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By A Croll

A panel cave using LHDs for ore extraction came into production at Premier in 1990 at a depth of 630 metres below surface on the western side of the mine in the BA5 mining block. A post-undercut mining sequence was used with all development on both the undercut and production levels completed prior to the undercut being advanced over the pre-developed drawbells. Support and rock mass damage on the production level was extensive as the undercut moved overhead. Undercutting and coarse fragmentation created problems. The mining sequence was changed to an advance undercut with the minimum of development and support undertaken on the production level prior to the undercut moving overhead. Only once the abutment stresses had stabilised were drawbells developed and final support installed. The height of the undercut drill design was decreased from 18 to 13 metres. The changes resulted in markedly less rock mass and support damage on the production level. Lessons learned in the BA5 mining block on the 630 level were incorporated into planning and scheduling the BB1E mining block which came into production on the 732 metre level on the eastern side of the mine in 1996. An advance undercut mining sequence was planned, undercut height was minimised and undercutting parameters were optimised in terms of the BA5 experience. Numerous problems still occurred. As the undercut area increased in size severe spalling from the cave back resulted in vertical propagation of the cave to a height of 30 metres instead of the planned 13 metres. The resultant coarse fragmentation created secondary blasting problems and an excess of undercut ore that had to be loaded and trammed, slowed the rate of undercut advance. The planned mining sequence was compromised and considerable support and rock mass damage resulted on the production level below. Once these problems had been overcome the undercut advanced at the planned rate and continuous caving initiated at the predicted hydraulic radius. At a later stage the unexpected ingress of water hampered undercut drilling and slowed the rate of undercut advance in a section of the cave. Leads and lags between adjacent tunnels and the overall face shape could not be developed as planned. The rate of natural horizontal cave propagation exceeded the rate of undercut advance and three undercut drilling tunnels were extensively damaged. More tunnel development on the production level prior to undercutting than was planned resulted. The slow advance of the undercut and high abutment stresses caused extensive damage to installed support and the rock mass on the production level, 15 metres below. Experience in the BB1E mining block on the 732 metre level has taught that an advance undercut mining sequence reduces damage on the production level markedly. Extremely tight control on the rate of undercut advance, leads and lags between adjacent tunnels and overall undercut face shape as well as extraction ratio, tunnel development and support sequence on the production level below is required. Premier Mine plans to implement a block cave at a depth in excess of 1000 metres within the next decade. All the experience gained on current mining levels together with data collection and numerical modeling is being used to plan the proposed mining operation. The geotechnical challenge of mining at this depth in weak rock has been identified as the greatest risk to the project. Challenges centre around adopting the correct mining sequence, limiting the extent of rock mass damage associated with undercutting and effective support. The hydraulic radius needed to initiate caving, fragmentation, drawpoint spacing, secondary blasting and the possibility of seismicity are geotechnical concerns that are being addressed. Results to-date suggest that a pre-undercut mining sequence with all development and support on the production level carried out only after the undercut abutment stresses have passed overhead will have to be implemented.

Jan 1, 2000

By E Ah Mu and C R Lilley, A D. Campbell

Cave propagation is a complex process due to interacting variables such as mine geometry, rock mass heterogeneity and complex structural networks and stress fields. The Ernest Henry sublevel cave (SLC) is directly below an open pit, which provided an opportunity to observe and measure rock mass failure as the cave initiated and propagated through the pit wall. This paper describes interaction between the open pit and SLC as well as rock mass failure mechanisms observed from the start of the SLC to surface breakthrough.Cave propagation and slope failure mechanisms were found to be governed by intermediate structures, while the cave shape was largely controlled by cave-scale faults. The open pit, production-level geometry and production draw strategy were also important factors for cave and subsidence growth. Cave propagation was episodic and asymmetric in shape due to the orientation and relative position of geological structures, combined with the effects of the increasing SLC geometry and drawdown from the underlying production levels. The precursors and failure mechanism of a 2.5 Mt wall collapse are also reviewed in detail.Cave growth was simulated using a 3D, non-linear, discontinuum finite element model coupled with Newtonian Cellular Automata. Model results are compared to field observations and monitoring data to determine the accuracy of forecasts and compared models versus actual rock mass response during cave propagation.CITATION:Campbell, A D, Ah Mu, E and Lilley, C R, 2016. Cave propagation and open pit interaction at the Ernest Henry Mine, in Proceedings Seventh International Conference and Exhibition on Mass Mining (MassMin 2016), pp 311–318 (The Australasian Institute of Mining and Metallurgy: Melbourne).

