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International Journal of Mining Science and Technology 2019年第1期29卷 27-33页

作者： Peter Zhang Dave Gearhart Mark Van Dyke Daniel Su Essie Esterhuizen Berk Tulu NIOSH Pittsburgh Mining Research Division(PMRD) Department of Mining Engineering West Virginia University

Roof falls in Longwall headgate can occur when weak roof and high horizontal stress are present. To prevent roof falls in the headgate under high horizontal stress, it is important to understand the ground response to high horizontal stress in the Longwall headgate and the requirements for supplemental roof support. In this study, a Longwall headgate under high horizontal stress was instrumented to monitor stress change in the pillars, deformations in the roof, and load in the cable bolts. The conditions in the headgate were monitored for about six months as the Longwall face passed by the instrumented site.The roof behavior in the headgate near the face was carefully observed during Longwall retreat.Numerical modeling was performed to correlate the modeling results with underground observation and instrumentation data and to quantify the effect of high horizontal stress on roof stability in the Longwall headgate. This paper discusses roof support requirements in the Longwall headgate under high horizontal stress in regard to the pattern of supplemental cable bolts and the critical locations where additional supplemental support is necessary.

关键词： Longwall mining Longwall headgate High horizontal stress Supplemental support

Influence of canopy ratio of powered roof support on Longwall working stability——A case study

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International Journal of Mining Science and Technology 2019年第4期29卷 591-598页

作者： Sylwester Rajwa Tomasz Janoszek Stanis?aw Prusek Department of Extraction Technologies Rockburst and Mining Support Central Mining Institute

The case study describes Longwall coal seam A in a hard coal mine,where Longwall coal face stability loss and periodic roof fall occurrences had been registered.The authors have attempted to explain the situation based on in-situ measurements and observations of the Longwall working as well as numerical simulation.The calculations included several parameters,such as powered roof support geometry in the form of the canopy ratio,which is a factor that influences load distribution along the canopy.Numerical simulations were realized based on a rock mass model representing realistic mining and geological conditions at a depth of 600 m below surface for coal seam A.Numerical model assumptions are described,while the obtained results were compared with the in-situ measurements.The conclusions drawn from this work can complement engineering knowledge utilized at the stage of powered roof support construction and selection in order to improve both personnel safety and Longwall working stability,and to achieve better extraction.

关键词： Coal mining Modelling Powered roof supports Longwall workings Safety Stability

Impact of geo technical factors on strata behavior in Longwall panels of Godavari Valley coal field-a case study

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International Journal of Mining Science and Technology 2019年第2期29卷 335-341页

作者： Veera Reddy Boothukuri Ram Madhav Bhattacharjee Durga Charan Panigrahi Gautam Benerjee Singareni Collieries Company Limited (SCCL) Indian Institute of Technology Indian School of Mines CSIR-Central Institute of Mining and Fuel Research

Understanding the cantilevers formed by thick, massive beds in the near-seam overburden above Longwall panels and the associated loads and strata fracturing effects developed during caving(main and periodic weightings) are key elements for the successful implementation of Longwalls. Such caving mechanisms rely on the geotechnical conditions within the panel. In India, the majority of Longwall downtime and/or roof failures were caused by a lack of knowledge on overburden caveability, in particular when the main and periodic weightings will impact the face and Longwall support selection to effectively mitigate such weightings. Godavari Valley Coal Fields is no exception as Longwall faces were adversely affected due to the presence of thick, massive beds in the near-seam overburden at both Godavarikhani(GDK) 7 and 9 Incline mines. In contrast, overburden weightings were negotiated successfully in GDK10 A and Adriyala Longwall Project(ALP) mines by detailed geotechnical studies, the use of adequate Longwall support capacities, and effective operational practices. Thirteen Longwall panels with varying face width, at different depths have been extracted under massive sandstone beds of 18 m to28 m thickness at GDK 10 A and ALP mines. This study elucidates that the main roof weighting interval decreases with an increase in face width and attains a constant value with further increases in face width under the same geo-mining conditions. In addition, this study also concludes that with increases in face width, the periodic roof weighting interval decreases and shield loads increase. Similarly with increasing panel width to depth ratio, the main and periodic roof weighting intervals decrease but shield loads again increase. Lastly, the strata behaviour of the Longwall face retreated along up-dip direction is demonstrated. The results of this paper improves the mechanistic understanding of the impact of face width,depth and main roof thickness on periodic weighting and associated roof control problems on the Longwall face.

