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Effects of overburden characteristics on dynamic failure in underground coal mining

International Journal of Mining Science and Technology 2017年第1期27卷 121-129页

作者： Lawson Heather E. Tesarik Douglas larson mark k Abraham Habte NIOSH Office of Mine Safety and Health ResearchGround Control BranchSpokane WA 99207USA

Dynamic failures, or ‘‘bumps", remain an imperative safety concern in underground coal mining, despite significant advancements in engineering controls. The presence of spatially discrete, stiff roof units are one feature that has been linked to these events. However, an empirical stratigraphic review indicates that no significant difference exists in the relative commonality of discrete units between bumping and non-bumping deposits. Instead an apparent relationship exists between reportable bumping and the overall stiffness of the host rock. However, this initial study is too simplistic to be conclusive; to weight the relative impact of changes in a single variable, such as the thickness or location of sandstone members, it must be examined in isolation—i.e., in a setting where all other variables are held *** modelling provides this setting, and the effects of variability in a stiff discrete member in a hypothetical longwall mining scenario are investigated within the context of three stratigraphic ‘‘types",Compliant, Intermediate and Stiff. A modelling experiment examines changes in rupture potential in stiff roof units for each stratigraphic type as discrete unit thickness and location are manipulated through a range of values. Results suggest that the stiff-to-compliant ratio of the host rock has an impact on the relative stress-inducing effects of discrete stiff members. In other words, it is necessary to consider both the thickness and the distance to the seam, within the context of the host rock, to accurately anticipate areas of elevated rupture-induced hazard; acknowledging the presence of a discrete unit within the overburden in general terms is an insufficient indicator of risk. This finding helps to refine our understanding of the role of individual stiff, strong roof members in bumping phenomena, and suggests that a holistic view of overburden lithology and site-specific numerical modelling may be necessary to improve miner safety.

关键词： Dynamic failure Coal mining Bumps Bounces

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Laboratory investigation of the anisotropic confinement-dependent brittle-ductile transition of a Utah coal

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International Journal of Mining Science and Technology 2021年第1期31卷 51-57页

作者： Bo-Hyun kim mark k.larson Mine Safety Branch CDC/NIOSH/SMRDSpokaneWA 99207USA

This paper was developed as part of an effort by the National Institute for Occupational Safety and Health(NIOSH)to identify risk factors associated with bumps in the prevention of fatalities and accidents in highly stressed,bump-prone ground *** of failure mechanism with increasing confinement,from extensional-to shear-dominated failure,are widely observed in the rupture of intact specimens at the laboratory scale and in rock *** the previous analysis conducted in 2018,both unconfined and triaxial compressive tests were conducted to investigate the strength characteristics of some specimens of a Utah coal,including the spalling limits,the ratio of apparent unconfined compressive strength(AUCS)to unconfined compressive strength(UCS),the damage characteristics,and the postyield *** mechanical characteristics were found to be strongly anisotropic as a function of the orientation of the cleats relative to the loading ***,the transition from extensional to shear failure at the given confinements was not clearly *** this study,a total of 20 specimens were additionally prepared from the same coal sample used in the previous study and then tested under both unconfined and triaxial compressive *** different confining stresses are used as analogs for different width-to-height(W/H)ratios of pillar *** the W/H ratios of the specimens were not directly considered during testing,the equivalent W/H ratios of a pillar as a function of the confining stresses were estimated using an existing empirical *** to this relationship,theW/H atwhich in-situ pillar behavior would be expected to transition from brittle to ductile is identified.

