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By S C. Dominy, R C. A Minnitt

Determination of the sampling constant and liberation diameter are of importance when applying the Fundamental Sampling Error (FSE) equation to optimise sampling protocols. The method for the direct determination of the sampling constant is based on the æGy 50-pieceÆ experiment and variants thereof, which is generally known as the heterogeneity test. In the coarse gold environment, the heterogeneity test is prone to poor repeatability and bias due to the very heterogeneity that it aims to quantify. A key issue is the large sample mass that can be required in the coarse gold environment, which may reach 1 t or more. The heterogeneity test often provides an evaluation of the background gold grade heterogeneity, but understates that of the high-grade coarse-gold component. This is because the total mass of fragments is usually too small to represent the mineralisation. Despite this relatively well-known problem, heterogeneity tests are often undertaken on deposits where the presence of coarse gold is ignored, not fully realised or vastly understated. Sampling types and protocol designs are frequently based on poor quality data that do not match the characteristics of the orebody. For this style of mineralisation, an empirical approach to define ore characteristics is recommended.CITATION:Dominy, S C and Minnitt, R C A, 2012. Application of heterogeneity testing to coarse gold ores, in Proceedings Sampling 2012 , pp 143-160 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 21, 2012

By L Dyer, A Keith, G D. Corder

As mining activity moves to remote and less developed locations globally, a holistic approach to mine development is fundamental for achieving a balance between strong financial returns and corporate social responsibility and transparency. Key inter-related fundamentals such as social licence to operate, life-of-mine operational planning, minimising environmental impacts and, most importantly, attractive investment returns for the mining company all contribute to the viability of any new mining project.However, the typical practice in the mining industry is often to treat environmental and social/community aspects as separate compliance issues that are dealt with at minimum cost and disruption to the project and resulting operation. This often results in less than optimum environmental and social outcomes, and presents considerable liabilities at the time of closure when rehabilitation programs continue to require funding when all revenue has ceased.The five capitals model seeks to identify each of the key contributors to sustainable development as financial, manufactured/physical, social, human and natural to formulate a type of triple bottom line approach balancing these often competing project factors. The SUSOP® sustainability risks and opportunities framework, developed by the mining industry, bases its approach on the five capitals model and proposes an approach that breaks down enterprise silos to identify innovative solutions for life-of-mine sustainability. This framework has been developed with the nature of mining projects in mind in order to produce approaches and outcomes relevant throughout the life cycle from the planning phases, through project design and construction into operation and closure.This paper argues the need for a more holistic approach to the development and operation of mining projects, and presents case studies where a holistic approach has been applied, in whole or part, and discusses the lessons learned from these case studies.CITATION:Corder, G D, Keith, A and Dyer, L, 2014. A capitals based approach – leading innovation in planning for life-of-mine sustainability, in Proceedings Life-of-Mine 2014, pp 499–512 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 16, 2014

Drilling underground can be a hazardous undertaking in many circumstances. Raiseboring and boxhole boring underground could form an integral part of the block caving production methodology and getting the right mix of technical capability, ergonomics and economical viability has been the goal of many machine manufacturers. With the introduction of the Terratec Universal Boring Machine concept, flexibility of raiseboring, downreaming and boxholing has been enhanced by the introduction of a single machine that will perform all three processes. In addition to its technical flexibility, additional safety features have been introduced that will eliminate many sources of injury by mechanising most of the operational procedures. Together with the one-man remote operation, this machine design addresses and solves many of the safety issues. This paper outlines the machine concept, details its safety features and shows the techno-economic advantages for use in the block caving environment. Block caving is a distinct caving method applied mostly to large massive orebodies because of the inherent low costs and high production capabilities. Areas of sufficient size are mined by undercutting so that the mass above will cave naturally. Extraction of the caved ore at the bottom of the ore column causes the caving action to continue upward until all of the ore above the undercut level is broken into sizes suitable for handling (Figure 1).