关键词： Longwall mining Roof weightings intervals Shield loadings Face width Cover depth

A case study of the stability of a non-typical bleeder entry system at a U.S.Longwall mine

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International Journal of Mining Science and Technology 2020年第1期30卷 25-31页

作者： T.M.Klemetti M.A.Van Dyke I.B.Tulu D.Tuncay NIOSH Pittsburgh Mining Research Division Pittsburgh 15236USA Department of Mining Engineering West Virginia UniversityMorgantown 26505USA

Longwall abutment loads are influenced by several factors,including depth of cover,pillar sizes,panel dimensions,geological setting,mining height,proximity to gob,intersection type,and size of the gob.How does proximity to the gob affect pillar loading and entry condition?Does the gob influence depend on whether the abutment load is a forward,side,or rear loading?Do non-typical bleeder entry systems follow the traditional front and side abutment loading and extent concepts?If not,will an improved understanding of the combined abutment extent warrant a change in pillar design or standing support in bleeder entries?This paper details observations made in the non-typical bleeder entries of a moderate depth Longwall panel—specifically,data collected from borehole pressure cells and roof extensometers,observations of the conditions of the entries,and numerical modeling of the bleeder entries during Longwall extraction.The primary focus was on the extent and magnitude of the abutment loading experienced due to the extraction of the Longwall panels.Due to the layout of the Longwall panels and bleeder entries,the borehole pressure cells(BPCs)and roof extensometers did not show much change due to the advancing of the first Longwall.However,they did show a noticeable increase due to the second Longwall advancement,with a maximum of about 4 MPa of pressure increase and 5mmof roof deformation.The observations of the conditions showed little to no change from before the first Longwall panel extraction began to when the second Longwall panel had been advanced more than 915 m.Localized pillar spalling was observed on the corners of the pillars closest to the Longwall gob as well as an increase in water in the entries.In addition to the observations and instrumentation,numerical modeling was performed to validate modeling procedures against the monitoring results and evaluate the bleeder design.ITASCA Consulting Group’s FLAC3D numerical modeling software was used to evaluate the bleeder entries.The results of the models indicate

关键词： Abutment loading Longwall Instrumentation Bore hole pressure cells Pillar loading Yield pillar Bleeder pillar

Analysis of monitored ground support and rock mass response in a Longwall tailgate entry

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International Journal of Mining Science and Technology 2018年第1期28卷 43-51页

作者： G.S.Esterhuizen D.F.Gearhart I.B.Tulu NIOSH Pittsburgh Mining Research Division PittsburghPA 15236USA West Virginia University MorgantownWV 26506USA

A comprehensive monitoring program was conducted to measure the rock mass displacements, support response, and stress changes at a Longwall tailgate entry in West Virginia.Monitoring was initiated a few days after development of the gateroad entries and continued during passage of the Longwall panels on both sides of the entry.Monitoring included overcore stress measurements of the initial stress within the rock mass, changes in cable bolt loading, standing support pressure, roof deformation, rib deformation,stress changes in the coal pillar, and changes in the full three-dimensional stress tensor within the rock mass at six locations around the monitoring site.During the passage of the first Longwall, stress measurements in the rock and coal detected minor changes in loading while minor changes were detected in roof deformation.As a result of the relatively favorable stress and geological conditions, the support systems did not experience severe loading or rock deformation until the second panel approached within 10–15 m of the instrumented locations.After reaching the peak loading at about 50–75 mm of roof sag, the cable bolts started to unload, and load was transferred to the standing supports.The standing support system was able to maintain an adequate opening inby the shields to provide ventilation to the first crosscut inby the face, as designed.The results were used to calibrate modeled cable bolt response to field data, and to validate numerical modeling procedures that have been developed to evaluate entry support systems.It is concluded that the support system was more than adequate to control the roof of the tailgate up to the Longwall face location.The monitoring results have provided valuable data for the development and validation of support design strategies for Longwall tailgate entries.

关键词： Longwall mining Support Tailgate Monitoring Coal mining

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 panel.The stress changes can result in significant deformation of the entries that may include roof sag,rib dilation,and floor heave.Mine operators install different types of supports to control the ground response and maintain safe access and ventilation of the Longwall face.This paper describes recent research aimed at quantifying the effect of Longwall-induced stress changes on ground stability and using the information to assess support alternatives.The 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 stress.The 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 scenarios.The 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 changes.This information is then used to assess the ability of support systems to maintain the stability of the roof.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 fall.The 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

Design of a water curtain to reduce accumulations of float coal dust in Longwall returns

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International Journal of Mining Science and Technology 2020年第4期30卷 443-447页

作者： Clara E.Seaman Michael R.Shahan Timothy W.Beck Steven E.Mischler National Institute for Occupational Safety and Health Pittsburgh Mining Research DivisionPittsburghPA 15236USA

Accumulation of float coal dust(FCD)in underground mines is an explosion hazard that affects all underground coal mine workers.While this hazard is addressed by the application of rock dust,inadequate rock dusting practices can leave miners exposed to an explosion risk.Researchers at the National Institute for Occupational Safety and Health(NIOSH)have focused on developing a water curtain that removes FCD from the airstream,thereby reducing the buildup of FCD in mine airways.In this study,the number and spacing of the active sprays in the water curtain were varied to determine the optimal configuration to obtain peak knockdown efficiency(KE)while minimizing water consumption.