关键词： Bump-prone ground conditions A Utah coal Anisotropic Equivalent W/H ratios of a pillar

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Development of a fault-rupture environment in 3D: A numerical tool for examining the mechanical impact of a fault on underground excavations

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International Journal of Mining Science and Technology 2019年第1期29卷 105-111页

作者： Bo-Hyun kim mark k.larson Spokane Mining Research Division CDC/NIOSH

While faults are commonly simulated as a single planar or non-planar interface for a safety or stability analysis in underground mining excavation, the real 3D structure of a fault is often very complex, with different branches that reactivate at different times. Furthermore, these branches are zones of nonzero thickness where material continuously undergoes damage even during interseismic periods. In this study, the initiation and the initial evolution of a strike-slip fault was modeled using the FLAC3D software program. The initial and boundary conditions are simplified, and mimic the Riedel shear experiment and the constitutive model in the literature. The FLAC3D model successfully replicates and creates the 3D fault zone as a strike-slip type structure in the entire thickness of the model. The strike-slip fault structure and normal displacement result in the formation of valleys in the model. Three panels of a longwall excavation are virtually placed and excavated beneath a main valley. The characteristics of stored and dissipated energy associated with the panel excavations are examined and observed at different stages of shear strain in the fault to evaluate bump potential. Depending on the shear strain in the fault, the energy characteristics adjacent to the longwall panels present different degrees of bump potential, which is not possible to capture by conventional fault simulation using an interface.

关键词： 3D fault zone Strike-slip fault FLAC3D Bump potential Energy characteristics

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Applying robust design to study the effects of stratigraphic characteristics on brittle failure and bump potential in a coal mine

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International Journal of Mining Science and Technology 2018年第1期28卷 137-144页

作者： Bo-Hyun kim mark k.larson Heather E.Lawson Spokane Mining Research Division NIOSH/CDC

Bumps and other types of dynamic failure have been a persistent, worldwide problem in the underground coal mining industry, spanning *** example, in just five states in the *** 1983 to 2014,there were 388 reportable *** significant advances in mine design tools and mining practices,these events continue to *** conditions have been associated with bump potential, such as the presence of stiff units in the local *** effect of a stiff sandstone unit on the potential for coal bumps depends on the location of the stiff unit in the stratigraphic column, the relative stiffness and strength of other structural members, and stress concentrations caused by *** study describes the results of a robust design to consider the impact of different lithologic risk factors impacting dynamic failure *** the inherent variability of stratigraphic characteristics in sedimentary formations,such as thickness, engineering material properties, and location, is significant and the number of influential parameters in determining a parametric study is large, it is impractical to consider every simulation case by varying each parameter ***, to save time and honor the statistical distributions of the parameters, it is necessary to develop a robust design to collect sufficient sample data and develop a statistical analysis method to draw accurate conclusions from the collected *** this study,orthogonal arrays, which were developed using the robust design, are used to define the combination of the(a) thickness of a stiff sandstone inserted on the top and bottom of a coal seam in a massive shale mine roof and floor,(b) location of the stiff sandstone inserted on the top and bottom of the coal seam,and(c) material properties of the stiff sandstone and contacts as interfaces using the 3-dimensional numerical model, *** completion of the numerical experiments, statistical and multivariate analysis are performed using

关键词： Bumps Robust design FLAC3D Plastic dissipated energy Multiple regression

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User-friendly finite element design of main entries, barrier pillars,and bleeder entries

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International Journal of Mining Science and Technology 2018年第1期28卷 3-10页

作者： William G.Pariseau mark k.larson Heather E.Lawson Douglas R.Tesarik Department of Mining Engineering University of Utah Spokane Mining Research Division NIOSH

This contribution describes development and application of a user-friendly finite element program,UT3PC, to address three important problems in underground coal mine design:(1) safety of main entries,(2) barrier pillar size needed for entry protection, and(3) safety of bleeder entries during the advance of an adjacent longwall *** the finite element method is by far the most popular engineering design tool of the digital age, widespread use by the mining community has been impeded by the relatively high cost of and the need for lengthy specialized training in numerical *** of UT3PC overcomes these impediments in three easy ***, a material properties file is prepared for the considered ***, mesh generation is automatic through an interactive process.A third and last step is simply execution of the *** using data from several western coal mines illustrate the ease of using the application for analysis of main entries, barrier pillars, and bleeder entry safety.