May 9, 2016

By M Wilson, D Whiteman, P Kuiper, S Talu, G Watt, A van As

Once the draw process has begun in a block cave, it is very difficult to identify which regions of the cave have successfully propagated, where the caved material is flowing from and where it is flowing to. The uncertainty around cave flow increases as the cave is drawn and can be further compounded by poor draw control practices. These uncertainties make it difficult to plan effective draw strategies to control dilution, as flow model predictions tend to gradually diverge from the actual state of the cave. There have been documented occasions where observed caving phenomena, such as muck pile surface rilling, could not be reproduced with the cave flow models of the time. The ultimate consequence of cave flow uncertainty is generally manifest as higher dilution and lower grades.In order to measure the real-time flow of caved material within an active block cave, CRC Mining and Elexon have developed, together with Rio Tinto, a cave flow monitoring system called Cave Tracker, which is being trialled at Argyle Diamond Mine (ADM) in Western Australia. The Cave Tracker system at ADM comprises electronic ‘beacons’ that have been installed down long HQ diameter drill holes located above the extraction level. As the cave-back propagates and the rock mass fragments, beacons are released into the muck pile and flow along with the caved material to the drawpoints below. At Argyle, the beacons are configured to emit a signal every three days. These signals are picked up by detectors installed on the extraction and undercut levels, allowing the positions of the beacons to be determined.By examining the real-time material flow in different regions of the cave, flow mechanisms can be better defined. Draw control strategies can then be actively tailored to manage the current state of the cave. Thus, previously undetectable indications of excessive rilling, rapid cave propagation, cave stall, air gaps and dilution entry can now be identified early and assessed continuously as the cave progresses. For the first time it is possible to amend draw strategies based on measurements from inside and outside of the fractured zones, allowing caves to be managed more effectively.CITATION:Whiteman, D, Talu, S, Wilson, M, Watt, G, Van As, A and Kuiper, P, 2016. Cave Tracker flow monitoring system installation at Argyle Diamond Mine, in Proceedings Seventh International Conference and Exhibition on Mass Mining (MassMin 2016), pp 479–488 (The Australasian Institute of Mining and Metallurgy: Melbourne).

May 9, 2016

By W. L. Nelson

The orebodies at Copper Mounta1n lie along and within a few hundred feet of the contact of an intrusive stock of gabbro with a series of bedded volcanic rocks of the Nicola formation. These. orebodies are all entirely within the volcanic series but in many cases the centre line of the orebody at depth is directly under the gabbro contact at the surface, due to a slight overhang of the gabbro. The gabbro and volcanic rocks are cut by a number of faults and fault zones which did not materially affect early mining operations, but, as undeground openings increased in size, the faults became more important factors in determining mining methods and procedure. Caving methods were adopted to take advantage of ground weakness in fault zones, and the effect of ground subsidence which resulted from the division of the ground 1nto large, independent blocks by faulting had to be considered in planning the sequence of mining of certain ore blocks. The faults have been divided into two classes: the longitudinal system and the cross faults, or 'breaks' as they are termed locally. In addition to the two classes of faults, the zones of parallel ore fracture also control mining procedure, but to a lesser degree, in regard to caving or ground subsidence. A third structural feature which influences mining procedure is the mine dyke system. The longitudinal or main fault system roughly parallels the gab? bro contact and is made up of a number of branches and auxiliary fractures. The main fault itself is essentially vertical, but there are a number of branches and fractures on each side of it which, though parallel m strike, may dip as flat as 50 degrees toward or away from the main fault. The full width of the main fault system has not been determined, but it is known to extend beyond the zone of mine workings. A marked schistosity follows the main fault and both schistosity and chloritic alteration have been noticed along the secondary faults of this system. Several prominent orebodies lie along the main fault and its branches. The influence of the main fault system on mining is probably related more to subsidence than to actual cavi.ng, although it is effective in both.

