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By Robert C. Dyni

The use of techniques and equipment designed to pneumatically place backfill into an underground mine opening through boreholes for subsidence abatement has historically met with limited success, largely due to the inability to directly monitor the placement of the backfill in the opening. The success of a backfilling project cannot be guaranteed if it is not known whether the underground opening has been completely filled with backfill material. To overcome the inability to directly monitor backfill placement, the U.S. Bureau of Mines developed a pneumatic backfilling system that allows for direct viewing of the backfill as it is placed in an underground mine opening. This system utilizes a recently developed pneumatic nozzle coupled with an instrumentation package that allows for real-time observations and measurements of backfill placed in an underground opening through a borehole. The nozzle utilizes a high-velocity airstream to redirect backfill falling through a pipe in the borehole and directly in front of the nozzle; the airstream redirects and propels the backfill horizontally into the .mine opening at over 100 ft/s. The instrumentation package, mounted directly to the nozzle, contains a video camera, high-intensity lamps, laser-rangefinder, electronic compass, and water sensor.

Jan 1, 2010

By D. R. Tesarik

As part of its research program to investigate ways of improving resource recovery and reducing subsidence, researchers from the U.S. Bureau of Mines placed instruments in the B-North ore body of the Cannon Mine, Wenatchee, WA, to monitor cemented backfill and rock deformation during mining. The vibrating-wire gauges proved to be reliable and versatile, and approximately half of the instruments are providing data after 2 years of use. A two-dimensional, finite-element model was used to analyze the Cannon Mine's multilevel bench cut-and-fill mining method and predict rock and backfill displacements. The model accurately predicted rock displacements, but the predicted and measured displacements in cemented backfill had a correlation coefficient near zero, indicating that the model should only be used to predict rock displacements and not backfill displacements. A finite-difference model was also used to evaluate the stability of a cemented backfill pillar. Results can be used to conservatively predict backfill stresses, but on-site observation of pillar failures coupled with in situ measurements are needed to make more accurate predictions. An ongoing evaluation of the mining system has indicated that filling the primary stopes tight to the back with cemented backfill allowed these pillars to carry overburden loads soon after the cemented backfill was placed.

Jan 1, 2010

By S. L. McGill

The U.S. Bureau of Mines has determined the microwave heating rates for a suite of minerals and reagent-grade compounds. Maximum temperature achieved for the samples and the time required to reach temperature are reported. Heating rates of powdered samples are presented as a function of incident powers up to 3,000 W at 2,450 MHz. Descriptions of the microwave cavities, test cells, and a thermocouple assembly used to measure temperature in the microwave field are given. Many minerals of value heated in the microwave field, whereas host rock or gangue materials did not. In general, heating rates increased as incident power was increased. Exceptions to this were some very good (CuO, Fe304, and PbS) and very poor (CaC03 and SiO2) microwave-absorbing materials that showed negligible changes with increased power. Applications demonstrating the use of microwave energy in mineral processing that are described herewith include oxidation-reduction reactions, mineral liberation, and mercury retorting-vaporization. Microwave data on mineral heating rates will provide insight to possible chemical and mineral processing applications as well as assist in predictions of processing parameters.

Jan 1, 2010

By Pierre Gouvin

This paper describes the design, installation and monitoring of a state of the art real time geotechnical/structural instrumentation monitoring system to facilitate tunnel construction under Interstate route I-5 in Seattle, Washington, USA. The project involved removal of existing highway foundation substructures on both North and Southbound lanes as well as the underground reversible high occupancy vehicle lanes. The system utilized state of the art 3-D pulsed laser scanning, wireless sensor networks, automated robotic total stations, tilt beam sensors, narrow angle tiltmeters, and in-place inclinometers. Dedicated real time data loggers, with a web based graphical interface, provided 24/7 access to critical measurements. In addition to the instrumented sections of wall and roadway subsurface which monitored physical measurements at known points, the pulsed laser scanning allowed complete site monitoring coverage where physical sensors were not located. This data allowed post processing at any location enabling the contractor and designer to respond to unforeseen structural responses to construction. Use of the instrumentation system resulted in the early detection of wall movement, and provided feedback to the designers to facilitate construction process changes in order to minimize further movement.

