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By Ana Carolina Ribeiro Duarte

A combinação de propriedades apresentada pelos aços perlíticos permite sua aplicação em diversos segmentos. O objetivo deste trabalho foi caracterizar a microestrutura do aço SAE 1070 deformado via trefilação para a fabricação de fiomáquina. O aço foi trefilado a seco por 12 passes com reduções médias entre 15 e 21%. A caracterização microestrutural foi realizada com o auxílio da técnica de microscopia eletrônica de varredura e microscopia de força atômica. O material teve ainda seu comportamento mecânico avaliado por meio de ensaio de dureza Vickers e ensaio de tração. O material deformado apresentou a estrutura “curling” na seção transversal, enquanto que na seção longitudinal a maioria das lamelas se encontrava alinhadas com a direção de trefilação. Os ensaios de tração e dureza revelaram um aumento considerável da dureza e resistência do material após o processo de trefilação.

Aug 16, 2017

By D Lees, D Gilchrist

Sydney has hundreds of kilometres of sewer tunnels. Many of these are over 50 years old and some have been in service for more than 100 years. The tunnels are predominantly constructed in Hawkesbury Sandstone and many are unlined.Principles have been developed over many years for the safety factor required in designing and constructing new tunnels but these do not necessarily relate to the operation and maintenance of existing tunnels, and in particular those that do not necessarily require personnel access for anything other than regular inspections.Assessment of the stability of these established tunnels needs to take account of their size, their age, their function, and their method of construction, as well as the geology in which they are situated and any support measures which have been installed. More importantly a stability review needs to take account of the consequences of a collapse, with regard to the inspection process, carrying out of any required repairs and the long-term performance of the tunnel.This paper is based upon the authors’ experiences inspecting and reviewing more than 200 km of tunnel in the last ten years. It will show some of the procedures and methods adopted by Sydney Water, how these can be presented as an acceptable procedure in line with other safety standards, and how they might be adopted for other similar historic rock tunnels.CITATION:Gilchrist, D and Lees, D, 2014. The development of a procedure for the inspection of unlined rock service tunnels, in Proceedings 15th Australasian Tunnelling Conference 2014 , pp 543–552 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 17, 2014

By M Sykes

Gold was initially discovered at Ballarat in 1851. After initial alluvial mining, underground quartz mining commenced in 1853, continuing until 1918. The historic miners were considered to be capable of mining anywhere in the world after overcoming the difficult conditions within the Ballarat goldfields. Whilst mining has changed dramatically since the early 1900s the challenges with underground mining at Ballarat have not. Modern pumping systems cope with the moderate water inflows. However, modern machinery and efficient mining methods influence opening sizes and extraction techniques. In some cases modern techniques have accentuated the challenging ground conditions and complex orebodies that were faced by the historic miners. As the Ballarat East project has progressed towards production, technical challenges relating to geomechanics and mine planning are being resolved resourcefully.

Jan 1, 2008

By R. S. Dean

MANY studies have been made of the properties of steel produced by adding varying amounts of sponge iron to the charges used in steel-making furnaces.1-3 The results of these previous studies, however, have failed to disclose a reason for the belief of steelmakers that steel made in this way is definitely different from steel made entirely from scrap or iron melting stock. This paper deals chiefly with the structure of the sponge iron, of the wrought iron made by welding the sponge iron into blooms, and of the steel made by melting the forged and rolled blooms. It is believed that the structure of the final steel is inherited from the ore and that this inherited structure produces marked differences in the properties of the steel and explains the feeling of steelmakers which is based on their experience. Three kinds of sponge iron were used in this investigation: One made from a limonite ore reduced with natural gas, one made from a hematite ore reduced with natural gas, and one made from a magnetite ore reduced with charcoal. The sponge iron made by reduction with natural gas

