VTechWorks Repository :: Browsing by Author "Haycocks, Christopher"

Browsing by Author "Haycocks, Christopher"

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An analysis of close seam interaction problems in the Appalachian coal fields
Wu, Wei (Virginia Polytechnic Institute and State University, 1987)
Mining into strata disturbed by previous mining operations either above or below may sometimes result in severe strata control problems. These interaction problems, associated with most multiple-seam mining operations, are very common in the Appalachian coal region and are the subject of this dissertation. On the basis of both theoretical and empirical analyses, using statistical analysis, numerical modeling, and photoelastic modeling methods in conjunction with the analysis of numerous case studies, a comprehensive, integrated model has been constructed and represented by a computer program called "MSEAM”. Using this comprehensive model, possible interaction problems under certain geological and mining conditions can be first predicted based on rules determined either empirically or statistically. Then, detailed analyses using different interaction mechanisms -- pillar load transfer, arching effect, upper seam subsidence, inner- burden bending, and innerburden shearing -- can further determine the area or degree of possible interaction in both under- and over-mining situations. Special geologic and mining factors controlling interaction are also summarized by indices for an independent interaction prediction. This integrated model has been validated by back·analysis of several case studies. Full descriptions of multivariate statistical analysis, photoelastic modeling technique, quantization of various interaction mechanisms, and development of the comprehensive model are included.
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.
A Characterization and Determination of the Coal Reserves and Resources of Southwest Virginia
Westman, Erik C. (Virginia Tech, 1999-04-14)
Coal mining and timber are the two primary industries supporting the people of Southwest Virginia. Coal mining has occurred for more than 100 years, but production has dropped since reaching a peak in 1990. In order to properly plan with remaining coal production a study was conducted to characterize and estimate coal resources. Seam thickness was found to be the parameter which most influenced resource levels. An economic model was developed to determine which portion of the reserves could economically be extracted. It was found that 3.95 billion tons, or 14% of the remaining resource, is economic under current mining conditions. More than 60% of these reserves, however, are in deep seams which require shafts to be constructed prior to initiation of mining.
Coal resource characterization using the theory of coregionalized variables
Unal, Ahmet (Virginia Polytechnic Institute and State University, 1986)
A typical coal resource characterization study calls for estimating thickness, density, and quality parameters over a block or node simultaneously. Traditionally, estimation has been done for each variable independent of the other variables. The methods range from the well known polygonal and distance weighting methods to the geostatistical method of kriging. None of these methods takes the correlations between the variables into account explicitly. A comprehensive study has been undertaken to determine whether the joint estimation technique of cokriging may be used to utilize intervariable correlations in increasing the accuracy of estimation. Seam thickness, density, ash, calorific value, and sulphur have been studied to determine whether they are cross-correlated. Significant cross-correlations have been found to exist between ash content, density, and calorific value, where the rank of the coal is stable. A survey and a case study indicated that seam thickness may also be cross-correlated with ash content and density. Subsequently, separate kriging and cokriging results have been subjected to comparison via a cross-validation procedure. After normalization, cokriging has provided substantial improvements over kriging in estimating thickness, density, and ash content. Moreover, cokriging performed well in replicating the correlation schemes where kriging occasionally failed. In this study, geostatistical methods have been found to produce results in compliance with their probabilistic premises. A general purpose geostatistics software package has been written to carry out modeling and part of the research on a personal computer. This package has been designed to provide many advantages over the existing costly and black-box type software.