Jan 1, 2010

By Thomas L. Vandergrift

To significantly increase the stability of underground excavations while exploiting the full advantages of confined rock strength, methods must be developed to actively control the distribution of stresses near the excavation. This U.S. Bureau of Mines study examines theoretical and practical aspects of rock pres¬surization, an active stress control concept that induces compressive stress in the wall rock through repeated hydraulic fracturing with a settable fluid. Numerical analyses performed by incorporating the rock pressurization concept into a variety of boundary-element models indicate that rock pressurization has the potential to improve underground excavation stability in three ways: (1) by relocating stress concentrations away from the weak opening surface to stronger, confined wall rock; (2) by inducing additional stresses in a biaxial stress field to reduce the difference between the principal stress components near the surface of the opening; and (3) by counteracting the tensile stresses induced in the rock around internally loaded openings. Practical aspects of the rock pressurization concept were investigated through a series of hydraulic fracturing experiments. The use of sulfur as a settable fluid for hydraulic fracturing was demonstrated, although problems related to sulfur viscosity suggest that other molten materials, such as wax, may be better suited to practical field application of the rock pressurization concept.

Jan 1, 2010

By Robert Hopler

THIS paper deals specifically with heading-driving as distinguished from the broader term tunnel-driving. A heading is a pilot or path-finder for the main tunnel. Some headings are complete tunnels in themselves; that is, conditions at times warrant driving a heading the full diameter of the proposed tunnel. A tunnel 10 ft. in diameter might be driven to advantage through a single heading, provided the nature of the material admits, but it usually pays to drive rock tunnels of large diameter through the headingand-bench system. Much depends upon the material, as in soft ground tunnels of much larger diameter are driven in a single heading.

Jan 1, 2010

From some of the largest tunnel projects in the some of the most vibrant cities, to smaller projects in remote corners of the globe, the Robbins Co. announced two tunneling projects in which its tunnel boring machines will be used. Robbins earth pressure balance (EPB) machines undercut Downtown Zhengzhou. Zhengzhou, a city of 7 million people, is set to become a crossroads for rail commerce in China. The country?s future main routes, traveling between Beijing and Guangzhou (North-South), and between Xuzhou and Lanzhou (East-West), will intersect in the city. The plan includes up to four rail lines in Zhengzhou itself, which will eventually link up to the national lines. Excavation of Zhengzhou Metro?s new Line 1 tunnels began on Sept. 28, 2010, when the first of two 6.3-m (20.7-ft) diameter Robbins earth pressure balance (EPB) machines was launched from a 16-m- (52-ft-) deep shaft.

Jan 1, 2010

By Essie Esterhuizen, John Ellenberger, Dennis Dolinar

"Underground stone mines in the United States use the room-and- pillar method of mining. The stability of the roof between pillars determines the mining dimensions and size of equipment that can be used. The findings of a survey of roof span stability issues and design practices are presented, and the observed factors contributing to roof instability are discussed. Identified stability issues are evaluated, such as maximum roof span, horizontal stress, and roof beam stability. The results of field observations, roof monitoring, and numerical analyses are used in the evaluation. The importance of the first roof beam thickness and its impact on roof stability and support requirements is presented. An evaluation of the current experience with stone mine roof spans relative to international experience is presented. A step-by-step design procedure is suggested which emphazises the need to collect adequate geotechnical data, understand the immediate roof stability, select a mining direction, and meet support requirements.INTRODUCTIONIn room-and-pillar mines, the roof between the pillars is required to remain stable during mining operations for haulage as well as access to the working areas. Roof and rib falls account for about 15% of all reportable injuries in underground stone mines (Mine Safety and Health Administration, 2009). Therefore, the stability of the roof is an important safety consideration. The size of the rooms in underground stone mines is largely dictated by the size of the mining equipment. Large mining equipment is used, requiring openings that are on average 13.5 m (44 ft) wide by approximately 7.5 m (25 ft) high to operate effectively (Esterhuizen et al., 2007). The dimensions of the roof spans are largely predetermined by the equipment requirements, and design is focused on optimizing stability under the prevailing rock conditions. If the rock mass conditions are such that the desired stable spans cannot be achieved cost effectively, it is unlikely that underground mining will proceed. In addition, large roof falls can extend across the full width of a room and may extend more than 5 m (16 ft) above the roof line. These large falls are a safety hazard and can have a significant impact on mine access and production. The National Institute for Occupational Safety and Health (NIOSH) research into stone mine roof stability has focused on identifying both the causes of roof instability and techniques to optimize stability through design."

