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Dynamic failure risk of coal pillar formed by irregular shape longwall face:A case study

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International Journal of Mining Science and Technology 2018年第5期28卷 775-781页

作者： Yixin Zhao Hao Wang Shimin Liu Zonglong Mu Zhiguo Lu Beijing Key Laboratory for Precise Mining of Intergrown Energy and Resources School of Resources and Safety Engineering China University of Mining & Technology Department of Energy and Mineral Engineering G3 Center and EMS Energy Institute Pennsylvania State University University Park School of Mines China University of Mining & Technology

Irregular shape workface would result in the presence of coal pillar, which leads to high stress concentration and possibly induces coal bumps. In order to study the coal bump mechanism of pillars, static and dynamic stress overlapping(SDSO) method was proposed to explain the impacts of static stress concentration and tremors induced by mining activities. The stress and deformation in surrounding rock of mining face were analyzed based on the field case study at 1303 workface in Zhaolou Coal Mine in *** results illustrate that the surrounding rock of a workface could be divided into four different zones,i.e., residual stress zone, stress decrease zone, stress increase zone and original stress zone. The stress increase zone is prone to failure under the SDSO impact loading conditions and will provide elastic energy for inducing coal bump. Based on the numerical modelling results, the evolution of static stress in coal pillar as the size of gob increasing was studied, and the impact of dynamic stress was investigated through analyzing the characteristics of tremor activities. The numerical results demonstrate the peak value of vertical stress in coal pillar rises from about 30 MPa with mining distance 10 m to 52.6 MPa with mining distance 120 m, and the location of peak stress transfers to the inner zone of coal pillars as the workface moves forward. For the daily tremor activities, tremors with high energy released indicate high dynamic stress disturbance on the surrounding rock, therefore, the impact of dynamic stressing is more serious during workface extension period because the tremor frequency and average energy after workface extension are higher than those before the workface extension.

关键词： Coal bump Coal pillar Tremor Irregular shape longwall face Static and dynamic stress overlapping

Numerical investigation into the effect of backfilling on coal pillar strength in highwall mining

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International Journal of Mining Science and Technology 2018年第2期28卷 281-286页

作者： Mo S. Canbulat I. Zhang C. Oh J. Shen B. Hagan P. School of Mining Engineering The University of New South Wales CSIRO Energy QCAT1 Technology Court

This paper attempts to quantify the effect of backfilling on pillar strength in highwall mining using numerical modelling. Calibration against the new empirical strength formula for highwall mining was conducted to obtain the material parameters used in the numerical modelling. With the obtained coal strength parameters, three sets of backfill properties were investigated. The results reveal that the behavior of pillars varies with the type and amount of backfill as well as the pillar width to mining height ratio(w/h). In case of cohesive backfill, generally 75% backfill shows a significant increase in peak strength, and the increase in peak strength is more pronounced for the pillars having lower w/h ratios. In case of noncohesive backfill, the changes in both the peak and residual strengths with up to 92% backfill are negligible while the residual strength constantly increases after reaching the peak strength only when 100%backfill is placed. Based on the modelling results, different backfilling strategies should be considered on a case by case basis depending on the type of backfill available and desired pillar dimension.

关键词： Highwall mining Backfill Coal pillar Strength Numerical modelling

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

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International Journal of Mining Science and Technology 2018年第1期28卷 21-27页

作者： Peter Zhang Berk Tulu Morgan Sears Jack Trackemas Ground Control Branch NIOSHPittsburgh Mining Research Division Department of Mining Engineering West Virginia University

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 *** risk of ground falls during pillar recovery increases in multiple-seam mining *** hazards associated with pillar recovery in multiple-seam mining include roof cutters, roof falls, rib rolls, coal outbursts, and floor *** pillar recovery is planned in multiple seams, it is critical to properly design the mining sequence and panel layout to minimize potential seam *** paper addresses geotechnical considerations for concurrent pillar recovery in two coal seams with 21 m of interburden under about 305 m of depth of *** 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 *** 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 *** 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 *** 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.

关键词： pillar recovery Room-and-pillar Retreat mining Multiple seam Mining sequence pillar design

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

Optimization of room-and-pillar dimensions using automated numerical models

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International Journal of Mining Science and Technology 2019年第5期29卷 797-801页

作者： Gian Franco Napa-García Tais Renata Camara Vidal Félix Navarro Torres Mining Instituto Tecnológico ValeSanta LuziaMG 33040-900Brazil Exploration and Mineral Projects VALE S.A.Santa LuziaMG 33040-900Brazil

This paper presents an optimization methodology for the geometric configuration of a room–and–pillar mining project,considering safety and operational restrictions while maximizing ore *** underground manganese mine was chosen as a case study to investigate the capabilities of the presented methodology.A software package(OPTIMINE)was implemented to address the computational demand in an automated ***–dimensional finite difference analyses were performed in FLAC3D and used as implicit functions to consider safety in terms of the factor of safety and room *** obtained results showed that recovery could be increased from 44%to more than 80%in a safe manner.

