VTechWorks Repository :: Browsing by Author "Karfakis, Mario G."

Browsing by Author "Karfakis, Mario G."

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Analysis of Seismic Signatures Generated from Controlled Methane and Coal Dust Explosions in an Underground Mine
Murphy, Michael M. (Virginia Tech, 2008-11-07)
Examination of seismic records during the time interval of the Sago Mine disaster in 2006 revealed a small amplitude signal possibly associated with an event in the mine. Although the epicenter of the signature was located in the vicinity where the explosion occurred, it could not be unequivocally attributed to the explosion. More needs to be understood about the seismicity from mine explosions in order to properly interpret critical seismic information. A seismic monitoring system located at NIOSH's Lake Lynn Experimental Mine has monitored nineteen experimental methane and dust based explosions. The objective of the study was to analyze seismic signatures generated by the methane and dust explosions to begin understanding their characteristics at different distances away from the source. The seismic signatures from these different events were analyzed using standard waveform analysis procedures in order to estimate the moment magnitude and radiated seismic energy. The procedures used to analyze the data were conducted using self-produced programs not available with existing commercial software. The signatures of the explosions were found to be extremely complex due a combination of mine geometry and experimental design, both of which could not be controlled for the purposes of the study. Geophones located approximately 600 m (1970 ft) and over from the source collected limited data because of the attenuation of the seismic waves generated by the methane explosion. A combination of the methods used to characterize the seismic signatures allowed for differentiation between experimental designs and the size of the explosion. The factors having the largest impact on the signatures were the mine geometry, size of the methane explosion, construction of the mine seal and location of the mine seal. A relationship was derived to correlate the radiated seismic energy to the size of the explosion. Recommendations were made, based upon the limitations of this study, on methods for better collection of seismic data in the future.
Analysis of Wireless Tiltmeters for Ground Stability Monitoring
Logan, Kenneth Scott (Virginia Tech, 2008-04-23)
Tiltmeters can be used in the mining environment to monitor slope stability by making use of gravitational force to measure angles of inclination relative to horizontal. Tiltmeters typically use accelerometers, which output a voltage measurement that can be related to angle of tilt. Though wireless tiltmeters already exist today, they lack certain ruggedness and sensitivity preventing use in mines. The purpose of this project was to investigate the feasibility of using already existing wireless tiltmeters in the mining setting. Additionally, a new wireless tiltmeter was designed which could be specially tailored for the needs of monitoring hazardous rock bodies in both surface and underground mines. By recording angles of any slope, either in a surface mine or underground, over extended periods of time, changes in readings can infer instabilities in the rock mass underlying the slope being measured. By placing many tiltmeters in a mesh on a surface slope or underground roof, rib, or other face, the entire surface can be monitored. Compared to the measurements of a single point using one instrument, a dense network can be extremely useful in detecting rock movement. Many monitoring techniques are in use already in mines. Traditional methods of monitoring, though undeniably useful, are often time consuming. By utilizing wireless devices that transmit data back to a single location, data acquisition and analysis time can be minimized, saving the mine employee hours as well as down time. As surface mines continue to deepen, and underground mines continue to progress further from the surface, the extent of necessary monitoring continues to increase: this widening range will require greater time for proper monitoring, unless an automated system is implemented. With proper wireless equipment, real time monitoring of an entire mine is possible.
Applications of Double-Difference Tomography for a Deep Hard Rock Mine
Kerr, Jeffrey Bryan (Virginia Tech, 2011-11-16)
Seismicity at a deep hard rock mine can be a precursor to ground failure events. Seismicity data can be used in double-difference tomography, which produce tomograms showing velocity distributions in the rock mass that can be used to infer relative stress of the rock mass. The data set used for the double-difference tomography inversion was from Creighton Mine in Sudbury, Ontario, Canada, and consisted of two months of data averaging 150 microseismic events per day. Three separate studies were conducted to evaluate the applications of double-difference tomography on a deep hard rock mine. These studies produced mine scale tomograms, stope scale tomograms of two active stopes, and stope scale tomograms for a cluster of events. TomoDD was used for the tomographic inversion, with other commercial programs used to view the results. All three studies produced results consistent with prior mine knowledge and basic concepts of rock mass stress redistribution. Mine scale tomograms accurately displayed a low velocity where the mined ore body is known to be with adjacent high velocity, stope scale tomograms of the two stopes both correctly demonstrated a low velocity relaxed zone near the stope following a production blast, and stope scale tomograms of an event cluster displayed consistency in results for two clusters in periods before, during, and after each cluster. The three studies show that double-difference tomography is a promising tool for observing rock mass stress redistribution that provides a baseline evaluation for the potential uses of the technology in a deep hard rock mine.
