ISMS 2016

Operational and Environmental Mine Health and Safety Practice and Innovation

Editors: H.S. Mitri, S. Shnorhokian, M.K. Kumral, A. Sasmito, A. Sainoki

Symposium Proceedings http://isms2016.proceedings.mcgill.ca

August 13-19, 2016 McGill University, Montreal, CANADA

3RD INTERNATIONAL SYMPOSIUM ON MINE

SAFETY, SCIENCE AND ENGINEERING

Operational and Environmental Mine Health and Safety Practice and Innovation

Published by McGill University (2016)

ISBN: ISBN 978-1-77247-005-5

EDITORS

HANI MITRI

SHAHE SHNORHOKIAN

MUSTAFA KUMRAL

AGUS SASMITO

ATSUSHI SAINOKI

i

Table of Contents

Preface v

Organizing Committee vi

International Advisory Committee vii

Part 1 b-value as a criterion for the evaluation of rockburst hazard in coal mines 1 Grzegorz Mutke, Aleksandra Pierzyna, Adam Barański Quantitative evaluation of stope damage induced by seismic waves 6 Atsushi Sainoki, Hani S. Mitri Influence of weak planes on rockburst occurrence 12 Amin Manouchehrian, Ming Cai A model of rockburst including geological dynamic conditions and mining 18 Jun Hana, Ting Rena, Tianwei Lana, Feng Zhua, Chen Caob, Hongwei Zhanga, Guoshui Tanga Rockburst experiences in Cheves Hydropower Project, Perú 24 Santiago Veyrat, Jose-Miguel Galera, Marcos Sancho, H. Andersson, W. Thoese, and, C. Rietschel Rockburst mitigation experiences on underground projects in the Cheves Hydropower project in the Peruvian Andes 38 Santiago Veyrat, Jose-Miguel Galera, Marcos Sancho Destress blasting on the border of safety pillars 45 Petr Konicek, Jiri Ptacek, Alejandro Mazaira Powered support selection for longwall workings in dynamic load conditions 54 Stanisław Prusek, Sylwester Rajwa, Andrzej Walentek, Wojciech Masny Evolution of grouting methods for dynamic supports in broken ground 60 Francois Charette, Trond Skogseth Large scale panel destress blasting parametric study 65 Isaac Vennes, Hani Mitri Improving ground control safety in deep vein mines 71 Joseph Seymour, Donovan Benton, Michael Raffaldi, Jeffrey Johnson, Lewis Martin, Shawn Boltz, Jerald Richardson Numerical investigation of EDZ development around a deep polymetallic ore mine 78 Mountaka Souley, Marwan Al Heib, Vincent Renaud Estimating the probability of unsatisfactory performance associated with the instability of mine developments 84 Wael Abdellah, Hani Mitri

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Numerical modelling of time-dependent skin degradation of an isolated pillar 90 Atsushi Sainoki, Hani S. Mitri Quantitative analysis of haulage system instability in deep hard rock mines using numerical modeling 96 Shahé Shnorhokian, Bryce MacNeil, Hani Mitri Minimum strength required for resisting cyclic softening/failure of cemented paste backfill at early age 102 Tikou Belem, Mamert Mbonimpa Analysis of failure in a salt room and pillar mine 108 Farid Laouafa, Mehdi Ghoreychi Lessons in slope stability management from Kinross’ Tasiast mine, Mauritania 114 Korhan Tasoren, Gillian Gardhouse, P.Eng., Dr. Jerry Ran, P.Eng. Effect of buttress on reduction of rock slope sliding along geological boundary 121 Ryota MORIYA, Daisuke FUKUDA, Jun-ichi KODAMA, Yoshiaki FUJII Validation of empirical rock mass classification systems for rock slopes 127 Hassan Basahel, Hani Mitri Application of InSAR for monitoring deformations at the Kiirunavaara Mine 133 Karola Mäkitaavola, Britt-Mari Stöckel, Jonny Sjöberg, Stephen Hobbs, Jonas Ekman, Michael Henschel, Anura Wickramanayake Modelling the impact of particle flow on rigid structures: experimental and numerical investigations 140 M.A. Meguid, Ge Gao, M.M. Abouelkair and M.Z. Abdelrahman A versatile model for the evaluation of subsidence hazards above underground extractions 145 Peter Cain, Ph.D., P.Eng., Dr. Ing. Karsten Zimmerman Slope stability analysis and prediction based on the limit equilibrium method of Luming Molybdenum Mine's West-I and North Region 154 HUANG Zhi-an, LIU Fang-zhe, WANG Hui, GAO Yu-kun Study on the similar materials simulation of the slope stability of the west-Ⅰ zone in Luming Molybdenum Mine 159 Huang Zhian, YangFei, Wang Hui, Zhang Yinghua, GaoYukun Stability and access implications of open pit mining through old underground mine workings 165 John G. Henning Thermomechanical impact of Underground Coal Gasification exploitation 170 Laouafa Farid Escapeway Solutions 176 Allison Deadman, Steven Durkin, Vincent Lawrence