关键词： Optimization Safety Room and pillar mining Ore recovery 3D numerical modeling

Surrounding rock control of gob-side entry driving with narrow coal pillar and roadway side sealing technology in Yangliu Coal Mine

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International Journal of Mining Science and Technology 2017年第5期27卷 819-823页

作者： Zha Wenhua Shi Hao Liu San Kang Changhao Key Laboratory of Safe and Effective Coal Mining School of Mining and Safety EngineeringAnhui University of Science&TechnologyMinistry of EducationHuainan 232001China

Gob-side entry driving can increase coal recovery ratio, and it is implied in many coal mines. Based on geological condition of 10416 working face tailentry in Yangliu Coal Mine, the surrounding rock deformation characteristics of gob-side entry driving with narrow coal pillar is analysed, reasonable size of coal pillar and reasonable roadway excavation time after mining are achieved. Surrounding rock control technology and effective roadway side sealing technology are proposed and are taken into field practice. The results showed that a safer and more efficient mining of working face can be achieved. In addition, results of this paper also have important theoretical significance and valuable reference for surrounding rock control technology of gob-side entry driving with narrow coal pillar under special geological condition.

关键词： Narrow coal pillar Gob-side entry driving Surrounding rock control Roadway side sealing technology

Influence of abnormal stress under a residual bearing coal pillar on the stability of a mine entry

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International Journal of Mining Science and Technology 2017年第6期27卷 945-954页

作者： Kang Jizhong Shen Wenlong Bai Jianbiao Yan Shuai Wang Xiangyu Li Wenfeng Wang Ruofan School of Mines China University of Mining & Technology School of Energy Science and Engineering Henan Polytechnic University Mewbourne School of Petroleum and Geological Engineering University of Oklahoma

Mine entries close to residual bearing coal pillars(RBCPs) will suffer large deformation that may cause rock burst. To better understand the deformation mechanism and develop safe and practical guidelines for entry design, most studies focus on the absolute size of the stress field in and around the pillar. In this paper, we present a new approach to analyze the abnormal stress field close to a RBCP that uses the stress concentration coefficient(SCC), stress gradient(SG), and coefficient of lateral pressure(CLP) to describe the stress state induced by the RBCP. Based on elastic theory and a mathematical model for the abutment stress in the RBCP, an analytical solution for the abnormal stress in the strata below the RBCP was derived and the characteristics of the abnormal stress for a case study of a coal mine in China were analyzed. The results show that the abnormal stress field around the pillar is characterized by four distinct zones: a zone of high SCC, high SG, and CLP less than 1, a zone of high SCC, low SG, and CLP less than 1, a zone of low SCC, SG close to 0, and CLP greater than 1, and a zone of SCC close to 1, SC close to 0, and CLP close to 1. Based on this zoning pattern, a numerical model was established to study the combined effects of the abnormal stress on the stability of the entry. The most stable zone was determined based on a model of the Xinrui coal mine and verified by field measurements at the mine. Our conclusions can be used as guidelines for designing safe entry layouts in similar geological and mining settings.

关键词： Residual bearing coal pillar Abnormal stress Entry layout Mechanical analysis Numerical computation

Design Optimization of pillar Bump Structure for Minimizing the Stress in Brittle Low K Dielectric Material Layer

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Acta Metallurgica Sinica(English Letters) 2020年第4期33卷 583-594页

作者： Xin-Jiang Long Jin-Tang Shang Li Zhang Key Laboratory of MEMS of Ministry of Education Southeast UniversitySipailou 2#Nanjing 210096China Jiangyin Changdian Advanced Packaging Co. Ltd.No.275 Binjiang RdJiangyin 214400China

Cu pillar bump offers a number of advantages for flip chip packaging,compared to the conventional solder ***,due to its rigidity structure,Cu pillar bump introduces a lot of stress to the chip,which causes the failure of packaging structures,especially for the advanced node devices which typically have brittle low K dielectric *** this paper,for the first time we propose two types of Cu pillar structures to reduce the *** first Cu pillar structure has bigger Cu dimensions at the *** other one is designed to add an additional Cu pad under the Cu pillar *** element analysis is used to study the stress of the both structures,and it is found that with the increase in pillar bump contact area over the chip surface,the stress decreases in both *** also indicate that the Cu pillar bump undercut induces higher stress,and thin Cu6 Snss intermetallic compound has less impact on the stress during flip chip mount *** study provides a novel way to improve the reliability by reducing the stress in the Cu pillar bump related packaging.

关键词： Cu pillar bump Flip chip Low K stress Undercut