Jan 1, 2000

By H Rossiter, A Maddever, J Market, P Jeanneau, A Virani

It is generally acknowledged that the head grade of the world’s copper resources is declining. Accordingly, there is an increase in the volume of resource material being mined and processed to maintain copper production. This has led to increases in cost base accompanied by reductions in Life of Mine (LOM) Net Present Value (NPV). The higher tonnages of material mined are driven by increased quantities of lower grade material required to satisfy the short term mine model. In turn, this has brought an increased focus on sampling and assay methods, since any error associated with estimating the grade of each block and determining its correct destination serves to magnify the losses that will occur. Presently most open-pit copper mining operations use blasthole sample assays to feed their shortterm model. The problematic nature of blasthole sampling is well documented (Engström, 2017), particularly the poor timeliness of the data and the significant errors that are inherent to the technique. Methods to improve grade control, such as drilling a separate grade control grid, have been proposed but come with their own cost, logistical, and accuracy shortcomings. A recent development in grade estimation is the Pulsed Fast and Thermal Neutron Activation (PFTNA) downhole logging probe. Deployed on an efficient semi-autonomous platform, PFTNA is being aggressively adopted in the Australian iron ore industry. The technology provides in-situ elemental analysis of the geological formation, delivering high accuracy, high efficiency, near realtime data from a sizeable measurement volume. In this paper we consider the application of the technology to copper. Whilst there are several operational components to such a value proposition, we focus on the benefits of improved gradeestimation. A simulated copper mine is used to model the quantum of improvement expected from a reduced grade-estimation error, which reduces the likelihood of misallocating material to the wrong destination, which in turn increases NPV.

Nov 10, 2020

By D R. Wines

The design of near-surface civil infrastructure requires detailed consideration of the geological/ geotechnical conditions, excavation geometry and sequence and ground support measures to ensure stability of the underground openings and minimal impact on overlying or adjacent infrastructure. Twin parallel road tunnels have been designed and built with connecting cross passages and a piggyback busway tunnel as part of a large infrastructure project in Australia. The tunnels were excavated in poor to fair quality rocks using road headers. Temporary ground support includes shotcrete, rock bolts and canopy tubes. Extensive numerical analyses have been performed to analyse the expected behaviour of the tunnels during excavation, including two-dimensional analyses using UDEC and three-dimensional analyses using FLAC3D. Structural defects in the rock are explicitly included in the 2D analyses to examine the potential for localised ground instability. The stress redistribution is captured by the 3D modelling with an accurate representation of the complex excavation geometry and the detailed excavation and support sequence. This paper presents the modelling methodology, numerical results and discussions on integrating both 2D and 3D analyses to achieve reasonable design.

Mar 8, 2011

By W L. Daniels, C Stilson, C Zimmerman

Mineral sands mining for ilmenite, rutile and zircon has disturbed over 1000 ha of prime farmland in Virginia (USA) since 1997 and additional areas are likely to be disturbed in Virginia and North Carolina (USA) over the next 15 years. Full-scale mining operations at the Old Hickory Project in Virginia were initiated in 1997 by Iluka Resources Inc. and restoration protocols have continued to evolve in response to a variety of economic, technical and social issues. Early on, the return of these lands to agricultural row-crop production was complicated by vertical stratification of tails + slimes and lateral variability in soil physical conditions in the reclaimed pits and by limited topsoil return. Virginia Tech and Iluka have worked cooperatively with all stakeholders for over 20 years to review the pre-existing research base, conduct new and innovative site-specific research and thereby provide reasonable expectations of post-mining soil productivity levels. In 2004, Virginia Tech, Iluka Resources and a local leaseholder (Carraway-Winn family) agreed to jointly manage a 45 ha research demonstration farm where the long-term effects of alternative soil reconstruction practices are being rigorously monitored for both row crops (corn and wheat) and forage production. All mined land crop yields are also compared to an adjacent undisturbed exceptional quality prime farmland soil. Row crop yields between 2005 and 2010 were significantly above county average yields (regulatory target level) and approximately 75 - 80 per cent of undisturbed adjacent prime farmlands. The state regulatory authority has recently relaxed its position on the necessity of topsoil return versus use of topsoil substitutes based on appropriate on-site research results and the ability of the reclaimed soils to meet comparative local county crop yield targets. This cooperative effort allows all clientele groups to objectively assess the post-mining productivity of these mined lands while providing an invaluable educational opportunity for the mining industry. CITATION:Daniels, W L, Stilson, C and Zimmerman, C, 2012. Development of effective rehabilitation protocols for mineral sands mining in Virginia, USA, in Proceedings Life-of-Mine 2012 , pp 97-104 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 10, 2012