Jan 1, 1935

By David A. Newman

In the 1950s, an underground limestone mine in the Camp Nelson Formation was developed from an outcrop exposure. The Camp Nelson Limestone met the requirements for DOT stone and aggregate. The mine ownership changed several times, which resulted in distinct mine designs in Level 1. Based upon the production requirements and an attempt to maximize limestone recovery from a single level, a variety of pillar dimensions and three mining heights (28 feet, 68 feet and 83 feet) were developed. This was sufficient prior to reaching the mineable extent of Level 1. Level 2 introduced previously unknown ground control challenges. These included: ??Pillar spalling and a significant back fall on the Level 1 - Level 2 decline; ??Laminated immediate back and the need to bolt the back on Level 2; ??Delamination of the back adjacent to the Level 1 - Level 2 decline resulting in bolt shearing, and floor heave in isolated areas of Level 2; ??Multiple level interaction, the need to design pillars based upon numerical modeling as columnization between Levels is infeasible: and ??Water inflow as the mine approached river. To meet the challenges, a testing program to determine rock strength and physical properties was implemented along with numerical (LAMODEL and FEM) modeling, and borescope inspections of the immediate back. The efforts to implement rock mechanics were re-focused as Level 2 approached its mineable limit and the initial attempt to drive a decline to Level 3 was unsuccessful. A second decline site was selected based on inter burden stability, a consistent shale parting for the Level 3 back horizon, results from numerical models of the immediate back and multiple level interactions, and the projected low water inflow. The mine is operating on Levels 2 and 3 with long-term planning and ground monitoring for Level 3.

Jan 1, 2014

By Alfredo Valdivia, Jesus Schabib, Vojtech Gall, William Cao, Curt Cicileo, Andrew J. Thompson

"The East Side Access Project (ESA) involves the construction of geometrically complex underground structures including a large number of caverns and bifurcations. Initially conceived as dual lined structures with either traditional concrete or shotcrete final linings (SFL), construction economy, advances in concrete placement technology and scheduling among others led to a wide use of what is referred to as freeform or pneumatically applied concrete (PAC) for the construction of tunnel final linings. PAC is a method of applying concrete without using formwork, where a wet mix concrete is pneumatically installed to encase reinforcement to full lining thickness. PAC has been widely adopted at ESA well beyond initial expectations. The paper addresses the design and construction aspects of the PAC method and contrasts it to traditional SFL lining placement. The experience made provides guidance for future PAC and SFL applications. THE EAST SIDE ACCESS PROJECT AND USE OF FREEFORM CONCRETE The Long Island Rail Road (LIRR) currently transports commuters from Long Island into Manhattan, terminating at the already congested Penn Station on the west side of Manhattan. Once completed, the ESA Project will provide LIRR commuters direct access to the east side of Manhattan underneath Grand Central Terminal. The ESA Project will help alleviate the congestion at Penn Station, which currently accommodates New Jersey Transit, Amtrak, and LIRR lines; reduce travel time for LIRR passengers traveling to the east side of Manhattan and facilitate connections to the New York City Transit (NYCT) Subway System and Metro North Rail Road. The construction includes mining and lining of new tunnels and facilities under Manhattan and Queens. The tunnels run from Queen’s Sunny Side Yard through the existing 63rd St. Tunnel, underneath Manhattan’s Park Avenue until termination at 37th Street. Differing types of tunneling methods and final lining systems are being used depending on the ground conditions, geometry and size of the excavation, site constraints and functional requirements. Mining of the Queens segment of the ESA Project involved soft ground tunneling by pressurized face tunnel boring machines, cut and cover construction, and conventional tunneling. The Manhattan segment of the ESA Project involves mining in hard rock by tunnel boring machines, drill and blast, and road header."

