Pillar design and coal burst experience in Utah Book Cliffs longwall operations

Longwall mining has existed in Utah for more than half a century.Much of this mining occurred at depths of cover that significantly exceed those encountered by most other US longwall operations.Deep cover causes high ground stress,which can combine with geology to create a coal burst hazard.Nearly every longwall mine operating within the Utah’s Book Cliffs coalfield has been affected by coal bursts.Pillar design has been a key component in the burst control strategies employed by mines in the Book Cliffs.Historically,most longwall mines employed double-use two-entry yield pillar gates.Double-use signifies that the gate system serves first as the headgate,and then later serves as the tailgate for the adjacent panel.After the 1996 burst fatality at the Aberdeen Mine,the inter-panel barrier design was introduced.In this layout,a wide barrier pillar protects each longwall panel from the previously mined panel,and each gate system is used just once.This paper documents the deep cover longwall mining conducted with each type of pillar design,together with the associated coal burst experience.Each of the six longwall mining complexes in the Book Cliffs having a coal burst history is described on a panel-by-panel basis.The analysis shows that where the mining depth exceeded 450 m,each design has been employed for about 38000 total m of longwall panel extraction.The double-use yield pillar design has been used primarily at depths less than 600 m,however,while the inter-panel barrier design has been used mainly at depths exceeding 600 m.Despite its greater depth of use,the inter-panel barrier gate design has been associated with about one-third as much face region burst activity as the double-use yield pillar design.

Strategic sill pillar design for reduced hanging wall overbreak in longhole mining

Steeply dipping,vein and tabular orebodies are traditionally extracted with longitudinal retreat mining methods such as Eureka and Avoca in a bottom-up sequence with delayed backfill.To increase productivity,sill pillars in the orebody are used to separate mining zones thus allowing production to take place simultaneously in two or more zones.While such mining methods are productive,they may be accompanied with high volumes of hanging wall overbreak causing significant unplanned ore dilution.In this work,it is shown through a mine design case study of a narrow vein deposit that a sill pillar could also play a significant role in limiting hanging wall overbreak.To demonstrate the role of sill pillar,a novel numerical modelling scheme is proposed to account for progressive stope wall overbreak.A numerical modelling approach of element death and rebirth is developed to allow for the detected stope overbreak to be immediately removed and replaced with backfill material before upper-level stope extraction.It is further shown that the average overbreak volume could be reduced by as much as 33%when the sill pillar is strategically placed in the lower half of a mine plan.

Analysis of coal pillar stability(ACPS): A new generation of pillar design software

Thirty years ago, the analysis of longwall pillar stability(ALPS) inaugurated a new era in coal pillar design.ALPS was the first empirical pillar design technique to consider the abutment loads that arise from full extraction, and the first to be calibrated using an extensive database of longwall mining case histories.ALPS was followed by the analysis of retreat mining stability(ARMPS) and the analysis of multiple seam stability(AMSS). These methods incorporated other innovations, including the coal mine roof rating(CMRR), the Mark-Bieniawski pillar strength formula, and the pressure arch loading model. They also built upon ever larger case history databases and employed more sophisticated statistical methods.Today, these empirical methods are used in nearly every underground coal mine in the US. However,the piecemeal manner in which these methods have evolved resulted in some weaknesses. For example,in certain situations, it may not be obvious which program is the best to use. Other times the results from the different programs are not entirely consistent with each other. The programs have also not been updated for several years, and some changes were necessary to keep pace with new developments in mining practice. The analysis of coal pillar stability(ACPS) now integrates all three of the older software packages into a single pillar design framework. ACPS also incorporates the latest research findings in the field of pillar design, including an expanded multiple seam case history data base and a new method to evaluate room and pillar panels containing multiple rows of pillars left in place during pillar recovery.ACPS also includes updated guidance and warnings for users and features upgraded help files and graphics.