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Estimating stope vein footwall stability using various constitutive modelling techniques 181 Andrew Pyon, Atsushi Sainoki, Hani S. Mitri Redesigning the geometry of the Makala Coal Mine to improve safety and productivity 187 Jean-Pierre Tshibangu, Fanny Descamps Shear behaviour of regular and irregular rock joints under cyclic conditions 193 S. M. Mahdi Niktabar, K. Seshagiri Rao, Amit Kumar Shrivastava 3D geological modelling method based on hybrid data model 199 Xue-xi Chen, De-fu Che Measurement and analysis of virgin-rock temperature in Huanren Metal Mine 204 CHANG De-qiang, LIU Jing-xian, MAO Ning, GE Shuang-you The tensile properties of GFRP bars at different loading rates 208 Wenxue Chen, Jun Wu, Yuzhao Jiao, Jiewen Zheng, Xue Li Part 2 A definition and evaluation index system of aging mines 214 MA Hui, LIAN Huiqing, ZHU Hongjie Numerical simulation of thermodynamic performance in a honeycomb ceramic channel 219 Bo Lan, You-Rong Li Dust Dispersion Analysis Based on the Rosen-Rammler Distribution Function 225 Yao Haifei, Zhang Qun Fuzzy comprehensive evaluation of emergency capability of port coal storage base with G1 method 231 Siheng Sun, Guozhong Huang, LongzheJin, Yage Li, Xue Zhao Study on External Protective System of Waterproofing Refuge Chamber in Guilaizhuang Gold Mine 236 Shengnan Ou, Longzhe Jin, Song Li, Shu Wang, Yage Li, Zhiling Huang Hazard detection and comprehensive control technologies of the integrated resource coal mine goafs in China 243 Wen LI Multi-bed type oxidation reactor applied to the coal mine ventilation air methane 248 Weifeng Zou, Bo Lan, Jiandong Kang Water disaster investigation and control in coal mine of Southern China 254 LIANG Qing-hua The lifting and separating system for ground maneuvering rescue equipment 258 GAO Yukun, GONG Xuejiao, HUANG Zhian, ZHANG Yinghua Safety and stability of the maneuvering rescue platform 264 GAO Yu-kun, Ji Yu-Chen, HUANG Zhi-an, ZHANG Ying-hua

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The performance optimization experiment of a wet high-frequency vibrating grid 268 Zhang Yinghua, Liu Jia, Huang Zhian*, Gao Yukun Borehole docking system design for underground refuge chamber and ground maneuver rescue equipment 276 ZHANG Ying-hua, SONG Shou-yi, HUANG Zhi-an, GAO Yu-kun Use of the Analytic Hierarchy Process in safety control of rescue equipment 281 Zhang Yinghua, Sun Qian, Huang Zhian, Gao Yukun Research on new high-water solidified materials to reinforce coal and eliminate gas outburst 285 Yinghua Zhang, Peiling Zhou, Zhian Huang, Yukun Gao, Qiang Luo Key technologies for extinguishing large-area goaf fires in closely spaced shallow coal seams 291 Botao Qin, Quanlin Shi, Junzhe Yang, Hetang Wang, Lihui Zhang The assessment of emergency capability of coal mines based on AHP-fuzzy comprehensive method 296 Shu Jiao Tong, Zong Zhi Wu, Ru Jun Wang, Ying Quan Duo Study on local temperature controlling technology and equipment in heat disaster coal well 302 Haijun Wu, Haifei Yao, Changfu Xu, Haiyan Wang, Laizai Tan Effect of forming technology on oxygen supply performance of oxygen candles in refuge spaces 308 Liu Jian-guo, Jin Long-zhe, Gao Na, Wang Wei-xiang, Shen Jie Experimentation on a new type of mining emergency rescue relay cabin 314 Shen Jie, Gao Na, Jin Long-zhe, Fan Lin-yu, Wang Wei-xiang, Liu Jian-guo Chemical equipment failure probability correction model based on the Multi-layer Grey Evaluation Method 319 Yue Zhang, Wentao Yang, Yuanyue Zhu, Kai Zhang Mechanisms and applications of formatting unsafe behaviour motivation 325 Yuebing Zhang, Zhiliang Wang Examining safety and sustainability in longwall coal mining through case studies of disasters and reviewing global trends in environmental stewardship 329 Ben de Wit, Xinglong Zhao, Malcolm Scoble Research on Safety Incentive Model of Coal Miners and Strategy Analysis 335 Cao Qinggui, Xie Changzhen, Zhang Shouming, Zhang Sai, Liu Weihua A new Virtual Reality training system for underground coal mines 341 Hui Zhang, Xueqiu He, Baisheng Nie, Hani Mitri

