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Utilising the scientific method to demonstrate that slender beam/column behaviour is the dominant behavioural mechanism leading to roof/rib failure

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International Journal of Mining Science and Technology 2021年第5期31卷 867-887页

作者： Mark Colwell Russell frith Colwell Geotechnical Services CaloundraQLD 4551Australia Mine Advice Pty Ltd BeresfieldNSW 2322Australia

As per most other earth science engineering problems,the underground coal geotechnical environment and the way in which roof and rib support interacts with the rock mass are complex *** is therefore generally recognised that without prudent simplification,the complexity of the problem will overwhelm all current geotechnical methods of modelling,not least for the reason that a rock mass can never be characterised to a level that allows a"non-simplified"*** fact that numerical models,which are commonly purported to be a"simulation"tool and the so-called epitome of advanced geotechnical engineering,always need to be"calibrated"to a known reality is taken to be conclusive proof of this *** the problem should not be oversimplified(*** dominant failure mechanisms or critical data input parameters should not be ignored),without question judicious simplification is at the heart of all engineering design,to the point that it has a well-established name–"reductionism".The hypothesis addressed in this paper,is that horizontal and vertical stress-driven slender beam and column behaviour(which includes unstable Euler Buckling)are respectively the dominant(but not only)roadway roof and ribline behavioural mechanism that(if not controlled)can lead to excessive deformation,failure and eventual *** a part of the Scientific Method,a hypothesis can only be tested via real-world observations,measurements and analyses in establishing it is a credible *** the Scientific Method,this paper demonstrates that slender beam/column behaviour is the dominant instability mechanism within a coal mine roof/rib subject to elevated horizontal/vertical stress conditions and therefore,must be representatively accounted for in any credible empirical,analytical,or numerical approach to coal mine roof/rib stability assessment and associated ground support design.

关键词： Prudent simplification Behavioural mechanisms Support design Delamination Axial stress Buckling

Coal pillar design when considered a reinforcement problem rather than a suspension problem

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International Journal of Mining Science and Technology 2018年第1期28卷 11-19页

作者： Russell frith Guy Reed Mine Advice Pty Ltd New South Wales 2282Australia

Current coal pillar design is the epitome of suspension design.A defined weight of unstable overburden material is estimated, and the dimensions of the pillars left behind are based on holding up that material to a prescribed factor of *** principle, this is no different to early roadway roof support ***, for the most part, roadway roof stabilisation has progressed to reinforcement, whereby the roof strata is assisted in supporting *** is now the mainstay of efficient and effective underground coal *** and reinforcement are fundamentally different in roadway roof stabilisation and lead to substantially different requirements in terms of support hardware characteristics and their *** suspension, the primary focus is the total load-bearing capacity of the installed support and ensuring that it is securely anchored outside of the unstable roof *** contrast, reinforcement recognises that roof de-stabilisation is a gradational process with ever-increasing roof displacement magnitude leading to ever-reducing *** roof support characteristics relate to such issues as system stiffness, the location and pattern of support elements and mobilising a defined thickness of the immediate roof to create(or build) a stabilising strata *** objective is to ensure that horizontal stress is maintained at a level that prevents mass roof *** paper presents a prototype coal pillar and overburden system representation where reinforcement, rather than suspension, of the overburden is the stabilising mechanism via the action of in situ horizontal *** roadway roof reinforcement principles can potentially be applied to coal pillar design under this *** merit of this is evaluated according to failed pillar cases as found in a series of published *** on the findings, a series of coal pillar system design considerations for bord and pillar type mine workings are ***

关键词： Coal pillar design Overburden stability Rock reinforcement Bord and pillar mining

Limitations and potential design risks when applying empirically derived coal pillar strength equations to real-life mine stability problems

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International Journal of Mining Science and Technology 2019年第1期29卷 17-25页