Computer aided blast fragmentation prediction
Exadaktylos, George E. (Virginia Tech, 1988-11-15)
The complex and non-linear nature of blast fracturing have restricted common blast design mostly to empirical approaches. The code developed for this investigation avoids both empiricism and large memory requirement in order to simulate the pattern of interacting radial fractures from an array of shotholes, at various burdens and spacings, and in simultaneous and delayed modes. The resultant pattern is analyzed and a fragment size distribution calculated. The rules governing the distribution of radial cracks and the way in which they interact are based on model scale experiments conducted by various investigators. Calculated fragment size- distribution agree with data from the field. Powder factor dependence of fragmentation results is also well described by the model. The effect of discontinuities on rock fragmentation by blasting is also incorporated into the model. Discontinuities which are open and filled with air or soil-like material affect destructively the transmission of strain waves and propagation of cracks in the rock mass. These discontinuities can be incorporated into the simulation by inserting cracks to represent them. The cracks representing discontinuities will then terminate the cracks produced by blasting where they intersect. On the other hand, tight joints without filling material or with filling material but with a high bond strength and acoustic impedance close to that of the medium do not affect in a negative way the transmission of shock waves in the rock mass. A mathematical model was developed to treat these discontinuities which was based on principles from Linear Elastic Fracture Mechanics theory and Kuznetsov's equation which relates the mean fragment size obtained to the blast energy, hole size and rock characteristics.
Economic and system feasibility study of municipal waste stowage in underground coal mines
Grimes, Janet A. (Virginia Tech, 1995-12-15)
Public concern about surface disposal of municipal waste offers the mining industry potentially enormous economic and environmental opportunities. If underground space created by mining can successfully be utilized for safe waste stowage during the mining process, there will be immediate and substantial benefits to all sectors of the underground mining industry. To investigate an integrated system of mining and waste stowage, an economic and feasibility model was developed. Major issues include waste transportation, emplacement area, waste characteristics after emplacement, and alterations to current mining operations. In this preliminary investigation, economic feasibility is the basis for comparison between alternative systems in this research. Past and existing underground waste disposal systems are used to evaluate the model.
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 Vibration on the Penetration Resistance and Pore Water Pressure in Sands
Bonita, John Anthony (Virginia Tech, 2000-07-28)
The current approach for using cone penetration test data to estimate soil behavior during seismic loading involves the comparison of the seismic stresses imparted into a soil mass during an earthquake to the penetration resistance measured during an in-situ test. The approach involves an indirect empirical correlation of soil density and other soil related parameters to the behavior of the soil during the loading and does not involve a direct measurement of the dynamic behavior of the soil in-situ. The objective of this research was to develop an approach for evaluating the in-situ behavior of soil during dynamic loading directly through the use of a vibrating piezocone penetrometer. Cone penetration tests were performed in a large calibration chamber in saturated sand samples prepared at different densities and stress levels. A total of 118 tests were performed as part of the study. The piezocone penetrometer used in the investigation was subjected to a vibratory load during the penetration test. The vibratory units used in the investigations were mounted on top of a 1m section of drill rod that was attached at the lower end to the cone penetrometer. Pneumatic impact, rotary turbine, and counter rotating mass vibrators were used in the investigation. The vibration properties generated by the vibratory unit and imparted into the soil were measured during the penetration test by a series of load cells and accelerometers mounted below the vibrator and above the cone penetrometer, respectively. The tip resistance, sleeve friction and pore water pressure were also measured during the test by load cells and transducers in the cone itself. The vibration and cone data were compiled and compared to evaluate the effect of the vibration on the penetration resistance and pore water pressure in the soil mass. The results of the testing revealed that the influence of the vibration on the penetration resistance value decreased as the density and the mean effective stress in the soil increased, mainly because the pore water pressure was not significantly elevated throughout the entire zone of influence of the cone penetometer at the elevated stress and density conditions. An analysis of the soil response during the testing resulted in the generation of a family of curves that relates the soil response during the vibratory and static penetration to the vertical effective stress and density of the soil. The data used to generate the curves seem to agree with the proposed values estimated through the empirical relationship. An evaluation of the effects of the frequency of vibration was also performed as part of the study. The largest reduction in penetration resistance occurred when the input vibration approximated the natural frequency of the soil deposit, suggesting that resonance conditions existed between the input motion and the soil. An energy-based approach was developed to compare the energy imparted into the soil by the vibrator to the energy capacity of the soil. The input energy introduced into the soil mass prior to the reduction in penetration resistance agrees well with the energy capacity of the soil, especially in tests at the low effective stress level where a high excess pore water pressure was observed.