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

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 safety.In principle, this is no different to early roadway roof support design.However, for the most part, roadway roof stabilisation has progressed to reinforcement, whereby the roof strata is assisted in supporting itself.This is now the mainstay of efficient and effective underground coal production.Suspension and reinforcement are fundamentally different in roadway roof stabilisation and lead to substantially different requirements in terms of support hardware characteristics and their application.In 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 mass.In contrast, reinforcement recognises that roof de-stabilisation is a gradational process with ever-increasing roof displacement magnitude leading to ever-reducing stability.Key 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 beam.The objective is to ensure that horizontal stress is maintained at a level that prevents mass roof collapse.This 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 stresses.Established roadway roof reinforcement principles can potentially be applied to coal pillar design under this representation.The merit of this is evaluated according to failed pillar cases as found in a series of published databases.Based on the findings, a series of coal pillar system design considerations for bord and pillar type mine workings are provided.This potentially allows a more flexible approach to coal pillar sizing within workable mining layouts, as compared to common industry practice of a single design factor of safety(Fo S) under defined overburden dead-loading to the exclusion of other relevant overburden stabilising influences.

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

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.

Design of crown pillar thickness using finite element method and multivariate regression analysis

Minerals are now being extracted from deep mines due to drying up of resource in shallow ground. The need for suitable supports and ground control mechanisms for safe mining necessitates proper pillar design with filling technology. In addition, high horizontal stress may cause collapse of hanging wall and footwall rocks, hence designing of suitable crown pillars is absolutely necessary for imposing overall safety of the stopes. This paper provides a methodology for the evaluation of the required thickness of crown pillars for safe operation at depth ranging from 600 m to 1000 m. Analyses are conducted with the results of 108 non-linear numerical models considering Drucker-Prager material model in plane strain condition. Material properties of ore body rock and thickness of crown pillars are varied and safety factors of pillars estimated. Then, a generalized statistical relationship between the safety factors of crown pillars with the various input parameters is developed. The developed multivariate regression model is utilized for generating design/stability charts of pillars for different geo-mining conditions.These design charts can be used for the design of crown pillar thickness with the depth of the working,taking into account the changes of the rock mass conditions in underground metal mine.

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

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 panel.While 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 methods.Implementation of UT3PC overcomes these impediments in three easy steps.First, a material properties file is prepared for the considered site.Next, mesh generation is automatic through an interactive process.A third and last step is simply execution of the program.Examples 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.

采动影响下井筒安全评估研究

针对升富煤矿周边煤矿工作面开采对其井筒安全影响问题,通过理论分析、现场实测和经验类比相结合的研究方法,划定了井筒保护煤柱范围,分析了工作面正常开采、区段煤柱开采和井筒煤柱压覆区域不开采三种方案下井筒不同位置处的移动与变形情况,提出了井壁采动损害等级、损坏分类及结构处理方法的评价指标分类,评价了采动影响下井筒安全稳定状况。结果表明:3煤01工作面正常开采和井筒煤柱压覆区域不开采两种情况下,主、副斜井不受采动影响,风井分别在距地面[0,50]m范围和[0,41]m范围为Ⅰ级(轻微)损坏,对井筒安全影响较小;若区段煤柱也开采,最不利情况下,主斜井在距井口[0,70]m和(70,250]m范围分别为Ⅱ级(一般)损坏和Ⅰ级(轻微)损坏,风井在距地面[0,33]m、(33,58]m和(58,90]m范围分别为Ⅲ级(较重)损坏、Ⅱ级(一般)损坏和Ⅰ级(轻微)损坏,风井损坏等级最高为Ⅲ级,将影响风井正常使用。

邮轮支柱设计

以国产首制大型邮轮为例,围绕其支柱的设计流程,从支柱的布置、设计载荷、规范设计和全船有限元分析等4个方面进行分析,总结该类船型的支柱设计特点。在规范计算中,主要考虑规范平均载荷和局部集中载荷2种情况下受压支柱的屈曲强度;在有限元分析中,主要考虑规范平均载荷与船体梁变形共同作用下支柱的屈曲强度和受拉支柱的屈服强度。通过全船有限元分析验证该设计满足要求,受拉支柱主要出现在艏部、艉部和上层甲板。研究成果及其实践可为后续类似船型的支柱设计提供参考。

迎采巷道围岩应力和塑性区演化规律及控制技术研究

迎采动工作面掘巷时,容易受到邻近工作面上覆岩层关键块体断裂、回转、下沉的动压影响,巷道变形量大、维护困难。以温庄煤矿15105运输顺槽迎15103回采工作面掘进为工程背景,采用数值模拟的方法,揭示了迎采全过程围岩的应力和塑性区演化规律,提出了以“上区段工作面采动影响区锚索补强支护+水力压裂切顶卸压技术”为核心的巷道围岩控制体系,并在现场开展了实验。现场监测结果显示,迎采段巷道整体控制效果良好。