关键词： Float coal dust Longwall Water spray Knockdown efficiency Explosion prevention Dust control

Influence of Longwall mining on the stability of gas wells in chain pillars

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International Journal of Mining Science and Technology 2020年第1期30卷 3-9页

作者： Peter Zhang Heather Dougherty Daniel Su Jack Trackemas Berk Tulu CDC NIOSH Pittsburgh Mining Research Division(PMRD)PittsburghPA 15236USA Department of Mining Engineering West Virginia UniversityMorgantownWV 26505USA

Longwall mining has a significant influence on gas wells located within Longwall chain pillars.Subsurface subsidence and abutment pressure induced by Longwall mining can cause excessive stresses and deformations in gas well casings.If the gas well casings are compromised or ruptured,natural gas could migrate into the mine workings,potentially causing a fire or explosion.By the current safety regulations,the gas wells in the chain pillars have to be either plugged or protected by adequate coal pillars.The current regulations for gas well pillar design are based on the 1957 Pennsylvania gas well pillar study.The study provided guidelines for gas well pillars by considering their support area and overburden depth as well as the location of the gas wells within the pillars.As the guidelines were developed for room-andpillar mining under shallow cover,they are no longer applicable to modern Longwall coal mining,particularly,under deep cover.Gas well casing of failures have occurred even though the chain pillars for the gas wells met the requirements by the 1957 study.This study,conducted by the National Institute for Occupational Safety and Health(NIOSH),presents seven cases of conventional gas wells penetrating through Longwall chain pillars in the Pittsburgh Coal Seam.The study results indicate that overburden depth and pillar size are not the only determining factors for gas well stability.The other important factors include subsurface ground movement,overburden geology,weak floor,as well as the type of the construction of gas wells.Numerical modeling was used to model abutment pressure,subsurface deformations,and the response of gas well casings.The study demonstrated that numerical models are able to predict with reasonable accuracy the subsurface deformations in the overburden above,within,and below the chain pillars,and the potential location and modes of gas well failures,thereby providing a more quantifiable approach to assess the stability of the gas wells in Longwall chain pillars.

关键词： Longwall mining Gas well Chain pillar Casing stability

Fracturing,caving propagation and influence of mining on groundwater above Longwall panels–a review of predictive models

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International Journal of Mining Science and Technology 2020年第1期30卷 49-54页

作者： Bruce Hebblewhite School of Minerals and Energy Resources Engineering University of New South WalesSydney 2052Australia

Historically there have been a number of different hypotheses and empirical models developed in an attempt to describe the nature of fracturing above Longwall panels in underground coal mining.The motivation for suchmodels varies,ranging fromunderstanding the impact ofmining on surface subsidence,to back-analysis of caving behaviour in the immediate roof behind the Longwall face.One of the most critical motivating factors that is taking on increased importance in many coalfields,is the need for better understanding,and hence prediction of the impact of mining on overlying strata,particularly strata units acting as aquifers for different groundwater horizons.This paper reviews some of the major prediction models in the context of observed behaviour of strata displacement and fracturing above Longwall panels in the southern coalfields of New South Wales,south of Sydney.The paper discusses the parameter often referred to as"height of fracturing"in terms of the critical parameters that influence it,and the relevance and appropriateness of this terminology in the context of overlying sub-surface subsidence and groundwater impact.The paper proposes an alternative terminology for this parameter that better reflects what it is and how it is used.The paper also addresses the potential role of major bedding shear planes mobilised by mining and their potential influence on overlying subsidence and groundwater interference.

关键词： Longwall mining Subsidence Groundwater Caving Underground coal mining

Simulation of recovery of upper remnant coal pillar while mining the ultra-close lower panel using Longwall top coal caving

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International Journal of Mining Science and Technology 2020年第1期30卷 55-61页

作者： Guorui Feng Pengfei Wang College of Mining Engineering Taiyuan University of TechnologyTaiyuan 030024China

With the depletion of easily minable coal seams,less favorable reserves under adverse conditions have to be mined out to meet the market demand.Due to some historical reasons,large amount of remnant coal was left unrecovered.One such case history occurred with the remnant rectangular stripe coal pillars using partial extraction method at Guandi Mine,Shanxi Province,China.The challenge that the coal mine was facing was that there is an ultra-close coal seam right under it with an only 0.8–1.5 m sandstone dirt band in between.The simulation study was carried out to investigate the simultaneous recovery of upper remnant coal pillars while mining the ultra-close lower panel using Longwall top coal caving(LTCC).The remnant coal pillar was induced to cave in as top coal in LTCC system.Physical modelling shows that the coal pillars are the abutments of the stress arch structure formed within the overburden strata.The stability of overhanging roof strata highly depends on the stability of the remnant coal pillars.And the gob development(roof strata cave-in)is intermittent with the cave-in of these coal pillars and the sandstone dirt band.FLAC3D numerical modelling shows that the multi-seam interaction has a significant influence on mining-induced stress environment for mining of lower panels.The pattern of the stress evolution on the coal pillars with the advance of the lower working face was found.It is demonstrated that the stress relief of a remnant coal pillar enhances the caveability of the pillars and sandstone dirt band below.

关键词： Simulation Remnant coal pillars Ultra-close Dirt band Longwall top coal caving