Blasting Design Using Fracture Toughness and Image Analysis of the Bench Face and Muckpile
Kim, Kwangmin (Virginia Tech, 2006-07-21)
Few studies of blasting exist because of difficulties in obtaining reliable fragmentation data or even obtaining consistent blasting results. Many researchers have attempted to predict blast fragmentation using the Kuz-Ram model, an empirical fragmentation model suggested by Cunningham. The purpose of this study is to develop an empirical model to relate specific explosives energy (ESE) to blasting fragmentation reduction ratio (RR) and rock fracture toughness (KIC). The reduction ratio was obtained by analyzing the bench face block size distribution and the muck fragment size distribution using image analysis. The fracture toughness was determined using the Edge Notched Disk Wedge Splitting test. Blasting data from twelve (12) blasts at four (4) different quarries were analyzed. Based on this data set, an empirical relationship, ESE=11.7 RR801.202 KIC4.14 has been developed. Using this relationship, based on the predicted blasting energy input for a desired eighty-percent passing (P80) muckpile fragment size the burden and spacing may be determined.
Bump control design protocol for room-and-pillar retreat mining
Campoli, Alan A. (Virginia Tech, 1994-05-08)
A stress control design protocol was developed to minimize coal mine bumps, which are the explosive failure of highly stressed pillars. The protocol was developed for room-and-pillar retreat mining conducted with available continuous miner technology. The inability of existing coal pillar equations to accurately represent the wide total extraction pillars required, forced the development of the pseudoductile coal pillar strength model. A confined pillar core is assumed to reach a maximum stress when surrounded by a yielded perimeter. The width of the yielded perimeter is assumed to increase linearly with increased coalbed thickness. The pseudoductile model was employed in the development of supercritical and subcritical width section design criteria. The supercritical design procedure assumes an infinitely long pillar line, composed of uniformly sized pillars, extracted against an infinitely wide gob area. Tributary area theory was combined with a linear shear angle concept to estimate the loads applied to total extraction pillars adjacent to gob areas. The boundary element code MULSIM/NL was utilized in the development and implementation of a systematic subcritical design procedure to apply the stress shield concept to retreat room-and-pillar coal mining, under bump hazard. The complex distribution of gob side abutment load between the side abutment pillars and the chain pillars in the total extraction zone made computer simulation a necessity. Section layouts were determined for the mining of a 6 ft thick coalbed under overburden up to 2,200 ft thick. The sections consist of total extraction areas separated by continuous abutment pillars. A spreadsheet program LAYOUT was created to summarize and provide for efficient utilization of the bump control design protocol. Based on overburden thickness, coalbed thickness, abutment load linear shear angle, and pillar dimensions entered by the user, LAYOUT calculates a stability factor for the first and second pillar row outbye the expanding gob for supercritical width sections. If the overburden and coalbed thickness conditions do not allow a supercritical section design, LAYOUT develops a subcritical design.
Classification and analysis of longwall delays
Dunlap, James,1963- (Virginia Tech, 1990-06-15)
Spectacular production rates have been achieved by certain U.S. longwalls, and yet a large number of longwall operations have failed to meet anticipated production targets. This study attempts to identify the primary factors which contribute to the production shortcomings of many marginal longwall operations. This study presents details of the classification and analysis of delay data for a group of thirty-nine longwall sections located in the eastern and mid-eastern United States. Downtime data correspondIng to over fourteen-thousand shifts were collected and classified according to equipment type, delay type, and specific delay event. A dBase IV-based database was constructed to allow flexible interrogation of the data. The relative downtime contributions of the various equipment components and of the delay types have been determined. Machine availabilities and system availabilities are presented. Probability density functions have been flit to the time-to-failure and to the time-to-repair data sets, both for the principal equipment types and for the longwall system as a whole. Recommendations are made for increasing the availability of longwall systems.