浅埋厚煤层大巷保护煤柱尺寸留设研究

留设煤柱护巷道目前仍是中国许多矿井的主要护巷道方式,但同时也损失了巨大的煤炭资源。煤柱留设的长度也是影响煤柱稳定性和巷道围岩稳定性的关键所在,其安全长度的留设,更有利于改变围岩应力分布条件,隔离工作面采空区,维护巷道围岩稳定具有重要的作用。区段煤柱留设宽度与煤矿采区埋置深度、工作面倾角、煤层高度、巷道顶底板围岩等具有相关联系。不同煤矿开采条件不同,不同矿区都有自己留设煤柱的宽度方法。因此,本论文针对某煤矿西翼带式运输大巷煤柱安全宽度等问题展开研究,分析煤柱内的应力分布、变形特征和塑性区分布,最终得出安全煤柱宽度留设,论证该尺寸煤柱下,确保被保护的巷道在掘进过程中不引起失稳,这对于煤矿的安全生产来说至关重要。

切顶卸压自动成巷无煤柱开采方案设计与效果评价

针对某煤矿存在巷道顶板压力大、煤炭资源回收率低等问题,制定了顶板预裂切缝的实施方案,设计了巷道临时支护方案,通过实际试验,结果表明:底鼓量约为98 mm,巷道顶板下沉量约为177 mm,实体煤帮变形量约为88 mm,采空区帮变形量约为125 mm,两帮和顶板的收缩率分别为4.26%,8.6%,降低了顶板压力,延长了矿井的使用寿命,共产生营收约890万元。

防隔水煤柱切顶卸压定向爆破参数设计及工程应用

针对煤矿井下紧邻断层的防隔水煤柱稳定性保护问题,以鹤壁中泰矿业3309工作面防隔水煤柱为工程背景,对防隔水煤柱切顶卸压定向爆破参数设计及工程应用进行研究。通过对切顶卸压前后防隔水煤柱支撑压力分布进行对比分析,揭示了切顶卸压定向爆破作用机理,采空区顶板垮断时大悬臂结构被切断进而迅速垮落,防隔水煤柱上方侧向支撑压力缓慢上升然后延伸至深处缓慢下降到原岩应力。利用FLAC3D和ANSYS/LS-DYNA软件建立不同不耦合系数定向聚能爆破模型,数值模拟结果显示,切顶卸压后应力峰值降低了约27.8%,且峰值位置与3309工作面煤柱帮的距离明显增大,改善了3309工作面回风巷道附近区域应力环境;综合考虑切缝效果和炸药利用率,确定了不耦合系数1.7为正常段最优装药结构;根据数值分析结果和断层分布情况对3309工作面回风巷道进行系统性差异化爆破参数设计,现场应用表明切顶卸压定向爆破效果良好,对防隔水煤柱的保护起到了有效的作用。

上社煤矿双巷掘进巷道布置及支护设计研究

以上社煤矿9217双巷掘进工作面为研究对象,采用UDEC数值模型分析了双巷掘进阶段及首工作面回采过程中不同煤柱尺寸下裂隙扩展演化及围岩变形特征。确定了合理的煤柱宽度为12 m,并设计了9217回风顺槽锚索支护参数。将方案成功应用于上社煤矿的工程实践中,取得了理想的围岩控制效果,显著提高了开采效率,同时缓解了开采接替紧张的问题。

付家焉煤业孤岛工作面区段窄煤柱合理宽度研究

为了提高工作面煤炭资源回收率,保证孤岛工作面安全开采,本文运用理论分析、数值模拟和现场实测的方法,通过理论计算及数值模拟研究不同煤柱宽度下,巷道应力分布、屈服破坏等特征,最终确定了8 m的窄煤柱尺寸。现场实测结果表明,10105孤岛工作面运输巷道两帮移近量最终稳定在320 mm,顶底板移近量稳定在270 mm左右,能够保证工作面安全回采。

