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Pillar design and coal burst experience in Utah Book Cliffs longwall operations

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International Journal of Mining science and Technology 2021年第1期31卷 33-41页

作者： Christopher mark Michael Gauna Mine safety and Health Administration Technical support PittsburghPA 15236USA

Longwall mining has existed in Utah for more than half a *** of this mining occurred at depths of cover that significantly exceed those encountered by most other Us longwall *** cover causes high ground stress,which can combine with geology to create a coal burst *** every longwall mine operating within the Utah’s Book Cliffs coalfield has been affected by coal *** design has been a key component in the burst control strategies employed by mines in the Book ***,most longwall mines employed double-use two-entry yield pillar ***-use signifies that the gate system serves first as the headgate,and then later serves as the tailgate for the adjacent *** the 1996 burst fatality at the Aberdeen Mine,the inter-panel barrier design was *** this layout,a wide barrier pillar protects each longwall panel from the previously mined panel,and each gate system is used just *** paper documents the deep cover longwall mining conducted with each type of pillar design,together with the associated coal burst *** of the six longwall mining complexes in the Book Cliffs having a coal burst history is described on a panel-by-panel *** analysis shows that where the mining depth exceeded 450 m,each design has been employed for about 38000 total m of longwall panel *** double-use yield pillar design has been used primarily at depths less than 600 m,however,while the inter-panel barrier design has been used mainly at depths exceeding 600 *** its greater depth of use,the inter-panel barrier gate design has been associated with about one-third as much face region burst activity as the double-use yield pillar design.

关键词： Longwall Ground control Coal burst Pillar design Yield pillar

Reusing oxide-based pulverised fly ash and medical waste particles to develop electroless nickel composite coatings(Ni–P/fly ash and Ni–P/siO2–Al2O3)

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International Journal of Minerals,Metallurgy and Materials 2020年第8期27卷 1147-1156页

作者： Franco Mayanglambam mark Russell school of Natural and Built Environment Queen’s University BelfastBelfast BT71NNUK Centre for Nanotechnology Indian Institute of Technology GuwahatiGuwahati 781038India

Recycling and reusing materials from waste have become a nexus in the development of sustainable materials,leading to more balanced *** this study,we developed a composite coating by co-depositing recycled ceramic particles,pulverised fly ash(PFA)and medical ceramics(MC),into a nickel–phosphorus matrix using a typical electroless plating *** electron microscopy(sEM)images indicated well-dispersed particles in the Ni–P ***,compared with the MC particles,the PFA particles were distributed scantily with a lower content in the matrix,which could be due to the less impingement effect during the co-deposition.A modified microstructure with refined grains was obtained for the PFA-incorporated composite coating,as seen in the sEM *** X-ray diffraction result of the MC-incorporated composite coating showed the formation of Nix siy phases in addition to the typical Ni3 P phases for the heattreated electroless Ni–P *** heat treatment,the PFA-reinforced composite coating,due to a modified microstructure,exhibited a higher microhardness up to HK0.05818,which is comparable to that of the traditional siC particle-embedded composite coating(HK0.05825).The findings can potentially open up a new strategy to further advance the green approach for industrial surface engineering.

关键词： electroless plating waste ceramics fly ash particles microstructure microhardness

Effects of fertilization on the growth dominance of Inland Northwest forests of the United states

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Forest Ecosystems 2022年第3期9卷 407-416页

作者： Cen Chen Andrew sNelson Terry shaw mark Kimsey University of Idaho Department of ForestRangeland and Fire SciencesMoscowID83844USA

Large trees have disproportionally large competitive advantage in access to light, which has been proposed to increase growth dominance of large trees (e.g., a larger proportion of volume growth than standing volume is in large trees in a stand). Tree growth may also be limited by the availability of other resources besides *** deficiency, especially of nitrogen, is considered common among temperate forests including mixedconifer forests of the Inland Northwest of the United states. Data from a long-term forest nutrition study across four Inland Northwest states were analyzed to evaluate nitrogen×potassium fertilization?s effects on growth dominance over an eight-year period following treatment. Our results show that growth dominance varied substantially across plots in each vegetation series and fertilization treatment, and its mean values generally were at minuscule magnitudes, negative, and not significantly different from 0. We propose that this lack of a clear pattern in growth dominance was the result of the mixed-species composition where shade-tolerant species remained in lower crown positions, yet their relative growth kept pace with large trees. Limited moisture availability at dry sites may have hampered the development of growth dominance. Growth dominance also was lowered by mortality observed among relatively large trees. The largely negative growth dominance across fertilization treatments indicated that small trees seem to have maintained higher relative growth rates than large trees, even if absolute growth was higher among large trees. In the case fertilization does improve stand growth, a significant part of this improved growth will be lost in density-dependent mortality over time if not captured through thinning/harvesting.