Jan 1, 2010

By H. William Zeller

The U.S. Bureau of Mines evaluated the effects of two iron-based fuel additives on diesel particulate matter (DPM) emissions. The 5.6-L, six-cylinder test engine is typical of engines used in underground mines. One additive, ferrous picrate, did not measurably affect exhaust emissions. This report is mainly about a ferrocene-based additive that reduced DPM between 4 and 45 pet., depending on engine operating conditions. The report concludes that the DPM reductions were caused by the catalytic oxidation properties of a ferric oxide coating that developed inside the engine's combustion chamber. The ferric oxide coating also decreased gas-phase hydrocarbons and O2, but it increased CO2 and NOx, The increase in NOx, of about 12 pet, is considered the only adverse effect of the ferrocene-based fuel additive. The results suggest that the effectiveness of ferrocene was partially offset by increased sulfates because of the high-sulfur fuel used. Recommendations for continuing fuel additive research are presented.

Jan 1, 2010

By T. Diering

Gemcom PCBCTM is a software package which has been developed over the last 22 years for the planning and scheduling of block cave mines. This paper presents an update of the various research and development activities done to PCBC recently. It also provides an overview of the current capabilities of the software including tools for both feasibility type studies as well as tools for operating mines. PCBC is used extensively by prospective and operating block cave mines and some of the recent applications are described.

Jan 1, 2010

By Peter Moser, Michael Messner, Florian Bauer

The existence of ammonia in underground blasting fumes was frequently measured in various field tests (6, 7). Ammonia in fumes with a TLV (threshold limit value) of around 30 ppm (slightly different in various countries) is a toxic gas but not considered to be a high risk for the underground work force as ammonia smells very itching and is extremely annoying. This might be the reason why ammonia is hardly measured in routine underground blasting fumes control. Another reason for the lacking measurement might be the circumstance that ammonia is a very reactive gas and the ammonia sensors available on the market are very cross sensitive to other gases like carbon monoxide. Nevertheless, especially since the introduction of bulk emulsion explosives in underground blasting, complaints from miners about ammonia in the blasting fumes increased. Research work by various institutions [8] around the world relates the ammonia in the fumes back to various mechanisms. Amongst others these comprise: a) non ideal (low temperature) detonation of explosives, with NH3 in the reaction products; b) reaction between rock and non detonated bulk explosives (especially when the rock is of a basic nature (high pH value); c) reaction between shotcrete and non detonated bulk explosives. Numerous blasting tests in an experimental underground set up have been made in order to check these hypotheses for ammonia origin in blasting fumes. None of them has been found to be responsible for sometimes high concentrations of ammonia in the fumes. The major reason for ammonia concentration in blasting fumes has been found in mine water of a high pH value (either natural or from using shotcrete). The mechanism identified is as follows: the moment a non detonated ammonium nitrate bearing explosive comes in contact with mine water of a high pH value, ammonia is formed immediately. The source for the undetonated explosive is twofold: firstly there is a certain spillage of explosives when the holes are charged (especially when using bulk products) and secondly not the entire explosives detonate completely. These undetonated remaining of the explosives end up in the muck pile after blasting. In case there is water of a high pH value the reaction between the explosives and the water starts immediately. This explains also the observation why ammonia can be measured in the blasting fumes quite a long time after the blast. The majority of the ammonia is not formed during the detonation; it is formed inside the muck pile even a considerable long time after the blast.