Jan 1, 1950

By The Staff

BEFORE going into detail on the subject to be presented, a brief outline of the Company's earl y history would not be out of place. Prospecting and mining on a small scale was started in 1876 on the site of the present open pit at Thetford Mines. The property was purchased from the Crown in 1878 and Johnson's Company was incorporated in 1885. It is owned and operated today by descendants of the original shareholders. Many employees, through their fathers and grandfathers, have service records dating back three generations. The principal asbestos deposit at Thetford Mines is pear-shaped, with surface dimensions of about 2,200 feet in length by 1,300 feet in maximum . width. Its long axis strikes northeast and the dip is nearly vertical, but irregular in detail. It is known to extend to a depth 1,200 feet below the original surface, but its area at that depth has not been determined. Ownership of this deposit is divided among three active Companies: the Asbestos Corporation, Limited; Bell Asbestos Mines, Limited; and John-son's Company. Johnson's Company owns a section about 1,000 feet in length and 500 feet in width, bounded on the northeast by the King mine of the Asbestos Corporation and on the northwest by the Bell pit. On Johnson ground, there was originally a large outcrop o~ asbestos rock which dipped toward the south below overburden. This was mined until recently by open pit, the overburden being stripped off as far southward from the original outcrop as was economically possible. As the. pit was deepened, within side walls maintained at a maximum safe slope, its floor area, of course, became progressively smaller, and eventually the pit would have wedged out against the Bell property line. It became necessary, there-fore, to introduce some other method of mining before production became seriously curtailed by a shrinkage of the pit area.

Jan 1, 1941

By Hamid Maleki

Having developed a methodology for estimating mining-induced seismicity resulting from slip along geological discontinuities in 2003, in this paper, the importance of measurements are high-lighted in the study of caving and seismic source mechanisms as applied to mine designs. Geotechnical data is analyzed from four case studies to address cave condition, load transfer, and potential effects on stability and resource recovery in four Utah mines using measurements and observations conducted over the last three decades. Cave conditions are evaluated on the basis of measurements in the gob of a western U.S. operation mining under the massive Castlegate Sandstone and indirectly using the results of measurements and boundary-element modeling at panel boundaries at a mine where strata behave elastically. Together with subsidence measurements and microseismic monitoring, regional caving and load transfer in multiple-panel extractions are addressed while the effectiveness of barrier pillars in reducing stress and seismic response where mining under massive stratigraphic units is analyzed using measurements and three-dimensional computer modeling.

Jan 1, 2006

By D P. Sainsbury, B L. Sainsbury, A Vakili, H-D Paetzold, P Lourens

The cave propagation behaviour of a jointed rock mass is strongly governed by the unique nature of joints and discontinuities, together with the intact strength of rock bridges that make up the rock fabric. A discrete finite difference (DFD) modelling technique has been developed to allow for the detailed consideration of the rock mass structural fabric at many scales and through many different stress paths that can be used for complex mine-scale analysis. The DFD methodology uses interfaces to explicitly represent large-scale structures and ubiquitous joints embedded within the simulated rock mass matrix to characterise intermediate structures. Through simulated testing of DFD materials, properties such as strength anisotropy and scale effects can be obtained. This paper discusses the successful application of implementing a DFD modelling technique for the back-analysis of caving-induced subsidence behaviour of Lift 1 at the Palabora mine.CITATION:Sainsbury, D P, Sainsbury, B L, Paetzold, H-D, Lourens, P and Vakili, A, 2016. Caving-induced subsidence behaviour of Lift 1 at the Palabora block cave mine, in Proceedings Seventh International Conference and Exhibition on Mass Mining (MassMin 2016), pp 415–426 (The Australasian Institute of Mining and Metallurgy: Melbourne).