关键词： Finite element Coal Mine layout design Main entries Barrier pillars Bleeder entries

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Investigation of the anisotropic confinement-dependent brittleness of a Utah coal

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International Journal of Coal Science & Technology 2021年第2期8卷 274-290页

作者： Bo-Hyun kim Gabriel Walton mark klarson Steve Berry CDC/NIOSH 315 E.Montgomery Ave.SpokaneWAUSA Department of Geology and Geological Engineering Colorado School of MinesGoldenCOUSA Department of Geological Engineering Montana TechButteMTUSA

Changes of failure mechanism with increasing confinement,from extensional to shear-dominated failure,are widely observed in the rupture of intact specimens at the laboratory scale and in rock *** an analysis published in 2018,both unconfined and triaxial compressive tests were conducted to investigate the strength characteristics of 84 specimens of a Utah coal,including the spalling limits,the ratio of apparent unconfined compressive strength to unconfined compressive strength(UCS),the damage characteristics,and the post-yield *** mechanical characteristics were found to be strongly anisotropic as a function of the orientation of the cleats relative to the loading direction,defined as the included angle.A total of four different included angles were used in the work performed in *** authors found that the degree of anisotropic strength differed according to the included ***,the transition from extensional to shear failure at the given confinements was not clearly *** this study,a total of 20 specimens were additionally prepared from the same coal sample used in the previous study and then tested under both unconfined and triaxial compressive *** the authors already knew the most contrasting cases of the included angles from the previous work using the four included angles,they chose only two of the included angles(0°and 30°)for this *** the triaxial compressive tests,a greater confining stress than the mean UCS was applied to the specimens in an attempt to identify the brittle-ductile transition of the *** new results have been compiled with the previous results in order to re-evaluate the confinement-dependency of the coal ***,the different confining stresses are used as analogs for different width-to-height(W/H)conditions of pillar *** the W/H ratios of the specimens were not directly considered during testing,the equivalent W/H ratios of a pillar as a function of

关键词： Utah coal Spalling limit AUCS/UCS ratio Damage characteristic Post-yield dilatancy Anisotropic

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Investigating low dispersion isotope dissolution Lu-Hf garnet dates via in situ Lu-Hf geochronology,kanchenjunga Himal

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Geoscience Frontiers 2024年第3期15卷 137-145页

作者： kyle P.larson John M.Cottle mark Button Brendan Dyck Iva Lihter Sudip Shrestha Department of Earth Environmental and Geographic SciencesUniversity of British ColumbiaOkanaganKelownaCanada Department of Earth Science University of CaliforniaSanta BarbaraUSA Fipke Laboratory for Trace Element Research University of British ColumbiaOkanaganKelownaCanada

Re-examination of three specimens from the kanchenjunga Himal of Nepal via in situ Lu-Hf garnet geochronology yields evidence of multiple garnet growth *** analyses from grain cores in two specimens define Paleozoic regressions whereas analyses from grain rims in the same specimens define low-precision regressions consistent with the timing of Himalayan *** dates contrast with previously published low dispersion,ca.290 Ma isotope dissolution(ID)Lu-Hf garnet dates for the same *** of Lu and spot age distribution in representative grains from the specimens examined yields calculated dates that approximate the Permian-age regressions through the original ID *** findings demonstrate that it is possible to generate low dispersion ID Lu-Hf data from multigenerational garnet with significantly different-age growth events when approximately equal proportions of the different age reservoirs are included in multi-component aliquots.