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Study of roadside packing to go with gob-side entry retaining technology on crisp surrounding and blasting face in the Xinzhuang mine 346 Ya-ge LI, Wei-xiang WANG, Long-zhe JIN, Shu WANG, Jiang LU Optimization of bit nozzle parameters of reverse circulation sampling used in coal mines 351 Kang Jianning, Hu Qianting, Zhang Rui Electrical equipment certification in Canadian underground coal mines – problem solved? 358 Ronald (Ron) F. King, P.Eng., Peter Cain, Ph.D., P.Eng. Improving shovel safety using SAFEmine’s situational awareness technology 364 Marco de Werk, Todd Ruff Risk acceptance and risk perception of the Soma underground coal mine disaster 368 H. Şebnem Düzgün, Evren D. Yaylacı From operational hazards to organizational weaknesses: changing the focus for improvement 375 Georges Loiselle, Dragan Komljenovic, Mustafa Kumral Risk management in the mining sector through complex systems 381 Maria S. Q. Domingues, Adelina L. F. Baptista, Miguel T. Diogo Application of Cognitive Task Analysis in mining operations 387 Serenay Demir, Elie Abou-Jaoude and Mustafa Kumral Avoiding workplace accidents: the importance of pre-job safety analyses 393 Colin Morrish Notification systems and risk management 398 Maria M. Antunes, Miguel T. Diogo, Joaquim Góis Full-scale fire experiments in an underground mine 403 Rickard Hansen Diesel exhaust exposures in an underground mine 409 Hugo Coulombe, Guillaume Lachapelle, Eve Neesham-Grenon, Stéphane Hallé, Maximilien Debia Liquid-solid coupling analysis of tailings dam under complex engineering conditions 413 Shuren Wang, Haiqing Zhang, Zhengsheng Zou, Xiliang Liu Numerical analysis of Westwood Mine tailings embankment stability during the restoration phase 419 Yaya Coulibaly, Tikou Belem, Li Zhen Cheng Application of an economy comparison model for mine cooling system technology 426 Miao Dejun, Chang Dehua, Tan Dongwei

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Behaviour of cable bolts in shear: experiment and mathematical modelling 432 Naj Aziz, Ali Mirza, Haleh Rasekh, Jan Nemcik, Xuwei Li Operating conditions of a mine fan under conditions of variable resistance 442 Zhang Yinghua, Chen Li, Huang Zhian, Gao Yukun Analysis of slag debris flow initiation based on laboratory tests of slag 447 Hongbiao Zeng, Hongming Yu Hydrogeological challenges and strategies at McArthur River Operation 453 Xiaoyou Yun, Baoyao Tang, Greg Murdock, Brian McGill, Brian Mattie Investigation and design of a mining emergency rescue relay cabin 459 Jie Shen, Longzhe Jin, Na Gao, Linyu Fan, Weixiang Wang Part 3 Mathematical model for gas diffusion from non-homogeneous coal particles 465 Yanwei Liu, Mingju Liu, Hani S. Mitri Permeability prediction for coal reservoirs and reconstruction of a different scales pore-fractures network 471 Ni Xiaoming, Chen Wenxue, Li Zheyuan, Gao Xiang Quantitative risk assessment on large-scale oil depots of opencast coal mine 477 Ru Jun Wang, Shu Jiao Tong Development and realization of a coal and gas outburst simulation device 482 NIE Baisheng, HU Shoutao, LI Xiangchun, MENG Junqing, FAN Penghong The distribution and origin of hydrogen sulfide abnormal enrichment coal mines in China 487 Deng Qigen, Liu Mingju, Zhang Sai, Cui Xuefeng, Wen Jiejie Accumulation pattern of groundwater containing Hydrogen Sulfide in the southern Junggar basin in China 494 Deng Qigen, Liu Mingju, Cui Xuefeng, Wen Jiejie Application research on gas drainage technology at low permeability coal seam 498 Shengchu Huang, Li Zhang Influence of temperature on gas desorption-diffusion laws of coal particles 503 Linchao Dai Numerical simulation of gas migration tule in mining-induced fractures field 508 Cao Jie, Li Minghui, Li Wenpu Methods of measuring the effective drainage radius of 3# coal seam in Huoerxinhe coal mine 514 Linchao Dai, Kai Wang, Jie Cao, Bo Wang

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Temperature Variation of Coal during the Gas Adsorption Process 520 Tao Yang, Baisheng Nie, Xuexi Chen, Peng Chen Statistical analysis of coal mine accidents in China from 2005-2013 527 Xinsheng Hu, Zongzhi Wu, Rujun Wang, Yingquan Duo Analysis of coal crack and permeability characteristics slotted by water jet and the effect on gas outburst 531 Chunming Shen, Baiquan Lin, Lang Zhang, Dong Wang Numerical simulation on Gob gas migration law 536 He Ning, Xiang Cong Research on the negative pressure distribution law and its application for boreholes in coal seam bedding gas extraction 540 Linchao Dai, Kai Wang Mathematical simulation and experiment of CBM detection 547 LIANG Qing-hua Numerical modelling and rescaled range analysis on spontaneous combustion under surface methane drainage in a Chinese coal mine 552 Xincheng Hu, Shengqiang Yang, Wei Victor Liu, Jiawen Cai, Xiuhong Zhou The laws of gas-solid coupling of coal-bed gas in deep high gassy coal seams 557 Zhou Aitao, Wang Kai, Shen shangkun Numerical simulation for propagation characteristics of outburst shock wave and gas flow when outburst prevention facilities fail 564 Zhou Aitao, Wang Kai, Kong Yuyu, Liu Ang Influence of Fundamental Internal Parameters to Low-Temperature Critical Temperature in Coal Self-Ignition Process 574 WANG Hai-yan, YAO Hai-fei, ZHENG Zhong-ya, XU Chang-fu, ZHANG Qun, ZHU Hong-qing Experimental study of negative pressure gas drainage influences on coal moisture content 581 Shaojie Chen, Longzhe Jin, Xianglong Liu The laws of gas-solid coupling of coal-bed gas in deep high gassy coal seams 585 Zhou Aitao, Wang Kai, Shen shangkun Grey Correlation Model of influence factors analysis of ventilation time in single-way tunnel 591 Yang Cao, Hongguang Ji Numerical research on the airflow distribution in mine tunnels 595 Cui DING, Xueqiu HE, Baisheng NIE Application of a Ventilation Management Program for improved air quality 600 Euler De Souza