Defining Stress Changes Ahead of a Tunnel Face and Design of a Data Acquisition System
Murphy, Michael M. (Virginia Tech, 2005-12-13)
With increasing world population, demand for underground construction is expected to accelerate in the future. Design of tunnels in rock is still largely empirical, while rock failure in underground mines and tunnel construction continues to claim lives. A seismic method to aid in increasing safety during excavation is tomography. Seismic tomography is a non-invasive technique to map the stress changes induced by mining ahead of the active face. Seismic tomography maps the velocity distributions of elastic waves traveling through a rock mass. The velocity distributions mapped in the tomograms can relate to anomalies in the rock such as fracture zones and highly concentrated stresses. In order to develop a relationship between stress and elastic wave velocity, laboratory tests in a controlled environment are required. In the current study tomographic tests were conducted on Berea sandstone and Five Oaks limestone samples. The stress redistribution in the sandstone samples could be imaged by mapping velocity distributions. On an unconfined test the sandstone sample acted much like a coal mine pillar where the stress redistributes to the least confined area. On a sandstone test where the sample was indented by a steel platen the velocity contrast was seen directly under the load and the velocity remained almost unchanged over the rest of the sample. For the limestone tests, the stress redistribution could not be mapped in the tomograms. The ability to map the stress distribution in the tomograms were attributed to the elastic and non-elastic characteristics of the stress-strain curve. For sandstone, a porous rock, the stress redistribution could be mapped and for limestone, a stiff rock, the stress redistribution could not be mapped. A field data acquisition system to apply tomography to ground control problems in a mine was designed and calibrated. Data acquisition hardware were assembled and programmed in LabVIEW to collect seismic data in a mine. The design of a geophone array that will fit into a miniature 5.08 cm (2 in) diameter borehole is presented.
Design and Testing of a Laboratory Ultrasonic Data Acquisition System for Tomography
Johnson, Wesley Byron (Virginia Tech, 2005-12-02)
Geophysical tomography allows for the measurement of stress-induced density changes inside of a rock mass or sample by non-invasive means. Tomography is a non-destructive testing method by which sensors are placed around a sample and energy is introduced into the sample at one sensor while the other sensors receive the energy. This process is repeated around the sample to obtain the desired resolution. The received information is converted by a mathematical transform to obtain a tomogram. This tomogram shows a pixelated distribution of the density within the sample. Each pixel represents an average value at that point. The project discussed in this paper takes the principle of ultrasonic tomography and applies it to geomechanics. A new instrumentation system was designed to allow rapid data collection through varying sample geometries and rock types with a low initial investment. The system is composed of sensors, an ultrasonic pulser, a source switchbox, and analog to digital converters; it is tied together using a LabVIEW virtual instrument. LabVIEW is a graphical development environment for creating test, measurement, and other control applications. Using LabVIEW, virtual instruments (VIs) are created to control or measure a process. In this application LabVIEW was used to create a virtual instrument that was automated to collect the data required to construct a tomogram. Experiments were conducted to calibrate and validate the system for ultrasonic velocity determination and stress redistribution tomography. Calibration was conducted using polymethylmethacrylate (PMMA or Plexiglas) plates. Uniaxial loads were placed on limestone and sandstone samples. The stress-induced density contrasts were then imaged using the acquisition system. The resolution and accuracy of the system is described. The acquisition system presented is a low-cost solution to laboratory geophysical tomography. The ultimate goal of the project is to further the ability to non-invasively image relative stress redistribution in a rock mass, thereby improving the engineer's ability to predict failure.
