement is used in these areas for detection of instability and for application of secondary support: This has significantly increased safety and productivity.

Jan 1, 1987

By Khaled Morsy

In this paper a new method to evaluate the stability of yield pillars was introduced. The evaluation of yield pillar stability was conducted in three steps: (1) Estimation of pillar loading - numerical modeling is a good tool to estimate the pillar loading for most of the geological, geometrical and mining conditions. In this study. finite element technique was used to estimate the state of stress, strain, elastic strain energy and plastic energy, etc. at every point within the pillar. (2) Defining the yield pillar loading zones¬. The proposed method considered the non-uniform stress distribution of yield pillars by dividing the area of the yield pillar into three loading zones, namely core, transition and rib zones. (3) Estimation of stability indicators - an appropriate stability measure was proposed for each loading zone. such as; Core Stability Factor. CSF, Pillar Bump Index, PBI and Rib Instability Index. RIF. A case study of successful and unsuccessful yield pillar application was used to assess the applicability of the proposed method.

Jan 1, 2003