Jan 1, 2010

By Neale R. Neelameggham

"Most chemical process plants and metallurgical production facilities have some sort of cogeneration to minimize process energy costs. Use of Alternative Energy Production from sun and wind power with storage can become an integral part of a process plant utility. This will facilitate reduced fossil fuel usage and help minimize thermal emissions. This will be similar to Pollution Control equipment, which have become an essential part of process plants in the past four decades. Conceptual flow sheets of such Process Utility schemes are presented.IntroductionPower is supplied to industries, commercial and residential users. Over the past decade, Electric Utility companies have made major inroads, in introducing alternative energy resources in an attempt to somewhat reduce fossil fuel use in power generation. Now, on a much larger scale than in the early 1980s, residential users, motivated by government provided tax credits, have started installing alternative energy generators such as roof top wind mills or roof-top photovoltaic generators. This will minimize future energy costs, help control thermal emissions etc. This alternative power generation is typically connected to the existing power grid with two way power metering. However, the use of alternative energy generation has not been seen at large industrial sites yet.Paul Scherer Institute, Switzerland and the NREL laboratories in Colorado, are two of the several institutes which have been developing how solar thermal power can be used to supply the endothermic input energy in chemical and metallurgical processes. The theme of this present symposium addresses the above as well as the energy storage needs for such events to become continuous. This paper emphasizes the concept of how alternate energy can be used in the production of materials on a generic sense wherever there is a need for input energy – beyond endothermic process energy - while addressing how to reduce the thermal and carbon emissions.The alternative energy generation using wind or solar source is discontinuous due to the nature of the energy source. They are not only discontinuous but also variable. This necessitates storage of generated power for close to continuous use with variable loads. C Smith, et al pointed out in 2006, that 'the electric power industry has taken notice of the expansion of wind and its potential' in a summary article on integrating wind generation into utility systems.1 In 2009, the 1000 MW wind generation project in Texas had to be postponed to 2013 for lack of transmission.2 There are only a few large MW solar generation units in the US; the projects being slow mainly from lack of adequate storage and redistribution."

Jan 1, 2010

By David E. Siskind

The U.S. Bureau of Mines and the State of Indiana cooperated with AMAX Coal Co. and its consultants to determine the effects of coal mine overburden blasting on nearby pipelines. Five pressurized 76-m pipeline sections were installed on the Minnehaha Mine highwall near Sullivan, IN, for testing to failure. Four 17-to 51-cm-diameter welded steel pipes and one 22-cm PVC pipe were monitored for vibration, strain, and pressure for a period of 6 months while production blasting advanced up to the test pipeline field. In contrast to previous studies of small-scale, close-in blasting for construction, these tests involved overburden blasts of up to 950 kg per delay in 31-cm blastholes. Analyses found low pipe responses, strains, and calculated stresses from even large blasts. Ground vibrations of 120 to 250 mm/s produced worst case strains that were about 25 pct of the strains resulting from normal pipeline operations and calculated stresses of only about 10 to 18 pct of the ultimate tensile strength. No pressurization failures or permanent strains occurred even at vibration amplitudes of 600 mm/s.

Jan 1, 2010

By D. Lee Petersen, Travis Davidsavor

The 2003-2004 expansion of a Duluth medical center required rock blasting adjacent to the existing structures, a Mn/DOT retaining wall and other urban structures. This case history describes the methods of a blast damage assessment, based on blast parameters, excavation locations, and critical vibration receptors (including surgical suites, a linear accelerator and a major retaining wall). The assessment concluded that blast vibrations could be controlled, by limiting charge weight, to eliminate impact at the critical receptors. Prior to construction, we conducted preconstruction surveys on structures susceptible to vibration damage. During construction, we reviewed submittals, observed test blasts, reviewed blasting logs and monitored blasting vibrations. Up to 13 seismographs were used simultaneously. Close coordination with medical center operations personnel was necessary to prevent impacts to critical medical procedures. Measured vibrations were clustered around the predicted values, and attenuated at the predicted rate. High-frequency blast induced ground vibrations induced low-frequency vibration of an adjacent MnDOT retaining wall. Medical center structures were observed to significantly attenuate the ground-borne vibrations. This paper was first published in the Proceedings of the 56th Annual Geotechnical Engineering Conference, 2008, at the University of Minnesota.

