Search Documents

By Mario Dobrilovic, Zvonimir Ester, Vinko Skrlec, Vjecislav Bohanek

The first public garage in the city of Dubrovnik has been built in highly urbanized area, on location Ilina Glavica. The excavation of the building pit has been done partly by construction machinery, i.e. by hydraulic hammer for excavations and partly by drilling and blasting. In the vicinity of the building pit there are houses, buildings and two schools. Drilling operations and blasting have been performed during the working hours while regular school classes have been held and activities in other buildings took place. The nearest structures are some 5 to 10 meters (16.4 to 32.8 ft) away from the building pit, which makes it even more difficult to perform blasting operations in the urban environment. For the purpose of determining safe and permissible oscillation velocity limits, i.e. the proportion of seismic effects of blasting, a trial blasting has been conducted. The permissible mass of explosive charge has been determined by original method respecting the requirements of existing standards (ISO 4866, DIN 4150, US BM 8507), which determine the permissible oscillation velocities in relation to their frequencies. According to measuring results of the oscillation velocity during the test blasting the design parameters of blasting field have been corrected and zones have been established within the excavation area considering the possible effect of blasting to the building pit environment. Further blasting operations have been performed in stages, in smaller blasting fields with deck charge within a blast hole while respecting the requirements of the transport possibilities for the blasted rock mass within the building pit and performance of control measurements of oscillation velocity for each blasting. Through application of all the protection measures, design solutions and systematic control of performance of activities the complete excavation by blasting has been completed without any damage on neighboring structures/buildings. This article presents these solutions and methods for reduction of seismic impact of blasting to the environment.

Jan 1, 2009

Minerals contribute to the U.S. gross domestic prod-uct (GDP) at several levels?mining, processing and manufacturing finished products. In 2008, the estimated growth rate for the real GDP of the United States was 1.1 percent and the nominal GDP was about $14.3 trillion (Table 1). Trends in various sectors of the domestic economy are often reflected in mineral production and consumption rates. For instance, continued declines in the U.S. housing market during 2008 were reflected in further reductions in the production and consumption of cement, clays, construction sand and gravel and crushed stone (mineral commodities that are used almost exclusively in construction), and those associated with the related manufacture of goods, such as ceramic tile, heating and air conditioning equipment, paint, plumbing and sanitaryware, roofing, wiring and wallboard ? all used by the housing industry. The widespread effects of the slowing domestic economy became more apparent in the last three to six months of 2008 when prices for many mineral commodities declined sharply after reaching record highs earlier in the year, indicating significantly lower demand for those materials or products containing them.

Jan 1, 2009

By Paul Doherty

Expansion of the global piling industry has been coupled with significant research efforts investigating the mechanisms controlling pile capacity. Static pile design has transitioned from total stress approaches toward effective stress design, with associated improvements in predicting pile performance. As a result, the available literature is heavily skewed toward static capacity prediction. However, when considering piles offshore, the majority of loading is not static but highly variable and cyclic in nature. This paper outlines the additional factors that require consideration for cyclic pile design, including elevated loading rates, cyclic displacements and capacity degradation. A review of the literature identified a number of cyclic pile testing programs which are collated in this paper. General trends are established through comparison of the tests within the database and the conditions where cyclic loading is most likely to be a concern are identified. In particular, loading conditions which involve full plastic shear reversals are seen to cause the most extreme cyclic damage, with the degraded capacity as low as 31% of the precyclic static capacity. The underlying mechanisms which can result in cyclic damage are explored, with particular attention given to the pore pressure response, radial stresses, shear transfer and particle reorientation.

Jan 1, 2009

By Xingtian Hui

Due to variation in the geological natures of underground coal mines, especially when the entry?s roof/floor are soft and weak, it is vital to select an appropriate roof bolting system to ensure entry stability, coal production, and miner?s safety. No single type of roof bolting system perfectly fits for various types of openings, even within a mine. From the results of continuous research on roof bolting in the past 10 years, the authors used a novel concept of ?Self-screwed? mechanism to develop five types of roof bolting under a patented Self-screwed Tube Bolting System (STBS)©. This roof tube bolting system can be applied to meet different timing-strength requirements under varying mining conditions to increases the stability of mine workings. This paper outlines the structures and mechanisms of the five types of self-screwed roof bolting systems along with their unique characteristics, advantages and disadvantages, and limitations. Two case studies using a Self-screwed Tube Drilling Bolting (STDB)©, one of the five types of roof tube bolting systems, show the principles of mechanics, suitability and parameters for a mine entry and a subway?s construction/ supports in the surrounding soil layers and soft sands, respectively are presented. The results confirmed the time dependent anchorage capacity between predictions and on-site measurements. Currently, other types of the self-screwed tube bolting systems are also being applied to different coal mines in China to increase entry stability and meet safety requirements.