Jan 1, 2016

By D. Gill, R. Burgess, B. Kyslinger

"There is always a demand in the mining industry to improve the safety and efficiency of roof bolting. Since 2008, Anglo American and Fletcher® have been working together to develop a new roof bolter concept that is safer and more ergonomic while maintaining current production rates. The recognized types of machines currently used in South Africa are always under constant review for improvement; however, there are limitations to the current design. The majority of the machines in South Africa are the “Man in Position” roof bolters. There are currently over 200 of these roof bolters in South Africa, with the bulk of the machines being twin-boom units. When operated correctly, these machines are safe, versatile, reliable and productive. However, with the operators located close to the drilling and bolting operations, they can be exposed to operational hazards. In addition, the major amount of material handling can be quite difficult on an operator. Anglo American, with a desire to improve safety, approached Fletcher to develop a remote style machine with simplified controls that maintained the productivity of the twin-boom machines. After several prototypes, the current model was developed. The chassis was designed for better operator comfort. A dual mast drill module was implemented to reduce the total time to bolt a cut. A remote operator’s station was incorporated to remove the operator from the front of the machine. The design was all about producing a safe and ergonomic machine from front to rear. This paper will explain the evolution and technological advancements from earlier prototypes to the current production machine. INTRODUCTION With mining, especially coal extraction, comes the necessity of supporting the roof. Since the 1950’s, the primary method for roof support has been the use of roof bolts. Roof bolting is considered one of the most hazardous jobs in underground coal mining. In 2004, there were 3,405 injuries reported to MSHA (Mine Safety and Health Administration). Of those injuries, 17 percent were associated with bolting machines (593 injuries). The majority of the injuries resulted from rock falling from supported roof. However, injuries involving a part of the body being struck by, or caught between, during bolting and drilling occurred with relatively high frequency (Burgess and Steiner). Roof drilling and bolt installation is labor intensive and repetitive. These labor intensive and repetitive requirements can lead to cumulative trauma. Operators are expected to perform a considerable amount of lifting, carrying, bending, reaching and stretching. Back and shoulders become sore from bending and twisting to install bolts or lift and position drill steels, wrenches and bolts. Confined operator spaces also contribute to difficult and awkward working positions for the operators (Cornelius and Turin)."

Jan 1, 2017

By R. C. Gilmore, J. McMack, G. E. Bogin, J. F. Brune, C. DeRosa

"Researchers at the Colorado School of Mines are designing and building a 1:40 scaled physical model of a fully operational longwall coal mine. The purpose of the model is to minimize the occurrence of methane explosion hazards by testing various ventilation strategies and determining optimal methane sensor placement throughout the longwall face. Fluid scaling factors were analyzed using Computational Fluid Dynamics software Ansys FLUENT™ at both full and 1/40th scales. Researchers were able to identify key scaling factors and subsequently developed suitable flow parameters that would maintain full scale accuracy of flow patterns in the 1/40th model. KEYWORDS Coal, Longwall, Methane, Explosion, Scale Model, Ventilation, Fluid Dynamics, Richardson, Gob, Porous INTRODUCTION Mine ventilation systems are a key component for ensuring a safe working environment by introducing fresh air from the surface and diluting explosive gases and hazardous contaminants. This holds true for longwall coal mines where the emission of flammable methane gas from the longwall face as well as the gob can create explosive mixtures of methane and air. Therefore, an effective ventilation strategy can help mitigate the potential for accidents within a mine. Developing an effective mine ventilation system (MVS) requires a detailed understanding of the physics of gas transport and how this relates to specific geometries and obstructions in the face. Researching this phenomenon requires the development of computational fluid dynamics models capable of simulating fluid flow and methane species transport that can be validated through physical experimentation. Unique site conditions determine ventilation layouts for every coal mine. Researchers have designed a 1/40th scaled physical model of a longwall coal face and adjacent gob that includes movable shield supports and a movable shearer with rotating cutter drums that can be adjusted to a variety of ventilation conditions. The proposed work will address the need for an improved Mine-wide Atmospheric Monitoring System (AMS), and provide the ability to link existing MVS models with AMS in real time. By accurately representing the coal face, the gob area and the mining equipment, gate roads and bleeder entries, the scaled model accurately represents all relevant structures, geometry, and dynamic conditions. A Plexiglas cover allows full optical access for sensor equipment as well as visual inspection of the fluid flow and species transport."