Jan 1, 2010

By Nadia C. Miller

In situ stope leaching is an innovative mining system that reduces the surface impacts of conventional underground mining. As in any leaching operation, stope leaching requires hydrologic site characterization and control of leaching solutions. Several tracer tests, using sodium chloride (NaCl) in various concentrations, were conducted by the U.S. Bureau of Mines (USBM) in an underground experimental stope to simulate a leaching environment. The tests were conducted in fractured crystalline rock that was partially water-saturated. As tests progressed, the surrounding fractures became more saturated. A predominant flow direction away from the stope was found during testing. Testing procedures, results, and a remediation plan for in situ leaching based on field observations are presented in this report.

Jan 1, 2010

By Robert J. Timko

This U.S. Bureau of Mines study examined spontaneous heating episodes in coal mine pillars in an active underground coal mine. The information obtained from these incidents was then analyzed to learn which sampling methods provided the earliest indication of pillar heating. The objective of this study was to discover if the location of future events of pillar spontaneous heating could be inferred from the available information. The spontaneous heating-prone area in this evaluation involved pillars located just inby the mine portals. Several detection methods were used to determine gas levels outside as well as inside the affected pillars. It was hoped that, by incorporating external and internal sampling methods into an organized pro-gram, locations undergoing spontaneous heating could be determined more readily. This study found that by drilling small-diameter boreholes into the pillars, then obtaining gas samples from the affected pillars, the ability to locate early spontaneous heating episodes was improved. However, the ability to accurately predict future spontaneous heating events remains in question.

Jan 1, 2010

By W. Lum

In the U.S., flexible metal pipe culverts are designed by ring compression theory because the pipes are capable of deflecting and deriving side support from surrounding ground. For economy, tunnel liners are often designed as flexible structures that depend on the lateral pressure of the surrounding ground to maintain stability. In this paper, simple formulas are presented to determine the maximum deflection a concrete tunnel liner may assume and the ring compressive strength of the deflected liner. A tunnel can then be constructed to work within these limits. Similar techniques may be used to design concrete pipes.

Jan 1, 2010

By J. M. Pei

In this paper, the nonlinear finite element analysis is used to study the support system of a tunnel which is designed to pass through deep-embeded stratum. The rock mass is rather intact, though a section of tunnel will pass through the weak belt. Under the influence of the high ground stress, the condition of stability and the form of support become complicate. This paper, talcing into account the nonlinear properties of rock mass and the Interaction between rock, and support, makes a comparison between the two kinds of soft and rigid support systems, and analysed the changes of their bearing forces.

Jan 1, 2010

Australia is a hub for mining technology development. The paper describes many of the key players involved in mining research in this country along with some of the interesting research outputs to emerge over the past decade.

Jan 1, 2010

By J. Bélanger, B. Semlali, M. Grenon

RÉSUMÉ La conception des fosses ainsi que l'évaluation des ressources géologiques et des réserves minières sont désormais réalisées entièrement à l'aide d'outils informatiques spécialisés. Cependant, plusieurs analyses, pourtant essentielles à l'évaluation de la viabilité du projet, sont réalisées en parallèle sans véritable optimisation ni synergie avec l'ensemble des données disponibles. Cet article présente deux approches permettant d'intégrer certains types d'analyses aux modèles de blocs miniers. Ces approches permettent de quantifier la broyabilité du massif rocheux ainsi que d'étudier la stabilité des pentes minières à même les outils d'optimisation et de planification minières. Cette méthode permet dès l'étude de faisabilité d'un projet minier de maximiser les données disponibles, menant ainsi à une approche plus intégrée en conception minière. De plus, ces approches sont flexibles et permettent d'évaluer rapidement plusieurs scénarios, tout en laissant la possibilité de bonifier le modèle et de revoir la conception tout au long du projet minier.

Jan 1, 2010