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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

Numerical simulation of roof cavings in several Kuzbass mines using finite-difference continuum damage mechanics approach

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International Journal of Mining Science and Technology 2020年第2期30卷 157-166页

作者： Mikhail Eremin Gabriel esterhuizen Igor Smolin Institute of Strength Physics and Materials Science Siberian BranchRussian Academy of SciencesTomsk 634055Russian Federation National Institute for Occupational Safety and Health PittsburghPA 15236USA National Research Tomsk State University Tomsk 634050Russian Federation

An essential stage of mine design is an estimation of the steps of the first and periodic roof caving in longwall mines.Generally,this is carried out using the field experience and can be much enhanced by numerical simulation.In this work,the finite-difference method was applied coupled with the continuum damage mechanics(CDM)approach to simulate the stress-strain evolution of the rock mass with the underground opening during coal extraction.The steps and stages of roof caving were estimated relying on the numerical simulation data,and they were compared with the field data from several operating mines in the south of the Kuznetsk Basin,Russia.The dependence of the first roof caving step in simulation linearly correlates with field data.The results correspond to the actual roofs of longwall panels of the flat-dipping coal seams and the average rate of face advancement is approximately 5 m/day.

关键词： Longwall mining Rock mass Underground openings Roof caving Abutment pressure Numerical simulation

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

Evaluation of stress-control layout at the Subtropolis Mine,Petersburg,Ohio

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International Journal of Mining Science and Technology 2020年第1期30卷 77-83页

作者： Anthony Iannacchione Tim Miller Gabriel esterhuizen Brent Slaker Michael Murphy Natalie Cope Scott Thayer Department of Civil and Environmental Engineering University of PittsburghPittsburghPA 15216USA East Fairfield Coal Company North LimaOH 44452USA National Institute for Occupational Safety and Health(NIOSH) Pittsburgh Mining Research DivisionPittsburghPA 15236USA Mine Vision Systems Inc. PittsburghPA 1520USA

The Subtropolis room-and-pillar mine extracts the Vanport Limestone(Allegheny Formation,Pennsylvanian System)near Petersburg,Ohio.Strata instability problems associated with excessive concentrations of lateral stress caused the mine operator to implement a change in layout design.This mining method has been identified as a stress control layout and has been used by other underground stone mines in the past with varying degrees of success.Practical experience has shown that entry headings advance in the direction of the principal lateral stress,producing lower stress concentrations with better mining conditions.It is important to minimize stress concentrations along the mining front,so an arrowshaped advance is recommended.This technique advances more developments(headings)in a"good"direction and reduces developments(crosscuts)in the"bad direction."As is expected,the stress control layout enhances the potential for shear failures in crosscuts.It is,therefore,important to focus crosscut engineering interventions that either:(a)lower stress concentrations(for example,an arched roof)or(b)enhance strength of the strata containing the shears(for example,rock reinforcement).This study focuses on observing strata conditions on a regular basis and monitoring the response of these strata to changing geologic and mining conditions through 3D Dynamic LiDAR scans.

关键词： Horizontal stress Stress-control layouts Underground stone mines

Bleeder entry evaluation using condition mapping and numerical modeling

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International Journal of Mining Science and Technology 2021年第1期31卷 137-143页

作者： Ted M.Klemetti Mark A.Van Dyke Gabriel S.esterhuizen National Institute for Occupational Safety and Health Pittsburgh Mining Research DivisionPittsburghPA 15236USA

One of the most common critical areas of longwall mining in terms of ground stability are the gateroad and bleeder entries.These critical entries provide much-needed safe access for miners and allow for adequate ventilation required for dilution of hazardous airborne contaminants and must remain open during mining of a multi-panel district.This paper is focused on the stability of the longwall entries subjected to a single abutment load such as bleeders,first tailgate,and last headgate.First tailgate and last headgate are also referred to as blind headgate and tailgate.A study of a longwall district through conditions mapping,support evaluations,and numerical modeling was conducted and evaluated by researchers from the National Institute for Occupational Safety and Health(NIOSH).The condition mapping and support evaluations were performed on entries that spanned the previous five years of mining and relied on a diverse selection of supports to maintain the functionality of the entry.Numerical modeling was also conducted to evaluate various support types with further investigation and comparison to the condition mapping.The study demonstrated the importance of the abutment load decay versus distance from the gob edge,the potential for a reduction in material handling related injuries,as well as optimal usage of secondary and standing support.