关键词： Lu-Hf geochronology In situ Lu-Hf geochronology kanchenjunga Himal

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Geochemistry and in-situ U-Th/Pb Geochronology of the Jambil Meta-Carbonatites, Northern Pakistan: Implications on Petrogenesis and Tectonic Evolution

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Journal of Earth Science 2023年第1期34卷 70-85页

作者： Asad khan Shah Faisal kyle P.larson Delores M.Robinson Huan Li Zaheen Ullah mark Button Javed Nawab Muhammad Farhan Liaqat Ali Muhammad Ali Department of Geology FATA UniversityFR Kohat26100Pakistan National Center of Excellence in Geology University of PeshawarPeshawar25130Pakistan Department of Earth Environmental and Geographic SciencesUniversity of British ColumbiaOkanaganKelownaBCVIV 1V7Canada Department of Geological Sciences the University of AlabamaBevill BuildingTuscaloosaAlabama35487USA key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring Ministry of EducationSchool of Geosciences and Info-PhysicsCentral South UniversityChangsha410083China Department of Environmental Sciences Abdul Wali Khan UniversityMardan23200Pakistan Marine Science Department Zhejiang UniversityZhoushan316021China

The putative Jambil meta-carbonatites of Swat,northern Pakistan,occur as discrete intrusions into the Proterozoic Manglaur Formation,which are difficult to be distinguished from nearby calc-silicate marble because both rock types experienced regional metamorphism during Himalayan orogenesis that resulted in similar mosaic textures and mineral *** are often significant repositories of economic mineral resources and,therefore,are important to be distinguished from calc-silicate *** present new geochemical and geochronology data to distinguish between the two rock types and interpret the petrogenesis and tectonic evolution of the Jambil *** rock chemical data from the Jambil meta-carbonatites show characteristically high rare earth element(REE),Sr contents and lack of negative Eu anomaly,consistent with average calcio-carbonatite values worldwide and an igneous *** than 0.5 wt.% SrO in the metacarbonatites and SrO> 0.15 wt.% in constituent rock forming calcite are discriminating signatures of the Jambil ***,the Jambil meta-carbonatites are relatively depleted in Rb,Nb,Ta,Ti,Zr and Hf,relatively enriched in Ba,Th,Sr,and have a high LREE/HREE ratio when normalized to primitive *** carbon and oxygen isotope compositions vary from-3.5‰ to-4.3‰and from 9.7‰ to 12.3‰,*** geochemical characteristics indicate generation of the carbonatites through small degree of partial melting from a carbonated eclogitic ***-situ,U/Pb analysis of titanite indicates that the Jambil meta-carbonatites were emplacement at 438 ±3 *** combined with regional geological observations,we interpret the emplacement of the Jambil metacarbonatites to have taken place during the Silurian back arc extension within greater Gondwana and mark a transition from a compressional tectonic regime,brought about by collision of microcontinental blocks along the northern margin of Gondwana,to post-orogenic

关键词： Swat N Pakistan meta-carbonatites geochemistry LA-ICP-MS titanite&monazite UTh/Pb geochronology C and O isotopes Gondwana margin

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Evaluating a combined bowel preparation for small-bowel capsule endoscopy:a prospective randomized–controlled study

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Gastroenterology Report 2020年第1期8卷 31-35,I0001,I0002页

作者： Stephanie L.Hansel Joseph A.Murray Jeffrey A.Alexander David H.Bruining mark V.larson Thomas F.Mangan Ross A.Dierkhising Ann E.Almazar Elizabeth Rajan Division of Gastroenterology and Hepatology Mayo ClinicRochesterMNUSA Division of Biomedical Statistics and Informatics Mayo ClinicRochesterMNUSA