Estimation of Southwest Virginia coal reserves
Westman, Erik C.; Haycocks, Christopher; Zipper, Carl E. (Virginia Cooperative Extension, 2000)
Coal mining in Virginia's Richmond basin was the first recorded production in the United States (Henderson, 1985). Since that production, more than 2.1 billion tons of coal have been extracted from three primary areas within the state: the Richmond basin, the Valley coal fields, and the Southwest Virginia coal field (Brown et al., 1952; VCCER, 1998).
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.
Forecast of Virginia coal production
Crabtree, Walter A. (Virginia Tech, 1995-04-15)
This thesis provides a model for forecasting coal production rates in southwest Virginia. A multiple linear regression model is developed for the forecasting process. The model includes six independent variables: Virginia coal price times Virginia coal mining productivity (x₁), Virginia mining company production levels (x₂), Virginia coal reserves (x₃), U.S. domestic electricity consumption (x₄), U.S. coal exports (x₅), and U.S. domestic industrial (includes coke) coal consumption (x₆). Historical values for the six variables from 1979 to 1993 were used in generating the multiple linear regression model coefficients. The model captures 86.87% of the variation in Virginia coal production over this period. The forecast from 1994 to 2010 was generated by using forecasted values for the six independent variables. The sensitivity of the model was tested by slightly changing the values of selected independent variables. The results indicate a decline in Virginia coal production to approximately 32 million tons in 2010. Under more favorable conditions, the model results indicate that the coal production levels will remain approximately steady. Under less favorable economic conditions, the model results indicate that Virginia coal production levels will be reduced by more than 50% by the year 2010. These results were also supported by a curve fitting exercise based on the work of M. King Hubbert (1969 and 1973). Hubbert states that the production of a non-renewable natural resource follows a normal or lognormal curve. The peak production level will occur when approximately have of the reserves have been mined or slightly before. Approximately 2 billion tons of coal has been mined in southwest Virginia. Current recoverable reserves are estimated at 1.5 billion tons.
Gateroad Design in Overlying Multi-Seam Mines
Luo, JunLu (Virginia Tech, 1997-05-02)
There are two major design problems for upper seam longwall gateroads operating in a multi-seam environment. The first is to determine the location, magnitude and duration of stress transferred from lower seam mines; and the second is to predict the effect of stress transferred from lower seam mines on opening stability. To solve these problems for both longwall and room-and-pillar mines, case study data were collected and analyzed to develop empirical models predicting upper seam damage created by mining activities in the lower seam. Analysis showed vertical movement in the upper seam and roof CMRR (Coal Mine Roof Rating) to be the controlling factors in damage prediction and, therefore, gateroad planning and design. The relationship between the predicted damage rating and the gateroad stability was established and quantified. To simplify the application of design procedures developed for longwall gateroad systems, the criteria were incorporated in a Windows-based, multi-interface software , UGLY (Upperseam Gateroad Longwall Stability). The programming language was Visual Basic, and the program's design capabilities were validated and demonstrated using case study data.
Geotechnical charcterization of coal refuse for use as a backfill material
Bowman, Charles H. (Virginia Tech, 1991-04-19)
Both active and residual mine subsidence resulting from underground coal mining have caused surface damage to land and structures. A method of subsidence mitigation successfully used abroad, and to a much lesser extent in U.S. coal mines, is backfilling. In addition to the possible benefits of subsidence mitigation, backfilling has the potential to increase coal recovery, enhance ventilation control, and to minimize mine fires. Backfilling can also be used as a means of mine refuse disposal, provided the refuse is a suitable fill material. A Iiterature review has been made of the various backfilling practices and stowing materials that have been used in both underground hardrock and coal mines. The mechanics of fill support were also reviewed, as well as how the physical properties of a stowing material affect its ability to provide ground support. Based on this review, a testing program was conducted to examine properties of coal refuse which are pertinent to its placement and its ability to act as a ground support material. The testing program consisted of the slake durability test, plasticity test (Atterberg's Limits), grain-size analysis, standard Proctor compaction test, falling-head permeability test, and triaxial compression test. Based on the geotechnical properties of the refuse which was sampled, it was determined to be inadequate as a backfill material.