May 9, 2016

By José Divo Bressan

Present work examines material surface damage by cavitation erosion of metals or the wear phenomenon from water bubbles collapse near the metallic surface. Material surface damage by cavitation erosion is due to wear mechanisms of liquid micro-jets impingement and shock waves. Experimental cavitation in tap water was investigated, using the proposed new design of compact rotating disk equipment. In this device, a rotating disk with cavitation inducers and specimens fixed on it ran in tap water to provide cavitating flow at constant high speed of 47.9 m/s similar to service conditions in pumps and propellers. Two types of cavitation inducers in the rotating disk were investigated: through-holes and pins. Carburized cast iron, aluminum, brass and bronze specimens were tested in this device. The cavitation damage mechanisms were observed by scanning electron microscope. Surface damage in the specimens was measured by mass loss and plotted in graphs of mass loss versus running time. After 25 hours testing, the specimens surface showed pitting formation and mass loss. All specimens presented surface damage: pit diameter size was about 100 or 150 to 300 micron. In aluminum specimen, damages by burned pit formation and plastic deformation could be seen, however, the mass loss was lower than the expected, possibly due to alumina film formation. Present equipment had quite good test reproducibility when compared with results from literature.

Jul 31, 2018

By Luis Armando Espitia

AISI 410 martensitic stainless steel specimens were low temperature plasma nitrided at 400°C in a mixture of 75%N2:25%H2, during 20 h. Active screen technic was used to avoid any edge effect The nitrided case is composed of expanded martensite (a’N) and e-Fe3N iron nitride, whilst chromium nitride precipitation was avoided. Surface hardness reached 1275 HV0.01. The transverse microhardness profile shows a gentle hardness gradient with a NHT nitrided case depth of 28 µm. Nanoindentation tests were carried out in order to assess the hardness (H), the Young modulus (E), the H/E and H3/E2 ratios and the elastic recovery (We) of both nitrided and non-nitrided specimens. The cavitation erosion mass losses were measured as a function of exposure time. The results showed a decrease of 27 times of the mass loss compared to the non-nitride specimens. Wear rate decreased from 2.56 mg/h for the non-nitrided condition to 0.085 mg/h after nitriding. The increment in the elastic recovery and the higher hardness values are responsible for the greater cavitation erosion resistance exhibited by the expanded martensite. Such results showed that low temperature plasma nitriding and the formation of expanded martensite are effective to increase cavitation erosion resistance of AISI 410 stainless steel.