Jan 1, 2019

By P. Gao, J. W. Yu

"Magnetizing roasting-magnetic separation is an important route for the beneficiation of refractory iron ores. In this investigation, a pilot-scale fluidized magnetizing roasting reactor was introduced and used to study the effects of roasting temperature and the flow rates of reducing gas CO and fluidizing gas N2, on the magnetizing roasting performance of an Anshan-type carbonate-bearing fine iron ore. The results showed that the hematite was almost reduced to magnetite by a gas mixture of 4 m3/h CO and 1 m3/h N2 at a roasting temperature of 540 °C. Under the optimized conditions, a high-grade magnetic concentrate assaying 66.1 wt.% Fe with a recovery rate of 91.2% was achieved from an Anshan-type carbonate-bearing fine iron ore assaying 42.0 wt.% Fe. The XRD, VSM, and optical microscopy analyses revealed that the siderite was successfully converted to magnetite by roasting. Some coarse hematite particles were difficult to reduce to magnetite completely; however, these generated magnetite particles with a fine hematite core could also be effectively recovered by magnetic separation after liberation from gangue minerals due to their strong magnetism. INTRODUCTION Magnetizing roasting followed by low-intensity magnetic separation has been considered as an effective solution, both technologically and economically, when upgrading refractory iron ores (Zhang et al., 2012; Peng et al., 2012; Li and Zhu, 2012). According to the type of roasting reactor, the magnetization roasting can be divided into shaft furnace roasting, rotary kiln roasting, and fluidized bed roasting (Zhu and Li, 2014).Shaft furnace magnetization roasting system is mainly composed of heating and reduction processes. The hematite ore is first heated to 700~800 °C in the heating zone, then falls into reduction zone where the weakly magnetic hematite is reduced to magnetite by coke oven gas at 550~600 °C (Yan et al., 2012). However, several years of engineering practices indicate that the shaft furnace can only process the hematite ores with a granularity of 15 ~75 mm, and the shaft furnace roasting is also characterized by heterogeneity of roasted product. Hence, the shaft furnace magnetization roasting technology is gradually replaced by high-gradient magnetic separation with the development of high-gradient magnetic separator. The rotary kiln generally handles the hematite ores with a grain size of less than 30 mm (Zhu and Li, 2014), however the formation of clinker ring in the rotary kiln will affect the yield of iron resource. In the fluidized bed furnace, the hematite ore is shaken up by an upward current of gas which maintains the individual particles in suspension (Yu et al., 2018). The precise adjustment of the gas velocity to the particle size and the specific weight of the hematite ore, make it possible to generate a floating mixture of gas and solids which behaves almost like a liquid (Yu et al., 2017a). The process is reported to have the following advantages over the other roasting techniques: ease of control due to absence of moving parts within the reactor, homogeneity of roasted products, ability to handle fine particles, and high efficiency of heat transfer and mass transfer (Li et al., 2015; Yu et al., 2017b). However, the simultaneous heating and reductive magnetization of hematite ore occur at the same place in the conventional fluidized bed reactor. Therefore, the reductive atmosphere, as well as the safety and stability of anti-explosion are hard to be controlled. Besides, the roasting temperature for conventional fluidized bed furnace is usually up to 950~1150 °C (Liu et al., 2017). Thus, the formation of clinker ring caused by high temperature will affect the operating efficiency."

Jan 1, 2018

By Yukio Shigaki

Tendo como objetivo a melhoria contínua dos processos de laminação de produtos planos, foi elaborado um projeto de aplicação de modelos matemático-numéricos para a simulação dos laminadores de tiras a frio da Companhia Siderúrgica Nacional (CSN). A premissa principal é a de que esses modelos permitirão relacionar as diversas variáveis operacionais com o perfil emergente da tira e, baseado na variação da coroa entre a entrada e a saída, estimar a qualidade da sua planicidade. O presente trabalho apresenta os principais modelos aplicados, informações sobre os ensaios realizados para tomada dos dados industriais e alguns dos primeiros resultados com foco no perfil e planicidade. Resultados preliminares indicaram a modificação da coroa dos cilindros de trabalho do Laminador de Encruamento, levando à redução da quantidade de tiras com ondulado lateral. Também foram obtidos resultados satisfatórios na simulação das cadeiras do Laminador de Tiras a Frio no. 1, que é composto de cadeiras 6-high e 4-high.