Design of a Mine Roof Strata Analyis Device
Russell, Andrew James Reksten (Virginia Tech, 2015-04-22)
Because the roof lithology in an underground coal mine is typically variable and poorly known, the safety and efficiency of these mines is reduced. To address this shortcoming, a device for analyzing rock properties by way of scratching a mine roof borehole was designed and tested in multiple different media with the goal of determining in situ mine roof properties with a nondestructive technique. Tools were developed for measuring extraction force and position of the scratching mechanism and those values were compared versus time for multiple tests to look for changes in applied force over changing positions. Because of signal stability and inconsistencies in scratch depths the data were found to contain too much variation to determine any rock properties or changing rock conditions from the simulated roof material in the concrete block. However, further scratch tests in a sandstone block indicated that increasing the diameter of the wire scratchers (and therefore increasing their stiffness and accompanying normal force) from 0.045 inches to 0.055 inches increased the average pull force from 6.24 to 9.96 lbs. Similar to that test, a scratch test was performed in a PVC pipe where it was found that increasing the scratcher diameter from 0.045 inches to 0.051 inches increased the pull force from a 2.81 lb average to a 36.46 lb average, with considerably better gouging of the host material.
Design Optimization of Safety Benches for Surface Quarries through Rockfall Testing and Evaluation
Storey, Andrew Wilson (Virginia Tech, 2010-08-24)
The research presented in this thesis results from efforts to evaluate current design methodologies for safety benches in surface aggregate quarries. Proper bench design is important for preventing rockfall related accidents and injuries without wasting the reserves held in the benches. An in depth analysis has been performed using the results from 230 rockfall tests conducted at two surface quarries. The goal of this project is to give practitioners the tools they need for improved bench design. Principal Components and Cluster Analysis, techniques not previously applied to rockfall investigations, have been performed on the test data. The results indicate that both are valid analytical methods which show that the factors affecting the rollout distance of a rock are wall configuration, rock dimensions, and rock energy. The test results were then compared to the Ritchie Criteria, Modified Ritchie Criterion, Ryan and Pryor Criterion, Oregon Department of Transportation design charts, and RocFall computer simulations. Analysis shows that the lognormal distribution curves fitted to the test data provide an excellent yet quick design reference. The recommended design method is computer simulation using RocFall because of the ease of simulation and the site specific nature of the program. For the two quarries studied, RocFall analysis showed that 20 ft benches with a 4 ft berm will hold over 95% of rockfalls, a design supported by the field testing. Conducting site-specific rockfall testing is also recommended to obtain realistic input parameters for the simulations and to provide design justification to regulatory agencies.
Development of a Wireless Borehole Extensometer for Monitoring Convergence in Underground Mines
Thomas, William Robert (Virginia Tech, 2015-05-21)
An extensometer has been developed to continuously monitor roof extension in underground mines. The extensometer is designed to be installed in the MSHA-mandated test holes in the roof and measures the displacement between an anchorage point at the top of the borehole and the hole in the roof of the excavation. Once installed, the extensometer will report displacement through semi-wireless communications network. The extensometer is hard-wired into the permissible MIDAS datalogger, where results can be obtained wirelessly via the MIDAS user interface. Lab tests have indicated that the device produces displacement data. The device was installed in one underground coal mine to review its effectiveness in the field.