金融开放视角下跨周期与逆周期有机结合“双支柱”调控框架研究

金融开放带来经济发展的同时,也伴随着风险的增加,如何在开放中保持金融稳定,成为当前需要面对的重要问题。为此,本研究提出一种金融开放视角下跨周期与逆周期有机结合“双支柱”调控框架。该框架将货币政策和宏观审慎政策作为两大支柱,综合运用逆周期调节和跨周期调节手段,在逆周期调节方面,该框架通过货币政策等手段,对经济进行短期调控,以平抑经济周期波动;跨周期调节方面,通过宏观审慎政策等手段,引导金融机构和市场形成合理的运行机制,防范化解长期性、系统性风险。

基于PLC的智能手环全自动充电触点铜柱装配机设计

智能手环的市场需求量持续增大,但因其结构复杂精细,传统人工装配生产效率低下且易因疲劳导致装配精度较差等质量问题。对此,提出一款基于PLC集成的智能手环充电触点铜柱全自动安装设备。设备采用可编程控制器PLC作为核心控制器,通过光电传感器和磁性开关采集机械装置工作状态信息并进行实时反馈与控制,实现智能手环充电触点铜柱全自动安装,推动智能手环产能、装配质量与优品率协同提升。

Science of empirical design in mining ground control

Many problems in rock engineering are limited by our imperfect knowledge of the material properties and failure mechanics of rock masses. Mining problems are somewhat unique, however, in that plenty of real world experience is generally available and can be turned into valuable experimental data.Every pillar that is developed, or stope that is mined, represents a full-scale test of a rock mechanics design. By harvesting these data, and then using the appropriate statistical techniques to interpret them,mining engineers have developed powerful design techniques that are widely used around the world.Successful empirical methods are readily accepted because they are simple, transparent, practical, and firmly tethered to reality. The author has been intimately associated with empirical design for his entire career, but his previous publications have described the application of individual techniques to specific problems. The focus of this paper is the process used to develop a successful empirical method. A sixstage process is described: identification of the problem, and of the end users of the final product; development of a conceptual rock mechanics model, and identification of the key parameters in that model;identification of measures for each of the key parameters, and the development of new measures(such as rating scales) where necessary; data sources and data collection; statistical analysis; and packaging of the final product. Each of these stages has its own potential rewards and pitfalls, which will be illustrated by incidents from the author's own experience. The ultimate goal of this paper is to provide a new and deeper appreciation for empirical techniques, as well as some guidelines and opportunities for future developers.

沿空掘巷窄煤柱留设及围岩控制技术实践

为了缓解矿井采掘接替的紧张局面,改善巷道维护状况,最大限度提高资源回收率,针对花草滩煤矿实际生产条件,结合极限平衡理论及窄煤柱留设原则,通过理论计算及FLAC^(3D)软件数值模拟,确定合理的窄煤柱宽度为6 m。通过现场调研相似地质条件矿井的回采巷道围岩变形特征、围岩力学分析、围岩损伤和破裂分析、围岩破坏机理,并根据花草滩煤矿1109工作面地质资料及围岩状况,模拟分析部分支护参数对1109回采巷道围岩支护应力场的分布特征的影响,经现场试验的数据整理和验证,综合对比后确定了合理的支护参数,制定了窄煤柱掘进期间顺槽的合理支护方案。

Geotechnical considerations for concurrent pillar recovery in close-distance multiple seams

Room-and-pillar mining with pillar recovery has historically been associated with more than 25% of all ground fall fatalities in underground coal mines in the United States.The risk of ground falls during pillar recovery increases in multiple-seam mining conditions.The hazards associated with pillar recovery in multiple-seam mining include roof cutters, roof falls, rib rolls, coal outbursts, and floor heave.When pillar recovery is planned in multiple seams, it is critical to properly design the mining sequence and panel layout to minimize potential seam interaction.This paper addresses geotechnical considerations for concurrent pillar recovery in two coal seams with 21 m of interburden under about 305 m of depth of cover.The study finds that, for interburden thickness of 21 m, the multiple-seam mining influence zone in the lower seam is directly under the barrier pillar within about 30 m from the gob edge of the upper seam.The peak stress in the interburden transfers down at an angle of approximately 20°away from the gob, and the entries and crosscuts in the influence zone are subjected to elevated stress during development and retreat.The study also suggests that, for full pillar recovery in close-distance multiple-seam scenarios,it is optimal to superimpose the gobs in both seams, but it is not necessary to superimpose the pillars.If the entries and/or crosscuts in the lower seam are developed outside the gob line of the upper seam,additional roof and rib support needs to be considered to account for the elevated stress in the multiple-seam influence zone.