Oct 30, 2017

By Bruna Brito Freitas

O processo de soldagem por fricção é uma técnica recente que vem sendo desenvolvida a fim de melhorar a qualidade das estruturas offshore. Com a finalidade de aperfeiçoar essa técnica é importante estudar as propriedades metalúrgicas do material soldado. Este trabalho tem como objetivo avaliar a tenacidade ao impacto de um aço C-Mn soldado por fricção com pino consumível, conhecido como FHPP (Friction Hydro Pillar Process). Desta forma, no presente estudo o material foi soldado, tratado termicamente, e após avaliado através de análises metalográficas, de microdurezas e ensaios de impacto Charpy. Como resultados foram geradas microestruturas para as diferentes regiões da solda e foram obtidos valores de energia, segundo a norma ASTM E-23. Por fim, conclui-se que o material não processado apresentou uma tenacidade superior a região de interface soldada, devido as diferentes microestruturas geradas no processo.

Aug 16, 2017

By Leandro Nakamura Alves Vieira

O acirramento da competição no mercado de aço tem exigido esforços de inovação e redução de custos. Por sua vez, as técnicas agrupadas como ICME - Integrated Computational Materials Engineering vêm acelerando o desenvolvimento e a otimização de materiais e processos de fabricação. O emprego destas técnicas tem sido uma ferramenta extra para assegurar a competitividade na indústria. Neste trabalho o uso da termodinâmica computacional no desenvolvimento e processamento de aços elétricos é revisado através da discussão de exemplos. Cálculos de equilíbrios mais relevantes para o processo de fabricação destes aços (tanto de grão não orientado-GNO como orientado-GO) permitem obter informações sobre as transformações de fases, solubilização de precipitados (sulfetos e nitretos) essenciais para a obtenção de texturas cristalográficas ideais. Os cálculos são discutidos e comparados com resultados reais. Discutem-se ainda, cálculos no sistema aço-gás, e os efeitos da composição da atmosfera na formação de óxidos na superfície do aço. Tais cálculos são importantes para descrever previamente as transformações que ocorrem durante as várias etapas de fabricação, assim como os efeitos dos parâmetros de processo sob os aços elétricos. A aplicação da técnica permite otimizar o processamento e o desenvolvimento dos aços elétricos em diversos aspectos. As vantagens e limitações do método, assim como o potencial de outras técnicas de ICME, na área, são discutidas.

Aug 7, 2018

By H S. Shin, H Jin, B H. Ryu, J Lee

Prospecting ice on the Moon necessitates drilling systems to obtain subsurface samples and measure the composition of ice deposits. Landers and rovers equipped with drilling equipment are essential for analysing ice and subsurface resources located at the Moon’s poles. These devices must be small, lightweight, low-power, highly efficient, and high-performance units to function properly in the extreme conditions of the lunar environment. Researchers have developed a prototype drilling apparatus capable of operating in atmospheric and cold environments. A newly developed drilling system in Korea, capable of performing not only sampling but also subsurface investigation, is introduced.

Sep 1, 2024

By J Lombardi, M Weidenbach

"OZ MineralsÆ Prominent Hill copper-gold concentrator is located 650 km north-east of Adelaide, 130 km north-east of BHP BillitonÆs Olympic Dam operation and 130 km south-east of the regional township of Coober Pedy, in the Gawler Craton region of South Australia. The concentrator was built in 2008 and commenced commercial production in early 2009. The Prominent Hill concentrator is comprised of a conventional grinding and flotation processing plant with a 10 Mt/a ore throughput capacity, operating well over the design rate of 8 Mt/a. Increased throughput rates have seen a decreased water recovery from the tailing thickener due to operating above design. Subsequently, greater pressure was placed on the site water balance and bore field off-take rates due to increased evaporation losses from greater volumes of water reporting to the tailing storage facility. This resulted in a trade-off between water availability and milling rates as part of the operating strategy.Two projects were implemented to increase the tailing thickener underflow density, thus improving water recovery directly back into the operating plant, reducing water losses via evaporation and decreasing the reliance on the bore field system operating at maximum rates to maintain mill throughput. The two projects were: tailing thickener feedwell redesign implementation of the Manta Cube control system.This paper discusses the background, implementation and benefits attained from these two key projects. Combined they have allowed a two to three per cent increase in tailing thickener underflow density to be consistently achieved, which has allowed greater water recovery. As a result, the processing plant has been able to operate at higher throughput rates when required, with greater water availability in the process plant recirculating system and a reduction in occurrences of the plant being æslowed downÆ due to water supply shortfalls. Both projects have also delivered a significant reduction in flocculant usage.CITATION:Weidenbach, M and Lombardi, J, 2012. Tailing thickener operability and control improvements at Prominent Hill, in Proceedings 11th AusIMM Mill OperatorsÆ Conference, pp 137-142 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Oct 29, 2012