Jul 31, 2018

By Yuanping Cheng, Jingyu Jiang, Qiang Zhang

"With the increase of mining depths, deep-seated coal seams face threats from high ground stresses, high gas pressures, high gas content, and low seam permeability, which significantly increase the likelihood of coal and gas outbursts. Challenges continue to grow in coalbed methane (CBM) extraction fields, especially for short-distance gassy multiple-seams. Research has proved that the most effective way to increase coal seam permeability is to decrease the ground stress. Protective seam mining technology is a surrounding rock control technology, which can effectively reduce the ground stress and increase the permeability of the protected coal seam. In this paper, we try to use upper protective seam mining technology to simultaneously extract coal and gas. Findings are based on a FLAC3D simulation of stress variation during the mining of the No. 12 coal seam in the Daxing coal mine, Tiefa Coalfield, China. Results indicate that, after mining the upper protective seam, the pressure-relief effects of the rock mass generated three belts and five zones below the protective seam, providing the space and time for gas pre-extraction engineering. Within the protected area, the numerical simulation indicates that the stress of the No. 13/14 coal seam reduces 95.84% and 88.25% respectively, while the expansion deformation of the protective seams reach 6.87 ‰ and 6.70 ‰ respectively, which demonstrate that the protective mining technology can provide a significant pressure-relief effect to the outburst-prone coal seam. Combining stress relief in this manner with pressure-relief from engineered gas drainage (performed by crossing boreholes from the floor rock roadway) applied before the mining of the protective seam, it would not only be beneficial to CBM drainage but also can reduce the gas outburst risk of the protected seams.INTRODUCTION Internationally, since France used protective seam mining technology to control coal and gas outburst in 1939, it has been promoted and applied in many countries (?????, 1966). Since 1958, China has taken the mining test and engineering practice of protective seam mining technology in the Beipiao, Tianfu, Nantong, Zhongliangshan, Songzao, Huainan, Huaibei, and other coalfields (Yu, 1992). Long-term theoretical research and mining practice of outbursts and dangerous coal seams show that protective seam mining technology is the most effective, safest, and most economical outburst prevention measure (Cheng, Fu, and Yu, 2009; Hu et al., 2008; Cheng and Yu, 2007). Under the condition of high gas content coal seams, the safety and efficiency of simultaneous extraction of coal and gas can be realized through a reasonable mining sequence and an effective gas extraction method (Cheng and Yu, 2003). The in situ stress distribution of the protective seam (No. 1 coal seam) and protected seam (No. 2 coal seam) during protective seam mining in the Haishiwan coalfield formation (Figure 1) (Li et al., 2014). A comparison of the stress and displacement (five zones and three belts) of the rock mass below the protective seam, and in a multiple-seam context in the Dalong Mine, is shown in Figure 2 (Jiang et al., 2015). After mining protection coal in a close-distance seam group, the small spacing between the coal seams causes the protective coal and the protected coal between part of the rock to crack through each other until the protective layer of gob is through the area. This provides a desorption of gas to the protective layer of the mining space channel, making the coal seam permeability increase to several hundred times and improving the gas discharge capacity (Zhai, 2008)."

Jan 1, 2017

By Grigori Abramov

Borehole Mining (BHM) is a remotely operated underground and underwater method of extracting (mining) mineral resources by high-pressure water jets. It can be carried-out from the land surface, open pit floor, underground mine and floating platform or vessel. The method is currently in use in mining and exploration of such natural resources and industrial materials as: uranium, iron ore, quartz sand, gravel, coal, poly-metallic ores, phosphate, gold, diamonds, rare earths, amber and several more. Yet another application of Borehole mining technology is construction of subsurface collectors, ground walls and storage for compressed or liquefied gases, oil and other products.

By Elmer Peña Matta

Un estudio anterior sobre la mena Pb. Zn en la concentradora de Paragsha determinó que los finos encontrados en la alimentación de los molinos, se podía separar, evitando la remolienda y la alimentación directa del ciclón, para luego obtener los productos destinados a la flotación y molienda, respectivamente. En este sentido, el objetivo del texto, radica en mostrar los resultados del uso de los cedazos DSM en los molinos primarios, asi como el proceso de la adaptación del mismo. El acondicionamiento de los cedazos DSM es un proceso que permite recibir alimentación de una faja transportadora y descargar su cajón de alimentación original, que está diseñado para la descarga de la bomba. De forma que la aplicación de los cedazos DSM es factible en menas que no necesitan molienda, donde se aumenta la capacidad en el equipo de la molienda, se mejora la clasificación de los productos, y surgen nuevas perspectivas de incrementar la metalurgia, especialmente en especies friables. Asimismo la ubicación de un cedazo DSM varía de acuerdo a la necesidad, sea la entrada de molinos, ciclones, descargas de molinos de varillas, bombas con productos por clasificar, equipos de heavy medium, etc.

