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A field study of a roof bolter canopy air curtain(2nd generation)for respirable coal mine dust control

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International Journal of Mining Science and Technology 2019年第5期29卷 711-720页

作者： W.R.Reed S.Klima M.Shahan G.J.H.Ross K.Singh R.Cross T.Grounds CDC NIOSH Pittsburgh Mining Research DivisionPittsburghPA 15236USA Fletcher&Co. HuntingtonWV 25705USA Prairie State Generating Company LLC Lively GroveIL 62257USA

A 2nd generation roof bolter canopy air curtain(CAC)design was tested by National Institute for Occupational Safety and Health(NIOSH)at a Midwestern underground coal mine.During the study,the roof bolter never operated downwind of the continuous miner.Using a combination of personal Data Rams(pDR)and gravimetric samplers,the dust control efficiency of the roof bolter CAC was ascertained.Performance evaluation was determined using three methods:(1)comparing roof bolter operator concentrations underneath the CAC to roof bolter concentrations outside the CAC,(2)comparing roof bolter operator concentrations underneath the CAC to the concentrations at the rear of the bolter,and finally,(3)using the gravimetric data directly underneath the CAC to correct roof bolter operator concentrations underneath the CAC and comparing them to the concentrations at the rear of the bolter.Method 1 dust control efficiencies ranged from 53.9%to 60.4%.Method 2 efficiencies ranged from 150.5%to 52.2%,and Method 3 efficiencies ranged from 40.7%to 91%.Reasons for negative and low dust control efficiencies are provided in this paper and include:incorrect sampling locations,large distance between CAC and operator,and contamination of intake air from line curtain.Low dust concentrations encountered during the testing made it difficult to discern whether differences in concentrations were due to the CAC or due to variances inherent in experimental dust measurement.However,the analyses,especially the Method 3 analysis,show that the CAC can be an effective dust control device.

关键词： Coal roof bolter Respirable dust Underground mining

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

roof filling control technology and application to mine roadway damage in small pit goaf

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International Journal of Mining Science and Technology 2019年第3期29卷 477-482页

作者： Weiyi Cai Zechao Chang Dongsheng Zhang Xufeng Wang Wenhao Cao Yazhou Zhou School of Mines China University of Mining & TechnologyXuzhou 221116China State Key Laboratory of Coal Resources and Safe Mining China University of Mining & TechnologyXuzhou 221116China Key Laboratory of Deep Coal Re-source Mining Ministry of Education of ChinaChina University of Mining & TechnologyXuzhou 221116China

To recover coal resources that have been damaged by traditional mining methods and ensure stability of the lower roadway in a small pit goaf,the goaf area must be filled and reinforced.In this research,the 1202 working face of the Hanzui mine is considered as an example for classifying the roof of the mining tunnel under the small kiln destruction zone,the effect of the goaf on the roadway is determined based on the radio tunnel penetration method,a mechanical model to determine the roof filling control mechanism was established,and the duct foaming system and roof filling process were designed.The results show that the scope and degree of influence of the goaf on the mining lane are large,but safe tunneling can be ensured through the use of a steel shed and advanced grouting techniques.When the roof conditions are not similar,materials with different filling heights and filling strengths can be used to control the roof filling of the roadway.By combining field experience and laboratory tests,it was determined that a high-foaming material with a water-cement ratio of 1:0.6,a suitable high-foaming additive,and a water volume ratio of 1:30 is cost-efficient for filling and meets the filling strength requirements.Finally,the reliability of the proposed technology was verified by field experiments,which provide a reference for filling operations in similar mines.