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Numerical Study of simultaneous methane and coal dust dispersion in a room and pillar mining face 605 Yueze Lu, Saad Akhtar, Agus P. Sasmito, Jundika C. Kurnia Reducing Heat Stress Exposure in Mines 611 Ryan Anderson, Euler De Souza Effect of hydrogen on explosion of methane-air mixture 616 YANG Chunli, LI Xiangchun, Xu Teng, Qu Wenzhong, Liu Yanli Drilling escape and rescue system in Wangjialing coal mine 622 Zhiling Huang, Longzhe Jin, Yuntong Ma, Hongmin Zhu Effects of immediate roof thickness on lower sub key strata movement in ends of large mining height panel 628 Chuang LIU, Huamin LI, Dongjie JIANG, Huigui LI, Junfa FENG Study on the performances of a protective door in coal permanent refuge havens 634 Gao Na, Jin Long-zhe, Fan Lin-yu, Shen Jie, Wang Wei-xiang, Liu Jian-guo Numerical modelling of the goaf: methodology and application 640 Samar S. Ahmed, Marwan ALHeib, Yann Gunzburger, Vincent Renaud, Jack-Pierre Piguet A coal enterprise scientific-technical progress evaluation system based on the Internet 647 Shanyang Wei, Longlong Yang, Zhongbei Li, Shiwei Ding Simulation of strata behaviour laws of a coal mine in Jungar Coalfield 651 Zhu Bin, Li Ge, Kou Weifeng, Li Haibin Goaf area exploration in Anjialing surface mine based on the C-ALS 658 WANG Jun, ZHOU You, ZHAO Ruhui Application of the strength reduction method in coal mine roof support design 659 Gabriel Esterhuizen, Ihsan Berk Tulu Numerical simulation of the migration laws of supports and surrounding rock for coal seams of large dip angle 666 Huang Zhian, Feng Caiyun, Wang Hui, Zhang Yinghua, Gao Yukun Theoretical analysis of support stability in large dip angle coal seam mined with fully-mechanized top coal caving 672 Zhang Yinghua, Ji Yucheng, Huang Zhian, Gao Yukun, Ji Yuchen Theoretical research on roof damage of the fully mechanized top-caving mining coal seam with deep dip angle 677 ZHANG Ying-hua, LUO Qiang, HUANG Zhi-an, GAO Yu-kun Characteristics of acoustic wave velocity variation in the process of deformation and failure of loading coal 681 LI Xiangchun, NIE Baisheng, YANG Chunli, CUI Zhe, MAO Yanjun

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Numerical Simulation Technique for Gateroad Stability Analysis under Fractured Ground Condition 687 Lishuai Jiang, Atsushi Sainoki, Hani S.Mitri, Nianjie Ma

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ORGANIZING COMMITTEE Xueqiu HE – International Chair University of Science and Technology Beijing Xiaolin YANG – International Chair Henan Polytechnic University Hani MITRI – General Chair McGill University Baisheng NIE – Technical Program Co-chair China University of Mining and Technology Beijing Mustafa KUMRAL – Technical Program Co-chair McGill University Agus SASMITO – Technical Program Stream Chair McGill University Longzhe JIN – Technical Program Committee University of Science and Technology Beijing Mingju LIU – Technical Program Committee Henan Polytechnic University Atsushi SAINOKI – Technical Program Stream Chair McGill University Shahe SHNORHOKIAN – ISMS Secretary McGill University Wenxue CHEN – ISMS Secretary Henan Polytechnic University Xiangchun LI – ISMS Secretary China University of Mining and Technology Beijing Na GAO – ISMS Secretary University of Science and Technology Beijing Monika SKONIECZNY – Tradeshow McGill University Isaac VENNES – Field Trips McGill University Andrew PYON – Workshop McGill University Hui ZHANG – Web site China University of Mining and Technology Beijing

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INTERNATIONAL ADVISORY COMMITTEE

• Marwan AL-HEIB • Victor ARAD • Naj AZIZ • Manoj BAGDE • Ming CAI • Euler DE SOUZA • José-Miguel GALERA • Yann GUNZBURGER • John HENNING • Guozhong HUANG • Vlad KECOJEVIC • Jun-ichi KODAMA • Petr KONICEK • Farid LAOUAFA • Xiliang LIU • Rudrajit MITRA • Jan NEMCIK • Vic PAKALNIS • Jack-Pierre PIGUET • Stanislaw PRUSEK • Jerry RAN • Mani Ram SAHARAN • Malcolm SCOBLE • Jean-Pierre TSHIBANGU • Yongqiang YU • Yinghua ZHANG