Jul 20, 1960

By Deepak Vidyarthi

This paper deals with various measures adopted in protecting a conveyor duct (named after a Conveyor Belt that was numbered as ‘02’) housing a 1600 mm (63 inches) belt conveyor system in a large, heavily mechanized open cast iron ore mine, producing about 20.0 million tones of ore per annum.

Jan 1, 2008

By G. Kosick, G. Dobby

CEET, an acronym for Comminution Economic Evaluation Tool, was jointly developed by MinnovEX Technologies Inc. and 13 major mining companies for the purpose of designing and predicting the performance of grinding circuits. It fundamentally differs from other methods by using as its’ data set a geostatistically significant population of hardness data distributed across the mine block model. Historically the characterization of an orebody for the purpose of either designing a grinding circuit or predicting the performance of an existing circuit has been done with a relatively limited number of discrete samples. In addition to power selection, shell sizing, and costing for multiple circuit options, CEET also outputs tons per hour, P80, and operating cost on every mining block for subsequent integration back into the block model. This paper will provide an overview of what CEET is and how it works.

Jan 1, 2001

By P. R. A. Andrews, R. K. Collings

"There are more than thirty-five deposits or occurrences of celestite in Canada, chiefly in Newfoundland, Nova Scotia, New Brunswick, Ontario and British Columbia. Deposits of economic interest are the Lake Enon and MacRae deposits in the Loch Lomond district of Cape Breton Island, Nova Scotia. Two Cape Breton deposits were operated from 1969 to 1976 by Kaiser Celestite Mining Limited, which supplied an upgraded celestite concentrate to an associated strontium carbonate plant at Point Edward, near Sydney.The MacRae deposit is of current interest because of its possible development for strontium carbonate production using the ""black ash"" process. This process involves chemical leaching, rotary kiln calcining with petroleum coke, washing and treatment with carbon dioxide.Celestite is the basic material used in the manufacture of strontium chemicals, principally strontium oxide, carbonate, nitrate, chromate, chlorate, chloride, sulphide and phosphate. Strontium chemicals, in turn, are used in the manufacture of glass and ceramics, in pyrotechnic devices, in the production of strontium metal and in other metallurgical applications. Recently, strontium ferrites have been introduced into permanent ceramic magnets."

Jan 1, 1991

By Roland Kammel

For electrolytic recovery of silver from dilute aqueous solutions improved mass transfer is necessary to achieve favourable current efficiencies and high space-time yields. The many cell designs proposed for this application can be divided into two different groups: cells from which the silver must be redissolved and cells from which the deposit can be reclaimed as a metal. Introduction Electrolytic silver recovery methods have proven advantageous under technical and economic aspects for the treatment of rinse water, still rinses and spent silver solutions in the electroplating and surface finishing industry, of exhausted fixing baths from photographic processing, bleed electrolytes from silver refining processes and leach liquors. Examples of the compositions of typical dilute silver solutions are listed in Table I.

Jan 1, 1984

By C. -G. Zhang

This paper presents the results of a study on cellular acclimation of Acidithiobacillus ferrooxidans to sulfur biooxidation in terms of cells growth and changes in surface properties and morphologies of both cells and sulfur particles. The results showed that A. ferrooxidans cells were grown faster and demonstrated higher concentration in the soluble thiosulfate substrate than in nonsoluble hydrophobic S0 substrate. The results showed that A. ferrooxidans cells acclimated to the sulfur biooxidation by actively expressing some extracellular polymers substance and maybe some outer membrane proteins that modified the surface properties of both sulfur particles and the cells themselves. In addition, the results showed that the A. ferrooxidans cells were able to dynamically adsorb to or desorb from the surface of sulfur particles. The cells aggregating onto the S0 surface enhanced the use of S0 substrate by the bacteria cells. This mode may be one of the most important characteristics for the better growth and propagation of the cells in solid sulfur-containing media.