Jan 1, 2009

By G. S. Takenaka

When Bridger Coal Company transformed their operations from surface mining to an underground longwall operation their plans included not only the addition of new mining equipment but also surface fans for a blowing (supply) air ventilation system. The original system concept included a propane gas fired air heater to preheat the intake air during cold weather and a dual parallel fan and duct system. One fan operated to ventilate the mine while the other fan was for stand-by emergency operation. Equipment proposals were submitted in March, 2005 based on the dual parallel fan system. Discussions conducted during the equipment selection process revealed that several alternative system design concepts were available. The alternative concepts included innovation features that not only saved space and cost but also reduced operating expense as well. Many of the features were incorporated into the final design of the system. A comparison of the original system concept and final installation design are presented in the paper in addition to details of the features and the derived benefits.

Jan 1, 2009

By T Raynlyn, R J. Holmes, J R. Manuel, A Poliakov, L Lu

The prediction of sintering performance of iron ore fines and the possibility of targeted optimisation of specific sinter properties are very important for both the iron ore industry and related research organisations. Physical pilot-scale sinter runs require large amounts of raw materials and are expensive, so it is critical to target large test work programs with many different sintering parameters effectively. To predict values for sintering performance parameters such as tumble index (TI), low temperature reduction disintegration index (RDI) and productivity, a comprehensive database of pilot-scale sintering experimental results has been established and empirical modeling conducted. Similarly to earlier work, physical, chemical and mineralogical characteristics of the iron ores have been considered. However, in contrast to the previous work where only one textural parameter was taken into account, namely the proportion of dense haematite ore texture, the current model includes the abundances of several different textures which were combined into different textural factors corresponding to different sinter properties. Coefficients for the variables within specific regression equations can provide a better understanding of the effect of the variables on the corresponding sintering performance. The modelling results have also been used for predicting the sintering performance of mixtures that were not part of the database used for establishing the models. Comparison of experimental and modeling results for the verification test data is also reported in this paper.

Jan 1, 2009

By D. F. Scott

The purpose of this study was to determine if miners were at risk from exposures to chemicals used in the mining industry and determine the nature and sources of the illnesses and injuries. The U.S. Mine Safety and Health Administration?s (MSHA) employment and accident, injury and illness database was reviewed. There were 2,705 cases of chemical-related injuries and illnesses reported from 1999 through 2006, involving 66 different chemicals. The main source (cause) of chemical-related cases was acids/alkalis (about 39%). The primary nature (effect) of chemical-related cases was chemical burns (about 57%). The job classification where workers incurred the most chemical-related injuries and illnesses was cleaning plant operator/media operator/boney preparation plant operator/crusher worker (cleaning plant operators are responsible for maintenance of plants, media operators are responsible for handling reagents, boney preparation plant operators oversee removal of ?bone? from coal, and crusher workers use large crushers to break mined material). From 1999 through 2006, the rate of ?nonfatal days lost? and ?no days lost? (resulting from injuries) did not change significantly; however, the rate of illnesses decreased significantly. Chemical burns accounted for a large number of injuries; mining companies should carefully examine their personal protective equipment (PPE) requirements, training methods and safety culture to ensure that their workers are protected.

Jan 1, 2009

By A. C. Mulholland

The electrical control of three-electrode submerged-arc furnaces suffers from a number of complexities, mostly due to the nature of the furnace electrical circuit providing power to the furnace where the three electrodes are interconnected within the furnace through the molten metal bath. This gives rise to what is known as the interaction effect 2, where variations in one electrode?s current can cause comparable changes to the currents in the other electrodes, particularly in larger furnaces with low power factor. Resistance-based control of the electrode penetration has largely alleviated these problems, since the resistance encountered by each electrode is predominantly dictated by the length and conductivity of the current path from the electrode?s tip to the molten metal bath, which acts as the three-phase circuit?s floating neutral point. Hence resistance changes due to tip position or conductivity changes beneath one electrode do not affect the resistances beneath the others, effectively decoupling the control of the individual electrodes1. Although resistance-based control is therefore generally accepted as superior to current-based control for the regulation of submerged-arc furnace electrode penetration, a few furnace operators still prefer to use current control under specific furnace conditions. This paper presents the results of analysing the performance of both current and resistance-based control in typical scenarios encountered on industrial furnaces, taking into account a number of factors including electrode penetration, power distribution, efficiency and asymmetry of the electrode currents. In order to accomplish this, three typically encountered scenarios were simulated. The results obtained show that resistance control provides more benefit in all cases, however, the uneven electrode current distribution generated by resistance control when electrodes are on top stops may cause some concern if baking of the electrodes is required in this scenario.