Ground control ramifications and economic impact of retreat mining on room and pillar coal mines
Kumar, Arun (Virginia Polytechnic Institute and State University, 1986)
As the coal reserves at shallow depths become exhausted companies have to develop deeper deposits and increase percentage extraction to maintain production levels. Total extraction for room and pillar mines can only be achieved by pillar extraction. The unsupported roof increases during pillar extraction and hence the cost of ground control also increases. Nevertheless, pillar extraction where possible has many potential advantages such as decreased operating cost, increased utilization of reserves, and extended life of the mine. There are several variables such as depth, mining height, rock strength, mining geometry, roof and floor conditions, and retreat mining methods, which affect pillar extraction cost. Cost components of pillar extraction are classified as direct, indirect, fixed, and subsidence compensation costs. A discounted cash flow pillar extraction cost simulator has been developed and used to compute total pillar extraction cost for a variety of conditions and to explore the possibilities of optimizing ground control and retreat mining techniques to maximize extraction ratio. The computer program computes the safe and optimum pillar dimensions and determines the suitable pillar extraction method for the computed pillar width. Pillar extraction cost components are generated and totalled using the net present value method by the simulator. The total extraction cost simulator evaluates the potential advantages of pillar extraction and tests individual variables for sensitivity to changes in other variables attributable to ground control and pillar extraction techniques. Cost of pillar extraction per ton of coal versus depth is presented in the form of a simple nomogram by the simulator. The simulator can be used to determine the economic feasibility of pillar extraction at a particular depth, geologic and mining environment when the market price of mined coal is known.
An Improved Model for Prediction of PM10 from Surface Mining Operations
Reed, William Randolph (Virginia Tech, 2003-03-21)
Air quality permits are required for the construction of all new surface mining operations. An air quality permit requires a surface mining operation to estimate the type and amount of pollutants the facility will produce. During surface mining the most common pollutant is particulate matter having an aerodynamic diameter less than 10 microns (PM10). The Industrial Source Complex (ISC3) model, created by the United States Environmental Protection Agency (U.S. EPA), is a model used for predicting dispersion of pollutants from industrial facilities, including surface mines and quarries. The use of this model is required when applying for a surface mining permit. However, the U.S. EPA and mining companies have repeatedly demonstrated that this model over-predicts the amount of PM10 dispersed by surface mining facilities, resulting in denied air quality permits. Past research has shown that haul trucks create the majority (80-90%) of PM10 emissions from surface mining operations. Therefore, this research concentrated on improving the ISC3 model by focusing on modeling PM10 emissions from mobile sources, specifically haul trucks at surface mining operations. Research into the ISC3 model showed that its original intended use was for facilities that emit pollutants via smoke stacks. The method used to improve the ISC3 model consisted of applying the dispersion equation used by the ISC3 model in a manner more representative of a moving haul truck. A new model called the Dynamic Component Program was developed to allow modeling of dust dispersion from haul trucks. To validate the Dynamic Component Program, field experiments were designed and conducted. These experiments measured PM10 from haul trucks at two different surface mining operations. The resulting analysis of the Dynamic Component Program, ISC3 model, and the actual field study results showed that the Dynamic Component Program was a 77% improvement over the ISC3 model overall.
Improved quarry design using deterministic and probablistic techniques
Bullock, John C. (Virginia Tech, 1993-09-11)
Limestone and dolomite quarries were mapped to determine specific slope failure mechanisms for the various geological and structural conditions. Wedge failure and plane failure were determined to be the most influential mechanisms. Algorithms for analyzing these mechanisms were incorporated into the software package PSLOPE. The program is designed to facilitate progressive stability evaluation of quarry high walls as mining continues and permits calculation of safety factors and probabilistic reliability. Safety factor evaluations with the potential for back-analysis and sensitivity studies are included to investigate alternative high wall designs. Reliability analysis using Monte Carlo sampling minimizes uncertainty and allows the use of all available data in a stability evaluation. E~tensive "help" menus are incorporated into the program. The "help" menus include ranges of physical properties such as cohesion and friction angle for specific lithologic units determined from published research. This package includes an optimum design protocol that can be followed to avoid massive failure. The program was developed in conjunction with the quarry industry and is demonstrated through technical problem solving and a detailed case study. A large carbonate quarry in the eastern U.S. was studied in detail to demonstrate the utility of PSLOPE.