By João Francisco Batista Pereira

Nos últimos anos a indústria automotiva tem evoluído de forma significativa em relação à preservação ambiental (redução da emissão de CO2) e com respeito à segurança veicular. A Usiminas, alinhada com esse direcionamento, tem realizado diversos estudos visando obter novos produtos de alta resistência mecânica que possibilitem a redução do peso dos veículos e diminuição do consumo de combustível, além do aumento da segurança. O aço TRIP, desenvolvido e recentemente comercializado pela Usiminas, é um exemplo dessa nova geração de produtos avançados, que conciliam alta resistência mecânica e alta capacidade de conformação. O trabalho apresenta as características do aço TRIP desenvolvido pela Usiminas assim como os resultados de aplicação em peças automotivas da Fiat Chrysler Automobiles.

Aug 16, 2017

By Joselito Dásio da Silva

A Niobras é uma empresa do grupo China Molybdenum Internacional (CMOC), recentemente adquirida do grupo Anglo American, que extrai e beneficia minério de nióbio proveniente da Mina Boa Vista, situada no município de Catalão – GO, e transforma o concentrado de pirocloro em liga de ferro – nióbio em seu site situado em Ouvidor/GO, sendo este o produto final comercializado. A extração de minério na Mina Boa Vista iniciou-se no ano de 2000 com o objetivo de alimentar a Planta de Concentração Boa Vista com minério oxidado, para manter o nível de produção de nióbio, uma vez que a antiga mina estava em processo de exaustão. Com a exaustão do minério oxidado prevista para 2016, em 2011 foi desenvolvido um projeto chamado BVFR (Boa Vista Fresh Rock) para produção de nióbio através da extração e beneficiamento de minério contido em rocha fresca. O Projeto BVFR foi aprovado no início de 2012, concluído em outubro de 2014 e foram investidos mais de US$ 350 milhões para sua implantação. O Projeto BVFR aumenta a vida útil da mina (Life Of Mine) e do negócio em 20 anos, triplica a produção de nióbio da Niobras e incrementa o EBTIDA em mais de 250% e gerou um aumento de mais de 400 empregos diretos (entre contratadas e próprios).

Oct 30, 2017

By ANDERSON OLIVEIRA DA SILVA

Blindagens balísticas são projetadas para resistir a uma determinada ameaça com a menor relação peso/resistência balística possível, isto é, oferecer a melhor resistência à penetração de projéteis e fragmentos provenientes de armas de fogo com menor peso. Os materiais compósitos são, atualmente, aqueles que possuem a maior probabilidade de obter estes requisitos, por possuírem flexibilidade de alcançarem o conjunto de propriedades mais apropriadas para cada nível de proteção e por serem mais leves. Os compósitos reforçados por tecidos de fibra sintética são atualmente os mais utilizados. Com o foco nos aspectos ambientais, este trabalho produziu e avaliou um compósito híbrido laminado de matriz polimérica reforçado por manta de curauá e tecido de poliamida aromática. O compósito foi avaliado segundo o tipo de falha ocorrida após o ensaio balístico, utilizando a análise por microscopia eletrônica de varredura (MEV), bem como, a análise visual. Por meio da análise dos resultados, foi possível observar que o processo de microdelaminações na interface matriz/tecidos, bem como as falhas intralamelares (trincas na matriz) proporcionaram uma maior dissipação da energia de impacto.

