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By Lauro Lacerda

Shotcrete is a highly adaptable and widely used underground construction material at infrastructure and mining projects around the world. In fact, many projects could not have been completed without its utilization. As underground projects became larger the use of mechanized wet-mix spraying gradually replaced manual dry-mix shotcrete applications. This paper details some of the reasons for that and provides information on the equipment and operational factors including safety and productivity required to successfully complete underground shotcrete projects.

Jun 13, 2021

By Roland Arnold, Richard Gradnik, Martin Zeindl

This paper presents the details of the Kramer tunnel project in the Federal State of Bavaria, Germany. This road tunnel, which has been under construction since December 2019, is the key component of the western bypass of the town of GarmischPartenkirchen. Once completed, it will relieve the town’s central district from enormous volumes of traffic. The contractor is the joint venture named ARGE Kramertunnel consisting of BeMo Tunnelling and Subterra. The whole project will be completed and handed over to the project owner, Staatliches Bauamt Weilheim, in 2023. The opening of the entire bypass section including the tunnel to traffic is planned for 2024. The tunnel, with a total length of 3,609 m (2.24 miles) and an estimated cost of EUR 178 million (incl. VAT), is designed as a single-tube, double-lane structure with one traffic lane for each direction of travel. The safety issue that exists for single-tube tunnels is solved by a parallel escape tunnel passable for vehicles. All tunnels and ducts are excavated according to the principles of the New Austrian Tunnelling Method (NATM). In order to reduce the geological risk for the owner, the escape tunnel was supposed to be completed before the design process for the main tunnel ever began. The exploratory tunnel was awarded to a competitor with an separate contract.

Jun 13, 2021

By Mohamed Younis, Keith Ward

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Jun 13, 2021

By Jesse Salai, Colin Sessions

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Jun 13, 2021

By Anton Hupfauf, Peter Raleigh

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Jun 13, 2021

By Aaron McClellan, Eric Levonas

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Jun 13, 2021

By Renee Fippin

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Jun 13, 2021

By Dave Dorfman, Ben DiFiore

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Jun 13, 2021

By David Watson, Steve Price

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Jun 13, 2021

By L. Uotinen, M. Rinne, R. Mishra

Underground mining gives rise to geotechnical hazards. A formal geotechnical risk assessment can help to forecast and mitigate these hazards. Frequentist probability methods can be used when the hazard does not have many variables and a lot of data is available. However, often there is not enough data for probability distributions, such as in the case of new projects. The risk assessment is often subjective and qualitative, based on expert judgement. The purpose of this research is to present the use of Bayesian networks (BNs) as an alternative to existing risk assessment methods in underground mines by combining expert knowledge with data as it becomes available. Roof fall frequency forecasting using parameter learning is demonstrated with 1141 sets of roof fall data across 12 coal mines in the USA. The prediction is nearly identical for individual mines, but when multiple mines are evaluated it is difficult to find a single best fit distribution for annual roof fall frequency. The BN approach with TNormal distribution was twice as likely to fit the observed data compared to the Poisson distribution assumed in the past. A hybrid approach using BN combining multiple probability distribution curves from historical data to predict annual roof fall is proposed. The BN models can account for variability for multiple parameters without increasing the complexity of the calculation. BNs can work with varying amounts of data, which makes them a good tool for real-time risk assessment in mines.

Jun 1, 2021

By Q. Liu, S. Liu, Y. Cui

To reduce the frequency of mining incidents and improve safety and production efficiency, it is important to develop technology for the autonomous positioning and navigation of mining equipment, without the assistance of satellite navigation signals. In this study we review the current technological environment for positioning and navigation underground and present several integrated navigation strategies. Existing underground positioning and navigation technology is described, and the performances of different methods based on this technology analysed and compared. The combination types and positioning effects of underground positioning and navigation strategies are discussed. Recent research directions for filtering methods and positioning estimation algorithms for underground positioning and navigation are reviewed. Finally, we summarize the future direction of underground positioning and navigation technology and related algorithms.