Interactive prediction software for underlying multi-seam design
Kanniganti, Ravi S. (Virginia Tech, 1996-01-29)
An extensive review of multi-seam under-mining literature was conducted and a data base of case studies was compiled. A critical review of the design principles outlined in this literature resulted in the compilation of specific design criteria for the design of lower seam mines. Analysis of this criteria demonstrated the necessity for a protocol for the design of unsymmetrically loaded pillars. Such a design criteria was developed using finite element methods for a wide range of possible loading conditions. This design criteria can be utilized for underlying pillar design when the loading conditions can be determined. To facilitate using all the under-mining research results by field/planning engineers a Windows™ based software package was developed. This software package contains a multi-seam tutorial, analytical tools and a case history database. The software is very friendly and fully interactive and results of analysis can be verified against case study data included in the program.
Investigation into yield pillar behavior and design considerations
Chen, Gang (Virginia Polytechnic Institute and State University, 1989)
Adopting yield pillars has been considered an effective way of alleviating ground control problems and increasing production. The purpose of this research was to study the behavior of yield pillars and to develop the design criteria. After a literature review, two 2-D finite element models were developed, each following a different non-linear approach. The first model adopted the successive iteration technique incorporated with the Mohr-Coulomb yield criterion. The second followed the elastic—plastic approach, implementing a generalized Von Mises yield criterion. Extensive underground monitoring was conducted and the finite element models were compared with the field data, both yielding promising results. Three different longwall entry layouts were investigated. The yield-stable-yield pillar system was considered to be the best design. A parametric analysis was also performed. The triaxial factor and Poisson's ratio were found to be the most important material properties affecting pillar yielding. The progressive failure hypothesis for pillar design was critically examined. The analysis suggested that the formulation defining the stress distribution in the yield zone under this hypothesis may be satisfied only in extreme cases and, therefore, the actual distribution can be different. An improved equation, describing the stress distribution in the yield zone, was derived by statistically analyzing the results of finite element simulations. The latter equation fitted the observed field data better than did the original equation, and it was further developed for estimation of yield zone width. Consideration was also given to yield pillar design. Three possible yield pillar sizes were proposed in this paper. The maximum yield pillar size was considered to be twice the width of the yield zone. Based on the pressure arch concept, the minimum yield pillar size was determined by accepting that yield pillars were only supporting the rock strata under this pressure arch. A suggested yield pillar size was obtained by selecting a size which would force the peak stress at the center of the yield pillar to equal the average tributary stress. The case studies conducted in this research indicated that the predicted yield pillar sizes were reasonably accurate.
Investigation of a method for monitoring stress changes in the burst prone seams of southwestern Virginia
Gross, Brett Ivan (Virginia Tech, 1988-05-05)
A review of coal bumps. their nature. causes. prediction. prevention. and mitigation is presented. The design and construction of a borehole stressmeter is discussed. Laboratory testing. which yielded promising results of the stressmeter (inclusion) is presented along with preliminary field test results. Laboratory testing involved comparison with the results of a two-dimensional finite element model of the physical laboratory test with those of the physical test itself. Results correlated well. The results of the field test indicate the need for further research into the practical application of the solid inclusion method in the field.
Layout design for interactive zones in longwall multiple seam mining
Forrest, Peter (Virginia Tech, 1988-08-05)
Appalachia requires design guidelines for the increasingly popular multi-seam longwall method. Entry layouts often depart from the ideal when finally developed. The thesis examines the occurrence of ground control problems, and possibilities for improvements in strata control, in a variety of undermining situations. The effects of upper seam loading on undermining operations are invest~gated using physical modelling. Photoelastic stress analysis is used as a powerful research tool to analyze complex multiple seam entry systems. Yield pillar use is also examined, in anticipation of their widespread application for ground control. Case examples support the research findings, and specific conclusions aim to assist layout design in interactive zones.

Browsing by Author "Haycocks, Christopher"

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