Jan 1, 2009

By Yan Beygelzimer, Alexander Spuskanyuk, Victor Varyukhin

"A cellular model of the plastic deformation of polycrystalline aggregate is proposed and comprehensively described. Representative volume element (RVE) of a solid body, that is being deformed, is described as a population of interconnected units that, in turn, can consist of lower scale level units. Sliding along the various allowed sliding systems deforms simple units, which do not have an internal structure. For consideration of stress distribution within the limits of components, the approach of self-consistent field is used. Rotation of units and moment stresses connected with it are taken into account. Results of computer experiments are analyzed.1. IntroductionMicromechanical models of polycrystals are a link between the research of plastic deformation on micro and macro levels. Computer simulation of inelastic strain of polycrystals has found a great deal of interest as well. Despite the fact that this approach does not allow to obtain macroscopic constitutive relationships that are used in deformed solid body mechanics, it clarifies essential features of the phenomena in many aspects. First of all, it concerns effects stipulated by interdependence of micro-level and macro level of plastic deformation processes. Also, with the computing mechanics, instead of constitutive relationships, the adequate computer models can be used. Broad possibilities for computer simulation of various processes are opened by cellular automata approach. By means of numerical experiments, the cellular automata allows to study the macro behavior of the whole ensemble of cells depending on the local microscopic laws that define evolution of each cell and its interaction with the closest environment.We propose a mathematical model of a polycrystalline aggregate (the cellular model) based on a self-consistent scheme and on the interaction law similar to the one by Berveiller and Zaoui [1]. Our original solution is the self-similar structure of cellular automata that allows modeling of the fractal nature of real materials (Figure 1). The goals of this work are to present the major structures and relations of cellular model of polycrystal and to test this model for its adequacy as for describing known effects and dependencies. Identification of the model and its application for studying of concrete polycrystals are put aside for the future research."

Jan 1, 2001

By David Crouthamel, Raymond Henn

"The need to fill the void space or annulus created between an excavated tunnel or shaft and the final lining system has long been a requirement in underground construction. Most of those types of voids are created as a result of employing the two pass tunneling lining method. Filling of this void is called backfilling. For many years the materials used as backfill were primarily reinforced and non-reinforced concrete, sanded grout, neat cement grout, or blown-in sand/pea gravel. However, in the past 20 years the use of cellular grouts/cellular concrete as the backfill material has greatly increased. Most cellular grout is made of a mixture of water, Portland cement (with or without the addition of fly ash), a foaming agent and admixtures such as a water-reducer or superplasticizer.It is the authors’ preference to use the term cellular grout as opposed to cellular concrete since by ACI Concrete Terminology an ACI Standard (ACI CT 13), concrete contains aggregates. Normally cellular grout does not contain sand (finite aggregate), but almost never contain course aggregates.The authors believe there are several reasons for this increased use of cellular grout as backfill, such as:• The increase utilization of the various trenchless tunneling methods. Tunnels constructed using trenchless method tend to be smaller in size, excavated diameter or cross sectional area. Making man-entry for placing backfill from inside the secondary liner, utilizing pre-installed grout posts, more difficult if not impossible. It is these workspace restrictions that are the drivers as to when to utilize grout ports installed during the pipe/liner fabrication versus grout delivery pipes installed within the void/annulus space.• The ability of cellular backfills to be pumped and flow longer distances.• The unit weight of cellular grouts can be controlled by mix design and generally can range from 560 Kg/m3 (35 lbs/CF) to 1040 Kg/m3 (65 lbs/CF)."

Jan 12, 2017

By C. E. Doran

Since the early 1990s the underground mining industry has embarked on a vigorous program of improving process and eliminating costs. A leading development in this program has been the implementation of leaky feeder radio systems as an enabling infrastructure for future automation. El-Equip Inc. has led this development with more than 175 mines implementing mine-wide radio infrastructures for voice and data. In this paper, we describe the implementation of a digital radio network which supports existing installations through to an automation infrastructure employing full digital cellular communications with mobile video roaming capabilities. We outline the evolutionary path from existing low speed data communications links through to 155 Mbps and beyond.

Sep 1, 2001