Background:Capsule endoscopy(CE)is frequently hindered by intra-luminal *** aim was to determine whether a combination bowel preparation would improve small-bowel visualization,diagnostic yield,and the completion rate of ***:Single-blind,prospective randomized–controlled study of outpatients scheduled for ***-preparation subjects ingested 2 L of polyethylene glycol solution the night prior to CE,5mL simethicone and 5mg metoclopramide 20 minutes prior to CE and laid in the right lateral position 30 minutes after swallowing *** had no solid food after 7 *** night prior to CE and no liquids 4 hours prior to *** completed a satisfaction *** readers completed a small-bowel-visualization ***:Fifty patients were prospectively enrolled(56%female)with a median age of 54.4 years and 44 completed the study(23 patients in the control group and 21 in the preparation group).There was no significant difference between groups on quartile-based small-bowel visualization(all P>0.05).There was no significant difference between groups in diagnostic yield(P=0.69),mean gastric(P=0.10)or small-bowel transit time(P=0.89).The small-bowel completion rate was significantly higher in the preparation group(100%vs 78%;P=0.02).Bowel-preparation subjects reported significantly more discomfort than controls(62%vs 17%;P=0.01).Conclusions:Combined bowel preparation did not improve small-bowel visualization but did significantly increase patient *** CE completion rate improved in the preparation group but the diagnostic yield was *** on our findings,a bowel preparation prior to CE does not appear to improve CE performance and results in decreased patient satisfaction(***,***01243736).

关键词： bowel preparation capsule endoscopy small-bowel visualization patient satisfaction

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Large-diameter trees dominate snag and surface biomass following reintroduced fire

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Ecological Processes 2020年第1期9卷 475-487页

作者： James A.Lutz Soren Struckman Tucker J.Furniss C.Alina Cansler Sara J.Germain Larissa *** Darren J.McAvoy Crystal A.kolden Alistair M.S.Smith mark E.Swanson Andrew J.larson Department of Wildland Resources S.J.and Jessie E.Quinney College of Natural ResourcesUtah State University5230 Old Main HillLoganUtah 84322-5230USA School of Environmental and Forest Sciences University of WashingtonBox 352100SeattleWashington 98195USA Management of Complex Systems University of CaliforniaMerced5200 North Lake RoadMercedCalifornia 95343USA Department of Forest Rangelandand Fire SciencesCollege of Natural ResourcesUniversity of Idaho875 Perimeter DriveMoscowIdaho 83844-1133USA School of the Environment Washington State UniversityBox 646410PullmanWashington 99164-6420USA Wilderness Institute W.A.Franke College of Forestry and ConservationUniversity of Montana32 Campus DriveMissoulaMontana 59812USA

The reintroduction of fire to landscapes where it was once common is considered a priority to restore historical forest dynamics,including reducing tree density and decreasing levels of woody biomass on the forest ***,reintroducing fire causes tree mortality that can have unintended ecological outcomes related to woody biomass,with potential impacts to fuel accumulation,carbon sequestration,subsequent fire severity,and forest *** this study,we examine the interplay between fire and carbon dynamics by asking how reintroduced fire impacts fuel accumulation,carbon sequestration,and subsequent fire severity *** pre-fire,and continuing 6 years post-fire,we tracked all live,dead,and fallen trees≥1 cm in diameter and mapped all pieces of deadwood(downed woody debris)originating from tree boles≥10 cm diameter and≥1 m in length in 25.6 ha of an Abies concolor/Pinus lambertiana forest in the central Sierra Nevada,California,*** also tracked surface fuels along 2240 m of planar transects pre-fire,immediately post-fire,and 6 years *** years after moderate-severity fire,deadwood≥10 cm diameter was 73 Mg ha^(−1),comprised of 32 Mg ha^(−1) that persisted through fire and 41 Mg ha^(−1) of newly fallen wood(compared to 72 Mg ha^(−1) pre-fire).Woody surface fuel loading was spatially heterogeneous,with mass varying almost four orders of magnitude at the scale of 20 m×20 m quadrats(minimum,0.1 Mg ha^(−1);mean,73 Mg ha^(−1);maximum,497 Mg ha^(−1)).Wood from large-diameter trees(≥60 cm diameter)comprised 57%of surface fuel in 2019,but was 75%of snag biomass,indicating high contributions to current and future fuel *** of fire does not consume all large-diameter fuel and generates high levels of surface fuels≥10 cm diameter within 6 *** fires are needed to reduce surface fuel loading.

关键词： California Rim Fire Fuel reduction Sierra Nevada mixed-conifer Smithsonian ForestGEO Yosemite Forest Dynamics Plot Yosemite National Park

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