By C J. Greet

Oil can enter a flotation circuit from a number of sources (for example, from mining equipment, oil leaks from the grinding equipment and coatings on the grinding media, but to name a few). Folklore generally states that any oil that contaminates the ore entering the flotation circuit is considered to have a negative impact on flotation. That is, a loss in concentrate grade and recovery.This represents a dilemma for some grinding media suppliers, who use a variety of quenching medium (air, polymer, oil or water) to achieve the desired physical properties of the ball. In the case of high chrome grinding media it is necessary, in some instances, to quench in oil to give the ball the right degree of toughness, which invariably leads to these balls having a thin film of oil on their surface. Once the grinding media arrives on site and site personnel recognise that the balls are “covered” in oil, they generally insist that the oil will have a deleterious impact on flotation performance.Obviously, any supplier “worth their salt” would take remedial action at the point of manufacture to minimise this problem. However, does quenching oil actually present a significant “threat” to the flotation process? This paper provides both laboratory and plant data describing the effect quenching oil has on the flotation of copper sulphide ore, with surprising results!

Aug 8, 2011

By L Snyman, S Webster and J Samosir

Northparkes is located 27 km north of the township of Parkes in central New South Wales, Australia. The operations consist of underground block cave mines and an ore processing plant, which produces high-grade copper and gold concentrate. Production is currently sourced from the E48 Lift 1 block cave mine and open cut stockpiles. Mining commenced at Northparkes in 1994 as an open cut operation. Underground block cave mining began in 1997. Northparkes was the first mine in Australia to use the highly efficient block cave mining method, which relies on gravity and natural rock stresses to fragment and recover the ore.The E48 extraction level is located approximately 581 m below surface and consists of ten extraction drives and 214 drawpoints. Several stress measurements carried out at various levels in both E26 and E48 indicated a low underground regional stress environment and a low to moderate stress state in the E48 orebody. The E48 block used a post undercut strategy that was initiated in 2009, with production commencing in September 2010 and cave-through to the surface occurring approximately four months later in January 2011. Changes to the cut-off grade and fixed prices meant that Northparkes was able to develop an additional two drives to the north of the existing cave and one additional drive to the south. Modelling of the cavability of the additional drives indicated that the cave would not readily propagate to sufficient height of draw to mobilise the ore and tended to arch over to the existing cave shape. Based on modelling and a desire to reduce the risk of the project, preconditioning was adopted. Along with the requirement of safely hydrofracturing an active cave, a measure of the success of the preconditioning was desired. Few block cave operations have developed extension drives adjacent to existing caves.This paper summarises the lessons learnt from the development of this extension project, with a specific focus on ground control and monitoring.CITATION:Snyman, L, Webster, S and Samosir, J, 2016. E48 cave extension at Northparkes, in Proceedings Seventh International Conference and Exhibition on Mass Mining (MassMin 2016), pp 111–118 (The Australasian Institute of Mining and Metallurgy: Melbourne).

May 9, 2016

By D Davis

The prediction of ground-borne noise levels from tunnel construction activities requires knowledge of the input vibration forces from the vibration source(s) into the cutting face, knowledge of the vibration transmissibility through the surrounding medium, and knowledge of the receiver building’s vibro-acoustic response. The conversion of this vibration energy into sound pressure within the receiver building depends upon the vibration coupling of the soil and the building’s foundations, the structure’s response including floor-to-floor attenuation and amplifi cation due to resonance, the radiation effi ciencies of the internal structural elements, and the room’s acoustical properties. Beginning with a known input vibration spectrum at the cutting face, it is possible to predict the resultant ground-borne noise levels within a receiver building using either analytical and/or empirical techniques, or by numerical modelling. This paper presents an overview of the various methods available to estimate ground-borne noise levels from tunnel construction activities and discusses the advantages and limitations of each.