关键词： stand dynamics Forest management Nitrogen Potassium Douglas-fir Mixed conifer

Analysis of gateroad stability at two longwall mines based on field monitoring results and numerical model analysis

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International Journal of Mining science and Technology 2019年第1期29卷 35-43页

作者： Gabriel s.Esterhuizen David F.Gearhart Ted Klemetti Heather Dougherty mark van Dyke National Institute for Occupational safety and Health

Coal mine longwall gateroads are subject to changing loading conditions induced by the advancing longwall face. The ground response and support requirements are closely related to the magnitude and orientation of the stress changes, as well as the local geology. This paper presents the monitoring results of gateroad response and support performance at two longwall mines at a 180-m and 600-m depth of *** the first mine, a three-entry gateroad layout was used. The second mine used a four-entry, yieldabutment-yield gateroad pillar system. Local ground deformation and support response were monitored at both sites. The monitoring period started during the development stage and continued during first panel retreat and up to second panel retreat. The two data sets were used to compare the response of the entries in two very different geotechnical settings and different gateroad layouts. The monitoring results were used to validate numerical models that simulate the loading conditions and entry response for these widely differing conditions. The validated models were used to compare the load path and ground response at the two mines. This paper demonstrates the potential for numerical models to assist mine engineers in optimizing longwall layouts and gateroad support systems.

关键词： Coal mining Longwall Gateroad support Numerical models

science of empirical design in mining ground control

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International Journal of Mining science and Technology 2016年第3期26卷 461-470页

作者： mark Christopher MsHA Pittsburgh Safety & Health Technology Center

Many problems in rock engineering are limited by our imperfect knowledge of the material properties and failure mechanics of rock masses. Mining problems are somewhat unique, however, in that plenty of real world experience is generally available and can be turned into valuable experimental *** pillar that is developed, or stope that is mined, represents a full-scale test of a rock mechanics design. By harvesting these data, and then using the appropriate statistical techniques to interpret them,mining engineers have developed powerful design techniques that are widely used around the *** empirical methods are readily accepted because they are simple, transparent, practical, and firmly tethered to reality. The author has been intimately associated with empirical design for his entire career, but his previous publications have described the application of individual techniques to specific problems. The focus of this paper is the process used to develop a successful empirical method. A sixstage process is described: identification of the problem, and of the end users of the final product; development of a conceptual rock mechanics model, and identification of the key parameters in that model;identification of measures for each of the key parameters, and the development of new measures(such as rating scales) where necessary; data sources and data collection; statistical analysis; and packaging of the final product. Each of these stages has its own potential rewards and pitfalls, which will be illustrated by incidents from the author's own experience. The ultimate goal of this paper is to provide a new and deeper appreciation for empirical techniques, as well as some guidelines and opportunities for future developers.

关键词： Design Pillar stope Empirical statistics Modeling

sOME PROPERTIEs OF COMMUTING AND ANTI-COMMUTING m-INVOLUTIONs

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Acta Mathematica scientia 2012年第2期32卷 631-644页

作者： mark Yasuda 9525 Compass Point Drive south San DiegoCA 92126U.S.A.

We define an m-involution to be a matrix K ∈ Cn×n for which Km -= I. In this article, we investigate the class sm （A） of m-involutions that commute with a diagonalizable matrix A E Cn×n. A number of basic properties of sm （A） and its related subclass sm （A, X） are given, where X is an eigenvector matrix of A. Among them, sm （A） is shown to have a torsion group structure under matrix multiplication if A has distinct eigenvalues and has non-denumerable cardinality otherwise. The constructive definition of sm （A, X） allows one to generate all m-involutions commuting with a matrix with distinct eigenvalues. some related results are also given for the class s,, （A） of m-involutions that anti-commute with a matrix A ∈ Cnn×n.

关键词： Centrosymmetric skew-centrosymmetric bisymmetric involution eigenval-ues

An in situ monitoring campaign of a hard rock pillar at great depth within a Canadian mine

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Journal of Rock Mechanics and Geotechnical Engineering 2020年第3期12卷 427-448页

作者： Bradley Forbes Nicholas Vlachopoulos mark s.Diederichs Andrew J.Hyett Allan Punkkinen Department of Geological sciences and Geological Engineering Queen’s UniversityKingstonOntarioK7L 3N6Canada Department of Civil Engineering Royal Military College of CanadaKingstonOntarioK7K 7B4Canada YieldPoint Inc. KingstonOntarioK7M 4W9Canada Normet Canada Ltd. LivelyOntarioP3Y 0B3Canada