Jun 1, 2021

By A. K. Raina

Blast induced damage to the final wall of rockmass in any civil or engineering application is a major concern to the rock excavation engineers. There are at least four distinct techniques practised by blasting engineers to minimise the damage to the parent rock during blasting that are classified as contour blasting. One of the methods to achieve a smooth wall or rock surface in blasting is pre-splitting, where blastholes in the final row are mildly loaded with explosives and fired first in sequence before the rest of the holes in a round of blast to achieve a split in rockmass. Since blasting is one of the most adopted methods for achieving a final wall in a desired shape, while maintaining the rockmass integrity, the design of pre-split blast assumes importance. There are several variables that determine the final shape of the pre-split face including the rock type, the drill diameter, the explosive characteristics, the orientation of major joints with respect to drill hole, the linear charge density, the spacing of drill holes and inclination of the drill holes. This study attempts to determine the importance and sensitivity of variables in pre-split blasting using historical data from open excavations of a hydroelectric project in India. Keeping in view the multitude of variables, low correlation of independent variables with responses and high level of interactions between the variables that define the blast results, it was found suitable to use ANN to determine the importance and sensitivity of the variables involved. A new method to determine the blast induced damage to rockmass, namely, undamaged area (AUD%), is introduced. Half Cast Factor (HCF%) and AUD%were calculated for a high wall and trenches by digital image analysis technique using the Fragalyst software. Joint spacing and linear charge density emerged as most controlling variables in determining the final result of pre-blast. The relative importance of other variables assuming significance in the case of both the designed outputs is also discussed. A comparative analysis of HCF%and AUD%on the basis of results obtained from ANN analysis is also presented. A futuristic approach concept has also been introduced.

May 30, 2021

By Eugie Kabwe

The increase in depth of mines due to the depletion of surface deposits leads to unsafe tunnel construction and overall ore extraction. This is due to tunnel instability associated with the surrounding rock mass’s ability to exhibit creep that occurs over time. However, the explicit description of this mechanism using conventional constitutive models has proven to be difficult and inadequate. Hence, this paper presents an integrated viscoelastic viscoplastic visco-damage model with the Duvaut-Lions function. The presented model is calibrated by experimental data to determine the viscoelastic viscoplastic and visco-damage parameters. It is further implemented in a finite volume numerical code and verified on an experimental scale by numerical modeling of a cylindrical specimen. It describes the 3-phase creep mechanism perfectly as compared to the inbuilt conventional integer-order derivative model. Results from the conducted verification show that it can successfully be employed to describe the long-term behavior associated with the creep mechanism.

May 16, 2021

By ZHONGLING ZHAO, WANTING SONG, GUOZHONG LIU, LEIXIN SHI, ZUI WANG, YUANYUAN LIU, KE GAO, DONGHONG JIANG, WANG LUO, PEICHAO LU, Jianwei Cheng, WANCHENG ZHENG, Gang Zhao, YUNGANG WANG, JIANBING ZHAO

Coal spontaneous combustion is one of the disasters occurring in underground coal mines. As a typical case, the spontaneous combustion of broken coal left in the longwall gobs often happen which could greatly interrupt the normal mining production. Such concealed thermal event is featured as rapid development and difficulty in locating “hot” spots. If such spontaneous combustion fails to be timely prevented and controlled, a large amount of toxic gases (mainly CO) and smoke could flow and diffuse in the underground working sections, which could present safety hazards for coal miners. In this paper, based on an coal spontaneous combustion event happened in a Chinese gassy mine, the fire ratios derived from the gas composition data obtained through the tube bundle mine atmospheric monitoring system are used in determining the fire status. A comprehensive and collaborative fire extinguishing effort including inert gas injection, underground pressure balance, and sealing enhancement are made to control the fire progress. Simultaneously, the effects of such works to control the spontaneous combustion event have also been quantified using the fire ratios to justify again. Finally, the danger of coal spontaneous combustion in gob is eliminated, and the longwall panel is successfully re-opened for normal production.