关键词： Stability assessment Bleeder entry Abutment loading Condition mapping Longwall Ground control

Analysis of roof and pillar failure associated with weak floor at a limestone mine

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International Journal of Mining Science and Technology 2016年第3期26卷 471-476页

作者： Murphy Michael M. Ellenberger John L. esterhuizen Gabriel S. Miller Tim Office of Mine Safety and Health Research National Institute of Occupational Safety and Health East Fairfield Company

A limestone mine in Ohio has had instability problems that have led to massive roof falls extending to the surface. This study focuses on the role that weak, moisture-sensitive floor has in the instability issues.Previous NIOSH research related to this subject did not include analysis for weak floor or weak bands and recommended that when such issues arise they should be investigated further using a more advanced analysis. Therefore, to further investigate the observed instability occurring on a large scale at the Ohio mine, FLAC3 D numerical models were employed to demonstrate the effect that a weak floor has on roof and pillar stability. This case study will provide important information to limestone mine operators regarding the impact of weak floor causing the potential for roof collapse, pillar failure, and subsequent subsidence of the ground surface.

关键词：石灰岩矿失效分析支柱顶板底板软弱矿山地面沉降

Analysis of alternatives for using cable bolts as primary support at two low-seam coal mines

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International Journal of Mining Science and Technology 2016年第1期26卷 23-30页

作者： esterhuizen Gabriel S. Tulu Ihsan B. Office of Mine Safety and Health Research NIOSH

Cable bolts are sometimes used in low-seam coal mines to provide support in difficult ground conditions.This paper describes cable bolting solutions at two low-seam coal mines in similar ground conditions.Both mines used support systems incorporating cable bolts as part of the primary support system.Two original cable bolt based support systems as well as two modified systems are evaluated to estimate their ability to prevent large roof falls. One of the support systems incorporated passive cable bolts,while the other used pre-tensioned cable bolts. The results and experience at the mines showed that the modified systems provided improved stability over the original support systems. The presence of the cable bolts is the most important contribution to stability against large roof falls,rather than the details of the support pattern. It was also found that a heavy steel channel can improve the safety of the system because of the ‘sling' action it provides. Additionally,the analysis showed that fully-grouted rebar bolts load much earlier than the cable bolts,and pre-tensioning of the cable bolts can result in a more uniform distribution of loading in the roof.

关键词：电缆螺栓支护方案预应力锚索支撑系统支持系统压煤煤层开采

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

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 cover.At 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

A case study of multi-seam coal mine entry stability analysis with strength reduction method

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矿业科学技术学报：英文版 2016年第2期26卷 193-198页

作者： Tulu Ihsan Berk esterhuizen Gabriel S. Klemetti Ted Murphy Michael M. Sumner James Sloan Michael Ground Control Branch NIOSH Office of Mine Safety and Health Research Pittsburgh PA 15216 USA Lone Mountain Processing Inc. St. Charles VA 24282 USA

In this paper,the advantage of using numerical models with the strength reduction method(SRM) to evaluate entry stability in complex multiple-seam conditions is demonstrated.A coal mine under variable topography from the Central Appalachian region is used as a case study.At this mine,unexpected roof conditions were encountered during development below previously mined panels.Stress mapping and observation of ground conditions were used to quantify the success of entry support systems in three room-and-pillar panels.Numerical model analyses were initially conducted to estimate the stresses induced by the multiple-seam mining at the locations of the affected entries.The SRM was used to quantify the stability factor of the supported roof of the entries at selected locations.The SRM-calculated stability factors were compared with observations made during the site visits,and the results demonstrate that the SRM adequately identifies the unexpected roof conditions in this complex case.It is concluded that the SRM can be used to effectively evaluate the likely success of roof supports and the stability condition of entries in coal mines.

关键词：稳定性分析强度折减煤层巷道多煤层开采实例数值模型煤矿井下应力影响