Mar 8, 2011

By B Twidle, D Bertoldi, J Meikle, R Dunne

The Waihi Gold Mine is situated in a high rainfall area (annual average of over 2 m) on the North Island of New Zealand. Water treatment and discharge at the mine has been ongoing for the last 25 years. The first water treatment plant consisted of a æstandardÆ water treatment facility (ferric chloride precipitation) and cyanide detoxification. With time the project has expanded and the volumes of water increased requiring additional treatment methods (reverse osmosis) to meet the water quality for discharge. This paper will provide information on the historical development of the water treatment flow sheets, performance data and operating costs.CITATION:Bertoldi, D, Dunne, R, Twidle, B and Meikle, J, 2013. Water treatment at the Waihi Gold Mine, in Proceedings World Gold 2013 , pp 503-508 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 26, 2013

By Haase W. C

The content of this paper will identify recent developments in walking dragline technology including utilisation of planetary swing dnves, high voltage generators, unique bucket configurations and increased machine capacity resulting from changes to front-end geometry. The benefits to mine operators for increased performance, reduced cost, improved availabilities, simplified maintenance, and ease of operation will be identified and discussed. The feasibility and application of the technology as a retrofit on existing equipment will also be covered in the presentation. All the technology being presented has been recently commissioned into operating Australian mining operations and will be presented from a practical, as well as theoretical perspective.When the Marion 8000-Series Dragline was introduced in the early-1970s, it quickly became the industry standard for high productivity and availability. Features like outboard bearing propel, four-chord deep section boom and the over/under fairlead have proven their superiority in thousands of hours of round-the-clock operations in a variety of tough digging conditions worldwide. Marion has currently sold 31 of these 8000-Series Draglines into the Australian mining community.

Jan 1, 1992

By M J. Schultz, R L. Rude, D M. Tomko

The US Mine Safety and Health Administration (MSHA) conducted compliance assistance diesel particulate matter (DPM) sampling throughout the underground metal and non-metal mining industry. Based on that sampling, MSHA identified mines that were having difficulty meeting the DPM limit. To provide further assistance, MSHA then visited approximately 60 of the mines that were experiencing difficulty complying with the DPM standard. As part of these visits, DPM exposures were measured and control technologies for DPM were observed and assessed. Controls consisted of ventilation, clean engines, environmental cabs, alternative fuels, diesel particulate filters (DPF) and work practices. The focus of the follow-up compliance assistance visits was to assess control effectiveness and to make recommendations to mines experiencing difficulty in meeting the DPM standard. At each mine visited, the ventilation controls were evaluated, engine emissions were determined for equipment in use, environmental cabs were examined, and operational practices were noted. Additionally, control technologies, including alternative fuels and DPF were evaluated in several mines. A comparison was made of mine and section airflow to equipment particulate indices. Based on engine emissions, horsepower and operating time, the contribution of individual engine emissions to total emissions was made. Environmental cab integrity, positive pressure and air filtration systems were checked and operational practices relating to DPM exposure were assessed. This paper summarises the preference and magnitudes of controls that were typically used or needed for successful control of DPM. Additionally, results of the assessments of alternative fuels (including bio-diesel and water emulsion fuels) and DPF are presented.