May 6, 2021

By J. Christophe Niyonzima, Ekata Emmanuel Edo, Sayaf Mustafa, Liqun Luo

Iron and manganese both are important ferrous metals, and they usually need to be extracted separately for better usage. Ferromanganese ore from the Yunnan Province of China was investigated by subjecting it to reduction roasting, leaching, magnetic separation, hydrometallurgical separation process, X-ray diffraction (XRD), electron probe micro-analysis (EPMA) and scanning electron microscopy/energy-dispersive spectroscopy (SEM-EDS). It is noted that the ferromanganese ore contains valuable components or elements of 21.41 wt%Fe2O3 and 19.88 wt%MnO, which are 14.99% and 15.40% of the total of Fe and Mn, respectively, with a large amount of impurities comprising 33.00 wt% SiO2, 9.81%wt%Al2O3, etc. After roasting, microscopic examination showed the presence of haematite, magnetite, pyrolusite, psilomelane, hollandite, marcasite, pyrite, limonite, braunite and manganite, while XRD analysis showed that the magnetite content increases with the increase in roasting temperature, reflecting the increase in conversion of haematite to magnetite. Based on EPMAand SEM-EDS analysis, it was shown that the haematite and magnetite interface were the main Fe-bearing minerals; however, the dissemination of the two minerals, that is, haematite andmagnetite with the coexistence of Fe- and Mn-bearing minerals, will result in difficulty in effective separation of Fe and Mn. The effective roasting temperature and roasting time were 800 °C and 60 min, respectively, to avoid the formation of a composite oxide of MnxFe3-xO4 beyond 800 °C. The Fe recovery via roasting and magnetic separation only was 66.56%, whereas a combination of magnetic separation which ensued after the leaching process showed a recovery of 80.08% and 59.95% of Fe and Mn, respectively.

Mar 26, 2021

By Juan J. Monsalve, AMAN SONI, ALEX PFREUNDSCHUH, Nino Ripepi

Ground control failures are one of the main causes of accidents in the underground stone mining industry. Some of the fundamental tools for rockfall hazard identification are related to rock mass characterization and geotechnical discontinuity mapping. Recent technological advances in these methods are related to remote sensing techniques and point cloud processing software for automated discontinuity mapping. Remote sensing techniques, such as LiDAR and photogrammetry, generate multimillion point clouds with millimetric precision, capturing the structure of the rock mass. The automated point cloud processing tools offer alternative algorithm-based methods to characterize and map these discontinuities. However, their applicability is constrained by multiple factors such as site specific conditions of the rock mass and the parameters used within the mapping algorithms. This paper evaluates the performance of automated discontinuity extraction software compared with manual virtual discontinuity mapping. Sampling windows from laser-scanned sections in an underground limestone mine are defined and mapped using discontinuity set extractor (DSE). Results from the virtual discontinuity software are compared with manually extracted fractures from I-Site based on reviewing orientation, trace length, spacing, number of extracted discontinuities, and processing time. The analysis determined that the automated mapping algorithm was able to identify the same discontinuity sets that had been manually mapped. The automated mapping software mapped an excessive amount of smaller fractures, which caused the comparison of both mapping techniques to be unsuccessful in terms of trace length and spacing.