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PREFACE The mining industry faces significant challenges associated with the extraction of deeper ore deposits having increasingly more complex geotechnical and geological conditions. This inevitably led to much greater attention to personnel and equipment safety research and practice. In addition to this development, safety science itself has made remarkable progress in recent decades owing to leap advancements in engineering technologies, human physiology, data analysis and processing, as well as new business and organization structures. In this scope, mining, nuclear and aerospace industries allocate important resources and create initiatives to engage increasingly more safety science and research. In line with this, McGill University organized and hosted the 3rd International Symposium on Mine Safety Science and Engineering (ISMS 2016) in Montreal in collaboration with its partners, the University of Science and Technology Beijing, China University of Mining and Technology (Beijing), and Henan Polytechnic University. The symposium was held from August 13 to 19, 2106 with the theme “Operational and Environmental Mine Health and Safety Practice and Innovation”. Essential objectives of ISMS 2016 were to discuss safety-related problems; to create awareness, synergy and recognition to mine safety; and, to ensure knowledge transfer and mobilization amongst industry practitioners, mining engineers and academics. The authors of the 119 papers in this volume of proceedings come from 12 countries – a testimony to the true international flavour of this symposium. The volume is organized in three main sections: (i) Hardrock (Seismicity and rock burst, blasting, support design, pillar and backfill stability, ground control, subsidence and slope stability); (ii) Technology (equipment, occupational health and safety, organizations and human factors); and (iii) Coal (gas and ventilation, ground control and coal mining techniques). All papers included in this set of proceedings have been peer-reviewed, edited and formatted to a uniform layout. The proceedings can be found online at

http://isms2016.proceedings.mcgill.ca

We would like to thank all the symposium sponsors for their generous support. We are indebted to members of the International Advisory Committee for their relentless efforts. Special thanks are due to the paper reviewers. We sincerely hope that this volume of proceedings will be interest to mine safety practitioners, researchers and technology developers. Editors Hani Mitri Shahe Shnorhokian Mustafa Kumral Agus Sasmito Atsushi Sainoki

Part 1

Hardrock

*Corresponding author – email: wre544@gmail.com

ISMS 2016 Paper No. 230 Estimating the probability of unsatisfactory performance associated with the instability of mine developments Wael Abdellaha, Hani Mitrib a,* Department of Mining and Metallurgical Engineering, Assiut University, Assiut, Egypt, 71516 b Department of Mining and Materials Engineering, McGill University, Montreal, Canada H3A0E8

ABSTRACT Mine developments are the main access to extract tabular ore deposits in deep underground mines. Therefore, their stability is considered the principal priority during the mine production plan. The success of ore extraction mainly depends on the stability and serviceability of mine developments. Mine development instability is expensive and is a risk to personnel and equipment and in turn, it raises operational costs (e.g, repair costs, slashing, rehabilitation costs, costs of adding secondary support, miners wages and delay of production) (Ellefmo, and Eidsvik, 2009; Abdellah et al. 2014a; 2014b; 2014c). This paper aims to develop a hybrid approach in which deterministic numerical modelling is integrated with probabilistic methods to estimate the probability of unsatisfactory performance (e.g. rating and ranking) associated with the instability of mine developments with respect to mining sequences adopting Rosenblueth’s Point-Estimate Method (RPEM). A three-dimensional, elastoplastic, finite difference model (FLAC3D) is created (Itasca, 2009). The results are presented and categorized with respect to the probability of instability and the mining stage. KEYWORDS: Mine developments; numerical modelling; Rosenblueth’s Point-Estimate Method (RPEM); probability of unsatisfactory performance 1. INTRODUCTION

Many Canadian metal mines adopt a sublevel stoping mining method with delayed backfill, as shown in Figure 1. In this method, ore is mined out into stopes (blocks), which are drilled and blasted. The blasted ore from each stope is mucked out with loaders and transported from a draw point to a nearby ore pass or dumping point. Mine developments (e.g., haulage drifts, cross-cuts and their intersections) are the only access where loaders and/or trucks travel through on multiple levels. Therefore, their serviceability must remain active for a few years (e.g., production plan of the mine) (Wei et al., 2012; Zhang and Mitri, 2008). The following five parameters should be considered in the design process: safety, serviceability (e.g., quality of technical solution), economics (e.g., cost), environment, and rockmass properties. For example rockmass properties alone are complex and are associated with uncertainty in deep underground mines. These five factors should be maintained and combined together in the decision-making process.