Jan 1, 2005

By N Lefebvre, M Jakeman, R Aseervatham

Semi-arid regions suffer from two afflictions; evaporation may exceed precipitation by multiples of two or more and variations in precipitation can be both extreme and difficult to predict. Many Australian mines are situated in semi-arid areas where communities are reliant upon locally sourced water or special purpose infrastructure is built as part of the mine construction. As the question of climate change looms, issues related to future water supply and sustainable water management become increasingly important. Across Australia several mining operations co-exist in a single surface water and/or groundwater catchment area. The management of water on a mine by mine or a community by community basis is illogical and must be reconsidered based on a single water catchment and a whole-of-community basis. Mine water should be considered on a full life cycle basis where the quality is assessed for specific mine site applications. This paper addresses technical challenges that include surface water and groundwater supply in semi-arid regions, operational water in the mining industry, beneficial uses of water, water economics and demand management. In much the same way as emissions trading evolved into a multi-stakeholder forum, mining regions offer scope for innovative thinking in water supply and reuse. In addition, this paper considers a number of initiatives taken by Australian mining companies that are entering a prefeasibility stage and contrasts these initiatives against the established success within a South African mining region. The challenges and potential solutions to this initiative are presented for future consideration.

Jan 1, 2006

By M J. Newton

As part of the AMIRA P843 project Keeney and Walters (2008) describe how the principal components analysis (PCA) method can be used to identify classes of samples with similar metallurgical characteristics. However PCA does not take account of the location of each sample in 3D space. This paper describes a study to analyse the spatial distributions of the classes and determine appropriate modelling methods to control the estimation of the comminution parameters and mill performance indices into a 3D block model. This includes but is not restricted to geostatistical techniques that are used for grade modelling. The starting point for the study is the class definitions and the regression models for estimating the comminution parameters and performance indices. Each sample is assigned a class and the spatial distribution of each class has been analysed using different techniques including the calculation of variograms. This establishes whether the classes can be used as domain control for estimation into the block model – a procedure similar to using geological rock type domains for controlling the estimation of grades for a resource model. However, standard geostatistical estimation methods such as ordinary kriging assume that the variable being estimated is additive or linear. This assumption is valid for variables such as grade but this is not necessarily the case for the comminution parameters or the performance indices. Therefore the estimation procedure must either use variables that are definitely additive or the effect of potential non-additivity must be tested and accounted for where possible.The results of the study show how performance indices such as recovery, throughput and specific power can be estimated into the block model. This model is then combined with the geological model to provide a multi-parametric model that is used to optimise the mine planning and scheduling activities which can lead to significant improvements in NPV.

Sep 5, 2011

By D P. Blair

There are two major aspects to wall control blasting – the potential for any blasthole to cause wall damage and the potential for a delayed sequence of blastholes to cause damage. The damage potential of individual blastholes is governed by standoff distance and charge weight. However, for locations sufficiently close to a highwall, dynamic finite element models and field measurements show that there is also a critical nature to those blastholes very close to the wall, over and above standoff distance. At many mine sites, the charge weight/standoff-distance is set by trial and error. Thus, a significant aspect of the present work is the determination of dynamic stress radiating from a blasthole. Unfortunately, the modelling and measurement of this dynamic stress is still faced with many difficulties. Typical models have questionable aspects, which casts serious doubt over their predictions, and it is shown that the Hustrulid Bar experimental technique does not correctly account for stress wave attenuation in extended media. In an attempt to solve the dynamic stress problem, the present work describes a model based on an exact solution under the assumption of viscoelastic material. The model takes full account of the rock mass elastic/viscoelastic properties, the explosive type, geometry and primer location and predicts a dynamic stress for direct comparison with the unconfined compressive strength of the local rock mass. This model predicts the standoff distance required to avoid damage due to a single blasthole. The behaviour of a delayed sequence of blastholes is analysed using an upgraded waveform superposition model, covering a range of initiation delay combinations, which predicts the peak particle motion (PPM) induced in the wall for each combination. This approach shows that there is no need to fire dedicated trim shots close to walls; all that is required is a carefully modified production shot. The mechanism of vibration screening is discussed, and its use in a superposition model highlights the potential of reverse firing (shield blasting) to reduce wall PPM. A conceptual model is also introduced to give a further insight to vibration screening and damage (via ground heave). This model predicts that a centre-lift blast will have a central heave profile and that a reverse-fired shot will produce a smaller power trough than that produced by a standard shot. It is demonstrated that the mechanism of presplit formation is not well understood; nevertheless, experimental evidence shows that presplits can be an effective method for reducing wall vibrations.CITATION:Blair, D P, 2015. Wall control blasting, in Proceedings 11th International Symposium on Rock Fragmentation by Blasting, pp 13–26 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 24, 2015