作者： Russell frith Guy Reed Mine Advice Pty Ltd

The method of determining coal pillar strength equations from databases of stable and failed case histories is more than 50 years old and has been applied in different countries by different researchers in a range of mining situations. While common wisdom sensibly limits the use of the resultant pillar strength equations and methods to design scenarios that are consistent with the founding database, there are a number of examples where failures have occurred as a direct result of applying empirical design methods to coal pillar design problems that are inconsistent with the founding database. This paper explores the reasons why empirically derived coal pillar strength equations tend to be problem-specific and should be considered as providing no more than a pillar strength ‘‘index." These include the non-consideration of overburden horizontal stress within the mine stability problem, an inadequate definition of supercritical overburden behavior as it applies to standing coal pillars, and the non-consideration of overburden displacement and coal pillar strain limits. All of which combine to potentially complicate and confuse the back-analysis of coal pillar strength from failed cases. A modified coal pillar design representation and model are presented based on coal pillars acting to reinforce a horizontally stressed overburden, rather than suspend an otherwise unstable self-loaded overburden or section, the latter having been at the core of historical empirical studies into coal pillar strength and stability.

关键词： Coal pillar design Pillar strength Overburden mechanics Limitations of pillar design

A causation mechanism for coal bursts during roadway development based on the major horizontal stress in coal:Very specific structural geology causing a localised loss of effective coal confinement and Newton’s second law

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International Journal of Mining Science and Technology 2020年第1期30卷 39-47页

作者： Russell frith Guy Reed Aaron Jones Mine Advice Pty Ltd BeresfieldNew South Wales 2322Australia

In 2017,one of the international authorities on coal bursts,Mark Christopher,published a paper entitled"Coal bursts that occur during development:A rock mechanics enigma",in which several relevant technical issues were *** paper outlines what is considered to be a credible,first-principles,mechanistic explanation for these three current development coal burst conundrums by reference to early published coal testing work examining the significance of a lack of"constraint"to coal stability and an understanding of how very specific structural geology and other geological features can logically cause this to occur in situ,albeit on a statistically very rare *** basic model is examined by reference to published information pertaining to the development coal-burst that occurred at the Austar Coal Mine in New South Wales,Australia,in 2014 and from the Sunnyside District in Utah,the United ***"cause and effect"model for development of coal bursts presented also offers a meaningful explanation for the statistical improbability for what are nonetheless potentially highly-destructive events,being able to explain the statistical rarity being just as important to the credibility of the model as explaining the local conditions associated with burst *** model could also form the basis for a robust,riskbased approach utilising a"hierarchy of controls",to the operational management of the development coal burst ***,the use of pre-mining predictions for likely burst-prone and non-burstprone areas,the use of the mine layout to avoid or at least minimise mining within burst-prone areas if appropriate,and finally the development of an operational Trigger Action Response Plan(TARP)that reduces the likelihood of inadvertent roadway development into a burst-prone area without suitable safety controls already being in place.

关键词： Development coal burst Wing-cracks Austar Mine Sunnyside Mine Major horizontal stress in coal

A holistic examination of the load rating design of longwall shields after more than half a century of mechanised longwall mining

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International Journal of Mining Science and Technology 2015年第5期25卷 687-706页

作者： frith Russell C. Mine Advice Pty Ltd.

It is a commonly asked question:how big should the longwall shields be? The answer is a key aspect of a longwall mining feasibility study when the consequences of inadequately rated shields are *** paper addresses this question based on the measured nature of the loading environment in which shields are required to operate,the various geological and geometrical controls of that environment and the various links between their load rating,a range of other relevant shield design factors and the loss event they are required to prevent a major roof collapse on the longwall *** paper concludes that despite the tremendous advances that have been made in shield design and load rating over the past50 years,the same drivers that caused longwall miners of the past to seek improved roof control on the longwall face via the use of ever-higher rated shields,are still as relevant *** at the current time,the limits of the largest available longwall shields have yet to be tested,therefore industry focus for the foreseeable future should possibly be in achieving the maximum level of roof control on the face via their optimum operational use rather than considering further shield rating increases and incurring the inevitable downsides in terms of capital cost and shield weight.