Development of an Underground Automated Thin-Seam Coal Mining Method
Holman, Darren Wayne (Virginia Tech, 1999-05-10)
It is predicted that coal mining in Southwest Virginia, and the economic stability that it brings to the area, will continue to decline over the next decade unless an environmentally sound, and economically viable means can be found to extract seams of high quality coal in the thickness range of 14 to 28 inches. Research into autonomous machine guidance, coupled with developments of thin-seam mining equipment, offer new opportunities for devising mining layouts suitable for extracting these thin seams in a cost effective manner. These layouts must involve well-planned transportation and ventilation routes that will allow safe conditions for personnel. This implies that the mining face, where coal is extracted, will be completely automated, ensuring the safety of the workers. This thesis presents a brief overview of current technologies utilized for underground coal mining in the United States. This is followed by a review of developments in highwall mining that are potentially applicable in underground mining of thin seams. Some past attempts at thin seam mining are discussed, and evaluated for their short comings. An overview of the more recent advances in the guidance systems for use in autonomous mining machines is also presented. The new advances that several manufacturers are developing to address the integration of mining and continuous haulage systems are also investigated. That background is employed in devising a conceptual mining system for the underground mining of coal seams in the 14 to 28 inch range of thickness. This thesis proves that adapting new technologies and concepts from existing ones can lead to meaningful advances in the field of natural resources recovery. This system utilizes a newly designed panel layout that takes into account haulage, supplying, ventilation, equipment, and machine guidance. This system is proposed to show that new ways can be developed to take advantage of the reserves in the 14 to 28 inch range of thickness. This shows that new technology and design innovation can turn currently uneconomic resources, into economic reserves. This kind of innovation is what is needed to keep this region of Southwest Virginia economically viable. This system is a huge step in the direction that thin-seam research needs to take. Most of the equipment suggested for this proposed system is already available.
The effect of zero point charge environment on rock fracture behavior
Akram, Muhammad (Virginia Tech, 1991-06-06)
This experimental investigation was conducted to assess the effect of zero point of charge (ZPC) environment on fracture behavior of rocks. The material parameters selected for this purpose were fracture toughness and specific work of fracture. These properties were determined for three rock types in five environments. Semi-circular bend specimens of dolomitic limestone, Sioux quartzite and Westerly granite were tested in aqueous solutions of aluminum chloride, calcium chloride and polyethylene oxide, all at ZPC conditions. These rocks were also tested in atmospheric air and distilled deionized water. For every rock type, the results obtained for the tests done in each of the ZPC environment were statistically compared with the results in water. This comparison was also made for air and water. The average fracture toughness in each of the ZPC environments, for all three rock types, was found to be less than the corresponding average in water. The specific work of fracture results also indicated reduction in ZPC environments as compared to water. The statistical analysis of the results, however, showed that this reduction was significant in some but not all of the rock-environment combinations tested in this investigation.
The Effects of Backfilling on Ground Control and Recovery in Thin-Seam Coal Mining
Donovan, James G. (Virginia Tech, 1999-05-12)
A large percentage of Southern Appalachian coal reserves are located in seams less than 36" thick. As thicker and currently more mineable, deposits are exhausted, methods of underground thin-seam extraction will have to be developed. These methods must be capable of removing coal efficiently and economically. Past experience with highwall mining of thin-seam coal has indicated that recovery rates tend to be lower than in conventional operations. It is suspected that this will also apply to underground thin-seam mining, regardless of proposed technology or mining method. A method of increasing recoveries from thin-seam mining operations is necessary in order to exploit thin-seam reserves. Backfilling is one alternative that may find applicability in thin-seam coal mining. The ability of backfill to provide additional ground support may enhance coal recovery by allowing for the design of undersized pillars. Backfill has been used extensively in hard rock mining but has found limited use in coal mining. Its adaptability to thin-seam coal mining has been examined and is presented in this thesis. Backfill is capable of providing additional ground support by restricting lateral deformation of surrounding coal pillars and roof. This additional support can result in significant increases in recovery from thin-seam coal deposits. However, the overall feasibility of backfill is dependent on the in situ behavior of the fill material, the properties of the fill, the effects of the filling method on the total mining operation, and the cost of filling per extra ton of coal recovered. The influence of these parameters has been studied and indicate that, in certain situations, backfilling for the purpose of increasing recovery rates from thin-seam coal mines is feasible.