Consequently, wrong decision may lead to unwanted risks. In order to facilitate decision-making, probabilistic analysis should be adopted (Einstein, 1996; Sturk et al., 1996; Abdellah et al.,

Figure 1: Section view shows sublevel stoping mining method

2014c). The stability performance of mine developments could be evaluated by adopting analytical, empirical, and numerical modelling techniques. The analytical methods such as those provided by Kirsch (1898), Bray (1977), Bray and Lorig (1988), and Ladanyi (1974) cannot provide adequate solutions for complex mining problems. Empirical methods such as the stability graph method, have become widely used in Canadian underground mines. These methods are based on the past experiences and rockmass classification systems.

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They employ certain geomechanical characteristics of the rockmass to provide guidelines on stability performance and to determine the rock support requirements. However, these methods cannot take all the important influence factors into account. Therefore, numerical methods have become widely accepted in mine design and feasibility studies.

Numerical methods have the potential not only to solve complex mining problems, but also to help engineers and researchers better understand and assess failure mechanisms, estimate geotechnical risks, and design rock reinforcement systems more effectively. Numerical analyses can be performed deterministically or probabilistically. In a deterministic analysis, the average values of the rockmass properties are used as input parameters, and a unique model result is obtained. However, no information can be obtained about the likelihood of failure due to the inherent variability of model input parameters. Thus, probabilistic methods are employed to carry out stochastic analyses to overcome this shortcoming. The uncertainty associated with the estimation of rockmass properties has a significant impact on the design of underground excavations. Thus, a reliable estimate of the strength and deformation characteristics of rockmass is required for the stability analysis. Therefore, probabilistic analysis is adopted in this investigation using Rosenblueth’s point-estimate method (RPEM). 2. FAILURE EVALUATION CRITERION

In order to assess the stability of the mine development intersection, a performance criterion must first be selected. This may be one of numerous conditions such as maximum permissible floor heave ratio or roof sag ratio, or allowable stress concentration factor (normally associated with linear elastic analyses), or a yielding condition such as Mohr-Coulomb or Hoek-Brown (Zhang and Mitri, 2008; Abdellah et al., 2012). The choice of a performance criterion is dependent on the application and field observations. In this current study, a yield-based criterion has been selected in which Mohr-Coulomb is used as the failure condition. The strength-to-stress ratio is a readily available parameter in FLAC3D (ITASCA, 2009) and a form of a safety factor. For mining applications, it is recognized that the factor of safety of permanent mine openings such as mine shaft and mine infrastructure should be higher than that used for mine developments, which are required to be opened and functional for the life of a mine (production) plan. Therefore, in this study, a strength-to-stress ratio of 1.4 was deemed an appropriate safety factor, given the fact that the required service life of the developments in the study area is only a few years.

Also, the unsatisfactory performance is determined when the extent of the strength-to-stress ratio contours, corresponding to Mohr-Coulomb strength-to-stress ratio <1.40 exceeds the anchorage limit of the rockbolt from the excavation surface. For a 2.40 m bolt, the minimum support limit from excavation surface is 2.10 m. Thus, the stability of mine development intersection becomes unsatisfactory if the following two conditions are met together:

Mohr-Coulomb strength-to-stress ratio based yielding <1.40.

Extent of the strength-to-stress ratio contours >2.10 m.

3. CASE STUDY

To examine the stability of mine development intersections, a plan view of the 1540 level is shown in Figure 2. The study zone is divided into the following three zones; hanging wall (HW), orebody, and footwall (FW). Haulage drifts, mine developments and their cross-cuts are driven into the footwall rockmass. The stope dimensions are 12×15×30 m (L×W×H). The stopes are extracted and then tight filled with a mixture of pastefill and waste rock.

Figure 2: Level plan shows the mine development intersection#6 under the study.

The orebody has a strike length of approximately

220 m. To maintain better ground conditions, the stoping sequence from one level to another and along the ore strike should follow a pyramid shape as shown in Figure 3. Such sequence helps mitigate stress concentration and facilitate secondary stope mining thus increasing safety and mining recovery rate. The stability analysis is conducted for the orebody, whereby a planned sequence of 72 stopes

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over six production levels (1600, 1570, 1540, 1510, 1480 and 1450) is simulated in the form of 18 mine-and-fill numerical model steps. While doing so, the strength-to-stress ratio is monitored on level 1540 at the intersection of the haulage drift with the cross cut #6 location.

Figure 3: Pyramidal shape stoping sequence along the

orebody strike. 4. NUMERICAL ANALYSIS

Rockmass properties are significant geotechnical design input parameters. These parameters are never known precisely. There are always uncertainties associated with them. Some of these uncertainties are due to lack of knowledge or limited collected data and some are intrinsic. Furthermore, some may arise from errors in testing (e.g. estimating strength of intact rocks, mapping the joint spacing, assessing the joint surface condition), and random data collection. All these uncertainties are attributed to the inherent nature of the rockmass characterization (Glaser and Doolin, 2000). Therefore, it is important to address the effect of these parameters on the design using probabilistic methods of analysis. Well assessment of uncertainty in rockmass characterization can assist to better understand how the decision of rock support design systems is affected by it.