Jan 1, 2009

The current economic climate and demand for iron ore has resulted in mine operators being prepared to accept aggressive slope designs and associated failures provided that they can be quantified (ie volume of failure and clean up costs, etc) and incorporated into the mining costs, at a feasibility study level. This has numerous implications for pit slope design/geomechanics. Typically when geotechnical engineers conduct slope stability modelling a single value, usually the average or mean value for model input parameters (ie structural orientations, material properties and hydrological conditions) are chosen. The implications resulting from using a single value for model input parameters will vary depending on how the modeller has chosen the value, ie should the modeller choose a mean value from a log-normal distribution of material strengths an optimistic representation of the stability may eventuate, consequently if the designer decides to conservatively downgrade the values by a nominal factor, a pessimistic representation of slope angles may occur, which would result in excessive stripping and mine development costs. A more realistic and representative way to model the inherent variability of geological/geotechnical conditions would be to do so probabilistically. Whereby the modeller can assess the variability of the geological structure as observed/recorded during the core logging process and a similar approach for the material strength properties. The final model output would be a distribution of factors of safety in relation to overall slope angles, ie probabilities of failure for individual slope angles could be determined. This output (graph) could be modified by the mining engineer to incorporate mining costs as well as clean up costs for the respective slope angles and associated failure volumes, ie probabilities of failure. The author intends to provide a detailed overview of the processes involved in deriving a geotechnical design, ie; starting from the data collection phase (core logging/face mapping), through to the data interpretation and formulation of slope parameters; determining the variability and uncertainties associated with each of the process; ensuring that it is adequately captured in the model input parameters; and how the mining engineer could utilise this information to derive final feasibility study mining costs.

Jan 1, 2009

This one day field trip is sponsored by the Denver Region Exploration Geologists? Society, May 14th 2009. The trip highlights major geologic features and some notable uranium occurrences along the north-south mountain-basin boundary southwest of Denver and continuing north to Fort Collins, Colorado. Uranium deposits visited include sandstone?hosted roll front type and polymetallic veins hosted in metamorphic rocks. A replacement ?episyenite? type occurrence is considered via description and hand samples but is not visited owing to logistical constraints. Recovery methods addressed include underground mining and in-situ leach recovery. Samples of Precambrian basement rocks, deposit host rocks, uranium ore samples, and ore polished sections viewed by reflected light microscopy will be available. A road map showing the locations of the stops serves as the front cover of this field guide. The Robinson episyenite-hosted occurrence (not visited) is labeled as Stop 6. A stratigraphic column is provided which shows the position of the host rocks at each stop (Figure 1-1).

Jan 1, 2009

By Jeffrey Shawn Peterson

Among underground coal miners, hearing loss remains one of the most common occupational illnesses. In response, the National Institute for Occupational Safety and Health (NIOSH) conducts research to reduce the noise emission of various underground coal mining equipment, an example of which is a roof bolting machine (RBM). After the removal of coal or rock, the remaining strata may be subject to fall, either from overhead (the roof) or from the side (the rib). One method used in underground coal-mines to prevent failures requires the installation of roof bolts. The roof bolting machine operator trams the machine to the required location, drills a hole into the strata, and then installs a roof bolt, supporting the roof or the rib, as the case may be. Field studies support the premise that, on average, drilling noise is the loudest noise that a roof bolting machine operator would be exposed to and contributes significantly to the operators? noise exposure. NIOSH has determined that the drill steel radiates a significant amount of noise during drilling. NIOSH is developing bit and chuck isolators to reduce vibration, and thus noise radiation of the drill steel, with the longer-term goal of reducing roof bolting machine operator noise exposure. Laboratory testing has shown that operator ear sound pressure levels may be reduced by 3 to 7 dB(A), depending upon the test configuration and drilling media.

Jan 1, 2009

By B. M. Satish

The aim of the present work is to study the effect of annealing on the vibration damping capacity of high-chromium (16%) ferromagnetic steel. The alloys were prepared from raw materials of 99.9% purity melted in a high frequency induction furnace under high vacuum. The samples were heat-treated in vacuum at various temperatures (800 to 1200°C) for 1 hour followed by slow cooling (120°C/h). The inverted torsional pendulum method was used to evaluate the vibration damping capacity. The results indicated that the vibration damping capacity of the alloys is influenced by annealing and there exists a critical annealing temperature after 1000°C. The damping capacity increases quickly below the critical temperature since the magnetic domains move more easily.