Enhancing Mine Subsidence Prediction and Control Methodologies for Long-Term Landscape Stability
Andrews, Kevin (Virginia Tech, 2008-06-23)
Prediction and control methodologies for ground deformation due to underground mining (commonly referred to as mine subsidence) provide engineers with the means to minimize negative effects on the surface. Due to the complexity of subsidence-related movements, numerous techniques exist for predicting mine subsidence behavior. This thesis focuses on the development, implementation, and validation of numerous enhanced subsidence prediction methodologies. To facilitate implementation and validation, the improved methodologies have been incorporated into the Surface Deformation Prediction System (SDPS), a computer program based primarily on the influence function method for subsidence prediction. The methodologies include dynamic subsidence prediction, alternative model calibration capability, and enhanced risk-based damage assessment. Also, the influence function method is further validated using measured case study data. In addition to discussion of previous research for each of the enhanced methodologies, a significant amount of background information on subsidence and subsidence-related topics is provided. The results of the research presented in this thesis are expected to benefit the mining industry, as well as initiate ideas for future research.
Experimental evaluation of polyester grout as a ground control measure in underground mines
Kan, Stephen Wai-Sing (Virginia Tech, 1995-03-05)
Chemical grouting has been used to insure the stability of underground mine openings for more than twenty years. The polyurethane grout, which is currently being used, has a limited range of mechanical properties that restrict its utilization. Polyurethane also poses serious threats to miners' health due to its toxicity and flammability, To overcome many of these problems and limitations, research has been conducted on a newly developed polyester-based grout. The assessment of mechanical properties of polyester grout is the focus of this work. Field experiences and laboratory research have defined properties which an effective grouting material should possess. Experimental results indicate that the polyester grout meets or exceeds these recommended properties and has the potential to expand the applicability of chemical grouting in ground control. By adjusting its formulations, mechanical properties of polyester grout can be engineered to solve specific ground control problems.
A Feasibility Analysis of Wind Power as an Alternative Post-mining Land Use in Surface Coal Mines in West Virginia
Duerksen, Alek Charles (Virginia Tech, 2011-09-19)
Surface coal mining in West Virginia has supplied energy to the eastern coast of the United States for over a century. Over the years, the coal mining industry has been forced to adapt as societal demands regarding health, safety, and environmental impacts have changed. More recent pressure has called for another iteration of change: long-term post-mining sustainability. The research presented in this thesis investigates one potential solution—or component of a solution—to improve the sustainability of surface coal mining in West Virginia: post-mining wind power. This thesis intends to demonstrate and explain the feasibility of synergistic mine closure and wind development. Wind conditions at three reclaimed mine sites in West Virginia were monitored in order to develop representative case studies for post-mining wind power. This report contains a summary of the literature consulted to plan the site assessments, the methodology employed to execute them, the analysis steps undertaken to derive conclusions, and a discussion of all findings. This research has found that significant cost savings can be yielded from synergistic mine closure and wind development, as compared to greenfield wind development. Though wind conditions themselves remain the primary driver for site feasibility, post-mining wind power is a practice with significant promise for improving project economics, contributing to renewable energy development, enhancing company-community relations, providing local employment opportunities, and exemplifying sustainable business practices in Appalachia.
Feasibility of an Integrated Thin Seam Coal Mining and Waste Disposal System
Basu, Kohinoor (Virginia Tech, 1997-12-15)
The depletion of more attractive thicker and easily accessible coal seams in the central Appalachia will direct attention towards the extraction of coal seams thinner than 28 in. This thesis investigates the feasibility of an integrated mining and backfilling system applicable to thin seams. Two conceptual mining systems, namely Auger mining and Self Advancing Miner, have been proposed for this purpose. Both these systems are designed to remotely mine coal from the seams. Several attempts were made in the past to mine coal in a similar fashion but were not very successful due to several problems inherent to thin seams. The lack of effective steering techniques, accurate coal/rock interface and pillar thickness detection techniques were the main shortcomings of the systems. These problems were addressed in the proposed conceptual mining systems. Several coal/rock interface and rib thickness detection techniques currently available in the market or in the prototype stage have been discussed. Recent developments in coal/rock interface detection and direction sensing techniques have good potential in alleviating the previously encountered problems. Sensitivity analyses have been performed to assess the of effect critical mining parameters on the production potential of these systems. The self advancing miner has been found to be more promising than auger mining. Conceptual panels and face layouts for both systems have been included. Two types of filling methods namely pneumatic and hydraulic are considered applicable under thin seam conditions. A backfilling technique using rubber hoses for fill placement can be applied with both methods. Sensitivity analysis have been performed to establish the relationship between face operation cost, filling cost per ton and development cost per foot. Resulting analyses indicate that panel cost per short ton of coal is more sensitive to filling cost than on development cost.