By Bhattacharyya A. K

A major constraint on sustaining high rates of production in the collieries of the Southern Coalfield of New South Wales is the inability to develop panels fast enough to match the rates of extraction. This inability is particularly crippling in the case of retreat longwall mining and is due to nearly half the time in roadway drivage being spent on strata control operations such as roof support.Increased rates of roadway drivage and significantly improved roadway stability can be achieved by the application of yield pillars between parallel roadways. These pillars are designed to yield immediately upon formation and transfer the damaging roof loads away from the immediate vicinity of the roadways. Since the width of the yield pillar is the key to their successful application, it was determined through the Yield Pillar Experiment conducted by Kembla Coal and Coke Pty Ltd at West Cliff Colliery.Three experimental headings, each nominally 5.5 m wide and 2.8 m high, were driven to form two tapering pillars. The width of these pillars progressively decreased from 24 m to 3 m over a length of 154 m. The convergence between the roof and floor of the headings measured at various cross-sections corresponding to predetermined widths of the pillars are analysed in this paper to evaluate the stability of the tapering pillars at the different widths.The width of the yield pillar in a three heading development layout at West Cliff Colliery was determined to be 7.5 m.

Jan 1, 1995

By J Allen, B Oats, S Palaniandy, M Lollback

The Julius Kruttschnitt Mineral Research Centre has conducted an intensive VertiMill® (VTM) survey program at the Cannington mine concentrator as part of the ‘collaborative research in stirred milling technology’ program funded by Metso Minerals. Since 2003, Cannington has progressively added grinding capacity into the circuit through VTMs operating in secondary and regrinding duties. Cannington was one of the first mines to adopt this technology in secondary duty by installing two VTM-1500-WBs as part of a capacity expansion to produce sub-100 µm rougher feed. Subsequently, an additional VTM-800-WB was installed in the lead regrind circuit to prepare sub-20 µm cleaner stage feed.Several surveys were carried out to evaluate the VTM performance over a range of changed conditions. Among the key changes in operating variables were circuit power draw, feed rate and water addition to the bottom of the mill. The average specific energy for secondary duty was 3.7?kWh/t. The lead and zinc regrind mills consume 8.1 and 15.3 kWh/t respectively. Generally, the VTM installations have successfully prepared feed for rougher and cleaner circuits by reducing the top size into the floatable regime with steeper particle size distribution, which has led to enhanced recovery. The survey results show the success of VTM installations in secondary (receiving feed from autogenous circuit) and regrind duties.CITATION:Palaniandy, S, Powell, M S, Hilden, M, Allen, J, Kermanshahi, K, Oats, B and Lollback, M, 2014. VertiMill® performance updates in secondary and regrind duties at Cannington mine, BHP Billiton, in Proceedings 12th AusIMM Mill Operators’ Conference 2014 , pp 263–272 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 1, 2014

By S Shafiee, N Abbate

The evaluation of mining projects requires a methodology that will give flexibility and manage the existing uncertainty within the projects. The discount cash flow (DCF) and other traditional evaluation approaches, which are widely used in evaluating a significant number of mining projects, have simply assumed that the main variables remain constant in their evaluation; elements such as discounted rate, mine life, operating cost and production rate. The DCF ignores managementÆs flexibility to adapt and reforecast and revise decisions. Real options valuation (ROV) is one of the modern evaluation methodologies that provide a tool to adapt and revise mining projects under uncertainty and future variables movements. ROV brings more variables into the evaluation model compared to DCF and assumes them as uncertain and dependent. Finally, ROV provides a range of solutions that can assist in managing this flexibility.This paper endeavours to compare ROV and DCF for mining projects comprehensively and applies these two techniques in the model. The paper shows that ROV will be inclusive of extra value in mining projects due to variables not allowed for, or even ignored, when the DCF model alone is used. One of the significant advantages of the ROV method is being able to evaluate mining projects under different scenarios from the inception of the projects. Furthermore, ROV gives the ability to evaluate the mining project while allowing for abandonment, temporary suspension, or expanding the mining project. In other words, the ROV evaluation process creates an analytical environment, which allows for optimisation of the mining plan within the mining project, as well as the ability to change the capital structure dependant on existing circumstances over the life of the project. The ROV is a new evaluation method that can add value in mining project analysis and offers opportunities to amplify gains, or to mitigate losses. This paper also discusses some of the reluctance to use ROV instead of DCF in current project evaluation.CITATION:Shafiee, S and Abbate, N, 2012. Now, this is the time for mining companies to choose - Real option valuation or discount cash flow, in Proceedings Project Evaluation 2012 , pp 225-234 (The Australasian Institute of Mining and Metallurgy: Melbourne).