关键词： Longwall genmechanics Longwall face instability Longwall shield design Periodic weighting of massive strata Longwall panel geometry

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 ***, 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 *** 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 *** 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 *** 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 *** 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 *** 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

An assessment of coal pillar system stability criteria based on a mechanistic evaluation of the interaction between coal pillars and the overburden

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International Journal of Mining Science and Technology 2017年第1期27卷 9-15页

作者： Reed Guy Mctyer Kent frith Russell Mine Advice Pry Ltd NewcastleNSW 2322Australia

Coal pillar design has historically assigned a factor of safety(Fo S) or stability factor(SF) according to their estimated strength and the assumed overburden load acting on them. Acceptable Fo S values have been assigned based on past mining experience or a statistical link between Fo S and probability of failure(Po F). Pillar width-to-height(w/h) ratio has long been established as having a material influence on both pillar strength and its potential failure mode. However, there has been significant disagreement on using both factor of safety(Fo S) and w/h as part of pillar system stability criterion, as compared to using Fo S in isolation. This paper will argue that there are valid technical reasons to bring w/h ratio into system stability criteria(other than its influence on pillar strength), as it is related to the post-failure stiffness of the pillar, as measured in situ, and its interaction with overburden stiffness. When overburden stiffness is also brought into pillar system stability considerations, two issues emerge. The first is the width-todepth(W/D) ratio of the panel and whether it is sub-critical or super-critical from a surface subsidence perspective. The second relates to a re-evaluation of pillar Fo S based on whether the pillar is in an elastic or non-elastic(i.e., post-yield) state in its as-designed condition, as this is relevant to maintaining overburden stiffness at the highest possible level. The significance of the model is the potential to maximise both reserve recovery and mining efficiencies without any discernible increase in geotechnical risk, particularly in thick seams and higher depth of cover mining situations. At a time when mining economics are, at best, marginal, removing potentially unnecessary design conservatism is of interest to all mine operators and is an important topic for discussion amongst the geotechnical community.

关键词： Coa] pillars Stability Overburden Post-failure behaviour Stability criteria

Effects of Acute Exercise on Verbal, Mathematical, and Spatial Insight Creativity

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Journal of Science in Sport and Exercise 2023年第1期5卷 87-96页

作者： Myungjin Jung Emily frith Minsoo Kang Paul D.Loprinzi Exercise and Memory Laboratory Department of HealthExercise Science and Recreation ManagementThe University of MississippiUniversityOxfordMS 38677USA Health and Sport Analytics Laboratory Department of HealthExercise Science and Recreation ManagementThe University of MississippiUniversityOxfordMS 38677USA Center for Healthy Aging College of Health and Human DevelopmentPennsylvania State UniversityUniversity ParkPA 16802USA

This experiment was designed to accommodate the diversified verbal,mathematical,and spatial skills of young adults,which have not yet to be collectively evaluated in research projects focused on acute exercise and creativity among college *** emerging research suggests that acute moderate-intensity exercise may influence human creativity,creativity during and after exercise has not been experimentally *** differences are plausible,as previous work demonstrates that memory can be differentially influenced based on whether the memory task occurs during or after ***,the purpose of this study was to examine the effects of acute moderate‐intensity treadmill walking,for 15 min,on verbal,mathematical,and spatial insight creativity performance while considering the timing of the exercise and creativity *** a sample of 20 undergraduate students,all completed three randomized laboratory visits in this within-subjects design:control condition,insight problem-solving following exercise,and insight problem-solving during *** also completed six insight creativity tasks(two verbal,two mathematical,and two spatial tasks)per visit,with the order of task-presentation randomized and counterbalanced across the three *** insight creativity scores were similar across the three exercise manipulations:That is,verbal insight[F(2,18)=0.689,P=0.51],mathematical insight[F(2,18)=0.033,P=0.97],and spatial insight[F(2,18)=1.0,P=0.38]performance were not statistically significant across the three ***,moderate-intensity acute exercise may not appreciably influence verbal,mathematical or spatial insight creativity.

关键词： Convergent thinking Creativity research methodology Embodied cognition Executive function Physical activity

Solar-powered Bamboo Culm Prefabricated Housing

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Chinese Forestry Science and Technology 2012年第Z1期11卷 20-28页

作者： frith Oliver B International Network for Bamboo and Rattan

The solar-powered hybrid energy system has been put into practice in Hunan bamboo culm prefabricated housing and was enrolled in this *** this paper,the experimental data which was taken from a demonstration house highlighted that this system has a high potential for integrated solar energy *** average thermal efficiency of the collector was 58.68%,and the thermal conductivity coefficient of bamboo culm prefabricated composite wall was 1.075 W/(m2 K).Based on these results,bamboo culms could be used as the main structural material and heat storage slow-release flooring in the prefabricated *** housing was lower in energy consuming.

关键词： solar energy bamboo culm prefabricated housing integrated technology