Mar 19, 2021

By P. K. Kankar, Manoj Khandelwal, Ramesht Shukla

One of the utmost severe mining catastrophes in underground hard rock mines is rock burst phenomena. It can lead to damage to mine openings and equipment as well as trigger accidents or even threat to life as well. Due to this, a number of researchers are forced to study some easy-to-use alternative methods to predict the rock burst occurrence. Nevertheless, due to the extremely multifaceted relation between mechanical, geological and geometric factors of the mines, the conventional prediction methods are not able to produce accurate results. With the expansion of machine learning methods, a revolution in the rock burst occurrence has become imaginable. In present study, three machine learning methods, namely XGBoost, decision tree and support vector machine, are utilized to predict the occurrence of rock burst in various underground projects. A total of 134 rock burst events were gathered together from various published literatures comprising maximum tangential stress (MTS), elastic energy index (EEI), uniaxial compressive strength and uniaxial tensile stress (UTS) that have been used to develop various machine learning models. The performance of machine learning methods is evaluated based on the accuracy, sensitivity and specificity of the rock burst prediction.

Mar 17, 2021

By G Capes, L Morizzi, N Mitkas, E Jones, D Grant

This paper describes the mining setting for the sub-level open stoping (SLOS) mining method used at Olympic Dam (OD), and investigates the range of stope performance conditions encountered over 30 years of production, using a qualitative description of the factors influencing performance. Utilising a continuous improvement tool, the Plan-Do-Check-Act (PDCA) process, and a forward-looking rock mechanics program, the intent is to identify the key factors driving productivity and performance to create a stable and achievable long term mine plan.

Mar 15, 2021

By Z Li, A Fleming, S Webster, L Snyman

Northparkes Mines is developing the E26 Lift 1 North block cave mine, which is adjoined to the existing E26 cave. This paper presents the challenges and methods used to design the ground support system during the feasibility study. Calibrated numerical simulations were conducted to forecast the levels of rock mass damage and to assist the ground support design. Generally, low to moderate rock mass damage is forecast on the extraction and undercut levels. However, poor ground conditions are expected in sheared and preconditioned zones adjacent the existing E26 cave. This will result in difficult ground conditions during development, undercutting and drawbell establishment. Empirical assessments were conducted to make sure the ground support system is able to handle both the static and dynamic load demand, and to accommodate the deformation values. A safety factor of 1.5 was used for the designs to cover the unknown rock mass conditions and potential for larger seismic events. Learnings from the E26 Lift 1 and SLC, also mining against the E26 cave, are incorporated into the design. Fibrecrete, mesh and resin bolts / mechanical anchors are the primary ground support system used, and cable bolts for intersections with a span of more than 6 m. Following undercutting and during the operating life of the mine, secondary ground support and rehabilitation will be required.

Mar 15, 2021

By G Balog, T Ormerod, D Sidea

Carrapateena is a copper-gold sub level caving operation located in the Gawler Craton, South Australia. One of Australia’s largest undeveloped copper deposits, the project will be a 4.25 Mtpa underground operation, with an estimated mine life of 20 years (OZ Minerals, 2017). First concentrate production was achieved in December 2019, within the Iron Ore Copper Gold (IOCG) hematite breccia complex. The Carrapateena orebody is overlain by 500 m of barren sediments of the Stuart Shelf, which hosts two aquifers. The cover sequence is dominated by shales, quartzites and sandstones in order of thickness. The cover sequence presented challenges to the mine ventilation system as a result of highly variable rock strengths. On this basis, the site developed the first vent rise, Vent Rise 5 (VR5), earlier than required as a means to test the empirical stability assessment. Assessment for VR5 was completed in 2017, with the mine yet to develop through much of the cover sequence. Due to the geotechnical data available at the time, it was anticipated that break out would occur within the vent rise walls as a function of the low strength Woomera shales. VR5 was developed to 4.5 mᴓ in late 2018. The timing of the VR5 development enabled the site technical team to calibrate empirical stability factors for the assessment of future vent rises. At the time of writing, four additional vent rises have been successfully developed to a diameter of 5.5 m. No significant overbreak has been observed within any of the vent rises. This paper is intended for geotechnical practitioners designing large-diameter vent rises in geological environments similar to the Stuart Shelf where a similar approach to vent rise design may be warranted.

Mar 15, 2021