Oct 30, 2017

It is well known that the ability to influence project value reduces significantly as planning progresses and decisions regarding project parameters are made. However, at the prefeasibility stage in particular, where one of the main aims should be to evaluate a wide range of options in order to select the best for more detailed further study, there is often a reluctance to spend the time and money needed to do this rigorously. This paper demonstrates, by a number of case study examples, how significant increases in value may be obtained by fully evaluating the combinations of alternatives for various project design parameters, including (though not limited to) mining methods, haulage methods, mining rates, processing methods and rates, sequencing of mining, and cut-off grades, with changes and upgrades over time where applicable. The additional value unlocked is typically orders of magnitude greater than the additional cost of the more comprehensive study. The dangers of misuse of simplistic sensitivity analyses and failure to identify how strategies might change in response to changes in external factors are also illustrated, and the importance of selecting the best ægrade descriptorÆ is discussed.

Jan 1, 2007

By M G. Wansbone, R Bhargava

The inferred ground conditions for the proposed mined cross passages at the northern end of the Waterview Connection tunnels consist of an overburden of alluvial and residual soils, with mixed face geology of highly weathered to unweathered extremely weak rock. This paper describes three-dimensional (3D) finite difference analyses undertaken to evaluate the stability of the cross passage headings and to validate the proposed sequence of excavation. The analyses undertaken incorporated the influence of the construction of the mainline tunnels and the breakout opening in the segmental lining for construction of cross passages.The stability analyses were carried out using FLAC3D™, version 4.0 (by Itasca Consulting Group) by progressive reduction of shear strength parameters to obtain a failure condition and estimate a factor of safety. For each step of strength reduction, corresponding increments of displacements of several points on heading faces were monitored. The stability obtained from numerical analyses was compared with analytical solutions. Interpretation of results of drained analyses indicated instability of the upper 2 m of heading face within the highly weathered rock mass. Additional analyses were undertaken by including grouted fibreglass dowels to reinforce the heading face. The results of the additional analyses showed significant reduction in displacements and yielding of ground around the face. The proposed temporary support comprised face reinforcement using grouted fibreglass dowels in conjunction with canopy tubes and perimeter support of steel fibre reinforced shotcrete. The stability of the construction sequence, which was related to the specific requirement of the proposed excavation equipment, was validated.CITATION:Wansbone, M G and Bhargava, R, 2014. Analysis of stability and design of face support for cross passages – Waterview Connection tunnels, Auckland, New?Zealand, in Proceedings 15th Australasian Tunnelling Conference 2014, pp 339–344 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 17, 2014

By V. O. Tenorio, P. P. V. Coronado

"INTRODUCTION Productivity in Open Pit mines depend on the observation and adjustment of critical phases of operation. As one of the most expensive activities in Open Pit production, optimization of the load-haul-dump cycle becomes a critical aspect to address. Using simulation techniques and an ad-hoc methodology for analyzing the Key Performance Indicators (KPIs) involved in the production cycle, it is possible compare actual performance and ideal operating conditions and develop an alert system when operating conditions are sub-par with the expected production standards. STUDY OBJECTIVES The purpose of this work is to implement a methodology for optimizing the haulage cycle by identifying and adjusting the factors that affect the cycle time performance. The methodology includes the implementation of an alert system emitting warning messages when one or several trucks are idle or the time of completing production tasks is falling outside a predefined value. This alert is compared with pre-defined Key Performance Indicators (KPIs) and determine corrective actions: • Demonstrate the benefits of time analysis and how this affects the productivity results in the mining process; • Demonstrate the utility of KPIs in the extraction of ore and waste, and how they help to identify equipment performance; • Develop software interfaces to visualize the Alert System in order to increase awareness in the operations supervisor; and • Make recommendations for future applications that can help improve the productive process of an Open Pit mine. PROBLEM STATEMENT Transporting material in Open Pit mines may require the utilization of high capacity equipment, which also represents an elevated cost per hour. A supervisory system that controls the adequate distribution of trucks and shovels by providing the operational status of each unit shall contribute to increase productivity and subsequently reducing operational costs. Nevertheless, there is an issue with certain dead times such as queue trucks for loading, trucks waiting to be loaded, and other delays. This creates inefficiencies in fuel consumption and energy utilization. For the identification of delays, a context-based system could be required in order to help optimizing the haulage cycle time by controlling delays in loading, haulage, and dumping. After applying this methodology, efforts were focused in correcting out-of-standard performance values."

Jan 1, 2016