关键词： Repeated mining Roadway roof control High foam material Filling mining

Numerical simulation and analysis of drill rods vibration during roof bolt hole drilling in underground mines

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International Journal of Mining Science and Technology 2018年第6期28卷 877-884页

作者： Shaowei Liu Mengxiong Fu Housheng Jia Wenbin Li Yafei Luo School of Energy Science and Engineering Henan Polytechnic UniversityJiaozuo 454000China The Safety of Coal Production Collaborative Innovation Center Jiaozuo 454000China

Structural deterioration in the roof in an underground mine can easily cause roof fall, and deterioration is difficult to detect. When drilling holes for roof bolts, there is a relationship between the vibration of the drill rod and the properties of the rock being drilled. This paper analyzes transverse, longitudinal, and torsional vibrations in the drill rod by using vibration theory. Characteristic indexes for three kinds of vibration are determined. Using the finite element analysis software ABAQUS, a model for drill rod vibration during the drilling of roof bolt holes was established based on the geological and mining conditions in the Guyuan Coal Mine, northern China. Results from the model determined that the transverse and the longitudinal vibration decrease as the rock hardness decreases. In descending order, sandstone,sandy mudstone, mudstone, and weak interbeds cause progressively less vibration when being drilled.The ranking for strata that cause decreasing torsional vibration is slightly different, being, in descending order, mudstone, sandstone, sandy mudstone, and weak interbeds. These results provide a theoretical basis for predicting dangerous roof conditions and the presence of weak interbeds to allow for adjusting bolt support schemes.

关键词： roof bolt holedrilling Drill rod vibration Vibration radius Vibration point amplitude Negative angular acceleration

Relationship between water inrush from coal seam floors and main roof weighting

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International Journal of Mining Science and Technology 2017年第5期27卷 873-881页

作者： Sun Jian Hu Yang Zhao Guangming School of Energy and Safety Anhui University of Science & Technology State Key Laboratory of Coal Resources and Safe Mining China University of Mining & Technology

A water-resistant key strata model of a goaf floor prior to main roof weighting was developed to explore the relationship between water inrush from the floor and main roof weighting. The stress distribution,broken characteristics, and the risk area for water inrush of the water-resistant key strata were analysed using elastic thin plate theory. The formula of the maximum water pressure tolerated by the waterresistant key strata was deduced. The effects of the caved load of the goaf, the goaf size prior to main roof weighting, the advancing distance of the workface or weighting step, and the thickness of the waterresistant key strata on the breaking and instability of the water-resistant key strata were analysed.The results indicate that the water inrush from the floor can be predicted and prevented by controlling the initial or periodic weighting step with measures such as artificial forced caving, thus achieving safe mining conditions above confined aquifers. The findings provide an important theoretical basis for determining water inrush from the floor when mining above confined aquifers.

关键词： Floor water inrush Main roof weighting Water-resistant key strata Forced caving

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

Fundamental principles of an effective reinforcing roof bolting strategy in horizontally layered roof strata and areas of potential improvement

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International Journal of Mining Science and Technology 2018年第1期28卷 67-77页

作者： Russell Frith Guy Reed Martin McKinnon Mine Advice Pty Ltd New South Wales 2282Australia

It is arguable that the development of reinforcing roof bolting systems has largely stagnated in recent times, primarily due to the prevailing industry view that few, if any, further improvements can be made to what currently exists.However, this paper contends that reinforcing roof bolting systems can be further refined by considering both the specific manner by which horizontally bedded roof strata loses its natural self-supporting ability and the specific means by which reinforcing roof bolts act to promote or retain this natural self-supporting ability.The Australian coal industry has insisted on minimising bolt-hole diameter to maximise load transfer and on targeting full-encapsulation by any means necessary for many years.This has led to a significant, albeit unintended, consequence in terms of overall roof bolting effectiveness, namely increased resin pressures during bolt installation and the associated potential for opening bedding planes that may have, otherwise, remained closed during the bolt installation process.Given that the natural self-supporting ability of roof strata is strongly linked to whether bedding planes are open or closed, logically, minimising resin pressures should be a significant benefit.This paper focuses primarily on three key issues that relate directly to the function of the roof bolting system itself:(1) the importance of proper resin mixing in the context of maximising load transfer strength and stiffness,(2) the importance of minimising resin pressures developed during bolt installation, and(3) the importance of maximising the effectiveness of the available bolt pre-tension.All mine operators should be invested in improving the individual effectiveness of each installed roof bolt, even by relatively small incremental amounts, so this is an important topic for discussion within the mining community.