Jan 1, 2009

By S Lockie, G Ivanova, J Rolfe

One of the consequences of mining expansion in the Bowen Basin region of Central Queensland in Australia has been a substantial increase in demand for housing, with subsequent impacts on housing and rental markets. Those pressures are reduced to some extent by a proportion of the workforce choosing to live in other centres and commuting to workplace for block periods. The main factors influencing location choice are: housing availability and affordability, basic urban services and lifestyle of the town and the town physical attractiveness such as coastal town. Low costs housing provided by the mining company acts as an attracting factor for some miners to live in the mining town. Recommendations for three short-term and two long-term strategic policy guidelines to address housing situation and location issues are provided.

Jan 1, 2009

By Baron Fidler, Dave Lilly, Matt Budin

Cumulative sum (CUSUM) statistical process control methods have been used in many industries to monitor quality control results. CUSUM charts are a method to determine when small changes in data indicate a major change in results. E.S. Page at AT&T developed the method in 1954. In many blasting situations, vibration and air blast readings vary slightly from blast to blast. Whether the change is significant or not can be hard to interpret from the raw data. CUSUM charts can assist in determining whether a major change is taking place and when the change began.

Jan 1, 2009

By Marcia L. Harris

The National Institute for Occupational Safety and Health (NIOSH), as part of its continuing research program for evaluating coal dust explosion hazards, has investigated several areas in which current practices may need to be updated in order to adequately protect mines against coal dust propagated explosions. In the United States, current rock dusting requirements remained largely unchanged since 1969. US Title 30 Code of Federal Regulations Section 75.403 is based on a coal dust particle size survey performed in the 1920s and later was supplemented by full-scale testing of the rock dust ability to inert a coal dust explosion. NIOSH recently conducted a comprehensive survey of US underground coal mines to determine the range of coal particle sizes found in dust samples collected from the mine entries. Due to advancements in technology and modern coal mining techniques, the current coal dust particles in intake airways are significantly finer than those found in the mines in the 1920s. According to past full-scale dust explosion test results, the current rock dusting practices used in today?s mines to inert a coal dust explosion may not be adequate. Other closely related issues such as rock dust testing methods and sampling procedures are discussed.

Jan 1, 2009

By N. Bahrani

Photogrammetry surveys were used to document a footwall slab failure that occurred at a surface coal mine located on the eastern slope of the Rocky Mountains. Photographs taken before and after the failure provided the pre- and post-failure geometry of the slope and the failed slab. A 2D finite element model was constructed using slope profiles. The model contained joint elements that represented the bedding surface upon which the slab slid and the model was used to analyze the footwall slope. The in situ stresses, rock properties and the bedding surface shear strength and stiffness properties are discussed. The process of mining out a valley and exposing a highwall was modelled. As expected, elastic valley rebound occurred in the model, but shear stress and shear displacement reversals along the slip surface were also observed. The modelling results provided new insight into shear strength degradation that occurs when the pit floor approaches and then passes a specific point in the highwall.

Jan 1, 2009

By Rob Jameson

"Although seismic retrofit is recognized as a key micropile application, widely-used reference documents do not clearly address design and testing recommendations for micropiles that are loaded primarily under seismic conditions. The principles of micropile design and construction and their application to seismic retrofit projects are well understood and executed by leaders in the field. As the micropiling market grows, a wider audience relies on the information presented by DFI and similar industry groups. State-of-practice updates appear periodically in conference proceedings, but examination of recent bid documents makes it clear that there are opportunities to improve the specification of load, deflection, testing and acceptance criteria on many seismic retrofit projects. Updates to the FHWA Manual or DFI Sample Specification that specifically address seismic retrofit cases would be useful tools to disseminate information and enhance the state of practice.Micropile Survey UnderwayAs one step in this process, I am distributing surveys to contractors and designers prior to DFI Super Pile ’09 (June 4-6, San Francisco) seeking recommendations for design and testing procedures applicable to seismically loaded micropiles. I am also requesting any existing references that could be promoted as a standard for these cases. Anyone interested in participating in this survey, should contact me at rjameson@malcolmdrilling.com. Seismic RetrofittingMicropiles are ideally suited to seismic retrofit applications. Their high-tensile and compressive capacity can sustain the large concentrated loads induced during seismic events. They can be installed within and around the access limitations of existing structures, and can be drilled through and grouted into the wide variety of soil and rock materials encountered in seismically active zones.Seismic retrofits have included micropiles since the early 1990s, and they are now widely specified in the Western U.S. In the San Francisco Bay Area alone, thousands of micropiles have been installed for seismic upgrades of highway and transit aerial structures, and retrofits of commercial, residential and public buildings. Micropile use is growing in both public and private sectors, with large-scale retrofit projects currently underway for both the Bay Area Rapid Transit (BART) system-wide upgrades and renovations at San Francisco Airport."