A recent research campaign at a Canadian nickel-copper mine involved instrumenting a hard rock sill drift pillar with an array of multi-point rod extensometers,distributed optical fibre strain sensors,and borehole pressure cells(BHPCs).The instrumentation spanned across a 15.24 m lengthwise segment of the relatively massive granitic pillar situated at a depth of 2.44 km within the *** May 2016 and March 2017,the pillar’s displacement and pressure response were measured and correlated with mining activities on the same level as the pillar,including:(1)mine-by of the pillar,(2)footwall drift development,and(3)ore body stoping *** displacements of the pillar,the extensometers provided high temporal resolution(logged hourly)and the optical fibre strain sensors provide high spatial resolution(measured every 0.65 mm along the length of each sensor).The combination of sensing techniques allowed centimetre-scale rock mass bulking near the pillar sidewalls to be distinguished from microstrain-scale fracturing towards the core of the ***,the influence and extent of a mine-scale schistose shear zone transecting the pillar was *** converting measured rock mass displacement to velocity,a process was demonstrated which allowed mining activities inducing displacements to be categorised by time-duration and cumulative *** over half of the analysed mining activities,displacements were determined to prolong for over an hour,predominately resulting in submillimetre cumulative displacements,but in some cases multi-centimetre cumulative displacements were *** time-dependent behaviour was more pronounced within the vicinity of the plumb shear *** measurements were also used to assess selected support member load and elongation mobilisation per mining *** was found that a combined static load and elongation capacity of reinforcing members was essential to maintaining excavation stability,while

关键词： Hard rock pillar Rockburst Rock mass bulking Distributed optical fibre strain sensing Extensometer In situ monitoring High stress Dynamic support

Assessing support alternatives for longwall gateroads subject to changing stress

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International Journal of Mining science and Technology 2021年第1期31卷 103-110页

作者： Gabriel s.Esterhuizen I.Berk Tulu Dave F.Gearhart Heather Dougherty mark Van Dyke National Institute for Occupational safety and Health Pittsburgh Mining Research DivisionPittsburghPA 15236USA West Virginia University MorgantownWV 26506USA

Longwall gateroad entries are subject to changing horizontal and vertical stress induced by redistribution of loads around the extracted *** stress changes can result in significant deformation of the entries that may include roof sag,rib dilation,and floor *** operators install different types of supports to control the ground response and maintain safe access and ventilation of the longwall *** paper describes recent research aimed at quantifying the effect of longwall-induced stress changes on ground stability and using the information to assess support *** research included monitoring of ground and support interaction at several operating longwall mines in the U.s.,analysis and calibration of numerical models that adequately represent the bedded rock mass,and observation of the support systems and their response to changes in *** models were then used to investigate the impact of geology and stress conditions on ground deformation and support response for various depths of cover and geologic *** research results were summarized in two regression equations that can be used to estimate the likely roof deformation and height of roof yield due to longwall-induced stress *** information is then used to assess the ability of support systems to maintain the stability of the *** application of the method is demonstrated with a retrospective analysis of the support performance at an operating longwall mine that experienced a headgate roof *** method is shown to produce realistic estimates of gateroad entry stability and support performance,allowing alternative support systems to be assessed during the design and planning stage of longwall operations.

关键词： Longwall Gateroad support design Coal standing support

Unanticipated multiple seam stresses from pillar systems behaving as pseudo gob–case histories

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International Journal of Mining science and Technology 2017年第1期27卷 131-137页

作者： Gauna Michael mark Christopher Pittsburgh safety and Health Technology Center Mine Safety and Health Administration(MSHA)PittsburghPA 15236USA

Underground coal mining in the U.s. is conducted in numerous regions where previous workings exist above and/or below an actively mined seam. Miners know that overlying or underlying fully extracted coal areas, also known as gob regions, can result in abutment stresses that affect the active mining. If there was no full extraction, and the past mining consists entirely of intact pillars, the stresses on the active seam are usually minimal. However, experience has shown that in some situations there has been sufficient yielding in overlying or underlying pillar systems to cause stress transfer to the adjoining larger pillars or barriers, which in turn, transfer significant stresses onto the workings of the active seam. In other words, the overlying or underlying pillar system behaves as a ‘‘pseudo gob." The presence of a pseudo gob is often unexpected, and the consequences can be severe. This paper presents several case histories, summarized briefly below, that illustrate pseudo gob phenomenon:(1) pillar rib degradation at a West Virginia mine at 335 m depth that contributed to a rib roll fatality,(2) pillar rib deterioration at a Western Kentucky mine at 175 m depth that required pillar size adjustment and installation of supplemental bolting,(3) roof deterioration at an eastern Kentucky mine at 400 m depth that stopped mine advance and required redirecting the section development,(4) coal burst on development at an eastern Kentucky mine at 520 m depth that had no nearby pillar recovery, and(5) coal burst on development at a West Virginia mine at the relatively shallow depth of 335 m that also had no nearby pillar recovery. The paper provides guidance so that when an operation encounters a potential pseudo gob stress interaction the hazard can be mitigated based on an understanding of the mechanism encountered.

关键词： Underground mining Coal Multiple seam Gob Ground control