Flow characteristics of jet fans in mines: experimental and numerical modeling
Konduri, Indu Mohan (Virginia Tech, 1996-12-05)
The use of induction fans for face ventilation in room and pillar mines has proved to be an efficient, flexible, and viable technique. In addition to their merits over conventional systems, induction fans enable remote controlled mine operations with low maintenance requirements. Theoretical investigations were conducted initially to verify the potential of free air jets in mine ventilation. A laboratory model using water as the fluid medium was designed to study the flow characteristics of a jet fan in a blind entry. The model was tested in a variety of brattice curtain and nozzle combinations to investigate the ventilating efficiency of jet fans. A jet fan was selected and tested in a full scale model and in a coal mine. Experiments were conducted to evaluate the laboratory flow models. Flow quantities and velocities in the entry were measured using state-of-the-art instrumentation to quantify various parameters. Air velocities near the face were found to be satisfactory to dilute contaminants from the face. A model for the axial velocity profile of the jet was suggested. Beyond 25m distance from the jet fan exit the jet tended to move away from the wall to the opposite wall. Carbon dioxide was used as a tracer gas to measure the effective ventilating air quantity near the face and re-circulation in various tests. The re-circulation involved in the system was found to be less than 40% in all the experiments. It was also found that the use of line curtains in combination with a jet a fan can eliminate any type of re-circulation. Numerical modeling of a jet fan in a typical coal mine heading was conducted to obtain details of the flow. The results of the simulation using computational fluid dynamics were similar to the flow patterns observed in the experiments. It was found that a jet fan can effectively ventilate an entry as deep as 40m. Fan positioning, airway geometry, airway surface properties, and mine layout severely affect its performance. It is therefore necessary to understand the flow mechanics of a jet fan in a mine heading before applying the technique for a particular situation.
Four-Dimensional Passive Velocity Tomography of a Longwall Panel
Luxbacher, Kramer Davis (Virginia Tech, 2005-12-12)
Velocity tomography is a noninvasive technology that can be used to determine rock mass response to ore removal. Velocity tomography is accomplished by propagating seismic waves through a rock mass to measure velocity distribution of the rock mass. Tomograms are created by mapping this velocity distribution. From the velocity distribution relative stress in the rock mass can be inferred, and this velocity distribution can be mapped at specific time intervals. Velocity tomography is an appropriate technology for the study of rockbursts. Rockbursts are events that occur in underground mines as a result of excessive strain energy being stored in a rock mass and sometimes culminating in violent failure of the rock. Rockbursts often involve inundation of broken rock into open areas of the mine. They pose a considerable risk to miners and can hinder production substantially. The rock mass under investigation in this research is the strata surrounding an underground coal mine in the western United States, utilizing longwall mining. The mine has experienced rockbursts. Seismic data were collected over a nineteen day period, from July 20th, 1997 to August 7th, 1997, although only eighteen days were recorded. Instrumentation consistsed of sixteen receivers, mounted on the surface, approximately 1,200 feet above the longwall panel of interest. The system recorded and located microseismic events, and utilized them as seismic sources. The data were analyzed and input into a commercial program that uses an algorithm known as simultaneous iterative reconstruction technique to generate tomograms. Eighteen tomograms were generated, one for each day of the study. The tomograms consistently display a high velocity area along the longwall tailgate that redistributes with face advance. Numerical modeling and mine experience confirm that the longwall tailgate is subject to high stress. Additionally, microseismic events are correlated with the velocity tomograms. Velocity tomography proves to be an effective method for the study of stress redistribution and rockburst phenomena at underground longwall coal mines, because it generates images that are consistent with prior information about the stress state at the mine and with numerical models of the stress in the mine.

Browsing by Author "Karfakis, Mario G."

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