关键词： roof bolts Strata reinforcement Partial-encapsulation Pre-tension Resin mixing Improved bolt effectiveness

Geologic data collection and assessment techniques in coal mining for ground control

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International Journal of Mining Science and Technology 2020年第1期30卷 131-139页

作者： Mark Van Dyke Ted Klemetti Joe Wickline NIOSH Pittsburgh15236 PAUSA Coronado Global Resources Inc. BeckleyWVUSA

The identification and mitigation of adverse geologic conditions are critical to the safety and productivity of underground coal mining operations.To anticipate and mitigate adverse geologic conditions,a formal method to evaluate geotechnical factors must be established.Each mine is unique and has its own separate approach for defining what an adverse geological condition consists of.The collection of geologic data is a first critical step to creating a geological database to map these hazards efficiently and effectively.Many considerations must be taken into account,such as lithology of immediate roof and floor strata,seam height,gas and oil wells,faults,depressions in the mine floor(water)and increases in floor elevation(gas),overburden,streams and horizontal stress directions,amongst many other factors.Once geologic data is collected,it can be refined and integrated into a database that can be used to develop maps showing the trend,orientation,and extent of the adverse geological conditions.This information,delivered in a timely manner,allows mining personnel to be proactive in mine planning and support implementations,ultimately reducing the impacts of these features.This paper covers geologic exploratory methods,data organization,and the value of collecting and interpreting geologic information in coal mines to enhance safety and production.The implementation of the methods described above has been proven effective in predicting and mitigating adverse geologic conditions in underground coal mining.Consistent re-evaluation of data collection methods,geologic interpretations,mapping procedures,and communication techniques ensures continuous improvement in the accuracy of predictions and mitigation of adverse geologic conditions.Providing a concise record of the work previously done to track geologic conditions at a mine will allow for the smoothest transition during employee turnover and transitions.With refinements and standardization of data collection methods,such as those described in this paper,along with

关键词： roof control Database Mapping Hazards Geology

Understanding roof deformation mechanics and parametric sensitivities of coal mine entries using the discrete element method

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International Journal of Mining Science and Technology 2020年第1期30卷 123-129页

作者： Rami Abousleiman Gabriel Walton Sankhaneel Sinha Department of Geology and Geological Engineering Colorado School of MinesGoldenCO 80218USA

Although conventional coal mine designs are conservative regarding pillar strength,local failures such as roof-falls and pillar bursts still affect mine safety and operations.Previous studies have identified that discontinuous,layered roof materials have some self-supporting capacity.This research is a preliminary step towards understanding these mechanics in coal-measure rocks.Although others have considered broad conceptual models and simplified analogs for mine roof behavior,this study presents a unique numerical model that more completely represents in-situ roof conditions.The discrete element method(DEM)is utilized to conduct a parametric analysis considering a range of in-situ stress ratios,material properties,and joint networks to determine the parameters controlling the stability of single-entries modeled in two-dimensions.Model results are compared to empirical observations of roof-support effectiveness(ARBS)in the context of the coal mine roof rating(CMRR)system.Results such as immediate roof displacement,overall stability,and statistical relationships between model parameters and outcomes are presented herein.Potential practical applications of this line of research include:(1)roof-support optimization for a range of coal-measure rocks,(2)establishment of a relationship between roof stability and pillar stress,and(3)determination of which parameters are most critical to roof stability and therefore require concentrated evaluation.

关键词： Numerical modeling Discrete element method Coal mine roof rating Analysis of roof bolt systems Sensitivity analysis Strain softening ubiquitous joints Discrete fracture network