In this investigation, the focus is the uncertainty arising from the rockmass properties (e.g. rockmass of footwall) and their effect on the stability of mine development intersections (e.g. which are driven in the footwall). Probabilistic methods provide a rational and efficient means of characterizing the inherent uncertainty that is common in geotechnical engineering. Because of the inherent uncertainty associated with parameters such as the rockmass properties around the openings, there is also uncertainty as to when and where additional rock support is required. Thus, predicting the probability of unsatisfactory performance using probabilistic analysis approaches together with the developed

numerical modelling (deterministic techniques) becomes necessary.

4.1 Deterministic analysis Deterministic analysis is performed to investigate the effect of mining sequence on the stability of the intersection #6 on level 1540. The physical and geomechanical properties of rockmasses used in the deterministic analysis are listed in Table 1 (Abdellah et al., 2013).

Table 1: Physical and geomechanical properties of rockmass properties used in the model (Abdellah et al., 2013).

The deterministic results show that the values of

strength-to-stress ratio deteriorates as mining progresses in the roof, wall, pillar corner left, and pillar corner right. However, the two conditions of failure evaluation criterion are met in the roof after mining step 6 until the end of mining activity (e.g., from step 6 to step 18), whilst the conditions are not met in the wall of the intersection #6 during the whole mining steps. The two evaluation conditions are achieved in the pillar corner left after mining step 9 and in the pillar corner right after mining step 10. The complete deterministic analysis results of strength-to-stress ratio with respect to all 18 mining steps modelled are plotted in Figure 4. As can be seen, the wall the strength-to-stress ratio is well above the threshold of 1.4 thus suggesting satisfactory performance (e.g., the depth of the boundary limit is zero along all mining steps). For the roof at the intersection #6, the strength-to-stress ratio drops below the 1.4 limit after mining step 6. For the pillar corner left and pillar corner right, the ratio drops after mining steps 9 and 10, respectively.

Rock Rockmass properties C

MPa 𝜑 (0)

σt MPa

E GPa

υ γ Kg/m3

Ψ (0)

HW 5.1 52 0.53 45.5 0.24 2780 13.0 ORE 4.3 46.7 0.56 43.8 0.30 4530 11.68 FW 5.7 54.9 0.51 65.0 0.23 3170 13.73 BF 1 30 0.01 0.01 0.30 2000 7.50

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Figure 4: Extent of strength-to-stress contours at ratio of ≤

1.4 at various mining step (deterministic analysis).

In light of these results, it can be said that secondary support may be recommended after mining step 6 in the roof (i.e. after 30 stopes have been extracted). For pillar corner left and pillar corner right, the secondary support may be recommended after mining step 9 (i.e., after 40 stopes have been extracted) and step 10 (i.e., after 44 stopes have been extracted), respectively. While these results are useful, the effect of the inherent uncertainty in rockmass properties is still unknown; hence the probabilistic analysis is necessary. This is presented in the following section. 4.2 Probabilistic analysis

Due to the heterogeneity of the rockmass, data from underground excavations are limited. Therefore, a great deal of uncertainty is inherent in the design of underground excavations. In order to develop a reliable design approach, one must use methods that incorporate the statistical variation of the numerical model input parameters representing the rockmass properties, i.e. mean, variance and standard deviation, as well as the design of rock failure criteria (Kwangho et al., 2005). Probabilistic material properties of the footwall are assigned (see Table 2). The means and standard deviations of these values are picked from the assumed normal distribution.

The sensitivity analysis can be carried out by varying a single parameter (random variable) at each run based on a specified coefficient of variation (COV) and monitoring the effect of this variation on the applied performance criterion. The variable at each run has one value of (µ − σ), or (µ + σ) while keeping all other parameters constant (no change in their average values). Sensitivity analysis gives a good understanding of the effect of certain parameters on the overall model behaviour. However, no distribution is obtained for the output parameters (random variables).

Based on the parametric study (sensitivity analyses) that has been conducted by Musunuri (Musunuri et al., 2009), the most influential model input parameters on the stability of mine haulage drift are Young Modulus (E), cohesion (C), and angle of internal friction (φ).

Table 2: Stochastic properties of footwall rockmass.

4.2.1 Probabilistic results

The stochastic material properties of the footwall are assigned as listed in Table 2 above. The mean and standard deviations of these values are selected from a normal distribution. The Rosenblueth’s (Rosenblueth, 1975) point-estimate method (RPEM) of 2n (i.e., where n is number of stochastic input parameters) is adopted in this investigation for the above three input variables. The stochastic analysis results are plotted in Figure 5 for an average of 8 simulations (i.e., 23 = 8).

Figure 5: Average extent of strength-to-stress contours at

ratio of ≤ 1.4 at various mining steps (stochastic analysis).