May 24, 2012

By R Goddard

An alternative stoping method has been adopted for narrow vein stoping at the Tasmania Mine in Northern Tasmania. Colloquially described as ‘Radial-in-Reef’ (RiR) stoping, the method employs the drilling of radial rings in the plane of the Reef from a drill stub located at the geographic centre of the proposed stope panel.Production from the Western Zone of the Tasmania Reef has been undertaken remotely from the Reef since 2007, after a detailed geotechnical engineering analysis indicated that the integrity of the sill drives could not guarantee an acceptable level of confidence should an anticipated seismic event occur within a radius of 10 m. The key tenet of the remote mining approach was the exclusion of personnel from sill drives once stoping had commenced. The remote mining method had to be ‘retrofitted’ to four existing stoping blocks totalling 11 sill drives which totalled 160 m vertically. The remote mining method proved to be complex, cumbersome and very expensive. However, the ore was extracted successfully.By early 2010, previously developed ore had largely been exhausted and the future development with an orebody open at depth presented the opportunity to review the current extraction method. However, the new extraction method needed to maintain the tenet of excluding personnel from sill drives of active stoping blocks, but seek opportunities to reduce the difficult and costly aspects of the previous method. The new ‘Radial-in-Reef’ stoping reduced the development requirement from six to two drives per ore block. Cost implications aside, the significant reduction in prestoping extraction ratio was expected to also reduce the likelihood of seismicity. Transverse production rings were designed to be drilled radially from a drill stub mined from a mid-stope footwall drive. Stopes totalling up to 7000 tonnes were planned be fired in a single electronic blast. Extraction was designed to take place from a basal sill drive under teleremote operation. At the time of writing, the method was under trial.

Mar 21, 2011

By H Zhang, A Lawrence

To accommodate the fast growing need for services in Singapore’s Marina Bay downtown area, Marina South, the construction of a common services tunnel (CST) was required. The CST includes various services such as telecom cables, power lines and water pipes. A deep excavation and temporary earth retaining system (TERS) was required to facilitate the construction of the tunnels. Marina Bay is reclaimed land over thick soft marine clay which is likely to be still consolidating. The deep soft marine clay poses a big challenge for deep excavations in downtown areas where highways and sensitive structures are close by. This paper presents a case study of part of the CST Phase 1B and 2 at Marina South, in particular a 26 m deep excavation supported by a 46 m diameter temporary caisson. The construction started in late 2006 and the basic structure was completed in early 2011. The caisson was formed by 1.0 m thick overlapping diaphragm wall panels with a capping beam and three ring beams at different depths. Two-dimensional finite element analyses were conducted to predict the ground settlement, lateral displacement, bending moment and hoop stresses in the diaphragm wall and ring beams during different excavation stages. A comprehensive instrumentation and monitoring scheme was established to verify the design predictions, control excavation safety and trigger the contingency plan to protect public safety. The impact of construction activity, unbalanced temporary stockpiles and adjacent deep excavation for a mole removal will be discussed.CITATION:Zhang, H and Lawrence, A, 2014. A case history of a deep excavation in a big circular shaft in Singapore marine clay, in Proceedings 15th Australasian Tunnelling Conference 2014, pp 581–588 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 17, 2014