Jan 1, 2009

By R R. J McAllister, K Moffat, S Heyenga

This paper examines the statistical relationship between quality of life indicators and the gross value of mineral production from Australian regions. We used quality of life indicators, aggregated for 673 local government areas, of household income, housing affordability, access to communication services, educational attainment, life expectancy and unemployment. We find no evidence of systematic negative associations between quality of life and the gross value of minerals production. Instead, mining activity has a positive impact on incomes, housing affordability and communication access across regional and remote Australia. Whilst we do not establish causality between mining activity and quality of life, our analysis prompts a rethink of the æresource curseÆ as it applies within a single country. Nevertheless, our findings are tempered by extensive anecdotal and empirical evidence of the negative social impacts of mining on specific demographic sectors, localities, families of fly-in, fly-out mining operations and individuals. This contrast may be a scale issue, with the regional benefits of mineral wealth masking highly-localised inequalities and disadvantage. We suggest that there is a need to better understand these impacts and, more importantly, the types of policy mechanisms government and industry can adopt to mitigate or avoid them.

Jan 1, 2009

By Anthony S. Spearing

The vast majority of the estimated 100 million rock anchors installed in mines in the USA per year use resin cartridges (Tadolini and Mazzoni, 2006). About 4.5 million per annum of these are bolts with a mechanical shell that if properly installed become effective active supports on installation. In addition, cable anchors (mostly passive) are installed with typically 4 ft of effective resin anchorage length sometimes with mechanical shells, which further makes the installation more difficult. This is because the cable (even with a stiffener tube) is not very rigid. When installing bolts with mechanical shells and cable bolts in the holes, the back-pressure can be so high that the installation is unsuccessful often creating a ?spinner? (an un-tensioned bolt) at best or buckling the bolt thus requiring another bolt/cable to be installed, or leaving a poorly functioning unit. The installation problems can create a significant potential safety hazard and waste time and money. Using a purpose designed test rig that physically inserts different rock anchors into pipes with resin and measure the back-pressure developed with time during the insertion/ installation. The test installation procedure is designed to mirror that used underground by rockbolt operators in coal mines. In addition a computer model has been calibrated that can predict the approximate back pressure of new anchor and resin combinations acting as a screen before physical testing. This research has lead to an understanding and quantification of the insertion back-pressures and this already resulted in improved prototype designs that could lead to more reliable mechanical shell and resin bolt installations.

Jan 1, 2009

By D Brereton, C J. Moran

Intensive resource extraction, in the form of multiple mining operations, presents significant assessment and management challenges for resource developers, governments, community and the environment. Cumulative impacts, ie the successive, incremental and combined impacts (both positive and negative) of an activity on society, the economy and the environment, can place significant pressure on social, economic and environmental capital and render conventional mine-by-mine approaches to management ineffective. Cumulative impacts can be what are most important to environments, communities and economies surrounded by multiple mining operations because cumulative impacts are what they experience. There is much to gain from increased consideration of cumulative impacts. Unmitigated impacts have the potential to delay or even prevent expansion of mining in existing and prospective areas. On the other hand proactive management of cumulative impacts can benefit regional environments and communities and contribute to the industryÆs social license to operate. Resources are often not the limiting factor to better cumulative impact management. More effective coordination of existing resources may go a long way toward mitigation and enhancement, and better planning and assessment may help avoid impacts and exploit opportunities for efficiency gains through reduced duplication. In this paper we draw from working examples to present five practical assessment and management strategies applicable to resource companies to enhance positive, and avoid and mitigate negative, cumulative impacts. The strategies are presented based on their capacity for achieving outcomes, ease of implementation and cost effectiveness and are drawn from a multi-year study on the assessment and management of cumulative impacts in the Hunter Valley, New South Wales and a follow-up study to improve cumulative impact assessment and management practice in the Australian coal mining industry, both reported elsewhere.  

Jan 1, 2009