As depicted in Figure 5, the stochastic analysis agrees with the deterministic analysis in terms of showing that the strength-to-stress ratio deteriorates as mining progresses. In the roof of intersection #6 at 1540 level, the strength-to-stress ratio falls below threshold (i.e., ratio <1.4 and length >2.1 m) after mining step 1, versus step 6 with deterministic analysis. In the wall, the ratio does not fall below the

0

2

4

6

8

10

12

14

16

18

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Exte

nt o

f stre

ngth

-to-s

tress

con

tour

s (m

) at

ratio

≤ 1

.40

Mining step

Roof Wall Pillar corner left Pillar corner right

0 2 4 6 8

10 12 14 16 18 20 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Ave

rage

ext

ent o

f stre

ngth

-to-

stre

ss c

onto

urs,

m (a

t rat

io <

1.4)

Mining step

Roof Wall Pillar corner left Pillar corner right

Rockmass property

Mean, µ

Standard deviation,

σ

Coefficient of variance,

δ Cohesion (MPa) 5.70 1.14 0.20

Friction angle, (º) 54.90 10.98 0.20 Young’s Modulus, (GPa)

65.0 13.0 0.20

Threshold = 2.1m

Threshold = 2.1m

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threshold in the deterministic analysis, whereas with stochastic analysis, it falls below threshold after mining step 15. For the pillar corner left, the performance criterion becomes unsatisfactory after mining step 5 with stochastic analysis where it deteriorates after mining step 9 with deterministic analysis. For pillar corner right, the failure also occurs after mining step 5 with stochastic analysis whereas its instability occurs after mining step 10 with deterministic analysis.

Comparing these two methods of analysis, stochastic results call earlier for secondary supports than with deterministic analysis (i.e., roof calls for secondary support after mining step 1 comparing with the deterministic analysis (after mining step 6)). Wall in deterministic analysis seems to be more stable and no support is required during the whole mining step comparing with probabilistic analysis (i.e., support may be required after mining step 15). Pillar corner left and right require support after mining step 5 with probabilistic analysis, compared with mining steps 9 and 10 with deterministic analysis. Thus, stochastic results appear to be more conservative than the deterministic analysis. The reason behind this is that the stochastic method takes into account the inherent uncertainty associated with input variables (i.e., rockmass properties). The deterministic analysis only uses the average values of rockmass properties as input parameters and gives only a single value as an output. However, the probability of unsatisfactory performance should be estimated to decide when and where secondary support is needed. 4.3 Probability of unsatisfactory performance

The probability of unsatisfactory performance is estimated for the roof, wall, pillar corner left and pillar corner right of intersection #6 at 1540 level, with respect to mining step. The suggested rating and ranking of likelihood of failure are given in Table 3. Standard normal distribution tables (Z-tables) are used to estimate the probability of failure, Pf. The Pf is obtained by subtracting the shaded

area �shaded area, Z∗ =

�Threshold (X)−average value(µ)standard deviation (σ)

��; under the probability

density function (PDF) curve from the unity which represents the total area�𝑃𝑓 = 1 − 𝑍∗� . The results for the probability of unsatisfactory performance are plotted and categorized in Figure 6. As can be seen, the probability of unsatisfactory performance at the roof of the intersection #6 is certain after mining step 4 (i.e., Pf >85%). Thus, the need for secondary support is necessary at this early stage (i.e., before

step 4). On the other hand, the wall calls for secondary support at latest stages (i.e., after mining step 16) as the probability of unsatisfactory performance becomes likely (i.e., 60<Pf <85%). The pillar corner right and left call for secondary support at middle stages (i. e., after steps 10 and 11, respectively) as the probability of instability becomes certain (i. e., Pf >85%).

Table 3: Suggested rating and ranking of probability of unsatisfactory performance (Abdellah et al., 2012).

Figure 6: Probability of unsatisfactory performance at roof,

wall, and pillar corner left and right of intersection #6 at level 1540 at various mining step.

5. CONCLUSION

Mine developments, such as haulage drifts, cross-cuts and their intersections, play a vital role in providing access to ore extraction areas for mine production. The stability of mine developments is thus of crucial importance during the life of a mine plan. This paper examines the stability of mine development access intersection #6 with respect to planned mining sequence. A 3D elastoplastic finite difference model is created using FLAC3D and employed in conjunction with the probabilistic method of analysis (RPEM) of 2n, for a development intersection situated 1.5 km below the ground surface. The stability or performance of the

Rating Ranking Probability of Unsatisfactory Performance, Pf

1 Rare < 5% May occur in exceptional circumstances

2 Unlikely 5%-20% Could occur at some time

3 Possible 20%-60% Might occur at some time

4 Likely 60%-85% Will probably occur in most circumstances

5 Certain >85% Expected to occur in most circumstances

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intersection is evaluated in terms of the strength-to-stress ratio. The stability performance of mine intersection is evaluated on the basis of the primary rock support length comprising 2.4 m resin grouted rebars in the roof and wall. The stability performance of the intersection is considered unsatisfactory if the strength-to-stress contours correspond to ratio <1.4 and extends beyond the anchorage limit of the rockbolt (i.e., >2.1 m).

The results are presented and categorized with respect to probability, instability, and mining stage. The probability of unsatisfactory performance, Pf, of the intersection #6 is certain (Pf >85%) in the roof after mining step 4, and is likely (i.e., 60<Pf <85%) in the wall after mining step 16 (i.e., at the end of the mining step). The pillar corners right and left call for secondary support at the mid of mining step (i.e., steps 10 and 11, respectively) as the probability of instability is certain (i.e., Pf >85%). Therefore, these results shed light on the requirement for the installation of enhanced support at the intersection during the planned mining step. 6. REFERENCES

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